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The influence of eccentric resistance training on bone mass and biochemical markers in young women

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The influence of eccentric resistance training on bone mass and biochemical markers in young women

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Content THE INFLUENCE OF ECCENTRIC RESISTANCE TRAINING ON BONE
MASS AND BIOCHEMICAL MARKERS IN YOUNG WOMEN
by
Edward Todd Schroeder
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment o f the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(BIOKINESIOLOGY)
August 2000
Copyright 2000 Edward Todd Schroeder
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UNIVERSITY OF SOUTHERN CALIFORNIA
T H E GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANGELES. CALIFORNIA 90007
This dissertation, written by
Edward Todd Schroeder
under the direction of his Dissertation
Committee, and approved by all its members,
has been presented to and accepted by The
Graduate School, in partial fulfillment of re
quirements for the degree of
DOCTOR OF PHILOSOPHY
Dean of Graduate Studies
Date
DISSERTATION COMMITTEE
Chairperson
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DEDICATION
My pursuit for higher education and the completion o f my Ph.0. degree,
represented by this dissertation, would not have been possible without the support and
love o f my best friend, my wife. She has given me a life outside o f academics, with
whom I share everything, and most importantly she has given me a son, Cole Thomas
Schroeder (aka Flip), who above all degrees, achievements, and accolades represents our
most magnificent accomplishment. Lastly, this dissertation is dedicated to all the
extended family that generously and lovingly provided Flip a warm place to sleep in their
arms (and the changing o f a few duty diapers) while this manuscript was in preparation.
Thank you!
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ACKNOWLEDGEMENTS
Most importantly I would like to acknowledge the unparalleled guidance, support,
and friendship o f my dissertation advisor, Dr. Victoria Jaque. Her youthful and spirited
personality made the laboratory environment fun and entertaining. Without Dr. Jaque’s
insightful knowledge and motivation, completion o f the Ph.D. in four years would not
have been possible. More important than the completion o f the degree itself is what was
learned and experienced on the journey to completion. On this journey I was given
advice and knowledge from faculty and peers that developed and strengthened my ability
to teach and conduct research. Dr. Bob Wiswell was always a resource for knowledge
and taught me the importance o f “numbers.” Dr. Fred Sattler introduced me to the rigors
o f preparing manuscripts for publication. And lastly, Dr. Steve Hawkins who as a peer
and later as a Ph.D. helped guide my research by always questioning what I was doing
and why. O f course, this study would not have been possible without the volunteers who
gave their time and muscle power while enduring my humor and entertaining shirts.
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TABLE OF CONTENTS
DEDICATION .............................................................................................................. ii
ACKNOW LEDGEM ENTS ........................................................................................ in
LIST O F TABLES AND FIGURES ..........................................................................vii
ABSTRACT ...................................................................................................................ix
CHAPTER I
INTRODUCTION ...............................................................................................1
Statem ent o f the Problem ............................................................................1
Background and Significance .................................................................... 2
Peak Bone Mass ..........................................................................................2
Sex Hormones .............................................................................................3
Resistance Exercise and Bone ..................................................................3
Eccentric Resistance Exercise .................................................................. 5
Direct Effect o f Eccentric Resistance Exercise on Bone ..........................6
Indirect Effect o f Eccentric Resistance Exercise on Bone ..................... 6
Resistance Training, Bone Mass, and Sex Hormone Levels .................. 7
Summary ..................................................................................................... 9
Significance .....................................................................................................9
Specific Aims ...................................................................................................10
Hypotheses ...................................................................................................... 10
Hypothesis I .................................................................................................10
Hypothesis II ............................................................................................... 1 1
Hypothesis in .............................................................................................. 1 1
HypothesisIV ..............................................................................................II
Hypothesis V ............................................................................................... 1 1
Hypothesis VI ..............................................................................................II
CHAPTER H
REVIEW O F LITERATURE ........................................................................... 12
Bone ................................................................................................................. 12
Bone Matrix .................................................................................................12
Bone CeDs ....................................................................................................13
Ossification ................................................................................................ 15
Compact and Trabecular Bone ...................................................................15
Bone Remodeling ........................................................................................16
“Coupling” Bone Remodeling .................................................................. 17
Osteoporosis ....................................................................................................17
Definition o f Osteoporosis ..........................................................................18
Measuring BMD ......................................................................................... 19
Markers o f Bone Turnover ....................................................................... .20
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Peak Bone M ass .............................................................................................21
Horm ones ........................................................................................................23
Estrogens .................................................................................................... 23
Aromitization ..............................................................................................24
Androgens ...................................................................................................26
Sex Hormone Binding Globulin (SHBG) ................................................ 27
Bone and Hormones .....................................................................................29
Oral Contraceptives ................................................................................... 30
Cytokines ...................................................................................................32
Growth Factors .......................................................................................... 33
Physical A ctivity and Bone .......................................................................... 34
Bone A daptation to Strain ..........................................................................37
Resistance T raining ......................................................................................39
Concentric Vs. Eccentric Training ............................................................ 40
Eccentric Exercise-Induced Muscle Damage ............................................42
Interleukin-6 (IL-6) ............................................................................... 44
Creatine Kinase (CK) ........................................................................... 45
Frequency o f Eccentric Training ................................................................47
Resistance T raining and Biochemical M arkers .......................................48
Resistance T raining and Horm ones ...........................................................49
Resistance T raining and M echanical Strain Effects on Bone................. 51
Direct Effects o f Resistance Training on Bone ........................................55
Slice Analysis ......................................................................................... 57
Indirect Effects o f Resistance Training on Bone .................................... 57
M uscle and Strength Relationships Utilizing DXA Slice Analysis ....... 58
Progression o f Study .................................................................................... 60
CHAPTER HI
M ETHODOLOGY .................................................................................................62
Subjects ...........................................................................................................62
Study Design ..................................................................................................63
Resistance Training Intervention ............................................................. 63
Procedures ...................................................................................................... 64
Strength Evaluation .................................................................................... 64
Bone Densitometry ................................................................................... 65
Body Composition ......................................................................................67
Sam ple Collection (Blood and Urine) ........................................................ 68
Bone Biochemical Markers .......................................................................69
Serum Androstenedione ............................................................................ 73
Serum Creatine Kinase (CK) ....................................................................74
Interleukin-6 (IL-6) ................................................................................... 75
Muscle Soreness .........................................................................................76
Menstrual, Physical Activity, and Health History Questionnaire ........... 76
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v i
Statistical Methods ........................................................................................76
Power Calculations .....................................................................................76
Statistical Analysis ...................................................................................... 79
CHAPTER IV
RESULTS ................................................................................................................. 80
Study Subjects .................................................................................................... 80
Strength .............................................................................................................. 81
Body Composition .............................................................................................84
Bone Mass ........................................................................................................... 85
Bone Biochemical Markers .............................................................................. 88
Serum Creatine Kinase (CK) ........................................................................... 95
Serum Androstenedione ................................................................................... 98
Serum Interleukin-6 (IL-6) ................................................................................102
CHAPTER V
DISCUSSION .......................................................................................................... 103
STUDY LIMITATIONS ........................................................................................126
RECOMMENDATIONS FOR FUTURE STUDY .............................................127
BIBLIOGRAPHY .......................................................................................................128
APPENDICES
APPENDIX A ...........................................................................................................147
Sensation o f Soreness Scale .............................................................................. 148
Entry Questionnaire ..........................................................................................149
Menstrual, Physical Activity, and Health History Questionnaire ..............151
Informed Consent ..............................................................................................161
APPENDIX B .......................................................................................................... 164
Biosynthetic Pathway for Steroid Hormones ................................................ 165
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vii
LIST OF TABLES
TABLE 1 Eccentric Resistance Training Protocol ..........................................64
TABLE 2 Baseline Characteristics o f Study Subjects .................................... 81
TABLE 3 Baseline and Week 16 Concentric Strength (kg) by 1-RM ......... 82
TABLE 4 Absolute Change in Concentric Strength (kg) by 1-RM ............. 82
TABLES Baseline and Week 16 Mid-Femoral Lean Mass Slice Values ....8 5
TABLE 6 Baseline and Week 16 BMC and BMD Measures by DXA .........86
TABLE 7 Baseline and Week 16 Mid-Femoral BMC and
BMD Slice Values ................................................................................88
TABLE 8 Baseline and Week 16 Deoxypyridinoline Values .........................89
TABLE 9 Baseline and Week 16 Osteocalcin Values ...................................... 92
TABLE 10 Baseline and Week 16 Creatine Kinase Values ............................. 95
TABLE 11 Baseline and Week 16 Androstenedione Values ............................ 98
TABLE 12 Baseline and Week 16 Interleukin-6 Values ...................................102
LIST OF FIGURES
FIGURE 1 Mid-Femur Segment Bone Mineral Density (BMD) From
Baseline to Week 18 ....................................................................... 56
FIGURE 2 Relative (%) Change From Baseline to Week 12 by DXA
Thigh Slice for Lean Mass Versus Leg Press Strength as
Measured by the 1-RM Method .................................................. 61
FIGURE 3 Relative (%) Change in Strength From Baseline to Week 1 6 .. 83
FIGURE 4 Spine Bone Mineral Content (BMC) From Baseline to
Week 16 ...........................................................................................87
FIGURE 5 Absolute Change in Deoxypyridinoline Crosslinks in the
Low-Intensity Resistance Training Group ................................ 90
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FIGURE 6 Absolute Change in Deoxypyridinoline Crosslinks In the
High-Intensity Resistance Training Group ................................91
FIGURE 7 Absolute Change in Osteocalcin in the Low-Intensity
Resistance Training Group ...........................................................93
FIGURE 8 Absolute Change in Osteocalcin in the High-Intensity
Resistance Training Group ...........................................................94
FIGURE 9 Absolute Change in Creatine Kinase (CK) in the
Low-Intensity Resistance Training Group ................................ 96
FIGURE 10 Absolute Change in Creatine Kinase (CK) in the
High-Intensity Resistance Training Group ................................97
FIGURE 11 Absolute Change in Androstenedione in the Low-Intensity
Resistance Training Group ...........................................................100
FIGURE 12 Absolute Change in Androstenedione in the High-Intensity
Resistance Training Group .......................................................... 101
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ix
ABSTRACT
The period o f peak bone mass accretion presents a window o f opportunity to
enhance a young woman’s bone mass prior to age- and hormone-related bone loss.
Resistance training offers a non-pharmacologic intervention strategy to assist in the
prevention o f osteoporosis. Therefore, the purpose o f this study was to determine the
effect o f eccentric progressive resistance training (PRT) on bone mass, biochemical
markers o f bone metabolism, muscular strength, lean mass, exercise-induced muscle
damage markers, and endogenous sex hormone levels in young women. Thirty-seven
female volunteers aged 24.4 ± 2.2 years were randomized to one o f 3 groups: Iow-
mtensity (75% o f a concentric 1-RM) eccentric PRT (LRT group), high-intensity (125%
o f a concentric 1-RM) eccentric PRT (HRT group), or control. Those randomized to
exercise trained six muscle groups twice per week on non-consecutive days for 16 weeks.
Measures o f bone mass by DXA, muscular strength by l-RM , serum osteocalcin,
androstenedione, creatine kinase (CK), Interleukin-6 (IL-6) and urinary
deoxypyridinoline and creatinine were assessed at baseline, and weeks 4, 8,12, and 16 in
the training groups and at baseline and week 16 in the control group. Data were analyzed
by ANOVA and ANCOVA to determine between, within, and interaction effects for the
dependent variables (p < 0.05). Concentric strength increased 20-65% in both groups.
Bone mineral content o f the lumbar spine significantly increased m the LRT group (0.855
± 0.958 g/cm) which was the only increases in bone mass measured in any group. Lean
mass significantly increased in both the LRT (0.7 ± 0.6kg) and HRT (0.9 ± 0.9kg)
groups. Osteocalcin significantly increased in the LRT group (165 ± 61%) and
deoxypyridinoline significantly decreased in the HRT group (56 ± 53%). Serum CK
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significantly increased in the LRT group (47 ± 51%). Lastly, no significant changes
in androstenedione and IL-6 were measured in any group. These findings suggest that
Iow-intensity eccentric PRT is more influential on bone mass, bone formation, muscular
strength, and markers o f muscle damage than high-intensity eccentric PRT.
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CHAPTER I
1
INTRODUCTION
Statement o f the Problem
As the mean age o f our society increases, as a result o f the rapidly rising elderly
segment o f the population, the need for successful interventions to help prevent
osteoporosis becomes more important. Bone loss accelerates after 30 years o f age,
increasing the risk o f developing the disease osteoporosis, which occurs in one thud o f all
women. Therefore, developing prophylactic measures early in life to prevent
osteoporotic fractures in women would be advantageous. The period o f peak bone mass
accretion presents a window o f opportunity to enhance a young woman’s bone mass prior
to age-related bone loss. Resistance training offers a beneficial non-pharmacologic
intervention in the prevention o f osteoporosis. More specifically, we have shown that
eccentric resistance training generates an osteogenic response (Hawkins et ai. 1999).
However, the factors associated with resistance training that influence bone remain
poorly understood. While a combination o f concentric and eccentric resistance training
has been shown to increase bone mass, no studies have reported the result o f a whole
body, multiple muscle group, eccentric progressive resistance training (PRT) program to
influence bone mass. The potential factors stimulating bone adaptation as a result o f
eccentric muscular contractions warrant exploration.
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Background and Significance
By the year 2030, 70 million Americans will be 65 years o f age and older, and
persons 85 years o f age and older will be the fastest growing segment o f the population.
Thirty percent o f American women will be affected by osteoporosis, resulting in
healthcare costs that are currently estimated to be $14 billion per year and projected to
reach $240 billion per year by 2040 (Wood 1998). The prevention and treatment o f
osteoporosis is receiving greater attention as the mean age o f our population increases.
Investigators have attempted to elucidate the complex interaction o f factors that
contribute to the pathogenesis o f osteoporosis in an attempt to develop effective treatment
interventions. It is well established that exercise (Boot et aL 1997, Morris et aL 1997,
Puntila et aL 1997) and hormones (Morris et ai. 1997, Nawata et ai. 1995, Sasano et aL
1997) are instrumental in developing and maintaining bone mass. However, it remains
unclear which hormones and types o f exercise may best regulate peak bone mass
accretion in young women and the important role they may play in the delay and
prevention o f osteoporosis. This study explored the influence o f eccentric PRT on bone
mass, biochemical markers ofbone metabolism, lean mass, strength, exercise-induced
muscle damage markers, and endogenous sex hormone levels in young women in an
attempt to identify osteogenic factors.
Peak Bone Mass
Peak skeletal bone mass is achieved by the age o f 25-30 years, after which bone
loss ensues at a constant rate until menopause (Eriksen and Cannon 1991).
Approximately 80% o f peak bone mass is genetically determined, while the remaining
20% is influenced by environmental factors and the endogenous levels o f sex hormones
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during adolescence (Pocock et aL 1987). The amount o f bone developed during
childhood and adolescence determines how much bone may be lost before a critical low
bone mass is reached, resulting in osteoporotic-related fractures. Therefore, prophylactic
measures to prevent osteoporotic fractures in women should be focused on maximizing
peak bone mass.
Sex Hormones
Alterations in the levels o f endogenous sex hormones (estrogens and androgens)
during childhood and adolescence significantly influence peak bone mass accretion
(Slemenda et aL 1996). Women with late onset o f menarche appear to have significantly
reduced peak bone mass (Armaneto-Villereal, VillereaL Avioli, and Civitelli 1992).
However, amenorrheic young women with high androgen concentrations appear to avoid
the detrimental effects o f estrogen deficiency on peak bone mass (Buchanan et aL 1988).
Additionally, young women with normal menstrual cycles and elevated levels o f
androgens have higher bone mass than women with normal androgen levels (Dixon et aL
1989). Therefore, both estrogens and androgens may be important contributors to the
development and maintenance o f peak bone mass in young women.
Resistance Exercise and Bone
Exercise may provide a successful non-pharmacologic intervention for the
enhancement o f bone mass in young women (Friedlander et aL 1995, Snow-Harter et aL
1992, Uusi-Rasi et aL 1998). The type, duration, and intensity o f the exercise impose
differential stimuli to the bone. However, the factor or combination o f factors which
is/are most osteogenic is presently unclear. High strains, high strain rates, and unusual
strain distributions are particularly osteogenic and should be incorporated into the
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4
designed exercise training to promote increases in bone mass (Lanyon 1992).
Resistance training establishes unique, high strain forces generated by muscular
contraction, which act directly on bone. Resistance training programs designed for young
women have been shown to significantly increase bone mass (Friedlander et aL). It has
been hypothesized that the direct tension generated from muscle contraction stimulates
increases in bone formation (Burr 1997).
In addition to acting directly on bone (e.g. muscle pull on bone), resistance
training may act indirectly by influencing factors that act systemicaDy (e.g. endogenous
sex hormones and cytokines). Studies have investigated the effects o f resistance training
on sex hormone levels in young women (Cummmg et aL 1987, Kraemer et aL 1993,
Kraemer et aL 1995, Kraemer et aL 1998, Sutton et aL 1973, Weiss et aL 1983,
Westerlind et aL 1987); however, no studies have reported how the alteration in the
female hormonal milieu may influence bone mass. It appears that high-intensity
resistance training may increase endogenous sex hormone (estrogen and
androstenedione) levels in young women while low-intensity resistance training has no
influence on these hormones (Kraemer et aL 1993, Weiss et aL). Therefore, designing a
resistance training study with varying intensities may contribute to the elucidation o f the
factors most responsible for augmenting peak bone mass.
Progressive resistance training (PRT) is an accepted method to enhance muscle
strength (Fleck and Kraemer 1997). The association between greater muscle strength and
increased bone mass has been clearly established (Burr 1997, Snow-Harter et aL 1990).
Whether the relationship between muscle and bone is direct or indirect is unknown. This
relationship may be a combination o f both direct (muscle pull on bone) and indirect (sex
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5
hormone and cytokine) factors inducing an osteogenic response. Repetitive, high force
muscle contractions that generate large peak tensions, such as those experienced during
resistance training, appear to directly stimulate increases in bone mass (Frost 1997, Khort
et aL 1997). Furthermore, increased lean body mass is associated with greater bone
mineral density in eumenorrheic college aged females, supporting the contention that
augmenting muscle mass may have a beneficial effect on bone in young women (Burr,
Madsen et aL 1998).
Eccentric Resistance Exercise
Eccentric resistance training can be defined as an active lengthening contraction
o f the muscle against an externally applied load (lowering the weight). This is different
from concentric muscle action, which is active shortening o f the muscle during
contraction (lifting the weight). Eccentric resistance training results m high levels o f
muscle damage compared to concentric resistance training, which is often experienced as
delayed-onset muscle soreness (DOMS) (Armstrong 1984). Furthermore, it is well
established that strenuous eccentric resistance training results in muscle stiflhess,
prolonged strength loss, increases in creatine kinase (CK), and morphological changes in
muscle (Chleboun et aL 1998, Ebbeling and Clarkson 1990, Mair and Artner-Dworzak
1992, Nosaka et aL 1991, Sorichter et aL 1997). The type and intensity o f training, as
well as the size o f the muscle group exercised may strongly influence the magnitude and
the factors associated with DOMS (Evans and Cannon 1991). Presently, it is not clear
whether high eccentric training intensities (100-130% o f a concentric one-repetition
maximum, 1-RM) generate a greater amount o f muscle damage than lower training
intensities when the same amount o f work is performed. However, eccentric training
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intensities larger than 130% o f a concentric 1-RM do not allow the muscle to develop
sufficient tension to slow and control the stretching force enough to produce a stimulus
for strength gain (Johnson et aL 1976). The limited numbers o f studies utilizing eccentric
resistance training have primarily trained a single muscle group 2-3 times per week for 6-
8 weeks (Hortobagyi et aL 1996, Komi 1986, Sorichter wt aL 1997, Staron et aL 1994).
The long-term effects o f multiple muscle group eccentric training on bone in young
women are unknown.
Direct Effect o f Eccentric Resistance Exercise on Bone
It has been suggested that tension production by the muscle may be the critical
stimulus for increased protein synthesis; therefore, training with eccentric contractions
may provide a greater stimulus for hypertrophy than other contraction types (Atha 1981,
Evans, Meredith, and Cannon 1986, Fielding et aL 1991, Hortobagyi et aL 1996).
Skeletal muscle eccentric (lengthening) contractions are able to generate greater levels o f
tension than concentric (shortening) or isometric (no joint movement) contractions (Doss
and Karpovich 1965, Hortobagyi et aL, Mayhew et aL 1995, Olson, Smidt, and Johnston
1972). Therefore, high-intensity o r maximal eccentric muscle action may provide a
significant osteogenic response (Hawkins et aL 1999).
Indirect Effect o f Eccentric Resistance Exercise on Bone
Strong correlations between muscle strength and bone mass at unrelated sites,
such as the quadriceps and spine (Nordstrom, Bergstrom, and Lorentzon 1996), suggest
that indirect or systemic factors accompanying high force contractions may influence this
relationship. Eccentric exercise induces local muscle damage that is characterized by
sarcolemmal disruption, Z-line streaming, and the release o f enzymes and mitochondria
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from damaged fibers (Friden and Leiber 1992, Hikida et aL 1983, Newham et aL 1983).
This local response to eccentric exercise-induced muscle damage stimulates a systemic
process known as the acute-phase reaction that results in inflammation, an immune
response, and the release o f cytokines (Nosaka and Clarkson 1996). Intriguingly, the
localized bone remodeling process appears to be controlled by cytokines generated in the
bone microenvironment (Marcus 1996), the same cytokines released in response to
eccentric muscle damage. Therefore, the release o f eccentric exercise-induced systemic
factors associated with muscle damage may indirectly influence bone metabolism,
resulting in increases in bone mass.
Resistance Training Rone Mass. and Sex Hormone Levels
In addition to the possible indirect effects o f cytokines on bone, eccentric
resistance training induced alterations in systemic endogenous sex hormone levels may
indirectly influence bone metabolism. Studies have investigated the effects o f resistance
training on bone mass and sex hormones in young women (Cumming 1987, Kraemer et
aL 1993, Kraemer et aL 1995, Kraemer et aL 1998, Sutton et aL 1973, Weiss et aL 1983,
Westerlind et aL 1987), however, no studies have focused on the effects o f eccentric
resistance training-induced sex hormone alterations and their influence on bone mass in
young women. Studies investigating the effects o f resistance training on sex hormone
levels in females have primarily concentrated on the alterations in estradiol and
testosterone (Cumming 1987, Kraemer 1988, Kraemer et aL 1993, Kraemer et aL 1995,
Kraemer et aL 1998, Sutton). However, Weiss et aL compared acute androstenedione
responses to weight lifting in men and women and reported an 8-11% increase for both
genders.
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Androstenedione levels are approximately 40% greater in women than in men
(Weiss, Cureton, and Thompson 1983), however, androstenedione is one-fifth as potent
an androgen as testosterone (McKerns 1969). Androstenedione (an adrenal produced
androgen) may be aromatized (converted) to estrogen in bone and other tissues (Purohit,
Flanagan, and Reed 1992, Schweikert, W olf and Romalo 1999, Tanaka et aL 1993).
Young woman with estrogen resistance o r aromatase (enzyme for aromitization)
deficiency have severely undermineralized bone (Saggese, Berteilone, and Baroncelli
1997). In feet, in contrast to more modest reports, Labrie et aL (1998) has estimated that
as much as 75% o f the estrogen production in premenopausal women occurs with the
peripheral conversion o f inactive adrenal precursors. Many studies on women have
reported significant correlations between androgens and bone density (Aloia et aL 1985,
Buchanan et al. 1988, Deutsch et aL 1987, MarshaO, CriUy and Nordm 1977, Slemenda et
aL 1996, Wild et al. 1987). Additionally, androstenedione has been shown to be the best
marker for the impact o f androgen on trabecular bone density (Buchanan et al.).
Furthermore, androgen receptors have been identified in bone tissue (Abu et al. 1997,
Bellido et aL 1993, Colvard et aL 1989, Orwell et aL 1991). These androgen receptors
are located within the nucleus and bind most androgens with varying specificities.
Androgens have been shown to indirectly inhibit bone resorption through the decrease o f
interleukin-6 (IL-6) production by osteoblasts or bone marrow cells (Bellido, Girasole et
aL 1992, Ryaby et al. 1993), through the inhibition o f prostaglandin E2 production
(Pfibeam and Raisz 1990), through inhibition o f the parathyroid hormone (PTH) effect on
osteoblasts (Fukayama and Tashjan 1989), and through inhibition o f osteoclastogenesis
(Bellido, Ryaby et aL 1993).
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Sum m ary
Sex hormones promote skeletal maturation, bone mineralization, and pubertal
growth (Slemenda 1996). Hormone and cytokine chemical messengers function to
mediate muscle and bone cellular events. Eccentric resistance training may offer a
successful intervention to elucidate how this type o f resistance training may influence
bone mass, either directly (muscle pull on bone), indirectly (systemic response), or as a
combination o f both. Furthermore, eccentric resistance training may help clarify which
factors associated with this specific training regimen may be important in augmenting
bone mass. Further exploration o f the interaction o f these sex hormones and muscle
damage related systemic factors are needed to better develop treatment strategies in the
prevention o f osteoporosis. While many investigators have studied the acute response o f
localized eccentric-exercise induced muscle damage; no studies have reported the effects
o f a whole-body eccentric resistance training intervention on bone mass adaptations.
Eccentric PRT o f bilateral, multiple muscle groups in both the lower and upper body may
generate a large enough stimulus to directly or indirectly influence bone. The study
design allowed the investigator to evaluate the importance o f eccentric muscle pull
(tension), eccentric resistance training induced alterations in systemic androstenedione
levels, and eccentric resistance training induced elevations o f muscle damage related
systemic factors on bone.
Significance
It is essential to determine the intensity o f eccentric resistance training necessary
to influence bone mass, which may contribute to the understanding o f load m agnitude on
bone adaptation. This information will contribute to developing effective resistance
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10
training protocols to increase bone mass. Additionally, understanding the factors
associated with eccentric resistance training and them potential influence on bone in
young women may facilitate the development o f successful non-pharmacologic
interventions for the delay and prevention o f osteoporosis.
Specific Alms
1) Determine if whole body, multiple muscle group, eccentric PRT wQl
significantly enhance muscle strength, lean mass, and bone mass.
2) Determine whether high-intensity (125%) eccentric PRT or low-intensity
(75%) eccentric PRT is more osteogenic.
3) Determine the magnitude o f muscle damage associated with the high- and
low-intensity eccentric PRT.
4) Determine the factors that may be responsible for influencing bone mass with
eccentric PRT in young women.
5) Determine the influence o f high- and low-intensity eccentric PRT on serum
androstenedione levels.
Hypotheses
Hypothesis I: Eccentric resistance training will significantly increase skeletal
muscle and bone mass in young women. Additionally,
osteocalcin (bone formation marker) will significantly increase
while deoxypyridinoline (bone resorption marker) significantly
decreases.
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Hypothesis II:
Hypothesis III:
Hypothesis IV:
Hypothesis V:
Hypothesis VI:
II
These muscle and bone adaptations will significantly increase
muscle strength and lean mass as well as bone mineral density
(BMD) and bone mineral content (BMC), respectively.
High-intensity eccentric resistance training will result in
significantly greater increases in muscle strength, lean mass, and
bone mass than low-intensity resistance training.
High-intensity eccentric resistance training will significantly
increase serum levels o f androstenedione while low-intensity
eccentric resistance training will not significantly influence
serum levels o f androstenedione.
Serum androstenedione will be correlated with increased levels
o f osteocalcin and bone mass and decreased levels o f
deoxypyridinoline.
High-intensity eccentric resistance training will induce a similar
magnitude o f muscle damage (as measured by creatine kinase
and IL-6 levels) as low-intensity eccentric resistance training.
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CHAPTER n
12
REVTEW OF LITERATURE
Bone
Bone provides a framework o f support and protection for the body as well as
acting as a reservoir o f minerals and producer o f differentiable cells. As a structural
support, this unique tissue is capable o f adapting to its' environment. Julius Wolff in
1892 described the distinctive characteristics o f bone and the ability o f bone to adapt to
mechanical usage. Translated in 1986 by Springer-Verlag, W olff summarized the ability
o f bone to adapt to the stresses and strains placed upon it (known today as W olffs law):
Every change in the form and function o f bones, or o f their
function alone, is followed by certain definite changes in their
internal architecture and equally definite secondary alteration in
their external conformation, in accordance with mathematical
laws.
The basis o f W olffs observations and theories has been the foundation o f modem bone
research. Herein, this study was developed with an understanding o f the basic principle
that bone will adapt to the loads placed upon it.
Bone Matrix
The inorganic (mineralized) portion o f the matrix comprises approximately 77%,
while the organic portion makes up the remaining 23% o f the bone matrix. The organic
portion o f the bone matrix is made up o f about 89% type I collagen. The remainder is a
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complex mixture o f noncollagenous proteins such as osteocalcin and proteoglycans
with small amounts o f carbohydrates and lipids (Recker 1992). The collagen-mineral
composite is the source o f the mechanical strength o f the skeleton. The mineral is
deposited along the length o f and between the collagen fibrils. The mineral is in the form
o f hydroxyapatite, a crystalline lattice in which the principle components are calcium and
phosphate ions. The composite arrangement o f collagen and mineral yields a material
that is very strong for its weight and much stronger than either component would be
alone. Because the collagen matrix component is a fiber, the direction o f the fiber
elements affects the material properties. The material properties o f bone become
important when specific forces and strains are generated by mechanical loading
conditions.
Bone Cells
The four primary types o f bone cells are the osteoblasts, lining ceOs, osteocytes,
and osteoclasts. Osteoblasts or bone formation cells appear as plump cuboidal cells that
line up on the surface o f unmineralized osteoid. As matrix formation progresses, the
osteoblasts decrease in number at the formation site and become more flattened. Bone
forming activity slows, and some o f the osteoblasts become incorporated into the formed
bone as osteocytes. Others remain on the surface as lining cells. The lifespan o f the
osteoblast depends on whether or not it becomes an osteocyte. The lifespan o f a team o f
osteoblasts at a particular remodeling site may range from 3-4 months to 1.5 years. The
average formation time is 5-6 months (Recker et aL 1988).
Lining cells are osteoblasts that remain on the surface after laying down matrix.
They alter their shape, becoming flat elongated cells that are visibly different from their
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original osteoblast form. Lining cells communicate with osteocytes through channels
named caniliculi. Caniliculi are small tunnels in the bone. Parathyroid hormone appears
to induce a contraction o f the boundaries o f the lining cells by secreting enzymes, which
clear a small area o f osteoid. This may be the first step that allows the osteoclasts to
begin bone resorption (Mcsheehy and Chambers 1986).
The osteocyte is a survivor o f a group o f osteoblasts from each forming site,
which became entrapped in the bone matrix as it was being laid down. Parfitt (1983) has
shown that fewer cells survive as osteocytes than were present as osteoblasts during bone
formation. The process by which osteoblasts disappear is unknown. The osteocyte cell
body is harbored in a region o f the matrix known as the lacunae. The entrapped
osteocytes have cytoplasmic processes that extend through caniliculi to communicate
with neighboring osteocytes and bone surface cells. Ion and nutrient exchange may occur
by flow along the fluid space between the cell wall o f the osteocyte processes and the
mineralized wall o f the caniliculi.
Osteocytes never divide and only one ever occupies a lacuna. Therefore, their
lifespan varies with the lifespan o f the particular bone tissue they are embedded. They
are destroyed when bone is resorbed. The primary function o f the osteocyte is unknown.
However, the location o f osteocytes, along with their network o f cytoplasmic
communication, suggests that they may play a role in sensing strain resulting from
mechanical force applied to the bone during mechanical usage (Gross et al. 1997,
Spadaro 1997). They may even act as part o f a transducer mechanism that converts
changes in the strain environment into organized bone cell work, known as
mechanotransduction (Salter, Robb, and Wright 1997).
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Osteoclasts are multinucleated, large bone resorbing cells that occupy small
shallow pits on bone surfaces called “Howship’s lacunae.” The osteoclast has a ruffled
border on the side that attaches to the bone. This region contains the highly acidic
molecules that assist in bone resorption. Osteoclasts are highly metaboIicaDy active and
sensitive to parathyroid hormone. The osteoclasts life span has been estimated to be
approximately 7 weeks. However, the average duration o f an active resorption site in
humans is about 4 weeks.
Ossification
Ossification o f bone begins with the appearance o f osteoblasts among the protein
matrix. The osteoblasts begin to mineralize the osteoid. The random order o f the
collagen fibrils o f the matrix at the early stages o f bone formation give the bone a woven
appearance, hence the name woven or primitive bone. As blood vessels invade the
woven bone, it begins to organize itself. Eventually, the woven bone is replaced by
highly organized, densely packed lamellar bone. The lamellar bone is either structurally
organized into compact or trabecular bone (Marcus 1996).
Compact and Trabecular Rnne
Compact (cortical) bone is the dense outer shell o f the skeleton, while trabecular
(cancellous) bone is the system o f plates, rods, and arches encased within the shell o f
compact bone. About 80% o f skeletal mass consists o f compact bone. However,
trabecular bone has a higher degree o f metabolic activity due to the extensive vascular
supply. Trabecular bone is found largely in the ends o f long bones and comprises the
majority o f the vertebral bodies. Therefore, regions such as the proximal femur and
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lumbar spine are common sites ofBM D measurement since osteoporosis appears to
have greater effects on these regions o f trabecular bone (Marcus 1996).
Bone Remodeling
Remodeling (bone turnover) is the term used to describe the process o f removing
bone and replacing it with new bone. Remodeling is essential to maintain skeletal
homeostasis, to provide elasticity o f the bone, and to produce a steady source o f
extracellular calcium (Manoiagas and Jilka 1995). Over time the repeated strain on the
skeleton from ordinary mechanical usage (physical activity) results in bone microdamage
that needs to be replaced or repaired. Without the repair o f bone microdamage, structural
failure will occur and the bone will ultimately fracture.
While bone remodeling occurs in compact bone, the process is more prominent in
skeletal sites rich in trabecular bone, such as the proximal femur, vertebrae, calcaneus,
and distal radius. Shallow excavations (Howship’s lacunae) are formed by the
osteoclasts and then filled in by a team o f osteoblasts. The pattern o f cell appearance is
very specific and tightly coupled. At the remodeling site, activation o f the osteoclasts is
the first step followed by resorption o f the existing bone. Subsequently, at the same site
formation takes place with the activation o f osteoblasts. The groups o f cells that are
involved at the remodeling site are referred to as the basic structural unit (BMU) (Frost
1989). The time sequence for the remodeling process to complete at a specific site may
be as brief as 4 months (Rosen and Tenenhouse 1998) or longer. Recker et al. (1988)
reported that in trabecular bone in young women the remodeling cycle is about 1 month
for resorption and 5 months for formation, resulting in a total o f 6 months to complete the
cycle.
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“Coupling” Bone Remodeling
During bone remodeling, osteoblasts synthesize cytokines and growth factors
essential for coupling bone resorption to formation. It is the perturbation (uncoupling) o f
the relationship o f resorption to formation that characterizes osteoporosis. Either too
much bone is removed during the resorption process or not enough bone is replaced
during formation, resulting in bone loss and skeletal fragility. The signals for the
initiation o f bone remodeling include systemic factors, such as growth hormone,
parathyroid hormone, and estrogen. Cytokines and growth factors (e.g., IL -l, IL-6, IL-
11, IGF-I, and TFG-P) trigger the bone synthesizing activity o f osteoblasts (Manolagas
and JQka 1995). Once the osteoblast is activated, cytokine synthesis and secretion result
in recruitment and differentiation o f osteoclasts at the remodeling surface, hence the
coupling o f bone resorption to formation.
The coupling o f bone resorption to formation and in particular the associated
coupling factors that are most instrumental in the process are poorly understood. Mundy
and Roodman (1987) have described the possible involvement o f bone lining cells, the
osteoclasts themselves or other cell types present in the resorption and reversal lacunae,
or factors released from bone matrix during the resorption phase in regulating the
coupling o f bone remodeling. There are many possible candidates for such coupling
factors that are intrinsic to bone and known to stimulate osteoblast replication and
differentiation.
Osteoporosis
Osteoporosis is one o f the most prevalent chronic health conditions among the
elderly. It is estimated that more than half o f women in the United States will experience
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osteoporotic fractures during their lifetime. However, many o f these fractures may be
preventable. Healthcare costs are currently estimated to exceed $14 billion per year and
projected to reach $240 billion per year by 2040 (Wood 1998). The proportion o f
individuals who have already had fractures is only a small fraction o f those potentially at
risk. Effective preventive measures rely on the early identification o f those at risk and
intervention enhanced development o f peak bone mass, because no symptoms occur prior
to fractures.
Definition o f Osteoporosis
In 1990 the Consensus Development Panel defined osteoporosis as a “disease
characterized by low bone mass and microarchitectural deterioration o f bone tissue,
leading to enhanced bone fragility and a consequent increase in fracture risk (Consensus
Development Conference 1991). Various operational definitions also have been
proposed. Some researchers and physicians rely on BMD measurements alone; others
restrict the term osteoporosis to persons who have had a nonviolent fracture or fractures
(Kanis 1990 and Kanis and MeCIoskey 1992). Although fractures often are the result o f
osteoporosis, this does not mean that fractures should be required for diagnosis, which
may be likened to requiring stroke for diagnosis o f hypertension. It is difficult to
comprehend how the condition o f a woman with low BMD and no fractures would not be
diagnosed as osteoporosis one day but would be considered osteoporosis if she had a
nonviolent fracture the next day.
The rationale for using BMD to define osteoporosis is that patients with a history
o f nonviolent fractures represent only a small proportion o f those at risk, just as only a
small proportion o f patients with hypertension have had strokes at any given time.
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Therefore, low BMD itself should be sufficient to confirm the diagnosis o f
osteoporosis. Cummings et aL (1995) reported that low BMD and previous fractures are
strong risk factors for future fractures. People with both risk factors are at higher risk
than those with a single risk factor. Recognizing th e, the World Health Organization
proposed three categories: 1) low bone mass, or osteopenia, defined as BMD values
between I and 2.5 standard deviations (SDs) below the mean for young (aged 30-40
years) healthy adults; 2) osteoporosis, defined as BMD values more than 2.5 SDs below
the mean for young adults; and 3) severe osteoporosis, with low BMD (>2.5 SDs below
the mean) and history o f nonviolent fracture (Kanis et aL 1994).
Bone mineral density is determined by genetic factors, hormonal status, calcium
intake, physical activity, and weight. Krall and Dawson-Hughes (1993) reported that 46-
62% o f the variance in BMD could be attributed to genetic factors in a study with parents
and their children. In another twin study, Pocock et al. (1987), showed that as much as
80% o f BMD is related to genetics. Although small (accounting for maybe as little as
20%), environmental factors when appropriately manipulated may favorably influence
the development o f peak bone mass.
Measuring BMD
The breaking strength ofbone is proportional to BMD squared. The elastic
modulus ofbone is proportional to BMD cubed. These properties suggest that continued
bone loss disproportionately increases fracture risk as BMD foils (Seeman 1997).
Therefore, assessing BMD early in life and providing proper treatment intervention (if
necessary) would be advantageous. The preferred measurement o f BMD is performed
using dual-energy X-ray absorptiometry (DXA). This method provides a safe,
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noninvasive, relatively inexpensive procedure that can identify large differences in risk
o f fracture between individuals. Furthermore, measurement o f BMD has sufficient
reproducibility to monitor changes over time with coefficients o f variation less than 1%.
A detailed description o f how DXA measures BMD is described in the Methods section.
Reported measurements o f BMD are often in terms o f the T score and Z score.
The T score assesses the risk o f fracture by comparing the subject’s BMD with the
predicted mean peak BMD (in an average 30-year old o f the same sex) and expressing
the difference in standard deviations (SDs). Therefore, the T score shows how the
subject’s BMD compare with the ideal level. For example, a subject whose BMD is 1 SD
below that o f an average 30-year-old has a T score o f— 1. At the spine, I SD is about
10%, so this individual has BMD about 10% below that o f the average 30-year-old. The
Z score determines whether the subject’s bone loss is out o f proportion with what is
expected. It compares the subject with the mean for age-matched, sex-matched, and
ethnic-matched controls and expresses the difference in SDs. For example, a 70-year-old
woman with a Z score o f -1 would be I SD below the BMD o f the average 70-year-old
woman, but her T score is — 3 because she would be 3 SD below the BMD o f the average
30-year-old.
Markers o f Bone Turnover
Markers ofbone turnover are biochemical markers ofbone formation and
resorption. The development o f assays, which allow us to monitor and measure the levels
o f a particular marker, have provided bone researchers with a valuable tool. Markers o f
bone turnover can be used in conjunction with densitometry measurements and provide
early assessment ofbone turnover rates (BOde 1997). These markers are classified as
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bone formation or bone resorption markers. All the markers are obtained from serum
or urine. Urine measurements must be normalized to creatinine, which increases the
variability o f the measurement. However, these markers provide quick, inexpensive
assessment o f changes in the bone environment.
Weaver et al. (1997) validated the use ofbone turnover markers, quantifying
biochemical markers ofbone turnover by kinetic measures ofbone formation and
resorption in young healthy females. They measured biochemical markers o f formation
(serum osteocalcin, bone-specific alkaline phosphatase, and total alkaline phosphatase)
and resorption (serum tartrate resistant acid phosphatase, urinary cross-linked N
teleo peptides o f type I collagen/creatinine, and hydro xypro line/creatinine) in females
aged 11-32 years. Highly significant correlations were reported between bone formation
and resorption measured by calcium kinetics and serum levels ofbone biochemical
markers o f formation and resorption, respectively. Weaver et aL concluded that
biochemical markers ofbone formation and resorption can be used to predict bone
formation and resorption rates during the skeletal growth and the early years o f formation
o f peak bone mass.
Peak Bone Mass
Understanding the kinetics o f peak bone mass accretion is important in
determining the optimal time point for intervention. Peak bone mass appears to be site-
specific and is often measured at clinically important sites such as the lumbar spine,
proximal femur, and radius. Bonjour et aL (1991) in a cross-sectional study using DXA
on 207 boys and girls aged 9-18 years reported skeletal mass growth appears to
dramatically slow down at the levels ofboth lumbar spine and femoral neck at 15-16
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years o f age in female adolescents. Theintz et al. (1992) in a longitudinal study with
198 adolescents, aged 9-19 years, reported strong evidence that peak bone mass at the
lumbar spine and femoral neck measured by DXA occurs 2 years after menarche.
Several researchers report bone accretion and increases in BMD into the beginning o f the
third decade o f life in young women (Buchanan et aL 1988, Prentice et aL 1991, Lu et aL
1994). Such findings account for only very small increases in BMD after the second
decade. There appears to be a small increase in BMD o f the radius in females at the rate
o f 0.2% per year after the age o f 18 years (Matkovic et al. 1991). The slow increase in
radial BMD is probably responsible for the general assumption in the literature o f the late
timing o f peak bone mass in the late 20’s and early 30’s (Buchanan et aL, Prentice et aL).
In a five-year longitudinal prospective study o f 156 college-aged women, Recker et al.
(1992) reported gain in bone mass o f 5.9% for lumbar spine BMD and 12.5% for total
body BMD.
After peaking, bone density remains stable or slightly declines from its peak until
the onset o f menopause (Lu et al. 1994). In a cross-sectional study by Teegarden et al.
(1995) with 247 women aged 11-32 years, total body BMD was measured by DXA.
Peak total BM D appeared to be reached by the beginning o f the third decade, while bone
mineral content (BM C) continued to increase until the latter part o f the third decade. If
BM C continues to change over the third decade while BM D remains the sam e, this
suggests that there is a change in the bone geometry during this period. With no
significant changes in height after the age o f 18 years in women, the changes in bone
geometry may be due to increases in the periosteal or endosteal surfaces. This suggests
that environmental factors such as exercise may contribute to bone accretion during the
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third decade o f life in women. Exercise, hormonal status, and calcium intake are the
primary factors reported as playing an essential role in the development o f peak bone
mass (Young et aL 1994, Buchanan et aL 1988, Snead et aL 1992, Lloyd et aL 1988,
Slemenda and Johnston 1993, Myerson et aL 1992, Marcus et aL 1985, Robinson et aL
1995).
Hormones
Estrogens
The primary hormones influencing bone acquisition and muscle growth in young
women are the sex steroids, estrogens and androgens. In the human, the biosynthesis o f
estrogens occurs at a number o f sites. The principal sites are the granulose cells o f the
ovary in premenopausal women and the stromal cells o f adipose tissue in postmenopausal
women. The ovary synthesizes primarily estradiol, whereas the placenta synthesizes
estrioL and adipose tissue synthesizes estrone (Simpson 1995). O f the three forms o f C18
estrogens produced, estradiol is the most potent (Sasano 1997). Estrogen may be
synthesized from cholesterol by specific enzymes resulting in several intermediate C19
structures. Cholesterol forms pregnenolone which can be converted into
dehydroepiandrosterone (DHEA) or progesterone. Both DHEA and progesterone can be
converted into androstenedione. Androstenedione may be aromatized (metabolized) to
estrone or reversibiy catalyzed to testosterone by the enzyme l7|3-hydroxysteroid
dehydrogenase (17[3-HSD). Additionally, estrone may be reversibiy catalyzed by 17P-
HSD to estradiol. Furthermore, testosterone may be aromatized to estradiol (Appendix
B).
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In normal eumenorrheic women o f reproductive age, the majority o f plasma
estradiol is derived by direct secretion from the ovary, and there is little if any estradiol
formation from testosterone by extraglandular conversion (Simpson 1995). Most
estrogen producing cells do not contain all the steroid biosynthetic enzymes necessary for
estrogen biosynthesis. For example, little estrone is formed by direct ovarian secretion,
and most estrone circulating in plasma originates from extraglandular conversion from
androstenedione and, to minor extent, from estradioL After puberty, estrogen helps to
protect against bone loss by suppressing the release o f Interleukin-6 (IL-6) in the bone
environment. Additionally, estrogen may also have a protective effect on muscle
(Holmes and Shalet 1996).
A rom atizatinn
As stated above, the ovary is the main contributor to circulating estradiol in
premenopausal women but estrogen biosynthesis after menopause is mainly peripheral,
through the conversion o f androstenedione or C19 steroids from the adrenal cortex and
ovaries (Miller 1991, Schweikert, Milewich, and Wilson 1976). This peripheral process
takes place in skin (Schweikert, Milewich, and Wilson), muscle (Miller, Hawkins, and
Forrest 1982), adipose tissue (Perel, Wilkins, and Kfllinger 1980), brain and bone
(Sasano 1997). One o f the primary sites o f conversion as it relates to bone mass is
adipose tissue. Estrogen biosynthesis by adipose tissue increases not only as a function
o f body weight but also as a function o f age (HemseQ 1974). Estrogen biosynthesis in
adipose may have beneficial consequences because osteoporosis is more common in
small, thin women than in large, obese women. Although this may be partially the
consequence o f the bones o f the larger women being subject to load-bearing exercise, it
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seems likely that the increased production o f estrogens by the adipose tissue o f obese
woman is a significant factor (Hemsell)-
The conversion o f androstenedione to estrone and the conversion o f testosterone
to estradiol are both catalyzed by the enzyme complex cytochrome P450 aromatase. The
aromatase enzyme is made up o f two proteins. The first is a member o f the superfamily
o f genes known collectively as cytochrome P450, the product o f the CYP 19 gene (KeDis
and Vickery 1987). This heme protein is responsible for binding the C19 steroid
substrate and catalyzing the series o f reactions leading to formation o f the phenolic A
ring characteristic o f estrogens. The second protein is NADPH-cytochrome P450
reductase that is responsible for transferring reducing equivalents from NADPH to
cytochrome P450.
Aromatization o f androgens to estrogens plays an important role in the
maintenance o f hormone levels in both men and women. Morishima et aL (1995)
reported a case study o f aromatase deficiency in male and female siblings caused by a
genetic mutation. Both the male and female had tall stature and osteoporosis at the age o f
28. The observations made after evaluating these patients were: 1) estrogens are essential
for normal skeletal maturation and proportions (but not linear growth) in men as in
women, the accretion and maintenance BMD and mass, and the control o f the rate o f
bone turnover; 2) estrogens have a significant role in the sex steroid-gonadatropin
feedback mechanism in the male, even in conditions ofhigh circulating testosterone; 3)
deficient estrogens in the adult male appear to be associated with hyperinsulinemia and
abnormal plasma lipids; 4) and placental aromatase has a critical role in protecting the
female fetus from fetal masculinization and the pregnant women from virilization.
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Androgens
Testosterone, produced by the Ieydig cells o f the testes, is the major circulating
androgen in men. A number o f androgen precursors and metabolites are also present in
the blood, but because their concentrations or biological activities are low relative to
those o f testosterone, they do not contribute to the overall androgen content o f blood. In
contrast, androgen precursors and metabolites make up a significant fraction o f total
circulating androgens in women (Bardin, Hardin, and Catterall 1995). This is true
because the majority o f the testosterone produced in women is not secreted by endocrine
organs but is produced in peripheral tissues as discussed above. However, the adrenal
cortex and ovaries secrete some o f the androgens in females. After puberty, testosterone
originates approximately 25% from the ovary, 25% from the adrenals, and as little as
50% (Simpson 1995) o r as much as 75% (Labrie et aL 1998) from the aromatization o f
androstenedione. Androstenedione is produced equally by the adrenal cortex and the
ovaries. In contrast, approximately 90% o f DHEA and 99% o f DHEA-S (sulfeted
DHEA) are produced by the adrenal cortex.
In eumenorrheic females, the circulating levels o f plasma androgens do not vary
significantly with weight and in feet may be slightly lower in overweight subjects (Azziz
1989). Adrenal androgen clearance appears to be increased in obese women and
peripheral aromatization is responsible for a large fraction o f this increased clearance
(Azziz). In addition, adipose tissue demonstrates a small degree o f 17p-HSD activity,
which promotes the conversion or clearance o f androstenedione to testosterone. Adipose
tissue also contributes to androgen clearance through steroid storage in the lipid fraction
o f the adipocytes (Azziz).
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Androgens, in particular testosterone, may be metabolized to a more active
steroid (dihydrotestosterone, DHT), to a much less active steroid (etiocholanolone) for
excretion, or to a hormone (estradiol) with an entirety different biological activity. The
biological activitiy o f testosterone is increased by 5a-reductase, an enzyme that reduces
testosterone to DHT. Dihydrotestosterone is two to three times more potent than
testosterone, and its production occurs in skin and in the tissues o f the male reproductive
tract (Bardin, Hardin, and Catterall 1995). Bruch et aL (1992) showed that testosterone
could be converted to DHT by 5a-reductase in human spongfosa and cultered osteoblast
like cells. Dihydrotestosterone enhances androgen action because it binds more tightly to
the androgen receptor than testosterone binds (Breiner, Romalo, and Schweikert 1986).
Androgens, having the unique feature o f being converted within a target cell to either the
nonaromatizable DHT or into estradiol, may therefore be expressed via activation o f the
androgen or estrogen receptor in bone tissue.
Androgen, as well as other steroid receptors are present in osteoblasts (Abu et al.
1985, BeUido et aL 1993, Colvard et aL 1989, Orwell et aL 1991). Receptor affinities are
comparable with those o f androgen receptors found in androgen target tissues such as the
prostate in men. However, receptor concentrations are very low when compared with
typical androgen target tissues (Orwell). Therefore, androgens may influence skeletal
homeostasis both directly (as testosterone or DHT via the androgen receptor) and
indirectly (after the aromatization via the estrogen receptor).
Sex Hormone Binding Glohultn fSHBCB
Because sex steroids are mostly insoluble in the aqueous portion o f body fluids,
they are transported bound to proteins. In the blood the major protein that binds
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androgens and estrogens is SHBG, which is produced by the liver.
Dihydrotestosterone followed by testosterone have the highest affinities for SHBG,
whereas estradiol has one-third the affinity o f DHT (Bardin 1995). The majority o f
testosterone is bound to SHBG, however, the majority o f estradiol (60%) is bound to
serum albumin with 38% bound to SHBG and 2% to 3% is free (Iqbal and Johnson
1979). It is believed that free and albumin-bound sex steroids enter the tissues and are
biologically active, whereas the SHBG-bound sex steroids do not enter the tissue and are
inactive. Clearance o f sex steroids from the blood is inversely related to the affinity to
SHBG, so that alteration in the concentration o f SHBG influences the target tissue action
(Iqbal and Johnson). Levels o f SHBG are increased by estrogens, pregnancy and oral
contraceptives, and thyroid hormones and decreased by androgens, hypothyroidism and
obesity (Anderson 1974). Furthermore, women have twice the concentration o f SHBG as
men. most likely attributable to the higher estrogen levels found in females.
Investigators have tried to determine the effects o f endogenous hormones on the
risk o f hip and vertebral fractures. In a study by Cummings et aL (1998), they compared
baseline serum concentrations o f selected hormones in women who later had hip or
vertebral fractures with randomly selected control women from the same cohort. They
found that postmenopausal women with undetectable serum estradiol concentrations and
high serum concentrations o f SHBG had an increased risk o f hip and vertebral fracture.
Additionally, results o f other studies o f the same cohort demonstrated that low serum
estrogen concentrations and high serum concentrations o f SHBG were associated with
lower bone density and more rapid bone loss (Parisien et aL 1994, Finkelstein 1996).
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Bone and Hormones
Sex steroids promote skeletal maturation, bone mineralization, and pubertal
growth. Estrogens as well as androgens are important in bone mineralization (Slemenda
et aL 1996). The presence o f androgen receptors in bone marrow stromal cells (Bellido et
al. 1993) and hi osteoclasts-like multinucleated cells (Mizuno 1994) suggests that
androgens could directly inhibit bone resorption. As stated in the introduction, androgens
have been shown to indirectly inhibit bone resorption through the decrease o f IL-6
production by osteoblasts o r bone marrow cells (Bellido, Girasole et al. 1992, Ryaby et
a l 1993), through the inhibition o f prostaglandin E2 production (PQbeam and Raisz
1990), through inhibition o f the parathyroid hormone (PTH) effect on osteoblasts
(Fukayama and Tashjan 1989), or through inhibition o f osteoclastogenesis (Bellido,
Ryaby et aL 1993). Additionally, the inhibitory effects o f estrogens on bone resorption
are well established. As androgens may be converted into estrogens by aromatase, their
effects may also depend upon their conversion into estrogens.
Although hypogonadism represents a risk factor for osteoporosis in men, it is not
clear if there is a threshold concentration o f free testosterone associated with increased
risk for osteoporosis. Testosterone levels have not been correlated with bone density in
eugonadal adult men (McElduflf Wilkinson, Ward and Posen 1988). However, treatment
with nandrolone decanoate (synthetic testosterone derivative) in postmenopausal women
has been reported to significantly increase bone mass (Hassager, Riis, Podenphant, and
Christiansen 1989a, Hassager et aL 1989b, Erdtsieck et aL 1994) Furthermore, androgen
concentrations are positively correlated with bone density in women (Aloia et aL 1985.
Buchanan et aL 1988, Deutsch et aL 1987, Marshall, Crilly and Nordm 1977, Slemenda et
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aL 1996, Wfld et al. 1987). In feet, Lea, Moxham, Reed, and Flanagan (1998) have
shown that androstenedione reduced the loss o f cancellous bone volume in rats in a dose-
dependent fashion by reducing bone turnover. Additionally, the effect o f
androstenedione was not inhibited by an antiaromatase, implying that the skeletal
protective effect o f androstenedione was not estrogen mediated.
Androgen excess in women may be associated with high body mass index and
low SHBG concentrations, which increases the levels o f bioavaOable concentrations o f
sex steroids. The condition o f precocious puberty, which is the early onset o f puberty in
young girls, shows an increased BMD for the child’s chronological age, but appropriate
for their bone age and pubertal stage. The pubertal increase o f BMD may be the result o f
coordinated activation o f estrogen and androgen receptors at the bone level. It is also
possible that the protective effects o f androgens in women can be explained by the local
aromatization into estrogens as discussed above. Conversely, young women with
estrogen resistance or aromatase deficiency have a severely undermineraKzed skeleton
(Saggese et al. 1997). Buchanan et aL (1988) in a study o f 30 women 18-22 years o f age,
divided the women into three groups: sedentary, no exercise; eumenorrheic athletes; and
oligomenorrheic athletes. They concluded that androgens and estrogen function as
independent and additive determ inants o f peak trabecular bone density in young women.
Further, they reported that the quantitative impact o f aerobic exercise (without resistance
loading) appears to be less important than that o f the hormonal influence.
Oral Contraceptives
Oral contraceptive (OC) use offers a method ofhelping to prevent osteoporosis in
young women similar to that ofhorm one replacement therapy used by postmenopausal
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31
women. Although the majority o f studies investigating the impact o f OC’s on bone
mass have found beneficial effects o f long-term OC use (Recker et aL 1992, Fortney et al.
1994, Enzelsberger et aL 1988, Kleerekoper et aL 1991, Kritz-S ilverstein and Barrett-
Connor 1993), some studies have foiled to find any significant benefits (Hall, Heavens,
Cullum, and Ell 1990, Volpe, Sflferi, Genazzani, and Genazzani 1993). The differences
can be explained by study design or inadequate sample sizes to determine significant
differences. Recker et al. (1992) evaluated the relationship between BMD and OC use in
156 premenopausal women. O f the 156 women studied, 79 had never used OC’s, 34
were current users, and 43 were past users. Total body BMD measured by single- and
dual-photon absorptiometry was significantly correlated with OC use, and an 11.3%
increase in BMD was observed with continuous use o f OC’s.
In a large retrospective cross-sectional epidemiologic study by Kleerekoper et aL
(1991), 2297 women were examined for risk factors associated with low BMD (76% o f
the women were postmenopausal). Women were grouped according to BMD measured
by single- or dual-photon absorptiometry o f the forearm o r lumbar spine. Women with a
history o f OC use had a significantly lower risk ofhaving low BMD and were
significantly more likely to have high BMD. A significant association was observed
between duration o f OC use and BMD, with the greatest protection against bone loss in
women who had used OC’s for greater than 10 years. The proportion o f women who
were OC users was significantly higher among the quartile with the highest BMD than
the lowest. The long-term effects o f OC use on BMD were studied by Kritz-S ilverstein
and Barrett-Connor (1993) in 239 postmenopausal women. O f those women studied,
35% had a history o f prior OC use. The duration o f OC use ranged from 1-15 years, with
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32
a mean o f 4.1 years. Use o f OC’s for greater than 6 years was associated with a
significantly higher BMD o f the lumbar spine and femoral neck compared with nonusers.
While endogenous levels o f sex steroids appear to play an important role in the
maintenance ofbone mass, OC use also seems to contribute an additional benefit to
maintaining higher bone mass with chronic use. However, the interaction o f these
hormones and the other factors, such as cytokines and growth hormone (GH), which may
help regulate the bone environment remain poorly understood.
The sex steroids may influence the accrual ofbone mass directly or indirectly, via
cytokines, local growth factors, GH, and insulin-like growth factor I (IGF-I) (Saggese,
Bertellone, and BaronceQi 1997). In turn, GH and IGF-I stimulate the secretion o f sex
steroids by the gonads and augment their effects on bone and muscle. Growth hormone
and IGF-I function to increase the bone remodeling rate and ultimately increase BMD.
Additionally, GH and IGF-I have anabolic effects on muscle tissue. All these factors
appear to be important in the accrual and preservation ofbone mass.
Cvtokines
Cytokines are local, soluble factors (autocrine or paracrine) that are primarily
produced by immune, bone, and stromal cells. There is evidence that cytokines are
involved in both normal and abnormal bone remodeling. The localized bone remodeling
process appears to be under control by cytokines generated in the bone
microenvironment. They may function as both stimulators and inhibitors o f osteoclastic
bone resorption. Interleukin-6, transforming growth factor [ 3 (TGF-(3), and IL-1 are
several o f the many cytokines involved in bone processes. Interleukin-6 is a promoter o f
bone resorption by stimulating the formation o f cells with osteoclast characteristics. The
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33
osteoclasts express IL-6, TGF-p, and IL-1, which may regulate osteoclast formation
and function (Marcus et aL 1996). Furthermore, polymorphisms o f the IL-6 gene have
been shown to be associated with BMD, implying that there is genetic regulation ofbone
mass (Murray et aL 1997).
Transforming growth factor p inhibits osteoclast formation and is a powerful
stimulator o f osteoclast apoptosis. However, TGF-P may generate the production o f
prostaglandins, which have been shown to stimulate osteoclast formation and activity.
Alternatively, in muscle, TGF-P is a negative regulator that limits the development and
growth o f muscle cells. These osteoclast cytokines are probably released by dying
osteoclasts to produce a new generation o f osteoclasts.
Interleukin-1 exerts systemic as well as local actions on bone. The most is known
about this cytokine and its resorptive actions on bone. Interleukin-1 is a powerful
stimulator o f osteoclast formation and also stimulates prostaglandin synthesis. In
general, all the major cytokines are regulators ofbone resorption except for TGF-P and
macrophage colony stimulating factor (M-CSF), which are promoters ofbone formation.
Growth Factors
Growth factors, like cytokines help to regulate bone and muscle tissue. There are
many GF’s and often they are grouped into types o f cytokines. For example, TGF-P,
which was described above is a GF and often grouped as a cytokine. Growth factors, as
their name implies, generally promote formation ofbone and muscle tissue. Insulin like
growth factors have been shown to stimulate osteoblastic cell proliferation and
differentiation. Locally produced IGF’s by bone cells become incorporated into bone
matrix and may be released later during resorption (Linkhart, Mohan, and Baylink 1996).
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34
This may help to mediate coupling ofbone formation to resorption. In general, GF’s
are associated with osteoblastic function and bone formation, while cytokines are
associated with osteoclastic function and bone resorption. However, without regard to
classification, cytokines and G P s function to mediate the bone microenvironment.
Inclusively, hormones, cytokines, and G F s are important hi regulating many
cellular functions within the body. As discussed above, these messengers function in
concert with mechanical loading to alter bone and muscle. Exercise imposes mechanical
strain o f varying intensities on the skeletal system. These strains stimulate cells to
release hormones, cytokines, and GF’s to alter the cellular environment in preparation to
enhance bone and muscle mass. While the functions o f most hormones are understood,
many o f the actions o f cytokines and GF’s need further elucidation. Currently, it appears
that mechanical loading dominates the process ofbone formation and resorption, and that
the cellular messengers play an essential role in this process.
Physical Activity and Bone
Harold Frost (2000) has simply stated the importance o f mechanical usage and
physical activity on bone:
Bones have the main purpose o f providing only enough strength
to keep voluntary physical loads, whether subnormal, normal, or
supranormaL, from causing spontaneous fractures. Satisfying that
ultimate test o f a bone’s health would define “mechanical
competence” and constitute the main goal o f its biologic
mechanisms. Bones cannot foresee and adapt to one-time
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35
injuries, so they adapt their strength to their past and present mechanical
usage instead.
Robert Marcus (1998) in a review o f exercise and bone concluded that
attempts to improve peak bone mass in young women was a laudable goal;
however, improvements ofbone mass in the average individual were modest
at best. Importantly, Marcus does acknowledge the overall benefits o f
exercise on general health even if the training induced bone changes are
minimal.
Investigators have reported increased BMD in young women as a result o f
habitual exercise. Previous physical activity in women aged 18-31 years has been shown
to be modestly related to bone mineral measures (Teegarden et aL 1996). Ho et aL
(1997) in a cross-sectional analysis o f baseline data in a longitudinal study o f 273
women aged 21-40 years divided into two groups (21-30 and 31-40), reported that
together with age and lean body mass, physical activity and dietary calcium intake
accounted for 19% o f the variances o f BMD at the spine and 9-11% at the hip. In the
group o f 31-40 year old women physical activity was not associated with increased
BMD. The increases in the 21-30 year old group may have been due to a stronger
response ofbone remodeling to mechanical stimuli during the period when peak bone
mass is still taking place. Similarly, Uusi-Rasi et al. (1988) showed that both high
physical activity (measured as 9 METs) and high calcium intake were associated with a
higher total body BMC when compared with low activity (measured as < 2.25 METs)
and calcium intake.
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36
An eight month study by Snow-Harter et al. (1992) has shown that exercise
intervention hi college women (with a mean age o f 20 years) resulted in a significant
increase in BMD at the lumbar spine but not at the proximal femur. Friedlander et al.
(1995) in a study with 127 subjects aged 20-35 years participating in a two-year aerobics
and weight training program reported beneficial effects on BMD. Similar to Ho et aL’s
(1997) study, Friedlander et aL hypothesized that the skeleton is more responsive to
exercise stimulus during that particular age period (mean age less than 30) or that the
subjects are willing to exercise at a greater level o f intensity than are older individuals.
Valdimarsson et aL (1999) in a cross-sectional study with 254 women aged 16,
18, and 20 years found lean mass to have stronger correlations (ranging from r = 0.41-
0.77; p < 0.001) with BMC and BMD in the lumbar spine, proximal femur, distal
forearm, and total body, stronger than weight, strength, height, and fat mass. The authors
concluded that exercise and adequate muscle seem to be significant predictors o f the
attainment o f peak bone mass in women. In another study with college-aged women,
Madsen et aL (1998) reported that lean body mass and weight bearing exercise both
enhance BMD in eumenorrheic young adult women. The athletes classified as low body
weight had significantly greater total body, lumbar spine, and femoral neck BMD than
sedentary individuals classified as low body weight. Their results strongly support the
contention that lean body mass is more closely associated with BMD than absolute
strength and that the latter does not have an independent influence on BMD. Burr (1997)
in a review described several studies, which have shown that greater muscle
mass/strength is associated with greater bone mass, but not all findings have been
independent o f other body size measures. Interestingly, strong correlations between
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37
muscle mass/strength at one site and bone mass/strength at another unrelated site
suggest that the relationship may be related to the independent effects o f other stimuli.
The loss o f muscle mass precedes the loss o f bone mass with disuse (Kalbnan,
Plato, and Tobin 1990, Caimels, Vico, Alexandre, and Minaire 1995, Brooks and
Faulkner 1994). Physical activity results in the recovery o f muscle mass before the
normalization o f BMD (Burr 1997). This process demonstrates the direct cause and
effect association o f muscle mass and strength on bone mass. The extent to which
mechanical loading dominates the process o f bone gain and loss over other
nonmechanical factors can be determined by studies which combine variations in
hormone and cytokine levels with alterations in mechanical loading. Studies in rat
models have shown that estrogen deficient mice exposed to skeletal loading o r unloading
have different bone turnover rates (Burr). Investigators using these rat models have
concluded that bone turnover rates are determined by estrogen, but the balance between
resorption and formation is determined by mechanical loading. In addition, some data
suggests that estrogen might act to prevent bone loss partly by preserving muscle
strength. Therefore, it is known that mechanical loading influences bone mass and may
be dependent on nonmechanical stimuli such as the hormones, cytokines, and growth
factors that regulate the muscle and bone cellular environment.
Bone A daptation to Strain
High strains, high strain rates, and unusual strain distributions are particularly
osteogenic and absolutely integral in the development and maintenance o f the human
skeleton. Strain is simply the product o f mechanical usage on bone. Too much strain
results in fracture, while too little strain (below the individualized threshold) results m
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38
loss o f bone mass and fragility (osteopenia/osteoporosis). Rubin and Mcleod (1996)
and Lanyon (1992) have inclusively described the importance o f mechanical loading and
strain on bone with their investigations. It appears that weight-bearing, high-impact
loading is the most osteogenic promoter o f bone adaptation in young women. Examples
o f loading intensity would be that o f aerobic dance that has been reported to be 3.5 times
body weight and sprinting, which may be as high as 5.5 times body weight (Scharff-
Olson et al. 1997). Additionally, the high-impact movements o f gymnastics have been
recorded by McNitt-Gray (1995) to be as much as 9.3 times body weight. These and
other high-impact exercises may have positive long-term influences on BMD in young
women, particularly if similar types o f mechanical loading were performed during
childhood and adolescence.
The importance o f strain imposed on the skeleton by impact loading is well
documented (Rubin and Lanyon 1985); however, the influence o f skeletal muscle
contraction induced strain receives less attention. Muscle contraction induces far smaller
strains on bone than impact generated strains (Rubin and Mcleod 1996). Nevertheless, a
characteristic often overlooked is the ability o f muscle induced strains to be sustained for
extended periods o f time (e.g., postural muscle activity). Rubin and Mcleod (1996) have
investigated the strain components during standing and gait in humans. They concluded
that although gait results in higher transient strain changes, the time averaged strains
measured while standing dominate the strain history. They report that the time averaged
strain history may better portray the wide range o f strain information present in bone and
that these persistent low amplitude signals may additively overwhelm peak strain
loadings.
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39
Rubin and McLeod (1996) describe some interesting trends o f muscle possibly
influencing bone. They have demonstrated the importance o f high frequency strain as an
osteogenic stimulus. With advancing age, high frequency muscle activity decreases due
to alterations in central nervous system firing rates o f motomeurons and muscle fiber
characteristics. These changes in muscle parallel changes in bone. Therefore, Rubin and
McLeod attribute declines in high frequency muscle activity, in part, explaining the
difficulty o f maintaining bone mass during aging even in the presence o f rigorous
exercise. They suggest that supplementation o f high frequency components o f the
endogenous strain environment could provide beneficial treatment strategy.
In contrast to findings by Rubin and McLeod (1996), Lu, O’Connor, Taylor, and
Walker (1997) reported that voluntary muscle forces place greater loads on bones than do
gravitational forces associated with weight. They implanted hip prostheses with strain
gauges mounted in the femoral heads in human volunteers. The analyses showed that
greater than 70% o f the bending moments on bone are transmitted by muscle force rather
than body weight. Therefore, if voluntary muscle contraction is capable o f generating
higher magnitude osteogenic strains, then mechanical usage that employs muscular
contraction, such as resistance training, may be an efficacious treatment to improve bone
mass.
Resistance Training
Resistance training establishes unique, high strain forces generated by muscular
contraction, which act directly on bone. It has been hypothesized that the direct tension
generated from muscle contraction stimulates increases in bone formation (Burr 1997).
Frost (1997) and Khort et aL (1997) have shown that repetitive, high force muscle
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40
contractions that generate large peak tensions, such as those experienced during
resistance training, appear to directly stimulate increases in bone mass. The type,
duration, and intensity o f the resistance training impose differential stimuli to the bone.
Therefore, selecting the appropriate training characteristics may have profound effects on
the treatment outcomes.
Concentric Vs. Eccentric Training
There are three primary types o f muscular contraction: concentric, isometric, and
eccentric. In a concentric contraction, tension develops in the muscle, a resistance is
overcome, and the length o f the muscle shortens. In an isometric contraction, muscle
length remains constant as muscle tension is developed. Lastly, in an eccentric
contraction the muscle develops tension, a resistance overcomes the muscle tension, and
the muscle increases in length. There are several important characteristics that differ
between concentric and eccentric muscle contraction. Fust, eccentric muscle contraction
is capable o f controlling heavier loads than concentric muscle contraction (Johnson,
Adamczyk, Tennoe, and Stromme 1976). Second, greater electromyographic (EMG)
activity is generated with concentric contraction (Olson, Smidt, and Johnston 1972,
Hawkins et aL 1999). And third, greater co ntractio n-induced muscle damage occurs with
eccentric contraction (Clarkson, Nosaka, and Braun 1992).
The different characteristics between contraction types have led investigators to
study the optimal type o f training to increase muscle size and strength (Komi and Buskirk
1972, Hortobagyi et aL 1996, Dudley, Tesch, Miller, and Buchanan 1991). It is accepted
that gains in strength and mass are proportional to the magnitude o f the training load
(Hortobagyi et al. 1996). Therefore, one would hypothesize that eccentric training with
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41
loads greater than could be accomplished with concentric training would result in the
largest strength and mass gams. This concept has been demonstrated in studies by
Hortobagyi et aL (1996) and Dudley, Tesch, Miller, and Buchanan (1991). Conversely,
some investigators have found no differences in strength and mass gains between
concentric and eccentric training (Jones and Rutherford 1987, Hortobagyi and Katch
1990).
The magnitude o f the load utilized in eccentric training is typically greater than a
concentric one repetition maximum. Johnson, Adamczyk, Tennoe, and Stromme (1976)
performed a number o f studies utilizing eccentric training. They reported that subjects in
their studies found that if the stretching force was greater than 130-140% o f a concentric
one repetition maximum they would be unable to slow it sufficiently, in a free movement
resisting gravity, to permit their muscles time to develop maximum tension. Based on
these observations Johnson et aL imposed loads o f 120% o f a concentric one repetition
maximum because such a load is near the maximum that can be used with eccentric
contractions in a free movement resisting gravity, or against pulley machine exercises,
since loads heavier than this accelerate the stretching muscles too rapidly.
Kellis and Baltzopoulos (1998) investigated the EMG activity and joint moment
(force) production between isokinetic eccentric and concentric contractions o f the
quadriceps and hamstrings. Twelve females (20.5 years o f age) performed isometric,
concentric, and eccentric contractions at angular velocities between 30-150 degrees per
second. They found that eccentric contractions generated significantly greater moments
and lower EMG activity compared to concentric contractions. The importance ofhigh
loads with eccentric contractions was demonstrated in a 4 week training study by
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42
Mayhew, Rothstein, Finucane, and Lamb (1995). Fourteen female and 6 male subjects
performed either concentric contractions o f their quadriceps femoris muscles at an
intensity o f 90% o f their maximal concentric power or eccentric contractions at the same
relative power level (90% o f their concentric maximum). They exercised 3 times per
week for 4 weeks at a constant speed o f 60 degrees per second on a Kin-Com
dynamometer. The authors reported findings o f greater muscle fiber hypertrophy and
isometric torque in the subjects that trained at the same relative power level with
eccentric contractions.
Eccentric Exercise-Induced Muscle Damage
One o f the landmark characteristics o f eccentric exercise is the increased
magnitude o f muscle damage associated with eccentric contractions. Although few (6
cases), some adverse events have been reported with eccentric exercise protocols (Sayers,
Clarkson, Rouzier, and Kamen 1999). Long-term inflammation and soreness associated
with rhabdomyo lysis requiring hospitalization to prevent kidney failure are the
characteristics describing these adverse events. Eccentric resistance training results in
high levels o f muscle damage compared to concentric resistance training, and is often
experienced as delayed-onset muscle soreness (DOMS) (Armstrong 1984). Delayed
onset muscle soreness is defined as pain or discomfort resulting from muscle damage
associated with unaccustomed or exertional exercise (Armstrong). Soreness usually
peaks 24-72 hours following an intense exercise bout and may last as long as 5-7 days.
Strength losses are evident in the first 24 hours and may last as long as several weeks
(Chleboun et aL 1998, Newham, Jones, and Clarkson 1987).
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43
It is well established that strenuous eccentric resistance training results in
muscle stiffness, prolonged strength loss, increases in creatine kinase (CK), and
morphological changes (Chleboun et al., Ebbeling and Clarkson 1990, Mair and Artner-
Dworzak 1992, Nosaka et aL 1991, Sorichter et aL 1997). The type and intensity o f
training, as well as, the size o f the muscle group exercised may strongly influence the
magnitude and the factors associated with DOMS (Evans and Cannon 1991). Local
muscle damage is characterized by sarcolemmal disruption, Z-line streaming, and the
release o f enzymes and mitochondria from damaged fibers (Friden and Leiber 1992,
Hikida et al. 1983, Hewham et al. 1983). The structural damage caused by eccentric
contractions allows substances (Le., calcium) to cross the muscle membrane unregulated.
Large amounts o f calcium are toxic to the mitochondria and have two effects on damaged
fibers. I) Calcium impairs mitochondrial function and disrupts oxidative
phosphorylation, leading to lower production o f adenosine triphosphate (ATP), which is
necessary for calcium ATP pumps to remove intracellular calcium. This generates a
vicious cycle. 2) Calcium activates proteolytic enzymes that degrade the Z-lines,
troponin, and tropomyosin. Tissue debris escapes the cell and acts as a chemoattractant
for recruitment o f neutrophils and macrophages that phagocytose damaged muscle. The
phagocytosis and necrosis result in edema and stimulation o f the class IV mocieceptors
responsible for the feeling o f diffuse pain within the muscle belly (DOMS) (Armstrong
1984).
Evans and Cannon (1991) have further described the process o f exercise-induced
muscle damage to include the acute phase reactants. The acute phase reactants are part o f
the acute phase response and include the complement system, acute phase proteins, and
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44
cytokines. Damaged and necrotic tissue activates the complement system, which
includes anaphlytoxins C3a, C4a, and C5a. The tissue fragments and complement act as
chemoattractants for phagocytic ceils. The complement also activate mast cells and
opsonization. Monocytes differentiate into macrophages in the tissue and are responsible
for degrading damaged muscle tissue along with the neutrophils. The phagocytic cells
release oxygen radicals and enzymes like elastase and coDagenase that promote further
muscle breakdown and also increase the vascular permeability. Monocytes and
macrophages mediate the response by releasing cytokines (IL -l, IL-6, and TNF). The
cytokines stimulate hepatic synthesis o f acute phase proteins like ceruloplasmin and a l-
antitrypsin, which function to neutralize toxic debris straying from the site o f injury. The
cytokines increase transendothelial transit o f leukocytes, leading to edema, and enhance
muscle proteolysis. Furthermore, the cytokines are essential for activating the release o f
growth factors.
Interleukin-6 fIL-6) Cytokines mediate a coordinated adaptive response to
muscle injury. The adaptive response, known as the acute phase response includes a
redistribution o f ammo acids and trace metals, and an accelerated synthesis o f proteins
assisting in tissue repair (Cannon et al. 1986, Rhode et aL 1997). Heilsten et aL (1997),
examining inflammation in skeletal muscle associated with eccentric exercise, noted
plasma IL-6 levels to be significantly higher 90 minutes after exercise and remained
higher than pre-exercise levels over the four days o f measurements. Similarly,
Bruunsgaard et al. (1997) conducted a study to test the hypothesis that the exercise-
induced increase in circulating cytokine levels was associated with muscle damage. This
comprehensive study tested nine male subjects (mean, 26 years) performing two high-
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45
intensity bicycle exercise trials separated by two weeks. The fist trial consisted o f 30
minutes o f normal bicycle exercise (concentric exercise), whereas the second consisted o f
30 minutes o f braking with reversed revolution (eccentric exercise). Blood was drawn
daily over seven days. Plasma CK and IL-6 increased significantly in the eccentric
exercise group while no significant changes occurred in the concentric exercise group.
Furthermore, the level o f IL-6 was significantly correlated to CK (r = 0.722, p = 0.028).
Bruunsgaard et aL, to the investigators knowledge, is the only investigator to report a
significant relationship between IL-6 and elevated CK levels with eccentric exercise.
This finding supports the hypothesis that post-exercise cytokine production is related to
skeletal muscle damage.
Creatine Kinase (CK) Elevated blood levels o f muscle proteins, such as CK,
resulting from eccentric exercise-induced muscle damage have been routinely measured
(Clarkson and Tremblay 1988, Byrnes et al. 1985, Ebbeling and Clarkson 1990,
Newham, Jones, and Clarkson 1987, and Nosaka and Clarkson 1992). Contrary to
Bruunsgaard et al.’s findings, Clarkson, Nosaka, and Braun (1992) reported that
investigators have been unable to demonstrate relationships o f increases in CK with any
other indicators o f muscle damage. And that this is likely due to the large inter-subject
variability in the CK response along with the small sample size used in most studies that
have evaluated CK increases after eccentric exercise. Serum levels o f CK reported
following exercise vary greatly depending on the type and duration o f the exercise
performed (Hayward et al. 1999). Elevated CK levels associated with running vary from
100% to 450% (Amelink, Kamp, and Bar 1988, Armstrong, Ogilvie, and Schwane 1983).
However, peak serum CK levels in subjects performing high-force eccentric muscle
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46
action may range from 2,000 IU/l to 10,000 IU/l (Clarkson, Nosaka, and Braun 1992,
Newham, Jones, and Clarkson 1987). Clarkson, Nosaka, and Braun have also classified
individuals as being low, medium, or high CK responders to eccentric exercise-induced
muscle damage. One reason for the large variability in CK response may be due to
differences in clearance (by the reticuloendothelial system) o f CK from the blood.
Individuals with a foster clearance will have lower CK levels measured in the blood. In
feet, a study by Hyatt and Clarkson (1998) demonstrated that accelerated clearance o f CK
seems to be one factor contributing to the blunted response o f the enzyme following a
repeated bout o f exercise.
Newham, Jones, and Clarkson (1987) examined the effect o f performing maximal
eccentric contractions o f the elbow flexors (for 20 minutes) on three occasions, spaced
two weeks apart, in five women and three men (aged 24-43). Creatine kinase was
measured before and after each exercise bout. Extremely high CK values were measured
(1,500-11,000 IU/L) after the first bout, but the second and third bouts did not
significantly affect the plasma CK. The method o f CK measurement by Newham, Jones,
and Clarkson results in mean values that are typically a third higher than other reported
values. In a study by Hayward et aL ( 1999) using the rat model, they report much lower
responses o f serum CK to eccentric downhill treadmill running. And more importantly,
Hayward et al. describe the importance o f dietary protein on CK levels. Serum CK was
measured in rats fed for 10 days on high (50%), normal (12%), and low (4%) protein
diets following a single bout o f eccentric exercise for 90 minutes. Serum CK
demonstrated peak activity immediately postexercise with increases reaching 910 ± 94,
594 ± 53, and 283 ± 52 IU/L for animals on high, normal, and low protein diets,
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47
respectively. Their data show that CK levels vary dependent on the type, duration, and
intensity o f eccentric exercise as well as the dietary protein intake. Additionally, protein
supplementation may be important since enhanced protein breakdown has been shown
after eccentric exercise (Fielding et aL 1991).
Frequency o f Eccentric Traminp
The enhanced muscle damage, strength loss, and DOMS associated with eccentric
resistance training contributes to a training protocol that needs to accommodate these
conditions. Few studies exist that define the optimal training frequency for heavy
eccentric resistance training (Sorichter et aL 1997). The limited training protocols
designed were only for a moderate 6-8 weeks with 2-3 training days per week (Komi
1986, Staron et al. 1994). With soreness lasting at least several days and muscle repair
even longer (Nosaka and Clarkson 1995) it seems plausible to design an eccentric
resistance training program that allows ample rest between trainings yet is often enough
to induce adaptations. Sorichter et aL developed a complex design to assess the influence
o f training frequency on muscular adaptation and strength during the early phase (first 5
weeks) o f an eccentric training task for the thigh muscles. Thirty male volunteers
participated in the study and were assigned to one o f three groups (A 3*Q - All groups
performed one training task o f 70 eccentric contractions at the beginning and end o f the
study. Group C only performed the training once at the beginning and once at the end o f
the study. Group A performed one training task once a week for five weeks and group B
twice a week for 2 weeks and three times a week during the subsequent three weeks.
Sorichter et aL reported that the additional eccentric exercise in group B is optimal for the
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48
increase in muscle strength during the early phase o f eccentric training without further
benefits for muscular adaptation (increases in mass or strength).
Resistance Training and Biochemical Markers
To the investigators knowledge no studies have reported the effects o f resistance
training on biochemical markers o f bone metabolism in young women. Fujimara et al.
(1997) studied the effects o f high-intensity resistance training on bone metabolism in 17
young adult males (23-31 years) by measuring markers o f bone formation and resorption.
The subjects were assigned to either a training group or control group. The training
consisted o f weight lifting 3 times per week for 4 months. In the training group, serum
osteocalcin and bone-specific alkaline phosphatase activity (bone formation markers)
were significantly increased within the first month after the beginning o f resistance
training and remained elevated throughout the training period. Urinary
deoxypyridino line excretion was transiently suppressed and returned to the initial value
but was never increased over the 4 month study intervention. Additionally, they also
reported no changes in total and regional bone mineral density. While no four month
resistance training interventions measuring biochemical markers o f bone turnover have
been reported in young women, assessment o f alterations in theses markers with
resistance training need to be interpreted cautiously as there are additional factors (e.g.,
hormonal fluctuations) in young women that may influence these measures.
Nielsen et aL (1990) evaluated the changes in biochemical markers o f osteoblastic
activity during the menstrual cycle; however, these were healthy women aged 20 to 47
years, not participating in resistance training. The data were analyzed normalizing cycles
by length and synchronizing by ovulation and phases. This method eliminated
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49
interindividual variations in cycle and phase length without violating the concept o f
physiological regulation o f ovarian sex hormones by gonadotropins. Blood was drawn 3
times per week, ending I week after the following menstruation. They found osteocalcin
varied significantly showing gradual increases throughout the menstrual cycle with the
highest levels peaking during the luteal phase (approximately the last 13 days o f the
cycle). Furthermore, osteocalcin correlated with estradiol the strongest (r = 0.069, p <
0.05) when osteocalcin was lagged about 7 days after estradiol suggesting a time lag
effect o f estradiol on osteoblastic activity. The investigators concluded that osteoblastic
activity is highest during the luteal phase and any direct or indirect effects o f fluctuations
in hormones could not be determined.
Resistance T raining and Hormones
Researchers examining the effects o f resistance training on sex hormone levels in
females have primarily focused their investigations on the alterations in estradiol and
testosterone (Cumming 1987, fCraemer 1988, Kraemer et aL 1993, Kraemer et aL 1995,
Kraemer et aL 1998, Sutton et al. 1973, Hakkinen et aL 2000). Kraemer et al. 1995
studied the follicular and luteal phase hormonal responses to low-volume resistive
exercise in eleven untrained, healthy women (20-28 years). The women were assigned to
an early follicular or luteal testing group. Estradiol, progesterone, growth hormone,
testosterone, and androstenedione were measured to ascertain whether the endocrine
responses were affected by the phase o f the menstrual cycle. The subjects completed
three sets o f bench press, Iat-pull, leg extension, and leg curl exercises at a 10 repetition
maximum. Blood was collected before, during, and after the exercise. Estradiol
concentrations were significantly elevated in both the follicular and luteal phase as a
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50
result o f the exercise. Additionally, growth hormone and androstenedione
concentrations were significantly elevated in the luteal phase in response to the low-
volume resistive exercise. However, progesterone and testosterone concentrations were
not affected. The absence o f a significant change in testosterone concentrations is similar
to findings from other studies utilizing young women as subjects (Kraemer et al. 1992,
Kraemer et aL 1993, Weiss, Cureton, and Thompson 1983).
The absence o f increases in serum testosterone with resistive training in women
suggests that other anabolic hormones (e.g. androstenedione, growth hormone) may be
contributing to the greater anabolic muscle adaptations that occur with resistance training
in women. William Kraemer, who has completed extensive studies in the area o f
hormonal adaptations to resistance exercise reported findings indicating that growth
hormone is the primary stimulus for muscle hypertrophy associated with heavy-resistance
exercise protocols (Kraemer et al. 1993). Interestingly, Kraemer et al. failed to measure
androstenedione levels in these young women even though this particular androgen
circulates at 40% greater levels in women than in men.
Examining the acute response o f testosterone and androstenedione to weight
lifting in men and women (18-30 years o f age), Weiss, Cureton, and Thompson (1983)
reported interesting results. The women were not using oral contraceptives and then-
menstrual cycles were regular. They performed three sets o f four exercises at
approximately 80% o f their one repetition maximum. The exercises completed were the
lat-puIL, supine bench press, arm curl, and leg press. Blood was drawn before and 30,60,
and 120 minutes after the exercise. Similar to K raem ers findings, Weiss, Cureton, and
Thompson observed no significant changes in serum testosterone in the women.
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51
However, the women’s serum androstenedione levels decreased significantly below
pre-exercise levels at two hours post-exercise. Whether this alteration is a transient
decrease in androstenedione and the serum concentration returns to baseline o r greater
after two hours post-exercise is unknown. The finding differs from that o f Kuoppasalmi
et aL (1976) who reported significantly higher androstenedione levels following interval
sprint running for six hours post-exercise. Similar to the finding by Weiss, Cureton, and
Thompson, in a weight lifting study on college-age women Westerlind, Byrnes,
Freedson, and Katch (1987) reported significant acute declines o f 25% in serum
androstenedione levels. However, they also reported 36% declines in the control group
and attributed the decreases in both groups to higher than normal values at baseline.
The type o f resistive exercise protocol may have an impact on the hormonal
adaptations. The total work or volume (sets x reps x intensity) o f resistance exercise
performed and the rest periods between sets may influence the hormonal milieu.
Training protocols with a larger volume o f work performed that employ moderate to
heavy resistance (e.g., ten repetition maximum sets) and 1-2 minute rest periods have
been reported to produce greater magnitude increases in hormone concentrations
compared to heavier resistances (e.g., five repetition maximum sets), longer rest periods
(three minutes), and smaller volumes o f work (Kraemer et al. 1990, Kraemer et aL 1991,
Kraemer et aL 1995, Kraemer et aL 1997, Hakkinen and Pakarmen 1993).
Resistance Training and Mechanical Strain Effects on Bone
Studies have investigated the effects o f resistance training on bone mass in young
women (Friedlander et aL 1995, Snow-Harter et aL 1992, Lohman et aL 1995, Uusi-Rasi
et aL 1998) and reported significant, although moderate gains in bone mass (0.5-2.5%).
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52
The 8 month study by Snow-Harter et aL has shown that resistance training
intervention in college women (mean age o f 20 years) results in a significant increase in
BMD at the lumbar spine but not at the proximal femur. Friedlander et al. in a two-year
longitudinal study followed young women (20-35 years), 32 o f which participated in a
combined aerobic and weight training regimen. They reported that spine and proximal
femur measures increased significantly 1.3 ± 2.8% and 2.6 ± 6.1%, respectively.
Furthermore, Friedlander et al. reported that an additional group o f 31 women that only
participated in a stretching program did not significantly alter BMD parameters.
Differences in reports o f resistance training induced bone changes at various sites may be
due to the type o f exercises performed and then1 bone loading characteristics.
As discussed above, mechanical strain on bone is an important regulator o f
skeletal maturation, maintenance, and strength. Heinonen et aL (1995) conducted a study
to examine BMD in female athletes representing sports with different loading
characteristics o f the skeleton. They measured the lumbar spine, femoral neck, distal
femur, patella, proximal tibia, calcaneus, and distal radius by DXA. The athletes
consisted o f aerobic dancers (n=27), squash players (n=18), and speed skaters (n=14).
The athletes were compared to a sedentary referent group. Heinonen et al. reported that
the squash players had the highest weight-adjusted BMD values while the aerobic
dancers and speed skaters had significantly higher BMD than the sedentary referent
group. Their findings support the concept that training, including high strain rates in
versatile movements and high peak forces, is more effective in bone formation than
training with a large number oflow-force repetitions- In contrast to the studies
suggesting the importance o f mechanical loading on bone, Vuori et aL (1994) trained 12
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53
young females (mean 21 years) unilaterally at 80% o f the one repetition maximum on
the leg press for one year. They reported significant increases in muscle strength with no
significant gains in BMD.
Data generated from animal and theoretical investigations suggest that for loading
to stimulate an osteogenic response, the training needs to be o f sufficient magnitude and
provide unique strain to the bone (Frost 1990, Burr 1997). Using the rat model,
Umemura et aL (1997) investigated the effects o f jump training on bone morphological
and mechanical properties. They had five jump-trained groups comprised o f 5-, 10-, 20-,
40-, and 100-jump groups and a control group. The rats were jump-trained five days per
week for eight weeks and the height o f the jump was increased progressively. Unemura
et al. reported that the 5-jump group had significantly greater bone fat-free dry weights,
fracture loads, and cortical area compared to the control group. Furthermore, there were
few differences in bone parameters between the groups suggesting that a large number o f
strains per day are not necessary for bone hypertrophy to develop in rats as long as there
is progressive unique strain to the bone. Resistance training provides high magnitude,
unique loads to bone through muscular contraction. Employing progressive resistance
training (PRT) (e.g., incremental increases in the training load) ensures that the training
stimulus or load will remain large and unique. Progressive resistance training is an
accepted method to enhance muscle strength (Kraemer and Fleck 1997).
The association between greater muscle strength and increased bone mass has
been clearly established (Burr 1997, Snow-Harter et al. 1990, Madsen, Adams, and Van
Loan 1998). Snow-Harter et aL examined the relationships o f muscle strength to BMD in
59 women (18-31 years) who ranged in exercise patterns from sedentary to active. The
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54
proximal femur and lumbar spine was measured by DXA. Strength was measured by
the one repetition maximum method for the back, elbow flexor, leg extensor, hip flexor,
extensor, adductor, and abductor muscles. Femoral neck BMD was significantly
correlated with back strength while trochanter and total hip BMD were significantly
correlated with biceps, back, and hip adductor strength. Snow-Harter et aL concluded
that muscle strength is an independent predictor o f BMD and accounts for 15-20% o f the
variance in BMD o f young women.
It is well accepted that greater muscle strength is associated with greater lean
mass (Maughan, Watson, and Weir 1983). It is also well accepted that resistance training
results in muscle hypertrophy increasing lean mass. Madsen, Adams, and Van Loan
(1998) investigated the relationship between body composition and weight, muscular
strength, physical activity, and BMD in 60 eumenorrheic college age females. Using
DXA they measured BMD and BMC at the proximal femur and lumbar spine. The
women were divided into three groups: 1) low body weight athletes involved in weight
bearing sports, 2) matched low body weight and sedentary, and 3) average body weight
and sedentary. The athletes had significantly greater total body, femoral neck, and
lumbar spine BMD than the low body weight sedentary group and only the femoral neck
BMD was greater than the average body weight sedentary group. Furthermore, lean body
mass was significantly correlated (r = 0.51, p < 0.05) with lumbar BMD for all groups
combined. Madsen, Watson, and Weir reported that their results suggest that lean body
mass and weight-bearing activity enhance BMD in young women.
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55
D irect Effects o f Resistance Training on Bone
It has been suggested that tension production by the muscle may be the critical
stimulus for increased protein synthesis; therefore, training with eccentric contractions
may provide a greater stimulus for hypertrophy than other contraction types (Atha 1981,
Evans, Meredith, and Cannon 1986, Fielding et aL 1991, Hortobagyi et aL 1996). As
discussed above, skeletal muscle eccentric contractions are able to generate greater levels
o f tension than concentric or isometric contractions (Doss and Karpovich 1965,
Hortobagyi et aL, Mayhew et aL 1995, Olson, Smidt, and Johnston 1972). Therefore,
high-intensity or maximal eccentric muscle action may provide a significant osteogenic
response. In a recent study, we (Hawkins et aL 1999) determined the contribution o f load
magnitude from muscle action on the site-specific osteogenic response. Twenty young
women (12 exercise, 8 control) trained three times weekly for 18 weeks on a KinCom
isokinetic dynomometer. One leg was trained using maximal eccentric knee extension
and flexion, and the opposite leg trained using maximal concentric knee extension and
flexion. Whole body and mid-femur segment BMD was measured by DXA. Both
exercised legs significantly increased strength and the gains were o f similar relative
change. However, only the eccentric trained leg significantly increased mid-femur
segment BMD (+3.9%, p < 0.05) (Figure I) and mid-thigh segment lean mass (+5.2%, p
<0.05).
The findings o f our study help explain the interaction between muscle and bone,
suggesting a direct effect o f resistance training utilising maximal eccentric muscle
contraction. Eccentric resistance training was more effective in increasing BMD than
concentric training. Additionally, the eccentric training was associated with greater peak
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56
Figure 1. Mid-Femur Segment Bone Mineral Density (BMD) From
Baseline to Week 18.
E
49
1.8
1.6
N
E
u
O
s
5 1.4
e
41
E
?
M 1.2
1.0
0.8
Concentric
Eccentric
Control
**
Week 18
‘ Significant increase from baseline.
"Significantly greater than control.
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57
force production and lower IEMG activity than the concentric training, suggesting
greater efficiency with eccentric exercise. Our results demonstrated that equalizing force
by ANCOVA abolished differences in bone adaptation between groups. These results
suggest that the major contribution o f muscle to bone formation is magnitude o f loading.
Slice Analysis Unique to our study (Hawkins et al. 1999), was the use o f site-
specific (slice) analysis by DXA. Not only were we able to demonstrate increases in
mid-femur segment BMD, but also in mid-thigh lean mass. Based on findings in the
literature, enhancement o f lean mass, particularly in muscles that have a close proximity
to bone (e.g., the quadriceps to the femur), may be beneficial in maintaining or
augmenting bone mass. Hypertrophy o f the muscles adjacent to bone may directly
influence bone mass by generating larger peak tensions resulting in high magnitude
strains on the bone. Furthermore, as described previously, Rubin and McLeod (1996)
reported the importance o f high frequency strains generated by muscle contraction that
directly influences the bone.
Indirect Effects o f Resistance Training on Bone
In our study (Hawkins et aL 1999), we hypothesized that in addition to the large
magnitude loads being responsible for the osteogenic response, an indirect effect o f
eccentric training may have contributed. Evans and Cannon (1991), in a review on the
metabolic effects o f exercise-induced muscle damage described an immune response to
eccentric training-induced muscle damage generating systemic and local factors known to
be osteogenic. It is possible that these factors, which would not be generated during
concentric exercise because o f less muscle damage, might have influenced the bone
adaptation noted m this study. Because we did not measure muscle rfamagg o r factors
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58
(cytokines and growth factors) associated with muscle damage we could only speculate
on the possible interaction.
Strong correlations between muscle strength and bone mass at unrelated sites
(Madsen, Adams, and Van Loan 1998, Snow-Harter 1990), such as the quadriceps and
spine (Nordstrom, Bergstrom, and Lorentzon 1996), suggest that indirect or systemic
factors accompanying high force contractions may influence this relationship. As
described above, cytokines and growth factors that function to regulate tissue repair also
function to regulate the bone microenvironment. Therefore, if these factors regulate
muscle and bone and are common to both, then alterations in one local milieu may have a
systemic effect influencing another milieu.
The actions o f cytokines and growth factors may also be influenced by alterations
in hormone concentrations. The sex hormones are essential to the development and
maintenance o f muscle and bone mass. The training induced changes in circulating
hormone concentrations may have a profound direct or indirect effect on bone and
muscle. The direct actions o f hormones work by their binding directly to hormone
receptors located in muscle and bone. Alternatively, the hormones may act indirectly by
influencing cytokines and growth factors through a cascade o f secondary reactions.
Whether it is an alteration in cytokines, growth factors, hormones, or the result o f
hormones influencing cytokines and growth factors, the training-induced alterations in
these factors may act to indirectly effect bone.
Muscle and Strength Relationships Utilising DXA Slice Analysis
Our findings in Hawkins et aL (1999) were demonstrated utilizing the unique
method o f site-specific slice analysis by DXA. To our knowledge, no other investigators
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59
have reported significant increases in bone and muscle mass o f the mid-femur as a
result o f training intervention using DXA. Based on our successful findings using DXA
slice analysis, we hypothesized that this method would be capable o f demonstrating
relationships between muscle and strength that have not been shown previously (Charette
et aL 1991, Davies et aL 1985, Dons et aL 1979, Fiatarone et aL 1990, Frontera et aL
1988, and Pyka, Lindenberger, Charette, and Marcus 1994). Therefore, we tested this
hypothesis by examining the changes in lean tissue by DXA slice analysis and related
those adaptations to changes in muscle strength in an intervention training study
(Schroeder et al. 2000). To further evaluate the usefulness o f DXA slice analysis we
compared it to cross-sectional measures o f muscle by magnetic resonance imaging
(MRI). We speculated that DXA slice analysis would be even more useful for highly
localized regional assessments o f LBM. With this mode o f DXA analysis, site-specific
measures o f muscle density were compared to the same selected area evaluated for
muscle cross-sectional area by MRI.
Twenty-three HTV positive men were randomly assigned to receive nandrolone
decanoate alone or in combination with PRT at 80% o f the one repetition maximum three
tunes weekly for 12 weeks. Muscles o f the right thigh were measured by MRI,
appendicular DXA, and DXA slice analysis at baseline and study week 12. Leg press
strength by l-RM increased significantly by 19% in the nandrolone only group and 54%
in the nandrolone plus PRT group. Significant within group changes were demonstrable
by MRI CSA, appendicular DXA, and DXA slice analysis. Only DXA slice analysis was
able to corroborate that greater changes in lower extremity lean tissue occurred with the
combination intervention (11 3 ± 1.4% versus 7 3 ± 1.3% in the nandrolone alone group,
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60
p=0.049). Regional changes in thigh lean mass by both appendicular D X A and D XA
slice analysis were significantly correlated with change in leg press strength (r=0.720,
p=0.013 and r=0.720, p=0.008, respectively) in the nandrolone phis PRT group (Figure
2). We concluded that with strategies intended to maximally increase muscle size and
strength, adaptations in thigh lean mass as determined by D X A slice analysis were well
related to strength gam s from PRT, while this relationship was not demonstrable with
MRI. This was the first study using imaging techniques to report that changes in muscle
size are predictive o f gams in muscle strength.
Progression o f Study
The findings we reported in Hawkins et aL (1999) suggested that large strains o f
high magnitude eccentric muscle contractions were osteogenic. However, we did not
assess the factors associated with eccentric exercise-induced muscle damage and whether
those factors may have systemically influenced the bone adaptations alone or in
conjunction with large strains. Furthermore, we did not relate increases in lean mass to
gains in strength, an observation that has been shown to be predictive o f bone mass.
Therefore, utilising the methods and findings from Hawkins et al. and Schroeder et aL
(2000) we have designed a study to test whether it is truly load magnitude from eccentric
muscle contraction or factors related to eccentric exercise-induced muscle damage and
hormone alterations that influence bone adaptation in young women.
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61
Figure 2. Relative (%) change from baseline to week 12 by DXA
thigh slice for lean mass versus leg press strength as
measured by the 1-RM method
(0
«
< c
e
(0
©
25
20
O 15
O
0 )
c
©
O)
c
(5
f
o
10
o
t Nandrolone Group
O Nandrolone + PRT Group
O
r=0.720, p=0.008
Oo
< 5 r=0.271, NS
— i —
20
- i—
40
— i —
60
i
80 100
% C h a n g e in L eg P r e s s S tre n g th
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CH A PTER i n
62
METHODOLOGY
Subjects
The volunteer subjects were females between the ages o f 18 and 28 years.
Subjects were recruited from the University o f Southern California (U SQ Health Sciences
Campus. They completed a brief informational entry questionnaire (Appendix A) and if
they met the inclusion criteria were contacted by the study staff All subjects were free
from conditions that would limit their participation in high-intensity resistance training,
such as musculoskeletal injuries, hypertension, coronary heart disease, chronic pulmonary
disease, osteoporosis, osteoarthritis, etc. Additionally, all subjects were free from
conditions known to influence bone, including diabetes, eating disorders, pregnancy,
polycystic ovarian disease, hyper- and hypo-thyroidism, hypercortiso lism, amenorrhea and
any other hormonal or metabolic disorders. Menstrual cycles had to be regular
(eumenorrheic) and between 26-31 days in length. Subjects taking oral contraceptives and
those subjects not taking oral contraceptives were both accepted into the study. Subjects
were nulliparous and those who had a recent series ofX-rays (such as radiation therapy)
were excluded. The subjects must not have participated in resistance training six months
prior to study entry. Subjects provided written informed consent prior to entry into the
study, which was approved by the Institutional Review Board o f the LAC-USC Medical
Center (Appendix A).
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63
Study Design
Subjects were randomly assigned to one o f three groups: high-intensity eccentric
resistance training; Iow-intensity eccentric resistance training; or control. All subjects
were asked to visit the laboratory on three occasions. The first visit included bone
densitometry, strength testing, and blood and urine samples. The first visit was scheduled
during the first 10 days o f the menstrual cycle. The second visit was also a baseline visit
to perform an additional strength test approximately 5 days after the initial strength test.
Additionally all subjects were asked to visit the laboratory for post testing after week 16
o f the study. Post testing included bone densitometry, strength testing, and blood and
urine samples. The subjects randomized to a resistance training group were asked to visit
the laboratory twice per week on non-consecutive days to participate in eccentric
resistance training for 16 weeks (32 training days). Additionally, blood and urine samples
were collected during the first 10 days o f each subsequent menstrual cycle.
Resistance Training Intervention
The training intervention was conducted two times per week for 16 weeks. Each
training session lasted approximately 30-45 minutes and consisted o f six exercises: seated
chest press; latissimus pull down; standing biceps curl; standing triceps extension; seated
single-leg extension; and seated double-leg extension. The high-intensity weight-lifting
group (125% o f the concentric 1-RM) performed 3 sets o f 6 repetitions and the Iow-
intensity weight-lifting group (75% o f the concentric 1-RM) performed 3 sets o f 10
repetitions o f each exercise to ensure that the total work performed was the same for both
groups (Table I).
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64
Table 1. Eccentric Resistance Training Protocol
Low-Intensity RT Group High-intensity RT Group
Intensity
75% of Concentric 1-RM 125% of Concentric l-RM
Frequency
2 Days/Week 2 Days/Week
Sets
3 3
R epetitions
1 0 6
Exercises
Seated Chest Press
Latissimus Pull Down
Standing Biceps Curl
Standing Triceps Extension
Seated Single-leg Extension
Seated Double-leg Curl
Seated Chest Press
Latissimus Pull Down
Standing Biceps Curl
Standing Triceps Extension
Seated Single-leg Extension
Seated Double-leg Curl
Procedures
Strength Evaluation
Strength testing was performed at baseline and week 16 in all groups and
approximately every two weeks in the treatment groups to maintain the appropriate target
training intensity. Eccentric strength is not effectively measured since it requires timing
the controlled lowering o f a weight against gravity through a range o f motion (a very
subjective measurement). Additionally, the 1-RM loads is extremely high relative to the
subjects’ maximum strength and increases the risk for injury. Hortobagyi et aL (1996) and
Hawkins et aL (1999) have reported cross-training effects with eccentric resistance
training that results in concentric strength gains. Therefore, muscle strength for the six
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65
exercises in this study were determined by the established concentric 1-RM method.
The 1-RM method is defined as the weight that can be lifted no more than one time using
proper form. Strength testing was preceded by five minutes o f warm-up on a cycle
ergo meter. Subjects received detailed instructions on each exercise, and performed each
exercise several times at very low resistance to enhance familiarization and warm-up. The
goal was to produce a 1-RM within 3-5 efforts to reduce the effect o f fatigue. To account
for learning and familiarization with the 1-RM strength testing procedure, two baseline 1-
RM tests were performed 5 days apart.
Bone Densitometry
BMD and BMC o f the total body, proximal femur, and lumbar spine were
determined by dual-energy X-ray absorptiometry (DXA) (Hologic QDR-1500, software
version 7.1). Scans were performed at baseline and post week 16 for all subjects to
provide total body and regional values o f bone, lean, and fat mass. The whole body scan
required the subjects to be placed supine with the arms and legs positioned according to
the manufacturer’s specifications. The proximal femur o f the subject’s non-dominant leg
was scanned with the leg internally rotated and secured to prevent movement. The lumbar
spine scans were performed with the subjects supine, the hip and knees flexed to 90-
degrees and supported by the company provided pad. The coefficient o f variation for
measures ofbone mass in our laboratory is less than 1%.
The Hologic X-ray generates a narrow pencil shaped beam at two alternating
power line frequencies (high, 140 kVp; low, 70 kVp) from beneath the subject. Above the
subject are solid-state detectors (both the source and detectors are in a “C” shaped arm).
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6 6
Before the beam passes through the subject, it is filtered through a rotating drum in
which alternating segments have calibrating radiocapacities equivalent to tissue, bone, and
air. When the beam is collected at the detector, information about the X-ray absorbing
characteristics o f the patient and the calibration materials in the drum are detected by the
amount o f the beam absorbed. The output o f the analog/digital (A/D) conversion from the
detectors calculates both the screen image and the basis for the calculation o f BMC and
BMD. The computer algorithm is based upon the principle that bone selectively
attenuates x-ray photons.
The Hologic QDR-I500 uses a very low level o f X-ray. Under standard operating
conditions, the entrance dose to the patient is less than five miDirad (mR) for single beam
scans, which is approximately 1/10 o f the exposure from a standard chest X-ray. Entrance
exposures for the different scans that were performed are 3.5 mR for the spine scan, 3.5
mR for the femur scan, and 1.0 mR for the total body scan.
Mid-femur segment BMD, BMC, lean, and fat mass were determined from the
whole body scan as a measure o f site-specificity. The mid-femur analysis was
accomplished by shifting the whole body scan into a function that allows the technician to
determine the segmentalization o f the image (Hawkins et aL 1999). The segment reported
here was the middle three pixels measured between the middle o f the knee joint and the
top o f the greater trochanter. Reproducibility o f BMD values, assessed in ten healthy
volunteers, ranged from 0.8%-2.0% for the whole body scan values and 0.5-1.0% for the
segment determination.
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67
Subjects T-scores (comparison to predicted peak bone mass) and Z-scores
(comparison to age-predicted bone mass) were obtained using normative values provided
by the software manufacturer. These scores are ± standard deviations from predicted
values, which represent a value o f zero. Measurements on the DXA are highly
reproducible, with precision standards o f < 1.0% for the spine scan and < 1.5% for the
femur scan as determined by the manufacturer. Reproducibility in our laboratory ranges
from 0.8-2.0%.
Body Composition
DXA provided an assessment o f three compartment body composition for the
determination o f total and regional lean body mass less bone mass. Body composition is
determined by DXA via the principle that the properties o f the human body can be
simulated by the dual-energy X-ray beam being attenuated by a step-wedge tissue bar
placed next to the subject during the scan. The step-wedge is composed o f a unique
combination o f aluminum (Al) and acrylic. The acrylic represents 68% fat and the acrylic
plus Al is equivalent to -10% fat, indicating that this step is about 10% leaner than the
leanest soft tissue in the body. The step-wedge measurements are traceable to a primary
calibration based upon stearic acid and pure water. These two materials form the basis o f
the primary body composition calibration and were utilized to determine the apparent fat
content o f the step-wedge by direct comparison. Low- and high X-ray energy attenuation
values are measured for each tissue point. As weft, low- and high-energy values are
determined for the three acrylic and three acrylic/aluminum steps o f the step-wedge. A
smooth curve is then fit to the data from the step-wedge for the low- vs. high-energy
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68
attenuation space and percent fat o f the wedge is determined based upon the X-ray
energies attenuation. The dual-energy attenuation is then compared to each point o f the
subject’s image and percent fat is determined based upon its relationship to a standard
curve. However, the soft tissue composition above and below the skeleton cannot be
measured directly because it is obscured by the image constructed for bone. Therefore,
this body composition is estimated from the composition o f the tissue immediately
adjacent to the bone (Hologic, 1994). This signal attenuation also allows for accurate
segmentation o f the body into various compartments, e.g., arm, leg and abdomen. A
recent study has demonstrated the Hologic QDR device provides accurate assessment o f
body composition in men and women aged 21- to 8l-yr. in comparison to
hydrodensitometry (Kohrt, 1998).
Sample Collection (Blood and Urine)
Blood samples and urine samples were collected for analysis o f deoxypyridinoline
and osteocalcin. Approximately six-ml blood was drawn from an antecubital arm vein into
a serum vacutainer tube with the subject at rest. The sample was allowed to clot for 15-
30 minutes and then immediately centrifuged for 10 min at 3000-x gravity and the serum
pipetted into storage vials. The serum was frozen at -80°C until analysis. Urine samples
were taken from first or second morning void (before 10 am), which subjects collected in a
container provided. One and one-half ml urine were pipetted into storage vials and frozen
at -80 °C until analysis.
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69
Bone Biochemical Markers
The organic matrix o f bone consists o f approximately 90% type I collagen
(Seyedin and Rosen, 1990). Trifunctional pyridinhim crosslinks, pyridinoline (Pyd) or
deoxypyridinoline (Dpd) form between hydroxylysine or lysine residues at the C- and N-
telopeptide ends o f one collagen molecule and the helical portion o f a neighboring
molecule during collagen maturation (Delmas 1995). This crosslinking provides structural
rigidity to the collagen fibril. Osteoclastic degradation o f bone collagen releases the
crosslinks into the circulation, and they are eventually excreted in urine. Though the
crosslinks are present hi a number o f tissues, the molar ratio o f Pyd and Dpd in urine is
very similar to that in bone, indicating that urinary concentrations o f both are derived
mainly from bone. Deoxypyridino line in particular, with a more limited tissue distribution
than Pyd, is derived almost exclusively from bone (Delmas, SeibeL, Robins, and Bilezikian
1992, Delmas et aL 1991, EastelL, ColwelL, Hampton, and Reeve 1997). As products o f
collagen maturation, they cannot be reused hi new collagen synthesis, nor are they further
metabolized (SeibeL, Robins, Bilezikian, Delmas et al.). O f the total pool o f urinary Dpd,
approximately 40-45% is free and the remainder is bound to peptides (Delmas, Delmas et
aL).
The total excretion o f Dpd measured by high performance liquid chromatography
(HPLC) is correlated with histomorphometric resorption indices o f iliac crest biopsies
(Colwell, Russell, and EasteQ 1993), and with radioisotope kinetic estimates o f whole
body bone resorption (Riggs 1991). Free Dpd can be measured both by HPLC and by a
highly specific enzyme immunoassay). Free Dpd levels measured by immunoassay are
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70
highly correlated with free or total Dpd measured by HPLC (r = 0.97 and 0.95,
respectively) (Riggs).
Increased urinary levels o f Dpd are observed among postmenopausal women
compared to premenopausal women and are associated with rapid bone loss (Bush et al.
1996, Hesley, Shepard, Jenkins, and Riggs 1998) and an increased risk o f hip fracture
(Chesnut et aL 1995, Devogelaer et aL 1996). Increased Dpd excretion is seen in a
number o f conditions characterized by excessive bone resorption, including osteoporosis,
Paget’s disease, hyperparathyroidism, thyrotoxicosis, malignant hypercalcemia, and
metastatic cancer (Delmas 1995, SeibeL, Robins, and Bilezikian 1992, Bush et al.).
Urinary Dpd was measured using the Pyrilinks (R) -D assay (M etra Biosystems,
Mountain View. CA, USA) Enzyme-Linked Immunosorbent Assay (ELISA). The assay is
highly specific for the Dpd molecule and does not cross-react significantly with
pyridinoline, other collagen crosslinks, or collagen peptides. Pyrilinks-D is a competitive
enzyme immunoassay in a micro titer stripwell format utilizing a monoclonal anti-Dpd
antibody coated on the strip to capture Dpd. Deoxypyridino line in the sample competes
with conjugated Dpd-alkaline phosphatase for the antibody and the reaction is detected
with the substrate, p-nitrophenyl phosphate. Color developed during the incubation o f
captured enzyme conjugate and substrate is measured at 405 nm in a microtiter plate
reader. Deoxypyridino line values o f unknown specimens are calculated from a calibration
curve fit (sigmoid) with a 4-parameter logistic equation. Deoxypyridinoiine values are
expressed in nM/L. Fifty pL o f urine diluted 1:10 in Assay Buffer per well (assayed in
duplicate) is required for determination o f Dpd.
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71
The detection limit was 1.1 nM/L. Intra-assay precision coefficient o f variation
was 4.7%. Inter-assay precision coefficient o f variation was 5.2%. Deoxypyridino line
levels were corrected for differences in urine concentration and output by dividing by
creatinine. The final creatinine-corrected results are expressed as aM/mM. Analysis o f
urinary creatinine was performed using the Kodak Ectachem DT-60 II (Johnson &
Johnson Clinical Diagnostics, Los Angeles, CA). The procedure involves a series o f
reactions in which creatinine is hydrolyzed to creatine and the concentration measured by
change in reflection density during an incubation period. A ten pL sample diluted 21-fold
with deionized water was deposited on a slide. Creatinine in the sample diffused to the gel
layers o f the slide where it was hydrolyzed to creatine by creatinine amidohydrolase.
Creatine was hydrolyzed to sarcosine by creatine amidhydrolase, which was then oxidized
by sarcosine oxidase to glycine, formaldehyde and hydrogen peroxide. Lastly, hydrogen
peroxide was oxidized by peroxidase to a colored dye. The rate o f change in reflection
density at 680 nanometers (nm) was measured during a 5.5-minute incubation at 37°C.
Creatine present in the sample was reacted within the first four minutes and the rate o f
change between 4.5 and 5.5 minutes was proportional to the creatinine concentration in
the sample. The manufacturer has established reference intervals for healthy
premenopausal women (3.0-7.4 oM/mM). However, the reference interval may be altered
depending on the time o f urine collection, due to the diurnal variation o f Dpd excretion.
Urine collection in this study was between 6-10 AM.
Osteocalcin in serum was determined as a marker ofbone formation. Osteocalcin,
also known as bone Gla protein, is a vitamin K-dependent, calcium-binding protein that is
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72
a major component o f the bone matrix. It is synthesized by osteoblasts in bone, and
synthesis does not occur in non-bone tissues. Therefore, serum osteocalcin originates
exclusively horn bone and measurement o f serum osteocalcin provides a marker o f
osteoblast activity. The assay was performed using an ELISA kit from Diagnostic
Systems Laboratories, Inc., Webster, TX. The assay is a one-step sandwich-type
immunoassay, in which standards and unknown serum samples were incubated with anti
osteocalcin polyclonal detection antibody labeled with the enzyme horseradish peroxidase
in mircrotitration wells coated with an affinity purified anti-osteocalcin mouse monoclonal
antibody. After incubation and washing, the wells were incubated with the substrate
tetramethylbenzidine (TMB). An acidic stopping solution was then added and the degree
o f enzymatic turnover o f the substrate was determined by dual-wavelength absorbance
measurement at 450 and 620 nm. The absorbance measured was directly proportional to
the serum concentration o f osteocalcin. The set o f osteocalcin values were used to plot a
standard curve o f absorbance versus osteocalcin concentration from which osteocalcin
concentrations o f the unknown samples were calculated. Osteocalcin o f unknown
specimens were calculated from a calibration curve fit (sigmoid) with a 4-parameter
logistic equation. Osteocalcin values were expressed in ng/mL. Intra-assay precision
coefficient o f variation was 6.5%. Inter-assay precision coefficient o f variation was 4.8%.
Samples were analyzed using a Dynex (Dynex Technologies, Inc., Chantilly, VA)
Opsys MR plate reader. The Opsys MR is a microprocessor-controlled photometer
designed to measure the optical density (OD) o f fluid samples in 96-well microplates in
order to quantify the absorbance o f various colorimetric chemical reactions. The light
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73
absorption by a material was determined by the Beer-Lambert Law, which states that
the absorbance o f light was directly proportional to the product o f pathlength (distance in
cm that the light beam travels through the absorbing material) and concentration
(expressed as moles per liter o f fluid). Equal volumes o f blanks, standards and test
samples dispensed into wells o f equivalent size and shape allow for accurate determination
o f absorbance values. Absorbance was determined by means o f a tungsten halogen lamp
which projects a light beam through a heat absorbing filter and a lens. The beam was
focused by the lens and passes through a filter (located on the filter wheel), which allows
only light o f the deshed wavelength range to pass. The beam was separated into 13
channels, one o f which was a reference while the other 12 directed upwards through a row
o f 12 weOs on the microplate onto silicon photodiodes. The photodiodes quantify the
intensity o f light transmitted through the reaction solution and absorbance was measured
in terms o f OD (Dynex, 1999).
Serum Androstenedione
Blood sampling was performed by 10 AM during the early follicular phase o f the
menstrual cycle (within 10 days o f the onset o f menses) when androgen levels are the most
stable in females (Buchanan et aL 1997, Steinberg et al. 1989, Weiss, Cureton. and
Thompson 1983, and Westeriind et aL 1987) for analysis o f androstenedione
concentrations. A phlebotomist drew approximately six-ml blood from a forearm vein at
each time point into a serum tube. The sample was allowed to clot for 15 minutes and
then centrifuged for 10 minutes at four degrees Celsius (°C) and 3000-x gravity and serum
pipetted into storage vials. The serum was frozen at -80 °C until analysis. Samples were
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74
analyzed for androstenedione concentrations using Enzyme Immunoassay (EIA) Kits
from Diagnostic Systems Laboratories, Inc., Webster, TX. The procedure for measuring
the concentration o f androstenedione follows the basic principle o f enzyme immunoassay
where there is competition between an unlabelled antigen and an enzyme-labeled antigen
for a fixed number o f antibody binding sites. The amount o f enzyme-labeled antigen
bound to the antibody is inversely proportional to the concentration o f the unlabeled
analyte present. Decanting and washing the wells removed unbound materials.
Absorbance was measured at 450 and 620 nm and concentration determined by plotting
against a standard sigmoid curve. The assay was performed on the Dynex Opsys MR
described earlier.
Serum Creatine Kinase (CK)
Serum CK, which can be used to represent the muscle damage associated with
eccentric resistance training, was analyzed by standard spectrophotometric techniques
(Ektachem D T II System, Johnson & Johnson, Rochester, New York). The procedure
began by placing a 10 p.L sample o f serum on a dry, multilayered film in a plastic support
(slide). The slide contained all the reagents necessary to determine the CK activity
including creatinine amidohydrolase, which hydrolyzes creatine. Creatine was hydrolyzed
to sarcosine by creatine amidhydro lase, which was then oxidized by sarcosine oxidase to
glycine, formaldehyde, and hydrogen peroxide. Lastly, hydrogen peroxide was oxidized
by peroxidase to a colored dye. The rate o f change in reflection density at 680
nanometers (nm) was measured during a 5.5-minute incubation at 37°C. Creatine kinase
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75
present in the sample was reacted within the first four minutes and the rate o f change
between 4.5 and 5.5 minutes was proportional to the CK concentration in the sample.
Tnterleulrin-6 (IL-6^
Measurement o f IL-6 levels in serum were conducted utilizing an assay
procedure that employed quantitative sandwich enzyme immunoassay technique. A
monoclonal antibody specific for IL-6 was pre-coated onto a microplate. Standards and
samples were pipetted into the wells and any IL-6 present was bound by the immobilized
antibody. After washing away any unbound substances, an enzyme-linked polyclonal
antibody specific for IL-6 was added to wells and color developed in proportion to the
amount o f IL-6 bound in the initial step. The color development was stopped and the
intensity o f color was measured on the Dynex Opsys MR described earlier. Intra-assay
precision coefficient o f variation was 3.1%. Inter-assay precision coefficient o f variation
was 3.8%.
The measurement o f IL-6 was insensitive to the addition o f the recombinant form
o f the EL-6 soluble receptor. Therefore, it is probable that experimental measurements
reflect the total amount o f IL-6 present, Le., the total amount o f free IL-6 plus the amount
o f IL-6 initially bound to soluble receptors, if any were present in the samples. High levels
ofhigh-aflfinity autoantibodies to IL-6 in the serum o f some normal blood donors have
been reported and such autoantibodies have the potential to interfere with the
measurement o f IL-6 by ELISA immunoassays.
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76
Muscle Soreness
In addition to assessing muscle damage by CK and IL-6 levels, a perceived
sensation o f intensity o f soreness scale was administered once per week (Appendix A).
The scale ranges from no soreness to extreme soreness. This scale was modified from a
scale used by MacIntyre et aL (1996). The subject was asked to choose the appropriate
indicator on the scale representing their peak soreness since the last training day.
M enstrual Physical Activity, and H ealth History Questionnaire
Subjects completed a m enstrual physical activity, and health history questionnaire.
The questionnaire included information about age at menarche, current menstrual history,
current and past oral contraceptive (OC) use, participation in sports and exercise, and
family heath history (Appendix A). Reported values were confirmed by oral interview.
Statistical M ethods
Power Calculations
A priori power analysis was performed to determine the statistical power needed
to detect significant differences and/or changes in muscle strength, muscle mass, bone
mineral density, and bone biochemical markers. The procedure was as follows.
In determining the appropriate sample size, four factors were considered; 1) level
o f significance, a , or the probability o f making a Type I error, 2) power o f the test, (3 , or
the probability o f making a Type II error, 3) the population error variance, o2, and 4) the
effect size (ES).
Significance (a ) was set a p riori at 0.05. A p rio ri determ ination o f power has
been suggested as a 4 :1 ratio o f ( 3 to a . Given an a o f 0.05, the corresponding power is
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77
I - 4(0.05) = 0.80. For a priori determination o f the population standard deviation, it is
acceptable to use a variance cited in the research literature. Thus, the formula for
determining sample size for two-tailed tests becomes:
n = 2tr2 (zft - ZnnXL
(ES)2
Where, using an a = 0.05 and a ( 3 = 0.80 for a two-tailed test;
zp = .842
Za = -1.96
If the researcher is willing to express the ES as standard deviation units (d), the
formula:
d = ES
C T
can be used to replace a 2 and (ES)2 in the sample size determination formula, which thus
becomes:
it= 2 £ z fi_ j_ z g/2)I
d2
In determining samples sizes needed to detect significance in this proposed study,
effect sizes and standard deviations were utilized from the research literature and from
results obtained in our laboratory. For serum osteocalcin, a four-month resistance training
study by Fujimara et al. (1997) demonstrated an ES o f 6.5 ng/ml at two months with a
standard deviation o f 4.84. Thus d = 13 4 , and;
n = 2r.842-(-l .96)12
(134)2 = 8.7 subjects
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78
For urinary Dpd, the same study demonstrated an ES o f 12.5 nmol/day at two
months with a standard deviation o f 64. Thus d = 0.20, and;
n=2 r .8 4 2 -(-1 .9 6 )l2
(.20)2 = 78.5 subjects
For muscle strength, a resistance training study in elderly women by Charette et aL
(1991) demonstrated increases o f 7.7 ± 1.3 to 16.8 ± 2.8 kg, depending on the muscle
group and exercise. Using the value for the leg curl, which showed the smallest increase
with an ES o f 7.7 and a standard deviation o f 1.7;
n = 2f.842-(-I.96)T2
(2.66)2 = 2.2 subjects
For muscle mass, the same study noted an ES o f 238 urn2 with a standard
deviation o f 212. Thus, d = 1.12, and;
n = 2 r . 8 4 2 - C - l . 9 6 1 1 2
(1.12)2 = 12.5 subjects
Lastly, for bone mass, results from a resistance training study in young women
from our lab yielded results that suggested 12 subjects were necessary to note a 1.6%
increase in bone mass as significant. Thus, given that the 79 subjects needed to determine
significance in Dpd was unrealistic and resistance training has been associated with an
increase in formation, not a decrease in resorption. Furthermore, the other parameters all
predicted that < 12 subjects would provide sufficient statistical power to detect significant
changes, 15 subjects per group were initially recruited for this study to account for a 20%
attrition rate.
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79
Statistical Analyses
Data were entered into a PC computer and analyzed using the Statistical Package
for Social Sciences software v. 9.0 (SPSS Inc., Chicago EL). A two-way analysis o f
variance (ANOVA) with repeated measures was used to determine differences between
and within the training and control groups for the dependent variables for baseline and
week 16 measures. A three (group) x five (time) ANOVA design was used. The main and
interaction effects were tested using the multivariate criterion o f Wilks’ lam M a Tukey
paired-samples T-tests were utilized as post-hoc tests for simple main effects and
interaction effects. Analysis o f covariance (ANCOVA) was used to control for group
differences when menstrual cycle length and oral contraceptive use was the covariate.
Additionally, ANCOVA was used to control for initial values, weight, and lean body mass
for bone and hormone changes. Standard stepwise regression was used to determine the
relationships between androstenedione, BMD, BMC, deoxypyridinoline, and osteocalcin.
Pearson’s correlations for relative change in androstenedione, deoxypyridinoline,
osteocalcin, and lean and bone mass measurements were used to determine the nature o f
the relationships o f these variables. Significance was set a priori at p < 0.05.
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CHAPTER IV
80
RESULTS
Study Subjects
Fourteen subjects assigned to Iow-intensity eccentric resistance training (LRT). 14
subjects assigned to high-intensity eccentric resistance training (HRT), and 9 subjects
assigned to the control (C) group completed DXA scans, 1-RM concentric strength, and
provided blood and urine samples at baseline and week 16 o f the study intervention.
Additionally, serum and urine samples were obtained at study weeks 4, 8, and 12 in the
LRT group from 11, 13, and 12 subjects, respectively. At study weeks 4 ,8 . and 12 in the
HRT group, 13, 13, and 11 subjects, respectively, provided blood and urine samples.
Four subjects initially assigned to the control group did not complete the baseline
measures. One subject did not want to make the tone commitment and the other three
subjects withdrew for unknown reasons. Three subjects in the HRT group, four subjects
in the LRT group, and five subjects in the control group were not taking oral
contraceptives. The remaining subjects were taking oral contraceptives prior to and for
the duration o f the study intervention. The study groups were generally comparable in
baseline characteristics. Age. height, weight, lean mass, and percent body fat did not
differ between groups (Table 2).
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SI
Table 2. Baseline Characteristics o f Study Subjects
LRT
n=14
HRT
n= l4
C ontrol
n— 9
Age (years) 24.4 ±1.9 24.0 ± 1.4 24.4 ± 2.2
Height (cm) 164.4 ± 6.5 165.8 ± 5.5 161.4 ± 8.8
Body Weight (kg)
56.8 ± 7.2 55.7 ± 6.0 58.2 ± 13.5
Lean Body Mass (kg)* 40.7 ± 4.2 40.2 ± 3.8 40.8 ± 7.5
Fat Mass (kg)* 13.9 ± 3.6 13.3 ± 3.2 16.6 ± 6.5“
Body Fat (%)* 24.3 ± 3.4 23.6 ± 3.9 25.1 ± 5.6
Mean values ± 1 standard deviation.
* Measured by Dual-energy X-ray Absorptiometry.
“Significantly greater than the Low- and High-intensity RT group.
Strength
Baseline and week 16 concentric strength measures are displayed in Table 3. At
baseline, measures o f 1-RM concentric strength were similar in the LRT, HRT, and C
groups. However, following 16 weeks o f study intervention the absolute gains in 1-RM
concentric strength increased similarly in both the LRT and HRT groups (Table 4) with
exception o f the chest press, which was almost two-fold greater in the HRT group (8.7 ±
7.8 kg, mean ± SD and 14.8 ± 5.6 kg, respectively). Furthermore, the gains in 1-RM
concentric strength in both groups were significantly different from the absence o f
strength change in the control group. Following 16 weeks o f study intervention, both the
LRT and HRT groups demonstrated significant relative increases in concentric strength
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82
for all exercises tested (Figure 3). No significant absolute o r relative (% change from
baseline) changes in concentric strength were measured in the control group.
Table 3. Baseline and Week 16 Concentric Strength (kg) by 1-RM
Exercise Low-Intensity RT High-intensity RT Control
n=l4 n=l4 n=9
Baseline Week 16 Baseline Week 16 Baseline Week 16
Chest Press 25.1173 39.919.2 283110.1 37.015.6 30.915.1 313153
LatPuD 34.716.9 42.017.7 34.616.8 41.9173 35.415.8 35315.7
Biceps Curl 20.514.4 24.1143 20.714.5 24.113.9 21313.4 21.8133
Triceps Ext.
14.414.4 18.015.0 14.612.9 17.9133 15.013.7 15.4143
Leg Extension
49.2110.1 61318.0 50.017.9 59.418.9 463173 47317.4
Leg Curl 39.817.4 52.618.9 403173 51.717.5 36.117.8 36.717.7
Mean values ± 1 standard deviation.
Table 4. Absolute Change in Concentric Strength (kg) by 1-RM
Exercise Low-Intensity RT
n=l4
High-intensity RT
n= 14
Control
n=9
Chest Press
8 .7 1 7 .6 1 4.815.6 0 3 1 0 .7
Lat Pull 7 .3 1 2 .7 7 .2 1 3 .5 0 .1 1 0 .4
Biceps Curl
3 .4 1 1 .9 3 .6 1 1 .0 0 3 1 0 .6
Triceps Ext.
3.3 1 1 .2 3 .5 1 3 .0 0 .4 1 0 .8
Leg Extension 9 .4 1 2 .1 1 2.0 1 4 .7 0 .8 1 1 .1
Leg Curl
11.414.9 12.814.8 0 .6 1 1 .5
Mean values ± 1 standard deviation.
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% Change
83
Figure 3. Relative (%) Change in Strength From
Baseline to Week 16
100
Control
Low -Intensity RT
H igh-intensity RT
Chest Lat Pull Biceps Triceps Leg Ext Leg Curt
Exercise
^Significant increase from Baseline to Week 16.
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84
Body Composition
At baseline, measures o f lean mass were similar in the LRT, HRT, and C groups
as measured by DXA (Table 2). No significant changes in lean mass were demonstrated
in the control group from baseline to week 16 o f the study. Following 16 weeks o f study
intervention, lean mass significantly increased in both the LRT (0.7 ± 0.6kg, p=0.002)
and HRT (0.9 ± 0.9kg, p=0.006) groups. However, there were no significant differences
between group change in lean mass (F = 1.54, p = 0.228). Furthermore, controlling for
baseline weight and lean body mass did not alter the findings o f this relationship.
At baseline, measures o f fat mass were similar in the LRT and C groups as
measured by DXA (Table 2). However, baseline fat mass in the control group was
significantly greater than the HRT group (F = 3.72, p = 0.012) by approximately 3 kg
(Table 2). Additionally, baseline fat mass in the control group was significantly greater
than the LRT group (F = 3.72, p = 0.026). Fat m ass significantly increased in the LRT
group (0.3 ± 0.6kg, p=0.05) while no significant change in fat mass was demonstrated in
either the HRT or C group. These alterations in lean and fat mass resulted in significant
total body weight gains only in the LRT group (1.0 ± 0.8kg, p<0.001). Combining the
exercisers (HRT + LRT) as one group abolished differences in fat mass between and
within groups.
Baseline and week 16 measures o f mid-femoral slice lean mass are presented in
Table 5. Mid-femoral slice lean mass significantly increased in the LRT (10.3 ± I8g,
p=0.05) group, whereas no significant lean mass changes were demonstrated in the HRT
or C groups following 16 weeks o f study intervention. Additionally, combining the
exercise groups did not demonstrate any significant increases in lean mass from baseline
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85
to week 16, nor were the means o f the combined exercise group different horn the control
means (F = 0.658, p = 0.521). Similarly to the lean mass findings, mid-femoral slice fat
mass significantly increased in the LRT (7.3 ± 12.4g, p=0.05) group, while there were no
significant changes in slice fat mass in the HRT or C groups. Combining the exercise
groups and comparing the means for change from baseline to week 16 did not
demonstrate significant within group differences. Additionally, comparing the combined
exercise groups to the control group did not demonstrate any between group differences
(F = 2.96, p = 0.06).
Table 5. Baseline and Week 16 Mid-Femoral Lean Mass Slice Values
Mid-Femoral Slice Low-Intensity RT High-intensity RT Control
(g)
n= l4 n=14 n=9
Baseline 493.2 ±71.4 522.6 ± 75.5 509.1 ±72.7
Week 16 503.5 ±66.0* 517.7 ± 71.0 502.8 ± 75.7
Mean values ± 1 standard deviation.
^Significantly greater than Baseline.
Bone Mass
At baseline, measures o f BMC and BMD were similar in the LRT, HRT, and C
groups as measured by DXA (Table 6). Following 16 weeks o f study intervention, the
LRT group demonstrated a significant increase in BMC (0.855 ± 0.958 g/cm. F = 5.52.
p=0.005) at the spine, while no significant change in spine BMC occurred in the HRT
and C groups (Figure 4). Additionally, combining the means ofboth exercise groups
resulted in a significant increase (p = 0.034) in spine BMC from baseline (57.4 ± 7.4
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86
g/cm) to week 16 (58.2 ± 7.6 g/cm). However, the changes in the combined exercise
group were not significantly different from the control group. Controlling for initial
weight, lean mass, and BMC measures independently did not abolish the significant
relationship.
Table 6. Baseline and Week 16 BMC and BMD Measures by DXA
Bone M ass Low-Intensity RT
/r=14
Baseline Week 16
H igh-intensity RT
n= 14
Baseline Week 16
C ontrol
n=9
Baseline Week 16
BMC (g/cm)
Spine
54.5±6.9 55.416.5* 60.217.0 61.117.7 52.2112.2 52.9113.1
Proximal Fern. 3l.l±4.0 31.414.3 31.615.5 32.115.5 25.915.6 26.915.8
Total Body
2187±172 21921182 22391339 22521359 20701483 20941508
BMD (g/cmz )
Spine
1 . 0310.07 1.0310.07 1.0710.09 1.0610.09 0.9810.01 0.9810.01
Proximal Fern. 0.98+0.10 0.9710.10 1.0110.12 1.0I10.I2 0.8910.01 0.9010.01
Total Body 1.0610.03 1.06+0.04 1.0910.08 1.0910.09 1.0310.09 1.0410.08
Mean values ± 1 standard deviation.
* Significantly greater than Baseline.
No significant changes in BMC or BMD were found in the regions o f the whole-
body and proximal femur in any group. To further evaluate the absence o f any
significant relationships in BMC and BMD, the exercise groups were combined and
compared to the control group. No significant between group differences were found.
Baseline, mid-femoral slice BMD and BMC values were not significantly
different in the LRT, HRT, and C groups as measured by DXA (Table 7). No significant
absolute or relative change in BMD or BMC was demonstrated from baseline to week 16
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Spine B M C (g/cm)
87
Figure 4. Spine Bone Mineral Content (BMC) From
Baseline to Week 16.
70
60
50
40
1 1 1
Control
Low-intensity R T
High-lntensity RT
Baseline Week 16
Time
^Significant increase from baseline.
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88
in any group (p > 0.05). Furthermore, when both exercise groups were combined and
compared to the control group, no between group differences were demonstrated.
Table 7. Baseline and W eek 16 Mid-Femoral BMC and BMD Slice Values
Mid-Femoral Low-intensity RT High-lntensity RT Control
Slice Values rc=14 n=14 n=9
Baseline Week 16 Baseline Week 16 Baseline Week 16
BMC (g/cm)
Mid-femur
16.2+2.2 I6J±2^ I6.6±2.6 16.7±2.7 15.5±3.5 I5.6±3.8
BMD (g/cm2 )
Mid-femur 1.44±0.14 t.4l±0.l5 1.46±0.14 1.48±0.17 I.41±0.I4 l.40±0.17
Mean values ± 1 standard deviation.
Bone Biochemical Markers
At baseline, measures o f deoxypyridinoline crosslinks (deoxypyridinoline/urinary
creatinine) and osteocalcin were similar hi the LRT, HRT, and C groups as measured by
ELISA. The absolute baseline and week 16 deoxypyridino line values are presented in
Table 8. When both exercise groups were combined, deoxypyridinoline showed a
nonsignificant decrease from baseline (6.0 ± 6.4 nM/mM) to week 16 (4.4 ± 3.5
nM/mM); however, this trend did approach significance (p = 0.057). The change in
deo xypyridino line in the combined exercise group was not significantly different from
the control group (p = 0.173). The measures o f deoxypyridino line in the LRT group at
the 5 time points are displayed in Figure 5. Following 16 weeks o f study intervention,
deoxypyridinoline in the LRT group did not significantly change. Furthermore, there
were no significant differences between the 5 time points measured, although there was
an interesting trend. At week 8 in the LRT group there was a nonsignificant (p = 0.124)
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89
2.5 fold increase in deoxypyridinoline compared to baseline. Following week 8 the
deoxypyridinoline values in the LRT group returned to baseline levels.
Table 8. Baseline and Week 16 Deoxypyridinoline Values
Deoxypyridinoline Low-intensity RT High-lntensity RT Control
(nM/mM) n=14 n=14 n=9
Baseline 4.7 ± 2 .5 7.4 ± 8.8 6.9 ± 6 .2
Week 16
4.6 ± 1.7 4.13 ±4.7* 5.9 ± 6.6
Mean values ± 1 standard deviation.
* Significantly lower than Baseline.
Deo xypyridino line levels in the HRT group followed a similar trend as in the
LRT group with the highest values peaking at week 8. However, in the HRT group,
deoxypyridino line decreased significantly from baseline 45 ± 89% (p=0.027) following
16 weeks o f intervention. Additionally, in the HRT group, deoxypyridinoline decreased
significantly from week 4 (15.3 ± 20.7 nM/mM) to week 16 (4.13 ± 4.7 nM/mM,
p=0.035) (Figure 6). Largely, the general trends o f changes in deoxypyridinoline were
similar in both groups with no significant difference between group changes (F = 0.443, p
= 0.643). No significant changes in deoxypyridinoline occurred in the control group over
the 16 weeks o f the study.
When both exercise groups were combined, osteocalcin showed a nonsignificant
increase from baseline (12.4 ± 4.9 ng/mL) to week 16 (18.0 ± 16.2 ng/mL); however, this
trend did approach significance (p = 0.086). The change in osteocalcin in the combined
exercise group was not significantly different from the control group (p = 0.291). The
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90
Figure 5. Absolute Change in Deoxypyridinoline Crosslinks in the
Low-intensity Resistance training Group
30
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15
10
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rr=13
n=14
n=12
B aseline Week 4
i i i
8 Week 12 Week 16
Time
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Deoxypyridlnoline/Urinary C reatinine (nM /m M )
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Figure 6. Absolute Change in Deoxypyridinoline Crosslinks in the
High-lntensity Resistance Training Group
60 -
50 -
40 -
30 -
20 -
10
0
•10
•20
B aseline Week 4 Week 8 Week 12 Week 16
Time
‘ Significant decrease from Baseline and Week 4.
n=13
n=13
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92
absolute baseline and week 16 osteocalcin measures are presented in Table 9.
Osteocalcin significantly decreased 51 ± 48% (p=0.007) in the LRT group over the first 8
weeks o f the study (Figure 7). From week 8 to week 16 osteocalcin increased
significantly in the LRT group 165 ± 61% (p<0.001). Following 16 weeks o f
intervention there was a significant increase in the LRT group from baseline o f 31 ± 61%
(p=0.037).
Table 9. Baseline and W eek 16 Osteocalcin Values.
Osteocalcin Low -intensity RT H igh-lntensity RT C ontrol
(ng/mL) n=14 n= l4 n=9
Baseline
9.6 ±5.3 14.4+3.9 10.2 ± 4.5
W eek 16
13.5 ±5.4* 22.5 ±21.8 9.8 ± 5.3
Mean values ± I standard deviation.
♦Significantly greater than Baseline.
Alterations in osteocalcin in the H R T group followed a similar trend as that found
in the LR T group; however, the magnitude o f change was greater in the H RT group.
Osteocalcin significantly decreased 200 ± 27% (p<0.001) in the H RT group over the first
8 weeks o f the study intervention (Figure 8). This relative decline in osteocalcin in the
H R T group was significantly greater (p = 0.030) than the significant decline in
osteocalcin in the LR T group from baseline to week 8. Following 8 weeks o f
intervention osteocalcin demonstrated a large 366 ± 418% increase from week 8 to week
16. although this change was not significant. Additionally, probably due to the large
variance in osteocalcin at week 16 in the H R T group, no significant increase was
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93
Figure 7. Absolute Change in Osteocalcin in the Low-intensity
Resistance Training Group
n=14
20
n=14
15 -
_J
s
c
n=11
n=12
c
o
a
o
o
a
S
Baseline Week 4 Week 12 Week 16 Week 8
Time
^Significant decrease from Baseline to Week 8.
^Significant increase from Baseline and Week 4.
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Osteocalcin (ng/mL)
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Figure 8. Absolute Change in Osteocalcin in the High-lntensity
Resistance Training Group
so i
40
30
20
10 -
T T T
Baseline Week 4 Week 8 Week 12 16 W eeks
Time
^Significant decrease from Baseline and Week 4.
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95
demonstrated from baseline. The change in osteocalcin from week 8 to week 16 was not
significantly different between groups. No significant changes in osteocalcin were
measured in the control group over the course o f the study.
Serum C reatine K inase (CK)
At baseline, measures o f serum CK were similar in the LRT, HRT, and C groups
(Table 10). In the LRT group, serum CK significantly increased 60 ± 55% (p=0.025)
from baseline to week 4. The mean serum CK levels were maintained above baseline
throughout the duration o f the study in the LRT group but tended to decrease slightly
after week 4 (Figure 9). Following 16 weeks o f study intervention, the LRT group
demonstrated a significant increase in serum CK o f 47 ± 51% (p=0.025). Similar to the
LRT group, the HRT group showed a significant 35 ± 49% (p=0.02I) increase from
baseline to week 4 o f the intervention. In contrast to the LRT group, following study
week 4 serum CK levels significantly decreased returning to levels sim ilar to baseline
values in the HRT group (Figure 10). No significant changes in serum CK were assessed
in the control group.
Table 10. Baseline and W eek 16 C reatine Kinase Values.
C reatine K inase (CK) Low -intensity RT H igh-lntensity RT Control
(U/L) n -1 4 n= l4
Baseline 86.9 ± 2 8 3 1193 ±51.8 99.6 ± 3 0 3
W eek 16
127.9 ±53.1* 128.6 ± 4 2 3 119.0 ± 2 3 3
Mean values ± 1 standard deviation.
^Significantly greater than Baseline-
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CK(U/L)
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Figure 9. Absolute Change in Creatine Kinase (CK) in the
Low-intensity Resistance Training Group
260
240
220
200
180
160
140
120
100
80
60
40
20
rr=11
rt=13
n=12
n=14
Baseline Week 4 Week 8
Time
i ■■ i -
Week 12 Week 16
‘Significant increase from Baseline.
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(i/n) n o
97
Figure 10. Absolute Change in Creatine Kinase (CK) in the
High-lntensity Resistance Training Group
260
240
220
200
180
160
140
120
100
80
60
40
n=13
n=14
rr=11
Baseline Week 4 Week 8
Time
Week 12 Week 16
Significant increase from Baseline to Week 4.
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98
Seram Androstenedione
At baseline, measures o f serum androstenedione were similar in the LRT, HRT,
and C groups (Table 11). The relative change in serum androstenedione in the LRT
group following 16 weeks o f study intervention was 22.8 ± 52.3% and although not
significant, this change did approach significance (p=0.06). Furthermore, from week 12
to week 16 o f the study serum androstenedione significantly increased (194 ± 51%,
p=0.0l 1) in the LRT group (Figure 11). O f interest, in the LRT group during the initial 4
weeks o f the study, androstenedione increased approximately 173%; however, this
increase was not significant due to the extremely high variance (±277%). In contrast to
the LRT group, androstenedione levels remained constant over the first 8 weeks o f the
study in the HRT group. Similar to the large variance in androstenedione measures found
at week 4 in the LRT group, large variances in the androstenedione measures were found
at all time points in the HRT group. Significant alterations in serum androstenedione
were demonstrated at week 12 (decrease from baseline) and week 16 (returned to
baseline) (Figure 12) in the HRT group. At week 12 androstenedione had decreased 135
± 50% from week 8. Following 4 additional weeks o f treatment (week 12 to week 16),
Table 11. Baseline and Week 16 Androstenedione Values.
Androstenedione Low-intensity RT High-lntensity RT Control
(ng/mL) n= l4 n— 14 n=9
Baseline
5.2 ± 2.8 5.5 ± 3.7 5.3 ± 2 .0
Week 16
7.4 ± 4 .6 5.7 ± 2.8 5.6 ± 1 .7
Mean values ± 1 standard deviation.
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99
androstenedione bad increased significantly 15S ± 158%, though no significant change
was demonstrated comparing baseline to week 16. No significant changes in serum
androstenedione were measured in the control group.
Menstrual cycle length may influence the relationship o f androstenedione to other
variables. Therefore, to control for differences in menstrual cycle length, comparison o f
changes between and within groups and interaction effect was attempted utilizing
ANCOVA where cycle length was the covariate. Controlling for cycle length did not
alter the nature o f the relationships demonstrated by ANOVA. Menstrual cycle length
averaged 28 days and ranged from 28 to 31 days in all subjects. In addition, to ensure
that women taking and not taking oral contraceptives (OC) did not confound the
androstenedione findings, a comparison o f changes between and within groups and
interaction effect was attempted utilizing ANCOVA where OC use was the covariate.
Controlling for OC use did not significantly influence the androstenedione findings
reported above. In fact, comparing all OC users to all non-OC users in the exercise
groups combined did not show any significant differences in androstenedione
concentration (F = 0.018, p = 0.89).
Utilizing stepwise regression techniques to determine how the change in
androstenedione might predict a change in BMD. BMC, deoxypyridino line, or
osteocalcin resulted in no significant correlations. Additionally, controlling for initial
weight and androstenedione measures did not result in any significant correlations.
Furthermore, performing standard Pearson’s correlations with relative change in
androstenedione, deoxypyridino line, osteocalcin, CK, IL-6 and bone mass measurements
o f the whole body, hip, and spine did not demonstrate any significant relationships.
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Androstenedione (ng/mL)
100
Figure 11. Absolute Change in Androstenedione in the
Low-intensity Resistance Training Group
50
40
30
20
10
0
-10
-20 - .> | ■ i 1 ■ 1 r 1 1 ■ 1 ■ t i i ■ i ■■■■[ - -
Baseline Week 4 Week 8 Week 12 Week 16
Time
^Significant increase from Week 12 to Week 16.
n=14
rt=14
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Androstenedione (ng/mL)
101
Figure 12. Absolute Change in Androstenedione in the
High-lntensity Resistance Training Group
10
8
"=14 n=13
n=14
n=13
— i i
Baseline Week 4 Week 8
Time
Week 12 Week 16
Significant decrease from Weeks 4 and 8 to Week 12.
^Significant increase from Week 12 to Week 16.
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102
Serum Interleukin 6 (IL-6)
At baseline, measures o f serum IL-6 were similar in the LRT, HRT, and C groups.
No significant changes in serum IL-6 were demonstrated in the LRT, HRT, or C groups
between any time point following 16 weeks o f study intervention (F = 0.622, p = 0.538)
(Table 12). Combining the exercisers into one group did not produce any between or
within group differences.
Table 12. Baseline and Week 16 Interleukin-6 Values.
Interleukin-6 (IL-6) Low-intensity RT High-lntensity RT Control
(pg/mL) n=l4 n=l4 n=9
Baseline
0.87 ± 1.20 0.89 ±0.76 0.82 ±0.60
Week 16
0.89 ± 0.94 0.86 ±0.96 0.85 ±0.86
Mean values ± 1 standard deviation.
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CHAPTER V
103
DISCUSSION
It was hypothesized that eccentric resistance training would significantly increase
bone mass. However, an intriguing finding o f this study was that eccentric resistance
training did not significantly increase whole body, proximal femur, or spine BMD or
BMC in either the low- or high-intensity eccentric training groups with exception to a
significant increase in spine BMC in the LRT group. If load magnitude is one o f the
primary factors contributing to an osteogenic stimulus, which has been well established
by Rubin and Lanyon (1985) and demonstrated in our prior study (Hawkins et al. 1999),
then why did the HRT group working at 125% o f them maximal concentric ability not
significantly enhance BMD o r BMC? Bone is a complex tissue that is regulated and
mediated by many factors. Nonetheless, the literature suggests that load magnitude is the
major contributor to bone adaptation even under non-optimal conditions. For example,
Robinson et aL (1995) reported that female collegiate gymnasts had significantly higher
BMD measures than those o f equivalently trained runners or than age-based normative
predictions even though many o f the women gymnasts had menstrual disturbances
(oligomenhorrea and amenorrhea), known to result in bone loss. It was suggested that the
high impact loading associated with gymnastics training provided adequate stimulus on
bone to overcome the hormonal disruption.
In this study, the high-intensity eccentric resistance training group was designed
to maximally load the bone through muscle contraction using the largest intensity
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104
possible that could be performed with a controlled lowering o f the weight. Based on
the literature, 125% o f a concentric one repetition maximum appears to be the most
appropriate maximal intensity, with intensities greater than 130% resulting in the
individual being unable to control the weight (Johnson, Adamczyk, Tennoe, and
Stromme 1976). The low-intensity eccentric resistance training group was designed to be
a moderate-intensity weight-lowering group. The difference in intensities between the
groups was designed to test the hypothesis that greater load magnitude with eccentric
resistance training would result in larger bone adaptations. To eliminate the variable o f
more work being performed in one o f the training groups, work was controlled for in the
design. The HRT group performed three sets o f six repetitions at 125% intensity while
the LRT group performed three sets o f 10 repetitions at 75% intensity. Therefore, since
both groups trained twice per week, total work (# o f days/week X # o f sets X # o f reps X
intensity) performed by each group was equal.
The absence o f a significant increase in BMD and most BMC measures in both
groups following 16 weeks o f eccentric training is perplexing; however, there are a
number o f variables that may have influenced these findings. One important issue is the
duration o f the study. The average turnover at a bone remodeling site is assumed to be 6
months; however, bone turnover can occur in as little as 3 months or as long as 18
months (Recker et al. 1988). Hawkins et aL (1999) demonstrated a significant 3.9%
increase in mid-femur slice BMD as measured by DXA following 18 weeks o f maximal
eccentric training on a KinCom isokinetic dynamometer. If mid-femur BMD measures
were assessed at 16 weeks in this study, the findings would be expected to be similar to
the significant findings o f a 3.9% increase in BMD in the previous study, since bone
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105
adaptations are relatively slow and BMD could not reasonably increase almost 4% in
two weeks. The mid-femur slice analysis as measured by DXA in the current study did
not show any significant changes in BMD or BMC at 16 weeks that were demonstrable at
18 weeks in the study by Hawkins et aL.
Most intervention training studies are conducted for less than one year for
logistical purposes and the high attrition associated with long duration training studies. It
is generally believed that, as opposed to muscle strength gams, which are maximal within
the first few months o f a study, increases in bone mass evolve more slowly, so longer
duration studies would be required to achieve more impressive gains in bone mass.
However, Lohman et aL (1995) reported gains in BMD measured by five months that
either remained stable or actually decreased over the next year, despite continued and
fairly dramatic increases in muscle strength through 18 months o f training. Additionally.
Friedlander et al. (1995) reported that lumbar spine, femoral neck, and trochanteric BMD
increased by only 1.3,0.5, and 2.6% after two years o f supervised training, demonstrating
that larger increases in BMD are not necessarily associated with long duration studies.
The HRT group not responding to the training protocol as hypothesized may be
due to a threshold o f eccentric training-induced muscle damage. It is possible that the
75% training intensity established in this study, which is considered borderline high-
intensity in many other studies, is as effective at inducing muscle damage as the 125%
training intensity. In feet, serum CK and perceived soreness findings in the LRT group
support the contention that muscle damage was sustained throughout the study
intervention, whereas the HRT group did not sustain continued muscle damage. I f an
eccentric training threshold exists then the absence ofbone adaptations m the HRT group
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106
may be expected. However, this does not explain why the findings in the HRT group
were not similar to the LRT group.
A possible explanation for the greater influences o f low-intensity eccentric
training on bone mass, biochemical markers, and androstenedione in the LRT group is
the time o f muscle contraction. The subjects in the HRT group maximally resisted the
weight, resulting in a controlled lowering o f the weight, which was approximately 2
seconds. Intensities greater than 125% result in the weight being lowered too fast and
intensities less than 125% result in variable contraction times. The LRT group subjects
were asked to perform the lowering o f the weight in 2 seconds; however, even with
supervision the subjects sometimes lowered the weight slower than 2 seconds. Although
eccentric training at 75% intensity does not feel difficult or heavy to the subject, the
possible additional time the muscle groups spent eccentrically contracting could have
generated a greater stimulus for adaptation on bone mass, biochemical markers, and
androstenedione m the LRT group.
Alterations in the hormonal environment by oral contraceptives may have
inhibited or blunted the bone mass adaptations to eccentric resistance training. Seventy
percent o f the subjects in the current study were using low-dosed oral contraceptives.
Hartard et aL (1997) reported findings from a cross-sectional study investigating the
influence o f exercise to and in combination with low-dosed oral contraceptives on BMD.
The authors reported that the highest BMD values were measured in the subjects that
participated in long-term exercise (9.5 ± 4.3 years) and had used oral contraceptives for
the shortest (1.6 ± 1.7 years) time. No beneficial eflect on BMD was demonstrated in
subjects that participated in long-term exercise (10.4 ± 4.1) and used oral contraceptives
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107
for longer periods (8.2 ±4.1 years). These findings are interesting because they
suggest that low-dose oral contraceptives are not beneficial to bone, as has been
demonstrated by higher dose oral contraceptive use, and that low-dose oral contraceptives
may be deleterious to exercise adaptations on bone.
No studies have investigated the effects o f eccentric resistance training in
combination with low-dosed oral contraceptives on bone mass; however, the absence o f
bone adaptations in the current study may be the result o f the alteration hi the female
hormonal milieu. Exogenous ingestion o f hormones disrupts the normal endogenous
production o f hormones. The elimination o f estrogen and progesterone peaks and the
maintenance o f lower constant levels o f these hormones as a result o f taking low-dosed
oral contraceptives may have inhibited the osteogenic response. Further investigations
are needed to determine the effect o f low-dosed oral contraceptives alone and in
combination with resistance training on bone mass. Polatti et aL (1995) reported the
effects o f low-dosed oral contraceptive use on BMC m women between the ages o f 19
and 22 years. The authors found that greater than 5 years o f oral contraceptive use does
not allow the attainment o f physiologic peak bone mass. In fact, the young women not
taking oral contraceptives had 7.8% greater peak bone mass accretion as measured by
BMC.
The type ofloading, although eccentric, was different between this study and that
o f Hawkins et aL (1999). The eccentric training in Hawkins et aL’s study was performed
isokinetically. Maximal isokinetic eccentric resistance is performed by pressing or
pulling against a resistance that is slightly greater than the individuals generated torque
(computer controlled); therefore, the subject cannot overcome the resistance and the
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108
particular joint is moved in a direction that lengthens the muscle as it maximally
contracts. If the subject is not providing a near maximal effort the lever arm will not
move. By contrast, this study utilized free weight eccentric resistance training, which
requires assessment o f an individuals maximal concentric strength and the selection o f
appropriate resistance greater than 100% o f their maximal concentric strength to provide
a maximal eccentric training intensity. While it was the intent o f the investigator to select
the greatest weight that could be lowered eccentrically with proper form in the HRT
group, the subjects most likely were not maximally resisting the eccentric load
throughout the range o f motion. Therefore, the HRT stimulus in this study may have not
been as large as the stimulus provided by isokinetic eccentric resistance training in the
Hawkins et al. study.
Another difference between the Hawkins et aL study and this one is the training
frequency. The eccentric training was performed three times per week in the Hawkins et
al. study, whereas the eccentric training in this study was performed only twice per week.
The additional training day may have contributed that much more o f a stimulus to result
in an osteogenic response that was not observable in this study. The observation suggests
that there may be a threshold for the frequency o f training to significantly influence bone
adaptation with eccentric training. However. Brazell-Roberts and Thomas (1989)
reported that strength gains in college females were equal (37%) when one group trained
twice per week and the other group trained three times per week. The twice per week
training in this study was chosen to reduce the risk o f injury and allow recovery o f the
eccentric training-induced muscle damage that often results in inflammation and strength
loss.
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109
The finding o f a significant, although meager, increase in spine BMC in the
LRT group was interesting for several reasons. First, it was hypothesized that the HRT
group would demonstrate the greatest increases in bone mass with eccentric training and
that the LRT group would show a much more modest increase. However, the HRT group
did not significantly increase BMD or BMC at any site and the LRT group did show a
small gain in BMC but only in the region o f the lumbar spine. Second, it is worthy to
note that the significant change hi BMC occurred at the lumbar spine, which was not a
region specifically targeted by the type o f exercises performed, such as the quadriceps
and hamstring muscles that are exercised to target increases in femur bone mass.
Exercises such as the squat, dead lift, and back extensions are examples o f exercises
designed to load the spine; however none o f these exercises were performed in this study.
Lastly, no other bone regions assessed by DXA demonstrated any significant changes in
bone mass. Because o f the absence o f additional regions showing increases hi BMD or
BMC the significant increase in spine BMC may be a spurious folding.
Site-specific loading o f bone has been demonstrated to be effective hi resistance
training studies. Revel et aL (1993) reported that one year o f site-specific low-intensity
resistance training in postmenopausal women could prevent bone loss. The use o f
postmenopausal women makes these findings difficult to translate to young women
because o f the differences in bone turnover rates and hormonal status. Sinaki et al.
(1996) completed a three-year site-specific moderate-intensity resistance training study in
white women aged 30-40 years. Bone mass measurement by DXA at baseline, one year,
and three years showed no significant changes, even though muscle strength increased
significantly at all measured sites, similar to the findings in this study. Additionally, the
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110
women participating in Sinaki et aL’s study were active, but not athletic
premenopausal women as defined as participating in regular sport activity.
Training status o f the participants recruited into training intervention studies can
have a major influence on the potential effects o f the intervention. Many investigators
that report findings on bone mass with training studies utilize sedentary subjects.
Sedentary subjects may demonstrate greater effects in bone mass changes with training
since they may have lower than normal BMD to begin with and are unaccustomed to the
type o f stimulus. In addition to load magnitude, unusual strain is very osteogenic
(Lanyon 1992). Therefore, sedentary subjects may have a lower threshold to unusual
strain provided by the new training stimulus since they are inactive individuals. In
contrast, athletes that participate in sports have been shown to have higher BMD than
sedentary and non-athletic individuals (Hemonon et aL 1993). Interestingly, several
investigators have suggested that the higher BMD found in young women athletes
compared to their weight-matched sedentary controls may be due to self-selection.
Rather than the large magnitude loading associated with their respective sports causing
the increases in BMD, the athletes could be genetically predisposed to acquire higher
BMD and may be more likely to choose and continue to participate in high loading
sports. Additionally, young women genetically predisposed to low BMD may drop out
o f athletics o r choose not to begin high loading activities. Although we cannot determine
direction o f cause and effect between BMD and the involvement in high loading sports, it
is unlikely that young women with genetically predisposed high BMD choose and
continue to participate in athletics more so than young women with lower BMD.
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I l l
The young women recruited into this study were active; not participating in
weight lifting exercises currently o r in the six months prior to study entry and were
allowed to continue any type o f aerobic training. The absence o f significant findings o f
bone mass increases may be attributed to the current exercise status o f the subject
population tested. All the young women volunteers were enrolled in health profession
courses on the USC Health Sciences Campus. It may be that this population is more
accustomed to regular exercise since they are aware o f the many health benefits
associated with exercise. Indeed, if this population participates in regular exercise than
they may be less responsive to eccentric resistance training and the unusual strain
distribution may not be as great as it would in a less active individual. In feet, the
volunteers in this study may have undergone a detraining effect on bone. It is well
documented that bed rest, space flight, and inactivity result in the skeleton altering its’
structure and density to adapt to the reduced loads placed on the bones (Burr 1997, Frost
1990). Bone adaptations to detraining usually are associated with decreases in BMD.
Therefore, if volunteers in this study were highly active prior to entry and reduced their
activity level during the intervention, then the increased inactivity may have resulted in a
detraining effect on bone. This detraining effect may not have resulted in a loss o f bone,
but prevented any significant increases in bone mass.
Subjects completed a physical activity questionnaire that assessed their present
and past involvement in recreational exercise and competitive sports. The majority o f the
study volunteers had participated in recreational exercise and competitive sports for many
years prior to study entry. Additionally, many o f the subjects had experience weight
lifting. However, as part o f the exclusion criteria for this study, subjects must not have
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112
participated in weight lifting activities in the previous 6 months. It is possible that
prior weight lifting experience reduced the osteogenic response o f bone to the eccentric
training intervention. More likely, is the reduction in activity level once the volunteers
commenced their studies in rigorous academic programs. Assessment o f the subjects’
participation hi exercise would contribute to the understanding o f a possible detraining
effect if the subjects reduced their activity levels. Unfortunately, activity logs were not
kept throughout the study intervention to monitor the subjects’ activity levels. Although
subjects did complain about not having enough time to workout as often as they had in
the months prior to starting their respective academic programs, they were asked to
maintain their normal level o f activity throughout the study.
To the investigators knowledge, this is the first study to employ a whole body,
multiple muscle group, isotonic, eccentric progressive resistance training program to
influence bone mass. Isotonic eccentric resistance training was chosen as the
intervention because o f the ability to generate high loads with eccentric contraction and
the unique characteristic o f eccentric contraction-induced muscle damage and associated
factors. The type o f resistance training may play a very important role in bone
adaptation. In a unique study using rats, Westerlind et al. (1998) demonstrated that with
progressive resistance training, cortical bone o f the tibia did not significantly change
while trabecular bone o f the tibia increased. The resistance training was comprised o f
operantly conditioned rats wearing weighted vests and performing the squat exercise,
which utilizes both concentric and eccentric contractions. Alternatively, as discussed
above, in Hawkins et aL (1999) concentric isokinetic resistance training did not result in
significant im reasss in cortical or trabecular bone while eccentric resistance training
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113
resulted in significant increases in cortical and trabecular bone. T hese findings
support the contention for training specificity.
Training specificity has been shown to be accompanied by cross-training effects
that influence muscle (Higbie, Cureton, Warren, and Prior 1996, Hawkins et aL 1999) but
not bone (Hawkins et aL, Vuori et aL 1994). Cross-training effects are defined as training
improvements hi one limb that are also demonstrated in the opposite untrained limb.
These types o f adaptations are common with muscle strength and are most likely
attributable to neuromuscular influences. Such findings o f cross-training effects in bone
o f the opposite trained limb would suggest an indirect or systemic effect o f training. This
study was designed to test whether direct or indirect effects o f eccentric training have a
greater influence on bone. It was hypothesized that direct effects ofhigh-intensity
eccentric training would have the greatest influence on bone compared to low-intensity
eccentric training; however, if bone mass increases occurred only in the LRT group then
these findings would suggest a possible indirect influence on bone adaptation. The small,
although significant, increase in spine BMC does not provide enough support for this
theory, but does bring into question solely addressing direct effects o f muscle loading on
bone.
Lean body mass was hypothesized to increase greater in the HRT group compared
to the LRT group (Hypothesis HI). The significant, yet very modest, similar increases in
lean body mass (0.7 ± 0.6kg in the LRT group and 0.9 ± 0.9kg in the HRT group) were
unanticipated. Higher force eccentric contractions are known to generate greater muscle
damage than other contraction types and, therefore should induce greater protein
synthesis, hence greater muscle hypertrophy. Indeed, Higbie et aL (1996) and
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114
Hortobagyi et aL (1996) have demonstrated that eccentric contractions result in
greater muscle hypertrophy than concentric contractions alone. It was hypothesized that
the greater muscle damage in the HRT group would result in significantly greater muscle
hypertrophy than in the LRT group. However, the HRT protocol did not induce greater
muscle damage (measured by CK and IL-6) than the LRT group. Based on the findings
o f this study, it appears that in young women performing either low- or high-intensity
eccentric PRT, the stimulus for muscle hypertrophy under drastically different loads is
similar, suggesting that perhaps a ceding effect with magnitude o f eccentric loading
exists.
The unexpected finding o f similar increases in muscle strength between both
groups supports hypothesis II and rejects hypothesis III. Hypothesis II stated that
eccentric resistance training will significantly increase muscle strength and hypothesis III
stated that these changes would be greater in the HRT group. O f the six exercises
performed, strength increased similarly in both groups except for chest press that was
almost two-fold greater in the HRT group. It is difficult to determine why eccentric
training at extremely high intensities (125% o f a concentric 1-RM) did not result in
greater increases in strength than training at low intensities (75% o f a concentric 1-RM)
when it is known that training concentrically with heavier loads results in greater strength
gains than training with lighter loads (Fleck and Kraemer 1997). One possible
explanation might be that regardless o f training intensity, both eccentric training groups
performed the same amount o f total work; thus, strength gains would be similar.
The greater increase in chest press strength in the HRT group may be due to the
uniqueness o f the exercise. Most females who resistance train primarily exercise
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115
common muscle groups, such as, the triceps, biceps, quadriceps, hamstrings, and back
without exercising the chest muscles. Therefore, in this study, large muscle strength
gains in the chest press and the greater gains demonstrated in the HRT group compared to
the LRT group may suggest a normal load-dependent, unaccustomed response to
eccentric training.
In this study, strength measurements were determined by the subject’s concentric
strength since eccentric strength cannot reliably be determined from eccentric
performance. Higbie et aL (1996) demonstrated that due to training specificity, greater
gains in strength are measured when the movement pattern tested is the same as the
movement pattern trained (Le., eccentric strength testing o f eccentric trained muscles).
Similar to the strength findings by Hawkins et al. (1999), the concentric strength gains in
both eccentric training groups ranged from approximately 20 to 40% with exception o f
the chest press strength gains in the HRT group. A number o f subjects experienced
strength loss upon 1-RM testing at week 2 o f the study, which was non-existent by week
4. The training intensity was not adjusted for the strength loss, but instead, remained
constant until the subject showed improvements in strength by 1-RM testing in
subsequent weeks. Prolonged strength loss is one o f the many factors associated with
eccentric exercise and the high degree o f induced muscle damage (Clarkson, Nosaka, and
Braun 1992).
It was hypothesized (hypothesis VI) that high-intensity eccentric resistance
training would induce a similar magnitude o f muscle damage as low-intensity eccentric
resistance training as measured by CK and IL-6. O f interest, the findings o f this study
show that CK levels in the LRT group increased significantly after four weeks o f
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116
intervention and remained significantly elevated by week 16. Alternatively, CK
levels in the HRT group significantly increased by week 4 and then returned to baseline
levels for the duration o f the study intervention. It appears that Iow-intensity eccentric
progressive resistance training is capable o f inducing and sustaining muscle damage even
though the loads are low in comparison to the load magnitude in the HRT group.
Typically, the higher the tension generated in the muscle with eccentric contraction, the
greater the muscle damage (Armstrong 1984). Although the muscle tension was
extremely high when the she repetitions were performed in the HRT group, the additional
four repetitions (total o f 10) performed in the LRT group might have provided enough
low-tension induced, repetitive muscle damage to produce sustained elevated serum CK
levels. Athematively, more important than the intensity o f training may be the greater
number o f contractions performed in the LRT group. Additionally, alterations in dietary
protein may have contributed to the difference in findings between the two groups.
Hayward et aL (1999) demonstrated significantly different CK levels postexercise
dependent upon dietary protein intake. Higher protein diets resulted in higher serum CK
levels.
The CK levels reported in this study are much lower than CK levels reported by
other investigators. Peak serum CK levels in subjects performing high-force eccentric
muscle action may reach as high as 10,000 IU/1 (Clarkson, Nosaka, Braun 1992)
compared to the 240 IU/1 measured in this study. The enormous difference in CK levels
reported between studies is largely dependent on the type and duration o f the exercise
performed. Investigators reporting elevated CK values as a result o f eccentric exercise
have designed studies that maximally load a single muscle for five to 30 minutes,
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117
creating much more muscle damage than the short duration multiple muscle exercises
performed in this study.
The soreness scale utilized in this study contributed additional information that
supports the CK findings o f sustained muscle damage in the LRT group for the duration
o f the study intervention. Soreness was assessed once per week. Subjects in the LRT
group rated perceived soreness either slightly intense or intense the first two weeks o f the
study, after which their perceived soreness ratings were reduced to moderate, mild, or
very mild. No subjects reported feelings o f no soreness at any time point. The reported
soreness findings support the hypothesis that eccentric exercise-induced muscle damage
was sustained at moderately low levels in the LRT group throughout the 16 weeks o f
study intervention. Perceived soreness ratings in the HRT group were reported to be
more intense, often receiving ratings o f very intense on the soreness scale in the first two
weeks o f the study. However, many subjects in the HRT group reported feeling no
soreness on subsequent assessments, even though some individuals reported mild to
moderate sensations o f soreness following increases in resistance. In feet, Hyatt and
Clarkson (1998) have reported that perceived soreness and CK levels are blunted
following repeated bouts o f eccentric exercise.
The absence o f significant change in serum IL-6 levels does not corroborate the
findings o f elevated CK levels in the LRT group; thus, suggesting that IL-6 may not be a
good marker for eccentric exercise-induced muscle damage. In feet, serum IL-6 levels
did not significantly change in any group measured. These findings are not uncommon
since most investigators have been unable to demonstrate significant relationships
between EL-6 and CK following eccentric exercise. Bruunsgaard et aL (1997) is the only
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118
investigator to determine significant correlations between IL-6 and CK following 30
minutes o f eccentric cycling. Alterations in IL-6 concentrations require the activation o f
the acute phase response associated with inflammation following eccentric exercise. In
this study, the magnitude o f the eccentric-induced muscle damage may not have been
large enough to activate the inflammatory process and hence stimulate measurable
increases in IL-6. Additionally, the extreme variation in IL-6 concentrations between
individuals reduces the chance o f finding significant alterations.
Assessment o f CK and IL-6 were hypothesized to provide information about the
degree o f muscle damage associated with eccentric training. Elevated levels o f these
factors may contribute to the understanding o f how eccentric resistance training increases
bone mass in young women; however, the indirect effects these factors could have on
bone cannot be determined from the findings o f this study. Only if increases in bone
mass at other skeletal sites, in addition to the spine, were demonstrated in the LRT group
would the importance o f these factors be observable. Based on the limited findings o f
increases in bone mass at the spine and elevated CK concentrations in the LRT group
there is very weak evidence suggesting an indirect effect o f eccentric PRT on bone mass.
Biochemical markers ofbone turnover provide an early systemic assessment o f
bone metabolism, specifically, the rate ofbone formation and resorption. One o f the
most compelling findings o f this study was the significant increase in osteocalcin (bone
formation marker) with no change in deoxypyridinoline (bone resorption marker) in the
LRT group, supporting the hypothesis that eccentric PRT increases osteocalcin
concentrations. Increases in osteocalcin suggests increased bone formation and
ultimately enhanced bone mass. While decreased concentrations o f deoxypyridinoline in
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119
conjunction with elevated osteocalcin concentrations would optimize the potential for
increased bone mass by decreasing resorption and increasing formation, the absence o f
change in deoxypyridinoline found in this study combined with increased osteocalcin
levels should result in enhanced bone formation in the LRT group. It is possible that the
eccentric PRT performed in this study needs to be continued for longer than 16 weeks in
order to potentially yield significant increases in bone mass at multiple skeletal sites.
Evidence to support possible increases in bone mass with a longer study
intervention can be observed by viewing the trends o f osteocalcin concentrations in both
the LRT and HRT groups. Following 8 weeks o f eccentric PRT, osteocalcin
concentrations significantly decreased in both the LRT and HRT groups. However, from
week 8 to week 16 large increases in osteocalcin were observed in both groups.
Although the magnitude o f increased osteocalcin concentrations following 16 weeks o f
study intervention was large in the HRT group, the large variance in values at week 16
probably precluded any significant findings. These trends demonstrate that the initial 8
weeks o f eccentric PRT results in suppressed osteocalcin levels, whereas, following 8
weeks o f training, osteocalcin concentrations begin to elevate and appear to continue to
rise, suggesting increased bone formation.
Additional findings in bone biochemical markers to support potential increases in
bone mass with a longer study intervention can be observed in the HRT group. As
described above, osteocalcin concentrations demonstrated a large nonsignificant increase.
Conversely, deoxypyridinoline significantly decreased following 16 weeks o f eccentric
PRT. These findings suggest a trend toward increased bone formation and a decrease in
bone resorption in the HRT group, optimizing bone turnover to augment bone mass.
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120
Indeed, Karlsson, Vergnaud, Delmas, and Obrant (1995) have shown that in actively
performing male weight lifters serum osteocalcin was 35% higher than controls
demonstrating that prolonged weight lifting induces bone formation.
In contrast to the osteocalcin and deoxypyridinoline findings in this study,
Fujimara et al. (1997) conducted a four-month high-intensity resistance training
intervention in men and reported significant increases in osteocalcin concentrations at
week 4 with transient decreases in deoxypyridinoline. However, similar to the findings
in this study, Fujimara et aL reported that osteocalcin was significantly elevated after four
months o f high-intensity resistance training while deoxypyridinoline concentrations
returned and remained at baseline levels for the duration o f the study intervention. O f
interest and similar to the findings o f this study was the absence o f any significant
alterations in total and regional bone mass measurements by Fujimara et aL even though
bone formation and resorption markers changed favorably to promote increases in bone
mass. Training three days per week for four months may require longer duration
resistance training intervention to assess changes in bone mass by densitometry.
The power analysis for deoxypyridinoline performed a priori suggested that
approximately 80 subjects would be necessary to demonstrate a significant change.
While other biochemical markers ofbone resorption show similar variance,
deoxypyridinoline is highly specific to bone and is often used by other investigators as a
good measure ofbone resorption. However, the large variances on measures o f
deoxypyridinoline in this study are most likely responsible for the absence o f significant
findings at many study time points. Deoxypyridino line is measured in the urine;
therefore, kidney filtration rates need to be corrected for and this is accomplished by
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121
dividing the deoxypyridinoline concentrations by urinary creatinine concentrations
also measured in the urine. The correction factor associated with determining
deoxypyridinoline concentrations introduces additional variance.
It was hypothesized that androstenedione concentrations would significantly
increase in the HRT group and not change in the LRT group (Hypothesis IV). Once
again, the most interesting changes occurred in the LRT group and not in the HRT group
that was hypothesized to demonstrate the greatest alterations in androstenedione. In the
LRT group serum androstenedione concentrations increased 22.8 ± 52.3%, approaching
significance (p=0.06), while androstenedione concentrations in the HRT group were
similar at baseline and week 16. Blood was collected during the follicular phase, in the
first 10 days o f the subject’s menstrual cycle, when androgen levels are the most stable.
However, Kraemer et aL (1995) reported that acute androstenedione concentrations were
significantly elevated in the luteal phase o f the menstrual cycle in response to low-
volume resistive exercise and not in the follicular phase. Therefore, it is possible that
andro stenedione concentrations may have been significantly elevated in the LRT group
during the luteal phase o f the menstrual cycle but were not measured in this study.
In contrast to the findings o f the current study, Weiss, Cureton, and Thompson
(1983) reported significantly decreased serum androstenedione concentrations below pre
exercise levels at two hours post-exercise in weight-lifting women. Whether this
alteration is a transient decrease in androstenedione and the serum concentrations return
to baseline or greater after two hours post-exercise is unknown. The finding differs from
that o f Kuoppasahni et aL (1976) who reported significantly higher androstenedione
levels following interval sprint running for six hours post-exercise. Although the studies
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122
are limited, it appears that the time point o f the blood draw (acute vs. chronic)
following the exercise bout may significantly alter the findings.
Androstenedione concentrations have most often been reported in the first couple
o f hours following a resistance training bout. The significant increases reported by
Kuoppasalmi et al. (1976) in androstenedione concentrations at six hours post-exercise
following interval sprint running suggest that blood samples taken at time points longer
than a few hours post-exercise may be important. However, these findings should be
compared with caution to other findings since the type o f exercise utilized in
Kuoppasalmi et aL's study was not resistance exercise. In the current study, blood
samples were obtained prior to an exercise training session; therefore, subjects had rested
approximately two days since the previous training. It has been suggested that
hemoconcentration following an exercise bout results in the measurable increase in
hormone concentrations post-exercise; however, the eccentric resistance training
performed in this study most likely was not substantial enough to alter fluid volumes and
hemodynamics two days following the exercise bout.
Furthermore, it may be that instead o f chronically altering sex hormone levels in
young women with resistance training, acute resistance training-induced elevations in
androstenedione are more effective at influencing bone mass. The findings o f this study
do not conclusively demonstrate that androstenedione concentrations may be altered by
eccentric PRT; although, nearly significant findings in the LRT group suggest that lower
intensity eccentric PRT is more influential on androstenedione levels than high-intensity
eccentric PRT.
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123
The type o f resistive exercise protocol performed may have an impact on
hormonal adaptations. The total work or volume (sets x reps x intensity) o f resistance
exercise performed and the rest periods between sets may influence the hormonal milieu.
In feet, several investigations utilizing training protocols with a larger volume o f work
performed that employ moderate to heavy resistance (e.g., ten repetition maximum sets)
and 1-2 minute rest periods have reported greater magnitude increases in hormone
concentrations compared to heavier resistances (e.g., five repetition maximum sets),
longer rest periods (three minutes), and smaller volumes o f work (Kraemer et aL 1990,
Kraemer et al. 1991, Kraemer et al. 1995, Kraemer et al. 1997, Hakkinen and Pakarinen
1993). The findings by these investigators support the findings in this study that lower
intensity resistance training appears to have a larger influence on hormonal
concentrations.
Additionally, it was hypothesized that changes in androstenedione would correlate
with increased levels o f osteocalcin and decreased levels o f deoxypyridino line
(Hypothesis V). No relationships were demonstrated between these variables in this
study. The findings o f no significant relationships o f androstenedione with osteocalcin
and deoxypyridino line suggest that the nonsignificant increases in androstenedione in the
LRT group do not predict significant increases in osteocalcin or are not related to
deoxypyridino line. Therefore, the indirect effect o f alterations in androstenedione
concentrations on bone mass are not supported by these findings. Furthermore, whether
eccentric PRT-induced alterations in androstenedione act directly on bone or indirectly
by influencing cytokine and growth factor actions cannot be determined from the findings
o f this study.
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124
It was the purpose o f this investigation to examine the factors associated with
eccentric resistance training that may influence bone mass. Unlike the findings by
Hawkins et al. (1999), this study was unable to corroborate that load magnitude with
maximal eccentric resistance training stimulates bone adaptation. To the contrary, the
findings o f this study support low magnitude eccentric PRT as influencing bone
metabolism; however, the factors associated with low-intensity PRT that may be partially
responsible for this adaptation are not clear. Therefore, whether eccentric PRT results in
a systemic influence on bone metabolism and bone mass requires further investigation.
In summary, the most unique finding o f this study was that Iow-intensity eccentric
PRT was more influential on bone mass, bone biochemical markers, serum CK, and
androstenedione concentrations than was high-intensity eccentric PRT. Specifically,
low-mtensity eccentric PRT significantly increased spine BMC. osteocalcin
concentrations, serum CK levels, and nonsignificantly (p=0.06) increased
androstenedione concentrations following 16 weeks o f study intervention. Conversely,
high-intensity eccentric PRT did not significantly increase BMD or BMC, osteocalcin
concentrations, serum CK levels, or androstenedione concentrations. However, high-
intensity eccentric PRT did significantly reduce deoxypyridinoline levels, but did
influence a trend in increasing osteocalcin concentrations following 16 weeks o f study
intervention. Both eccentric PRT groups were successful in enhancing muscle strength
similarly for all exercises except for the chest press, which was almost two-fold greater in
the HRT group. Furthermore, lean body mass was augmented significantly and to a
similar degree in both groups.
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125
In conclusion, Iow-inlensity eccentric PRT appears to stimulate bone
formation by increasing osteocalcin; however, these increases were not well represented
by DXA m easurem ents following 16 weeks o f eccentric training. High-intensity
eccentric PRT appears to decrease deoxypyridinoline concentrations, slowing bone
resorption and this alteration in bone metabolism was not demonstrable by DXA
following 16 weeks o f eccentric training. Eccentric resistance training-induced muscle
damage as measured by senm CK and perceived soreness remained elevated with Iow-
intensity eccentric PRT, providing meager support for possible indirect effects on bone
mass. Furthermore, strength gains were similar in both training groups suggesting that
when work is equal between the two groups, low-intensity eccentric PRT is as effective
as high-intensity PRT for enhancing muscular strength. The overall findings o f this study
do not support the importance o f load magnitude on bone adaptation (direct effect) and
are insufficient to conclusively demonstrate that eccentric resistance training-induced
muscle damage factors and androstenedione alterations indirectly influence bone mass.
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126
STUDY LIMITATIONS
1) The sample population was comprised o f University o f Southern California
graduate students in health related fields.
2) Diet was not controlled during the duration o f the study.
3) Physical activity was not assessed or recorded throughout the study.
4) Oral contraceptive use was not accounted for in the study design.
5) The study intervention was only 16 weeks.
6) Eccentric strength gains were determined by increases in concentric 1-RM’s.
7) Additional hormones, cytokines, and bone markers were not analyzed.
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127
RECOMMENDATIONS FOR FUTURE STUDY
Further investigations are necessary to determine the importance o f load magnitude and
factors associated with eccentric resistance training that may influence bone mass.
Conducting a longitudinal study o f 6 months or longer may help elucidate the
contradictory findings o f this study. Furthermore, measuring additional hormones,
cytokines, and bone markers that may be affected by eccentric resistance training might
provide enough information to draw more conclusive findings. The high usage o f low
dosage oral contraceptives by young women may influence the bone response to
resistance training; therefore, a study designed to determine the interaction o f oral
contraceptives and resistance training on bone mass would be informative. Lastly, a
study that investigates the type o f eccentric exercise (isokinetic vs. free weights) for a
given muscle group may help determine the specific loading conditions associated with
the various eccentric training programs that might influence bone adaptation.
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128
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178. Scfaroeder, E.T., Jaque, S.V., Hawkins, S.A., WisweD, R.A., Olson, C., and
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189. Spadaro, J.A. Mechanical and electrical interactions in bone remodeling.
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200. Unemura, Y., Ishiko, T., Yamauchi, T., Kurono, M., and Mashiko, S. Five
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204. Vuori, I., Heinonen, A., Sievanen, H., Kannus, P., Pasanen, M., and Oja, P.
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212. Young, D. Hopper, JX ., Nowson, C.A., Green, R_M., Sherwin, A J.,
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147
APPENDIX A
Sensation of Soreness Scale
Entry Questionnaire
Menstrual, Physical Activity, and Health History Questionnaire
Informed Consent
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148
Name _____________ Study # _____ Time Point
Rate Your Sensation of Intensity of Soreness
_____________________ (Please Circle One)
Extreme
Very Intense
Intense
Slightly Intense
Moderate
Mild
Very Mild
Faint
No Soreness
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Entry Questionnaire
Strength Training and Bone Mineral Density Study
149
All information in this survey win remain strictly confidential. I agree to complete the following questionnaire with the
understanding that all information is voluntary and completely confidential. I understand that my signature here does not
mean that I have agreed to participate in the actual study.
SIGNATURE___________________________
Name
Age_____________ Height________________ Weight________________
Ethnicity___________________________
Telephone Number (daytime)___________________ (evening)______________
Do you have any children? Yes No
Have you ever been pregnant? Yes No
If ves. how long was your pregnancy? months
If yes. how old were you when you became pregnant? _____ years old
Has your doctor ever told you that you had any of the following conditions?
Diabetes, high blood sugar Yes No
Thyroid diseases
Graves disease Yes No
Hashimoto's disease Yes No
Overactive thyroid Yes No
Underactive thyroid Yes No
Hyperparathyroidism Yes No
Hypogonadism Yes No
Hypercortisolism Yes No
Hypothalamic pituitary dysfunction Yes No
Hypothalamic pituitary failure Yes No
Ovarian failure Yes No
Ovarian cysts Yes No
Polycystic ovaries or Stein Levanthal syndrome Yes No
Rickets Yes No
Bone Marrow Disorders Yes No
Gastrointestinal disorders
Gastrectomy Yes No
Malabsorption Yes No
Primary billiary cirrhosis Yes No
Anorexia nervosa Yes No
Severe Malnutrition Yes No
Marian’s syndrome Yes No
Ehlcrs-Danlos syndrome Yes No
Rheumatoid arthritis Yes No
Osteogenesis imperfecta Yes No
Patellar tendon tracking problems Yes No
Are you aware of any conditions that may limit your participation in physical activity?
Yes * No
If yes. what are the conditions?____________________________________________
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150
Have you ever undergone
Long term immobilization Yes No
Ifyes, at what age? ______
Radiation therapy Yes No
Ifyes. at whatage? ______
Have you ever taken the following medications?
Glucocorticoids Yes No
Anticonvulsants Yes No
Gonadotropin-releasing hormone agents Yes No
Thyroid hormone Yes No
Dosage___________________
For how long?______________
Methotrexate Yes No
Cyclosporine Yes No
Heparin Yes No
Aluminum antacids Yes No
Isoniazid Yes No
Lithium Yes No
Have you ever taken oral contraceptives, or hormonal contraceptives in the form of pills, shots or implants?
Yes No
If ves. have you taken them in any form in the last vear?
Yes No
If yes, are you currently taking them?
Yes No
Have you had fairly regular menstrual cycles over the last 12 months, ranging from approximately 12-14 periods
calendar year (time from first day of bleeding o f one cycle to first day of bleeding of the next cycle. 25 to 31 days
length)? Yes No Don’t Know
On average, how many days pass from the first day of bleeding o f one menstrual period to the first day of
bleeding of your next menstrual period? ________
Can you usually predict your period within a day or two? Yes No Don’t Know
How many menstrual periods have you had in last 12 months? ________
Have you ever smoked a total o f 100 cigarettes m your fifetune? Yes No
Ifyes. are you currently smokmg? Yes No
If not currently smoking, how long ago did you q uit?____________
Are you currently participating in regular aerobic activity? Yes No
Ifyes. what type(s) of aerobic activity? ________________________
For each type of activity, please indicate your participation in hours/week:___________
Are you currently participating in resistance exercise (weight lifting)? Yes No
Ifyes. are you using free weights or machines?______________________
At what intensity (sets and repetitions)?____________________
Please indicate your participation in hours/week: ___________
Are you currently participating in competitive team sports? Yes No
Have you gained or lost more than 10 lbs, in the past year? Yes No______________________________
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. a .a
Strength Training and Bone Mineral Density Stndy
Subject Name____________________
Subject Number_________
151
l. Name_____________________________ Sex_______ SS#_ _
Address_______________________________________ Telephone_(_____ ).
Permanent Address Permanent Telephone (______ ).
Contact person in case you move:_________________
Contact person’s phone number (______ )__________
2. What is your date of birth?_____ -_______ -_ _ __
Month Day Year
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152
A. Demographies
A t this tim e the following measurements wiH be made:
3. Height without shoes:_________ inches
4. Waist girth:_________ inches
5. Hip girth:_________ inches
6. Weight:_________pounds
6.1 What would be a perfect body weight for you?________ pounds
6.2 What was your weight at age 18?________ pounds
63 What was your weight one year ago?_________ pounds
7. How many tones in your life have you lost the number of pounds shown below?
Number o f pounds
Number 5 10 20 30 40+
o f times_______ ____ ____ ____ ____ ____
8. How many times in your life have you gained the number of pounds shown below?
Number o f pounds
Number 5 10 20 30 40+
of times_______ ____ ____ ____ ____ ____
9. To which ethnic group do you belong? (circle)
Black/African American
White
Mexican/Mexican American
Other Hispanic
Native American
Hawaiian
Filipino
Japanese
Korean
Chinese
Pacific Islander
Other (specify)____________________
10. Where were you bom?______________________________ (stale or country)
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153
I t. What number of school years have you completed?________
12. List all occupations you have had. starting with current and working back over time. Indicate full or part time,
years, and give an estimate o f amount of physical activity involved using a scale of 1-5 with I meaning "very little” and 5
meaning “very much”. Did any o f the occupations listed above require you to consistently lift and/or carry moderate to
heavy loads?
Type of Occupation Full/Part Time Years Scale (1-5) Heavy Loads (Yes or No)
a._____________________________ ___________ ____ ________ _______________
b.
c.
d.
e.
B. Past and Present Health Status
13. Has a physician ever told you that you had any of the following? (Please check and give year of onset, if applicable.)
No Yes Yearofonset
a. Coronary heart disease:
1. Angina pcctoralis_____________ ___ ___ _____
2. Myocardial infarction ___ ___ _____
b. Heart arrhythmia ___ ___ _____
c. Stroke ___ ___ _____
d. High blood pressure ___ ___ _____
e. Diabetes mellitus ___ ___ _____
f. Chronic bronchitis_______________________ ___ _____
g. Chronic backpain ___ ___ _____
(diagnosis:________________ )
h. Arthritis___________________________ ___ ___ _____
(type:_____________________)
i. Osteoporosis________________________ ___ ___ _____
1. related fractures______________ ___ ___ _____
j. Anxiety disorder ___ ___ _____
k. Depression ___ ___ _____
L Anorexia Nervosa/Bulemia________________ ___ _____
m. Other Eating Disorders ___ ___ _____
n. Cancer ___ ___ _____
(site:__________________ )
o. Other major disease ___ ___ _____
(specify:__________________ )
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154
14. Father's Health History
14.1 Age if alive_ or
14.2
Coronary heart disease
Stroke
Cancer (site:________
Age at death______
Cause of death____________
No Yes Age at onset
Osteoporosis
IS. Mother's Health History
15.1 A geifalive_ or
15.2
Coronary heart disease
Stroke
Cancer (site:________
Osteoporosis
Ovarian Disease
Menopause
C. Lifestyle factors
16. Have you ever smoked cigarettes?
t6.i How many years did you smoke?_
16.2 Age started?________________
163 Age stopped?_______________
Age at death______
Cause o f death_____________
No Yes Age at onset
17. Have you ever smoked a total of 100 cigarettes or more in your lifetime?
18. Do you smoke cigarettes now?
I8.I How many on an average day?_______________
Yes
Yes
Yes
No
No
No
19. How many cigarettes do you or did you smoke:
19. 1__________per day
19. 2__________ per week
193
19.4
_per month
_peryear
20. Did you ever drink alcoholic beverages (beer, wine or spirits) on a regular basis (at least once per week for 6 months
or more)? Yes No
20.1 Ifves. how old were you when you started drmkmg at least once a week?___ years old
203 How many alcoholic beverages did you drink per week?
Beer_____________(cans/bottles)
Wine____________ (glasses)
Liquor___________ (I oz cups/shots)
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155
203 For how many years did this drinking continue? years
20.4 Do you drink alcohol now? Yes No
20.5 How many alcoholic beverages do you currently drink per week?
Beer_____________(cans/bottles)
Wine_____________(glasses)
Liquor___________ (I ozcups/shocs)
D. Exercise
21. Do you have any physical conditions which would limit your ability to perform exercise?
22. How many citv blocks nr their equivalent tin you regularly walk each day? blocfcs/dav
(Let 12 blocks = 1 mile)
23. What is your usual pace o f walking? (Please check one.)
a. Casual or strolling (less than 2 mph) b. Average or normal (2-3 mph)
c ._ _ Fairly brisk (3-4 mph) «L_ _ Brisk or striding (4 mph or faster)
24. How many flights o f stairs do you climb up each day?_____ flights/day
(Let I flight = 10 steps)
25. During the years before your first menstrual period, did you participate in regular physical activity for recreation or
(Itaess purposes? If so. please complete the section below. If not. skip this question.
Please note that recreation purposes do not include competitive/team sports. There is a separate question pertaining to
competitive/team sports.
Type o f Sport. Recreation Years Age Age
or Physical Activity of Began End
participation
Intensity ft weeks/year #session/weeks #m in/session
(vigorous,
moderate
or slow)
b._
c._
< L _
e ._
£
g-_
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156
26. During the years before your first menstrual period, were you ever a member o f a competitive team where you
attended practice sessions, workouts, training sessions or games?
This would include intramural, varsity, or amateur athletic union sports, serious participation in ballet or dance, and
regular jogging/running of at least one mile at each workout.
If so, please complete the section below. If not, skip this question.
Please note that these sports should not include those activities participated in for recreational purposes.
Type of Sport # Years of Age began Age ended # weeks/year #session/week ffmin/scssion
competing
d.
t
27. During the years alter your first menstrual period up to the present tune, did you participate in regular physical
activity for recreation or fitness purposes? If so. please complete the section below. If not. skip this question.
Please note that recreation purposes do not include competitive/team sports. There is a separate question pertaining to
competitive/team sports.
Type of Sport. Recreation Years Age Age Intensity # weeks/year tfsession/wecks #min/session
or Physical Activity of Began End (vigorous.
participation moderate
or slow)
a.__________________ _____ ______ ______ _______ _______ _______ ____
b.
c.
d.
e.
L
g-.
h.
L
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157
j-_________________ ____ _____ _____ ______ ______ ______ _______
28. During the years after your first menstrual period up to the present time, were you ever a member of a
competitive team where you attended practice sessions, workouts, training sessions or games?
This would include intramural, varsity, or amateur athletic union sports, serious participation in ballet or dance, and
regular jogging/running of at least one mile at each workout.
If so, please complete the section below. If not. skip this question.
Please note that these sports should not include those activities participated m for recreational purposes.
Type of Sport # Years of Age began Age ended # weeks/year #sessionAveek #min/session
competing
a. _____ _____ ______ _______ _______
b.
< L _
e._
L
g-_
29. At least once a week, do you engage in regular activity akin to brisk walking, jogging, bicycling, swimming, etc. long
enough to work up a sweat, get your heart thumping or get out of breath?
Yes How many times per week? Activity:______________________
No Why not?_____________________________________________________
30. When you are exercising in your usual fashion, how would you rate your level of exertion (degree of effort)? (Please
circle one number.)
0 0.5 1 2 3 4 5 6 7 8 9 10
Nothing very very weak mod* some* strong very very
at all very weak crate what (heavy) strong very
weak strong strong
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158
31. Currently, on a usual weekday and a weekend, hcrw much time do you spend on the following activities? Total for
each day should add to 24 hours.
Usual Usual
Weekday Weekend
Hours/ Hours/
Dav Dav
a. Vigorous activity
(digging in the garden, strenuous sports,
jogging, aerobic dancing, sustained
swimming, brisk walking, heavy carpentry.
bicycling on hills, etc.)______________________________ _____ _____
b. Moderate activity
(housework, light sports, regular walking,
golt yard work, lawn mowing, painting,
repairing, light carpentry, ballroom
dancing, bicycling on level ground, etc.) _____ _____
c. Light activity
(office work, driving a car. strolling,
personal care, standing with little motion, etc.)
< L Sitting activity
(eating, reading, desk work, watching TV.
listening to radio, etc.) _
e. Sleeping or reclining _
E. M enstrual History
32. Age when you began to menstruate_____________
33. Do you have fairly regular menstrual cycles? ( yes / no )
R egul ari t y o f m ens t rual cycl es, w i t hi n Ike h a t 3 yea n :
a. How often are your menstrual periods?____
b. How many days do they last?___________
c. Are you or have you been amcnorrfacic in the past 3 years?
If yes. how many times?___________ for how long?
and at what age(s)?__________
d. Any other menstrual problems?____________________
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c. Any hormonal problems that influence menstruation?
159
Pr i o r t o t he l ast 3 yean:
a. How often were your menstrual periods?.
b. How many days did they last?
c. Were you amcnonhcic?
If yes. how many times?. for how long?
and at what age(s)?
d. Any other menstrual problems?.
e. Any hormonal problems that influence menstruation?
34. From the time you started to menstruate, were your periods regular, frequent, infrequent, or did you skip any.
based on the definitions below?
(1) R egular: your menstrual periods come every 28-35 days.
(2) Frequent: your menstrual periods often start less than 28 days after your last period.
(3) Infrequent: your menstrual periods often start more than 35 days alter your last period.
(4) Skipped: you have gone more than 6 months without having your period.
If you did not have regular periods, at what ages and for how long were your periods either frequent, infrequent, or
skipped?
(F. I. S) age________ for_____________________ months
(F. I. S) age________ for_____________________ months
(F. I. S) age________ for_____________________ months
(F. I. S) age________ for_____________________ months
F. Oral Contraceptive Use
35. Have you ever taken oral contraceptives or hormonal contraceptives? Yes No
35.1 Have you taken them in the past year?________________________
35.2 Years of hormonal/oral contaceptive use?___________________________
35 J Age(s) started?______________ How long at each age?______________________
35.4 Reason for taking them?__________________________
35-5 Type of oral contraceptive(s) and dosagefs)?___________________________________
36. Have you ever been pregnant? Yes No
If yes. please complete the following:
Pregnancy
Duration
# Age (weeks)
I _____
Spontaneous
Miscarriage?
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2
3
160
G. Bone History
37. Have any members of your family had osteoporosis or crush fractures (Le. unexplained fractures, "humped back”,
wrist fractures, hip fractures, etc.)? Please explain.
37.1. No record or indication.__________
372. Possible_______________
373. One close relative_____________________
37.4. More than one close relative________________________
373. Other______________________________________________________________
38. Have you ever been diagnosed as having osteoporosis? Please explain.
39. Have you ever had unexplained or stress fractures? Please explain.
40. Have you ever bad any type o f bone fracture? Ptease explain.
4 1. Have you ever had any bone diseases, such as rickets, osteomalacia or osteoarthritis? Please explain.
If you have answered yes to 37-41 please answer questions 42-44:
42. Have you ever taken medications for bone disease? Please explain.
43. Have you ever taken any of the following medications? Please explain.
Calcitonin__________________ Bisphosphonates_________________ Fluoride______________
Hormones (Estrogens or Progestogens or Steroids)______________________________________
44. Have you ever modified your diet for bone disease? Please explain.
45. Have you ever had your bone mineral tested?_______________________________________
45.1. IF yes. do you know what type o f analyzer was used?_______________________
453. Do you know if your bone mineral was: above____ below or average for your age?
453. Within the fracture region?________________________________________
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161
TITLE OF PROJECT: The influence of eccentric exercise on bone m ass in young women.
PRINCIPAL INVESTIGATORS: E. Todd Schroeder. M A and S. Victoria Jaoue. Ph.D.
DEPARTMENTS: Biokinesjotoov and Physical Therapy
24-HOUR TELEPHONE: (3231442-2905
Participant Informed Consent
PURPOSE OF THE STUDY: You are invited to participate in a research study looking at how
weight lifting influences bone changes. You were invited to participate in this study because you
are a young women between the ages of 18 and 28.
PROCEDURE: If you decide to participate in this study, you will visit the laboratory once for pre
testing; then either once monthly or two times per week for 4 months, depending upon the group
you are assigned to; and lastly, once for post-testing. On your first visit, you will complete six
parts of the study. First, you will provide a urine sample. Second, you will complete
questionnaires regarding information on your age, physical activity level, diet, menstrual history,
and medical history. Third, your bone mineral density will be measured by X-ray. This is a non-
irtvasive (painless) procedure, and will involve you lying still on a table for approximately 45
minutes while the density of the bones in your whole body, back, and hip are scanned. Fourth,
your height, weight, and the size of your arms and legs will be measured. Fifth, you will
participate in an orientation to the strength exercises, followed by strength testing by the one
repetition maximum (1 RM) method. This will involve performing an exercise until we find the
weight that you can lift one time only. You will be given adequate warm-up and familiarization
time for each exercise. This procedure generally requires 3-5 efforts for each exercise. Sixth, a
doctor, nurse or phlebotomist will take blood from a van in your forearm or hand. Completion of
these six parts of the study will take approximately 2 1 /2 hours.
Following pre-testing, you will be randomly assigned (like flipping a coin) to either a low-intensity
weight lifting group, high-intensity weight lifting group, or a control group. The high-intensity
weight lifting group will visit the laboratory twice a week to train with weights at maximum
intensity. The low-intensity weight lifting group will also visit the laboratory twice a week to train
with weights at 75% of their maximum intensity. Both groups will attend the weight lifting
sessions for four months. Each training session will take approximately 45 minutes. The control
group will visit the laboratory for pre-testing and then once a month for four months for blood
draws and urine samples. You are asked not to participate in weight lifting outside of this study
and to maintain your sam e level of physical activity. The control group will not lift any weights in
this study.
Your final visit will take place following completion of the 4-month intervention program. On the
last visft, you will complete the same parts of the study a s on your first visit First, you will
provide a fasting (without food for 12 hours), second morning urine sample. Second, you will
complete a questionnaire regarding information on your age, physical activity level, diet
menstrual history, and medical history. Third, your bone mineral density will be measured by X-
ray. Fourth, height weight and the size of your legs and arms will be measured. Fifth, you will
participate in strength testing by the 1 R M method. Sixth, a doctor, nurse or phlebotomist will
take blood from a van in your forearm or hand. These six tests will take approximately 2 1 /2
hours.
RISK: Risks of having your blood drawn are like any blood specim ens taken for dinical
purposes. There is minimal risk of infection, bleeding, and bruising after the blood is taken. The
risk to you from a bone scan is minimal. The technique gives an accurate measure of bone
density with a very low exposure to radiation. The calculated radiation is approximately 1.0 —1.5
millirads to the skin or back side of the body, and less than 1.25 millirad to bone marrow, 0.8
millirad to the ovaries, and 0.1 millirad to the testes. This radiation dose is considered safe to
administer on several occasions to young women/men, providing the women are not pregnant
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Ail scans on young women of childbearing age will be done during the first 10 days following
onset of menstruation, as per state guidelines. For comparison, a person can be expected to
receive about 160 millirad per year from the environment There is risk of muscle injury as a
result of the strength testing and weight lifting training. Teaching of proper technique, proper
warm-up, and progressive increase in the workload will minimize this risk. This study will require
a large time commitment if you are assigned to an exercise group. This could also pose an
inconvenience.
BENEFITS: Your participation in this study will provide information of general interest to medical
science. The investigators cannot and do not guarantee any specific benefit to you from your
participation in this study. There is, however, the indirect benefit of knowing that you are
contributing to a study that may help us better understand how weight lifting influences bone.
ALTERNATIVES: An alternative would be not to participate in this study. Your decision will not
in any manner affect your routine medical care.
CONFIDENTIALITY: The investigators will maintain the confidentiality of your medical records
for this study. Any information that is obtained in connection with this study and that can be
identified with you will not be released or disclosed without your written consent accept as
specifically required by law.
OFFER TO ANSWER QUESTIONS: Your participation will be under the care of Todd
Schroeder at (323) 442-2905 who you may contact with any questions or concerns regarding
your participation. Any questions or concerns that you may have about study related injuries
should be discussed with the Principal Investigator, Todd Schroeder at (323) 442-2905. If you
have any
questions regarding your rights a s a study subject, you may contact the Institutional Review
Board Office at (323) 223-2340. You will be given a copy of this form to keep.
COERCION AND WITHDRAWAL STATEMENT: If you decide to participate in this study, you
are free to withdraw your consent and to discontinue participation at any time.
INJURY STATEMENT: If you require medical treatment as a result of injury arising from your
participation in this study, the financial responsibility for such care will be yours.
NEW INFORMATION: Any new information that is developed during the course of this research
which may be related to your willingness to continue or discontinue participation in this study will
be provided to you.
CALIFORNIA LAW REQUIRES THAT YOU MUST BE INFORMED ABOUT:
1. The nature and purpose of the study.
2. The procedures in the study and any drug or device to be used.
3. Discomforts and risks to be expected from the study.
4. Benefits to be expected from the study.
5. Alternative procedures, drugs, or devices that might be helpful and their risks and benefits.
6. Availability of medical treatment should complications occur.
7. The opportunity to ask questions about the study or procedure.
8. The opportunity to withdraw at any time without affecting your future care at this institution.
9. A copy of the written consent form for the study.
10. The opportunity to consent freely to the study without use of coercion.
11. Statement regarding liability for research-related injury, if applicable.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
163
AGREEMENT:
YOUR SIGNATURE INDICATES THAT YOU HAVE DECIDED TO PARTICIPATE HAVING
READ THE INFORMATION PROVIDED ABOVE.
Signature of Subject (or Responsible Relative) Date
Signature of Witness Date
Signature of Principal Investigator Date
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
164
APPENDIX B
Biosynthetic Pathw ays for Steroid Horm ones
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
165
Biosynthetic pathways for steroid hormones
Cholesterol
HO
CYP11A1
Pregnenolone
Mltoetisnaria
Encopiasmrc reticulum
H O
CYP17A1
HO
l7a-Hydroxypregnenoione
CYP1
Progesterone
CYP17AI
CYPttBl
C Y P 2 T A 1
OH
H C '
l7a-Hydroxyprogesterone Oehydroepianerosterene
CYPt7A l
Corticosterone G H
T astc-^rc~ .e Andrestencciene
CH
CYP19A1
Aldosterone
HO‘ HO‘
Oestradiol Oestrone
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
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Asset Metadata

Creator Schroeder, Edward Todd (author)

Core Title The influence of eccentric resistance training on bone mass and biochemical markers in young women

Degree Doctor of Philosophy

Degree Program Biokinesiology

Degree Conferral Date 2000-08

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag biology, animal physiology,health sciences, recreation,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-185464

Unique identifier UC11334475

Identifier 3065749.pdf (filename),usctheses-c16-185464 (legacy record id)

Legacy Identifier 3065749.pdf

Dmrecord 185464

Document Type Dissertation

Rights Schroeder, Edward Todd

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA