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The physiological effects of a single bout of eccentric versus concentric resistance exercise

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The physiological effects of a single bout of eccentric versus concentric resistance exercise

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Content THE PHYSIOLOGICAL EFFECTS OF A SINGLE BOUT OF ECCENTRIC
VERSUS CONCENTRIC RESISTANCE EXERCISE
by
Alberto Francisco Vallejo
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(BIOKINESIOLOGY)
August 2005
Copyright 2005 Alberto Francisco Vallejo
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UMI Number: 3196911
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DEDICATION
The completion of my Ph.D. degree represented by this dissertation would
not have been possible without the support and love of my family and friends. My
family has given me a life outside of academics, with which I share everything and
my friends have given a support of which only friends could give. It has been a long
road that has not come to an end but instead to a new beginning.
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ACKNOWLEDGEMENTS
iii
I would like to acknowledge the unparalleled guidance, support, and
friendship of my dissertation advisors, Dr. Fred R. Sattler, and Dr. E. Todd
Schroeder. Dr. Sattler has provided me with the guidance of an experienced
investigator and has helped me in understanding the importance of the scientific
method. Dr. Schroeder’s youthful and spirited personality made my four years at
USC full of positive experiences. Without his guidance I would have not made it
through my “rough” first year as a Ph.D. student. In addition, on this journey I was
given advice and knowledge from faculty and peers that developed and strengthen
my ability to teach and conduct research. In particular, Dr. Steve Hawkins who has
helped kept my research on track by providing insightful questions of what I was
doing and why. I would like to take this opportunity to point out how important
these people have been throughout my career, without the encouragement that they
have created within me I perhaps would not have had as a successful doctoral student
career as I did.
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TABLE OF CONTENTS
DEDICATION.....................................................................................................................ii
ACKNOWLEDGEMENTS..............................................................................................iii
LIST OF TABLES............................................................................................................. vii
LIST OF FIGURES...........................................................................................................viii
ABBREVIATIONS......................................................................... ix
ABSTRACT......................................................................................................................... x
CHAPTER I
OVERVIEW OF PROPOSAL............................................................................... 1
Statement of the Problem...........................................................................1
Hypotheses.................................................................................................. 3
Specific Aims..............................................................................................4
CHAPTER II
Background and Significance.................................................................................5
Impaired Physical Function During the Aging Process......................... 5
Sarcopenia....................................................................................... 5
Cardiopulmonary Considerations................................................ 7
Pulmonary Function...;.................................................... 7
Cardiac Function................................................................8
Resistance Training Augments Skeletal Muscle Strength...................12
Effects of Traditional Progressive Resistance
Training..................... 12
Effects of Eccentric Progressive Resistance
Training.........................................................................13
Potential Benefits of Eccentric Progressive Resistance
Training in a Frail Population.................................................15
Rationale for Study Design................................................................................... 18
Metabolic Efficiency and Cardiopulmonary Demands........................18
CHAPTER III
METHODOLOGY................................................................................................20
Study Overview........................................................................................ 20
Study Design..............................................................................................20
Specific Aim 1..............................................................................20
Specific Aim 2..............................................................................22
Specific Aim 3..............................................................................23
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Specific Aim 4..............................................................................23
Eligibility Criteria.....................................................................................25
Inclusion Criteria......................................................................... 25
Exclusion Criteria........................................................................25
Methods..................................................................................................... 26
Eccentric and Concentric Resistance Exercise Bouts............ 26
EKG Exercise Stress T e st......................................................... 27
Body Composition Analysis...................................................... 27
Laboratory Testing...................................................................... 28
Schedule of Events...................................................................................28
Group I: Young Men and Women.............................................28
Group II: Older Men and Women............................................. 28
Statistical Consideration and Data Management................................. 29
Statistical Considerations........................................................... 29
Study Design...................................................................29
Primary Outcome Measures..........................................29
Statistical Analyses........................................................ 30
Statistical Power Calculations................................................... 31
Young Men and Women............................................... 31
Older Men and Women................................................. 32
Data Management........................................................................32
Quality Control in Measurement and Standardization Procedures
and Equipment.................................................................................... 33
Potential Limitations................................................................................33
Study Time Line....................................................................................... 35
Gender and Minority Considerations.....................................................35
CHAPTER IV
RESULTS...............................................................................................................37
Study Subjects......................................................................................... 37
Maximal Force Measurements............................................................... 39
Metabolic Outcomes................................................................................ 41
Knee Extension/Flexion Exercise Bouts..................................41
Knee Extension/Flexion Bouts Corrected for Age Related
Appendicular LBM..................................................................45
Knee Extension/Flexion Bouts Corrected for Age Related
W ork ........................................................................................47
Parallel Knee Squat Bouts..........................................................49
Cardiovascular Outcomes....................................................................... 53
Knee Extension Bouts.................................................................53
Knee Flexion Bouts.....................................................................56
Parallel Knee Squat Bouts..........................................................59
Overview of Cardiovascular Changes for the
Three Exercises....................................................................... 59
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vi
Electromyography during Parallel Knee Squats.................................. 67
CHAPTERV
DISCUSSION.........................................................................................................69
Significance of Outcomes........................................................................ 69
Specific Aim 1...........................................................................................70
Specific Aim 2...........................................................................................76
Specific Aim 3...........................................................................................80
Specific Aim 4...........................................................................................84
Clinical Implications.................................................................................87
Potential Future Studies............................................................................89
Limitations................................................................................................. 92
CHAPTER VI
GLOSSARY OF TERMS..................................................................................... 94
CHAPTER VII
BIBLIOGRAPHY.................................................................................................. 95
CHAPTER VIII
APPENDICES......................................................................................................101
APPENDIX A .................... 101
HUMAN SUBJECTS............................................................................102
Description of the Involvement of Human subjects............ 102
Source of Research Materials..................................................103
Recruitment........................................... ....................................103
Potential Risks............................................................................104
Procedures for Minimizing Potential Risks............................105
Relation of Risks and Benefits to Participating Subjects.... 106
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vii
LIST OF TABLES
TABLE 1 Mean Values Pre & Post Training.............................................. 16
TABLE 2 Study Population Characteristics................................................ 38
TABLE 3 Maximal Force Measurements................................................... 40
TABLE 4 Metabolic Outcomes for Knee Extension.................................42
TABLE 5 Metabolic Outcomes for Knee Flexion...................................... 43
TABLE 6 Metabolic Outcomes for Parallel Knee Squat
(ECC vs CON)..............................................................................50
TABLE 7 Metabolic Outcomes for Parallel Knee Squat
(Bodyweight vs Load).................................................................51
TABLE 8 Cardiovascular Outcomes for Knee Extension......................... 54
TABLE 9 Cardiovascular Outcomes for Knee Flexion..............................57
TABLE 10 Cardiovascular Outcomes for Parallel Knee Squats.................. 60
TABLE 11 Summary of Resistance Training Recommendations by
ACSM........................................................................................... 74
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viii
LIST OF FIGURES
FIGURE 1 Age-associated left ventricular diastolic filling.................... 9
FIGURE 2 Performance on Task Dependent Leg Strength........................ 17
FIGURE 3 Change in V 02 during Exercise B o u ts.................................. 44
FIGURE 4 Change in V 02 corrected for appendicular LBM.................. 46
FIGURE 5 Change in V 02 corrected for Work (65% of 1 -RM)..............48
FIGURE 6a Change in V 02 (absolute) during Parallel Knee Squats........ 52
FIGURE 6b Change in V 02 during Parallel Knee Squats corrected for
appendicular L B M ...................................................................... 52
FIGURE 7 Change in Heart Rate................................................................... 62
FIGURE 8 Change in Systolic Blood Pressure........................................... 63
FIGURE 9 Change in Diastolic Blood Pressure......................................... 64
FIGURE 10 Change in Cardiac Index............................................................65
FIGURE 11 Change in Rate Pressure Product.............................................. 66
FIGURE 12 Raw EMG during Parallel Knee Squat.......................................68
FIGURE 13 Potential Future Study.................................................................. 90
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BP
CHF =
Cl
CON =
COPD =
DP
ECC =
HR =
N
RE -
RPP =
RT =
SBP =
VC02 =
V 02 =
W
IX
ABBREVIATIONS
blood pressure
congestive heart failure
cardiac index
concentric
chronic obstructive pulmonary disease
diastolic blood pressure
eccentric
heart rate
Newton
Resistance Exercise
rate pressure product
Resistance training
systolic blood pressure
volume of carbon dioxide (see Glossary section for definition)
volume of oxygen (see Glossary section for definition)
watts
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X
ABSTRACT
In frail and physically impaired populations, rehabilitation strategies that are
more efficient in generating beneficial muscle adaptations at lower metabolic and
cardiovascular demands are needed. Therefore, the hypothesis of this study is that
eccentric (ECC) bouts of resistance exercise (RE) will have lower metabolic costs
and therefore lower cardiovascular requirements than bouts of concentric (CON) RE
at the same workload. The physiological effects of ECC and CON contractions were
compared during bouts of RE (knee flexion, knee extension or parallel knee squats)
in young and older subjects at a submaximal intensity known to induce beneficial
functional muscle adaptations. Thirty eight subjects were recruited, and included 19
young men and women (10 females, 9 men, mean age 25±2 year) and 19 older
subjects (15 females, 4 men, mean age 64±4 year). Subjects were assigned to
perform ECC-only and CON-only (or visa versa) for each exercise bout 5-7 days
apart. Exercise bouts consisted of 3 sets of 10 repetitions for each exercise (knee
extension, knee flexion and parallel knee squat), and separated by a 5 minute rest
period, at 65% of their respective voluntary CON maximum force. Metabolic and
cardiovascular measures (VO2, VCO2, VE, HR, BP, Cl, and RPP) were obtained
during the exercise bouts for the 3 different exercises. Eccentric RE bouts were
associated with V 02, VC02, HR, SBP, Cl, and RPP measures that were
significantly lower (P<0.001) than during CON RE bouts. In addition, changes in
HR, SBP, Cl, and RPP were significantly less during ECC than CON bouts for both
age groups (P<0.001) but were lower in younger than older subjects with both
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exercise modes (P<0.001). Finally, there were no gender differences between ECC
and CON bouts (P>0.05). Thus, ECC RE bouts were more metabolically efficient,
and produced less cardiovascular stress. Therefore, this type of exercise should be
better suited for populations with low exercise tolerance (e.g. muscle wasting, heart
failure, chronic lung disease) and should be further evaluated.
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1
CHAPTER I
OVERVIEW OF PROPOSAL
Statement of the Problem
Classic progressive resistance training enhances skeletal muscle mass and
increases muscular strength, power, endurance and functional capacity. Resistive
exercises require a training stimulus of at least 65% intensity, relative to an
individual’s maximum voluntary strength, to produce muscle hypertrophy (Kraemer,
Adams et al. 2002). However, this intensity may not be achievable in certain patient
populations, including those with muscle wasting and frailty as may occur in persons
with cachexia caused by conditions such as, cancer, HIV, or in advancing age.
Moreover, the metabolic cost (e.g. oxygen consumption, carbon dioxide production,
or total expired ventilation) may be so great that traditional resistance training cannot
be performed safely in many disabled persons including the elderly with underlying
cardiopulmonary limitations (e.g. chronic lung disease or heart failure).
Resistance training programs typically emphasize the concentric phase of
muscle contractions whereby muscle is actively shortened under a load. However,
with eccentric resistance exercise, the muscle is actively lengthened under a load,
which may be more efficient. In particular, eccentric muscle contractions use less
ATP, and hence ventilatory requirements should be less than with concentric muscle
contractions when performed at the same workload. Further, greater force
production is possible with eccentric compared to concentric muscle actions
(Hortobagyi, Houmard et al. 1998). Thus, it is possible that a greater hypertrophic
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stimulus may be generated with eccentric than concentric contractions which should
be less demanding on the cardiovascular system.
Several studies have evaluated muscle adaptations (hypertrophy and strength)
of eccentric training protocols, but these studies have utilized an overload (supra
maximal) training stimulus and did not directly compare the metabolic effects of
eccentric versus concentric contractions at the same workload, or when utilizing a
submaximal training protocol the studies were performed on a specially designed
eccentric cycle-ergometer. Therefore, this proposal will investigate for the first time,
the physiological and cardiovascular effects of eccentric versus concentric muscle
actions of traditional resistance exercises (knee extension, knee flexion and the
parallel knee squat) at the same submaximal workload.
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3
Hypotheses
• Ventilatory requirements (oxygen consumption [V02], carbon dioxide expired
[VC02] and total expired ventilation [VE]) during eccentric resistance exercises
are less demanding than during concentric resistance exercises when performed
at the same workload.
• Heart rate (HR), blood pressure (BP), cardiac index (Cl) and rate-pressure
product (RPP) responses will be less during eccentric compared to concentric
exercise at the same workload.
• The differences in the ventilatory and cardiac responses to eccentric versus
concentric skeletal muscle contractions do not vary by age or gender.
• With concentric skeletal muscle contractions, V 02 is significantly less compared
to concentric contractions at the same workload because fewer actin-myosin
cross bridges are generated due to the contribution of stored potential energy
(passive tension) during the eccentric contraction.
Corollary: Because of the greater mechano-energy efficiency with eccentric
contractions, activation of fewer motor units is necessary to
perform the same workload.
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Specific Aims
1. Determine if V 02, VC02, and VE are different during a single eccentric and
single concentric resistance exercise bout at the same workload.
2. Determine if the HR, BP, Cl and RPP responses are lower with eccentric
versus concentric contractions during a single eccentric and single concentric
resistance exercise bout at the same workload.
3. Determine if ventilatory and cardiac responses are different in younger
subjects (21-30 years of age) than older subjects (60-80 years of age) and
according to gender during a single eccentric and single concentric resistance
exercise bout at the same workload
4. Obtain pilot data on the feasibility of determining if fewer motor units are
activated with eccentric contractions versus concentric contractions during
vigorous bouts of exercise at the same workload.
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5
CHAPTER II
Background and Significance
Impaired Physical Function During the Aging Process:
Sarcopenia
The aging process is associated with a number of changes in body
composition including the loss of muscle mass, which is termed sarcopenia.
Several studies have demonstrated that synthesis of mixed myofibrillar
(Urban, Bodenburg et al. 1995; Ferrando, Sheffield-Moore et al. 2002) and
contractile skeletal muscle proteins, namely, actin and myosin (Yarasheski,
Zachwieja et al. 1993) were significantly improved in older persons in
response to various anabolic stimuli (androgens, resistance exercises, etc.).
Moreover, the absolute and relative increases in contractile muscle protein
synthesis were similar to that in younger persons (Yarasheski, Zachwieja et
al. 1993). Thus, sarcopenia may not be an irreversible process. Regardless,
if untreated, sarcopenia may lead to decreases in basal metabolic rate thereby
promoting positive energy balance and accumulation of adipose tissue,
impaired thermoregulation, and further loss in muscle strength.
In addition, with aging, there is a progressive loss of maximal
voluntary strength beginning sometime after 30 years of age (Baumgartner,
Waters etal. 1999). Approximately 30% of lower extremity maximal
voluntary strength is lost between the age of 50 and 70 years. In a
longitudinal study of elderly men, there was a 20-30% reduction of knee and
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6
elbow flexor strength at various angular velocities (Frontera, Hughes et al.
2000). In two other longitudinal studies of elderly individuals conducted
over five and 11 years, there was a 27% and 35% respective decrease in
isokinetic strength (Gallagher, Visser et al. 1997). These reports and other
studies indicate that muscle strength declines by approximately 15% in the 6th
and 7th decade and about 30% thereafter (Jette and Branch 1981; Murray,
Duthie et al. 1985; Balagopal, Rooyackers et al. 1997). The progressive loss
of skeletal muscle strength often results in diminished functional capacity
with impaired gait speed (which may impair activities such as difficulty
crossing the street before the “don’t walk” signal appears), difficulty rising
from a chair or climbing stairs, carrying groceries, etc. Impaired physical
function may progress to frailty, which may result in increased risk of falls,
impaired activities of daily living (e.g. personal grooming such as shaving or
combing hair, doing house chores, preparing food, etc.) (Jette and Branch
1981; Fiatarone, O'Neill et al. 1994; Guralnik, Simonsick et al. 1994).
Moreover, impaired physical function is frequently associated with a
number of important adverse medical outcomes, including immobility
resulting in deep venous thrombosis and pulmonary embolism, loss of
balance and falls, aggravation of osteoporosis with spontaneous fractures,
central obesity with dyslipidemia and increased risks for cardiovascular
complications, loss of independence with social isolation and major
depression, etc. There are many factors that may contribute to sarcopenia
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7
and muscle weakness during advancing age, such as arthritis, neurological
disorders (both central and peripheral), limited cardiopulmonary capacity
from chronic lung disease and coronary atherosclerosis. Regardless, the loss
of muscle mass is frequently central to the pathogenesis of impaired physical
function.
Cardiopulmonary Considerations
Pulmonary Function:
With aging, there is progressive impairment in lung and heart
function. The forced expiratory volume in one second (FEVi) decreases by
about 30 ml/year in men and 23 ml/year in women after about age 20
(McKelvie, McCartney et al. 1995; Hortobagyi, Hill et al. 1996; McKelvie
2002). The annual decline in FEVi is relatively small at first but accelerates
with age (McKelvie 2002). The total forced vital capacity (FVC) decreases
as well, by about 14 to 30 ml/year in men and 15 to 24 ml/year in women
(McKelvie, Teo et al. 1995). The decreases in FEVi and FVC that occur up
to age 40 are thought to result from changes in body weight and strength
rather than from loss of lung tissue per se. With advancing age, airway
obstruction due to an accumulation of inflammatory injuries, largely from
environmental air pollutants, contributes to further lung impairment.
In non-stressful circumstances, pulmonary function is generally
sufficient in older persons to maintain tissue oxygenation and metabolism
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8
with only modest increases in the work of breathing. However, with
increased respiratory demands resulting from illness or exercise, breathing
capacity may not be adequate to supply sufficient oxygenation for body
tissues. Moreover, ventilation may not be adequate to remove C 02 generated
by increased oxidation of carbohydrate. These impairments may contribute
to the decreased capacity for individuals to perform activities of daily living
resulting from sarcopenia. Moreover, these effects are often magnified with
lung disease.
In fact, it has been estimated that by the year 2020, chronic
obstructive pulmonary disease (COPD) will be the fifth most common co
morbidity of aging and will be the highest medical and financial burden to
society on a worldwide basis. Economic costs are estimated at greater than
$14 billion in the United States alone. It is estimated that there are 14.0
million men and women in the United States with chronic bronchitis, 2.2
million with emphysema, and 14.6 million with asthma (Turato, Zuin et al.
2001).
Cardiac Function:
As individuals age, cardiac function is also progressively impaired.
There is gradual loss in the contractile strength of the heart, which is caused
in part by a decrease in calcium-myosin ATPase activity in addition to
myocardial ischemia. The heart walls then stiffen and there is delayed
ventricular filling. As a consequence, resting stroke volume decreases (on
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9
average about 115 ml at age 20 years to 100ml at age 80 years), thereby
impairing cardiac output (Schulman 1999).
In fact, aging is associated with a 25% reduction in cardiac index
between the ages 25 and 85 years (Schulman 1999). As shown in Figure 1,
early diastolic left ventricular filling rate progressively slows after age 20,
such that by 80 years of age, the rate is reduced by up to 50% (Schulman
1999). However, during exercise the early diastolic left ventricular filling
volume increases to compensate for metabolic demands. Thus, the end-
diastolic volume, even at peak exercise, is “not compromised” from the LV
rigidity, and stroke volume during exercise is maintained in older persons.
E A
Figure 1: Age-associated left ventricular diastolic filling.
The first wave (E wave) occurs during early filling: the second (A wave) is
due to atrial contraction. Modified from Schulman SP, Lakatta EG. Fleg JL.,
et al: “Age-related decline in left ventricular filling at rest and exercise.”
American Journal of Physiology 263(6 Pt 2): H1932-1938, 1992.
However, the ejection fraction (EF) of an older heart is limited during
maximal exercise. For example, at the beginning of a session of vigorous
exercise, the size of an older heart is larger than a younger heart, holding
approximately 120 ml versus 110 ml in a younger heart. At the end of
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10
ventricular contraction there is a 70 ml residual in the older heart compared
with approximately 35 ml in a younger heart (Schulman 1999). This inability
to increase EF causes the old heart to stretch (or dilate), and thus, its size at
both the start and end of the heartbeat is increased during vigorous exercise
compared to the size of the younger heart during vigorous exercise.
Moreover, the maximal heart rate that can be achieved declines with result of
age and therefore the heart cannot compensate for the decreased ejection
fraction. As a result, these abnormalities decrease blood flow to skeletal
muscle during exercise and oxygen cannot be sufficiently increased.
In a Canadian cardiac rehabilitation study, the effects of resistance
and aerobic training in patients with heart failure were examined (McKelvie,
Teo et al. 1995). One hundred eighty-one patients with cardiac ejection
fractions less than 40% were recruited. Study subjects were randomized to
an exercise group and performed resistance and aerobic training in a
supervised rehabilitation program for three months (two sessions per week)
or to a control group who were asked not to change or add any kind of
exercise activity. The resistance training (arm curls, knee extensions, and leg
press) intensity was started at 40% of the 1-repetition maximum and was
increased to 60% by the fifth week of training, and aerobic training
(treadmill, cycle and arm ergometer) was set at 60% to 70% of the measured
maximal heart rate response. After three months of training, the exercise
group achieved significant increases for arm (0.50±0.16 kg, and 1.20±0.23
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11
kg, respectively) and leg (1.07±0.65 kg and 2.48±0.79 kg, respectively)
strength compared to the control group (P<0.05). However, no significant
changes were observed in cardiac function (i.e. ejection fraction and cardiac
volumes). Thirty of the men had cardiac complications during the aerobic
exercising (abnormal rhythms, chest pain, blood pressure changes), but only
one had a cardiac problem during resistance training, suggesting that
resistance training may be a safer mode of exercise.
A study at the Tufts University Human Nutrition Research Center
examined the effects of a 10-week progressive resistance training (PRT)
program, three days per week in 16 older women (77±6 yr) with congestive
heart failure (CHF) (Pu, Johnson et al. 2001). Subjects participated in high-
intensity (80% of 1-repetition maximum) PRT training program. Exercise
consisted of leg press, knee extensions, chest press and triceps extensions.
The 16 women were compared with 80 age-matched peers without CHF, who
did not participate in a structured exercise program. At the end of the 10
weeks of training, skeletal muscle strength was improved by an average of
43±8% in resistance trainees versus -1.7±2.8% in the controls (P=0.001).
The gains in muscle strength ranged from 34±7% in the leg press to 68±13%
in knee extensions. Exercise training was well tolerated and resulted in no
changes in resting cardiac indexes (e.g. systolic and diastolic function) in the
patients with CHF. The investigators, therefore, concluded that the improved
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12
exercise capacity was the result of improved skeletal muscle function and not
improved heart function.
These studies demonstrate the potential hazards of certain forms of
exercise (particularly aerobic exercise) in patients with severe
cardiopulmonary diseases. Although there were no meaningful improvements
in cardiac function, resistance exercise was associated with improvements in
strength which could be important if associated with improved physical
function.
Resistance Training Augments Skeletal Muscle Strength:
Effects of Traditional Progressive Resistance Training
There is compelling evidence that progressive resistance training
(PRT) is an effective means to increase skeletal muscle strength in older
persons even into very advanced age and in persons with chronic illnesses
(Friedl, Hannan et al. 1990; Guralnik, Simonsick et al. 1994; Demers,
McKelvie et al. 2001). Indeed, Fiatarone et al. demonstrated in a randomized
controlled trial of octogenarians and nonagenerarians that significant
increases in skeletal muscle strength could be achieved with PRT (Fiatarone,
O'Neill et al. 1994). Bassey et al showed that the increases in strength with
i
PRT improved skeletal muscle power (Bassey, Fiatarone et al. 1992). Of
importance, improvements in skeletal muscle power have been well-
correlated with improved mobility and function in elderly persons (Larsson,
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13
Grimby et al. 1979; Danneskiold-Samsoe, Kofod et al. 1984). These studies
demonstrate that the aging musculoskeletal system is able to respond
favorably to PRT, and most importantly, the consequences of sarcopenia can
at least in part be corrected with significant improvements in levels of
physical function and over all activity to prevent or alleviate frailty.
However, because of the physical demands of this type of exercise and
limitations in cardiopulmonary function that may occur with aging (e.g. chronic
lung or coronary disease), traditional PRT that is based on concentric muscle
contractions may be too difficult to perform for older persons who have limited
exercise capacity.
Effects of Eccentric Progressive Resistance Training (EPRT)
Progressive resistance training may be designed to utilize primarily
eccentric contractions (defined as the force exerted by a muscle during active
lengthening). This form of PRT has a number of theoretical advantages over
standard PRT, which utilizes both concentric and eccentric contractions.
Eccentric contractions occur when the external force (weight) is greater than
the force generated by the muscle (i.e. the subject only controls the lowering
of the weight). Eccentric muscle contractions temporarily store potential
energy as a result of the tissue’s elastic component (stretching of the tissue)
and thus, may be associated with a higher mechanical efficiency (Lindstedt,
LaStayo et al. 2001). Moreover, neuronal activity as measured by
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14
electromyography (EMG) is less with eccentric compared to concentric
contractions during the performance of similar work suggesting that the
frequency of motor-neuron activation and recruitment needs is less with
eccentric contraction (Higbie, Cureton et al. 1996). In addition, results of
several studies suggest that long-term eccentric training can improve skeletal
muscle strength with a lower demand for oxygen compared to concentric
training (Dudley, Tesch et al. 1991; Lastayo, Reich et al. 1999). LaStayo et
al., measured the oxygen consumption required to do eccentric compared
concentric work on a specially modified two-way cycle ergometer (Dudley,
Tesch et al. 1991; Lastayo, Reich et al. 1999). The cycle was modified to
produce resistance during cycling backward, which requires primarily
eccentric muscle contractions. Forward peddling against resistance utilizes
primarily concentric muscle contractions. Nine healthy subjects were
randomly assigned to either an eccentric (reverse cycling) or a concentric
(forward cycling) training group. Both groups trained for six weeks,
progressively increasing their training frequency and duration on the cycle
ergometer. Oxygen consumption (V02) was measured once a week using an
open spirometer system while subjects performed knee extension exercises
on a Cybex dynamometer. For the eccentric cycle training group, V 02 was
significantly less than for those in concentric cycle training group. Although
these results suggest that eccentric exercise is more metabolically efficient,
the type of exercise training evaluated (aerobic cycling) is not typically used
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15
to augment muscle and strength. Whereas, RE has increased muscle quality
and performance in some older subjects without cardiopulmonary limitations
(Fiatarone 1996)
Potential Benefits of Eccentric Training in a Frail Population
To assess the effects of eccentric exercise on the risk of falling in an
elderly population, 21 subjects (mean age, 80 years, range 70-93; 11 male, 10
female) were randomized to an eccentric exercising (ECC group) or a
traditional resistance (concentric/eccentric) training (TRAD group.)
(LaStayo, Ewy et al. 2003) Subjects were selected for the study because
they had limited functional abilities based on pre-study assessment of
balance, stair ascent time, and the up and go. The ECC group exercised on a
recumbent leg cycle-ergometer described in the prior section. Eccentric
training consisted of pedaling for 20 minutes, gradually increasing workload
according to the study subjects’ perceived exertion. The TRAD group used
traditional resistance exercises with weight machines (leg press, leg
extension, mini-squat), and free weights. Traditional training sessions
consisted of 11 sets of 10 to 15-repetitions per exercise. Both groups
exercised three times per week. At the conclusion of the study, both groups
demonstrated improvements in exercise performance. The ECC group had a
60% increase in leg strength, 7% improvement in balance, and 21%
improvement in stair descending time (P<0.05 for each; Table 1). The ECC
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16
trained subjects reduced their up-and-go times by 4.7 second (Table 1). The
post-training test results were below 14 seconds for the up-and-go tests,
which is the threshold for increased risk of falls (figure 2).
Table 1: Mean Values Pre & Post Training
ECC Group TRAD Grouu
Pre-Training Post-Training Pre-Training Post-Training
Ouad Strength IN') 48.8±6.07 78.1±8.78*t 45.5±5.48 52.5±4.30
Fiber Area fum2 ) 3295±366 5273±963.5* 2999±313 4218±367*
Timed U d & Go fsl 16.65±0.81 11.96±0.72*f 17.20±0.87 15.55±1.45*
Stair Descent (s) 25.3±2.01 20.9±2.10*f 21.4±2.32 22.9±4.36
Berg Balance 49. 7± 1.14 53.4±0.64* 42.0±2.38 44.3±1.37
Notes: ’ "Significant differences (p<.05) within groups from pre- to post-training; f significant
differences (p<.05) between groups. ECC= eccentric, TRAD= traditional, Quad=quadriceps.
The TRAD group had a non-significant increase in quadriceps strength
(15%), and did not improve their balance and stair descent time. These data
demonstrate that lower extremity eccentric exercise on a cycle ergometer
improves muscle function. However, the study differs from the dissertation
proposal, since the investigators compared an aerobic exercise (eccentric
training) with a standard PRT (both eccentric/concentric muscle contractions)
and did not test EPRT per se. Regardless, these studies do suggest that
eccentric exercise may be better suited for patients with limited
cardiopulmonary capacity since the metabolic requirements for this form of
exercise are less demanding on the heart and lungs.
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17
s
t
in
.
High FH! Hi!;
ISO 280 sm 3 m 450 400 450
bometrio 6traij|th (N)
Figure 2: Performance on Task Dependent Leg Strength
Performance of the subjects (as measured both pre- and post-training) on a task
dependent on leg strength, i.e., the “timed up and go” fall-risk assessment. Any
improvement in leg strength in an elderly population likely has a clinical effect. Here
the TRAD group (circles) clinically improved their strength (15%). The ECC group’s
(triangles) strength and fall risk, however, though no different than the TRAD group
initially, did improve significantly (p<05) in strength (60%) and with the timed up and
go (4.7s). In fact, the larger magnitude increase in strength was coupled to a shift in the
ECC group from a high fall risk to a low fall risk following training. Error bars= 1
SEM.
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18
Rationale for Study Design
Metabolic Efficiency and Cardiopulmonary Demands:
Because many older persons have limited cardiopulmonary capacity
in addition to sarcopenia, they may not be able to safely perform traditional
PRT. In fact, with limited pulmonary function due to age or disease,
strenuous concentric based RE may lead to oxygen desaturation and risk for
serious or even fatal arrhythmias. Similarly, if these subjects have either
overt cardiomyopathy or impaired left ventricular function from
atherosclerosis, strenuous exercise may predispose them to cardiac ischemia
or even myocardial infarction because of greater oxygen demand than supply
for cardiac muscle.
Theoretically, eccentric resistance training should be better suited for
older persons with sarcopenia and cardiopulmonary impairments than
traditional PRT with both eccentric and concentric muscle contractions. This
supposition is based on observations that eccentric exercise appears to require
less ATP utilization than concentric exercise based on a few studies in
younger persons during cycle-ergometry. Eccentric exercise should,
therefore, be less demanding on the heart and lungs for individuals with
impaired cardiopulmonary function if oxygen requirements and the work of
breathing (ventilation) are less than with concentric based training programs.
However, in studies involving traditional resistance exercise in normal
volunteers, the eccentric training stimulus has involved an overload
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19
compared to the concentric exercise (e.g. eccentric training stimulus at 120%
of the 1-RM for concentric mode). For individuals with muscle wasting or
cardiopulmonary limitations, such an overload may not be feasible or
tolerable. Thus, studies comparing eccentric versus concentric RE at
submaximal loads that are sufficient to generate skeletal muscle hypertrophy
(Kraemer, Adams et al. 2002) to determine if at the same exercise stimulus
eccentric contractions are more metabolically efficient and less demanding on
the heart and lungs. If eccentric training in older persons can produce greater
hypertrophy than with concentric training at equal levels of exercise intensity,
this may facilitate training in those with cardiopulmonary limitations that
could not otherwise safely provide sufficient effort to augment muscle mass
with traditional PRT. Therefore, the purpose of this study is to determine if,
the metabolic requirements, primarily V 02 and VE, are less with eccentric
than concentric exercise at the same workload. The study will also assess
whether there are cardiopulmonary advantages of eccentric resistance
exercise in older compared to younger persons and whether there are gender
differences in these two age groups.
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20
CHAPTER III
METHODOLOGY
Study Overview: The study was a cross-sectional investigation involving two age
groups. Group I included young men and women 21-30 years of age and Group II
included older men and women 60-80 years of age. Both groups performed single
bouts of eccentric and concentric resistance exercises. The primary outcome
measures (V 02, VC02, VE, HR, BP, Cl and RPP) were assessed during the bouts of
exercise.
Study Design: To achieve the specific aims, the following procedures and tests
were performed.
Specific Aim 1: Determine if V 02, VC02, and VE are different during a single
eccentric and single concentric resistance exercise bout at the same workload.
All testing was done at the Clinical Exercise Research Center and Los Angeles
County— University of Southern California General Clinical Research Center. Pilot
EMG data was collected in the Musculoskeletal Biomechanics Research Laboratory
at the University of Southern California. In the first testing session subjects (men
and women) were randomly assigned to perform, either an eccentric or a concentric
bout o f exercise, which was followed 5 to 7 days later with a second bout of
resistance exercise testing using the opposite type of muscle contraction (i.e. if a
subject was assigned to perform eccentric in the first exercise session that subject
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21
performed the concentric bout of exercise in the following exercise session and vice
versa). Each testing session evaluated three different exercises:
• Knee extension on an isokinetic dynamometer (KinCom).
• Knee flexion on the KinCom
• Parallel knee squats on a modified Smith Squat Rack.
Exercise Protocol: Subjects were assessed for maximal voluntary force using the 1
repetition maximum (1-RM) method for the three exercises (knee extension, flexion
and parallel knee squats) in both eccentric and concentric modes (totaling six
different exercises). Eccentric and concentric strength of the knee extension
(quadriceps muscle groups) and knee flexion (hamstring muscle groups) was
assessed on a KinCom II isokinetic dynamometer (Chattex Corp., Hixon TN). Tests
were performed at 60 degrees per second. Both the right and left legs were tested for
the knee extension and flexion exercises. In order to prevent any dominant leg
influence on 1-RM measures, subjects were randomized to initiate testing with either
the right or left legs; both legs were tested at each session. The results of the right
and left legs for each exercise were added together.
Each subject was seated on the KinCom with the lateral epicondyle of the knee
aligned with the axis of the dynamometer and the inferior edge of the force pad
aligned across the hips, high, and ankle of each subject for stabilization. Gravity
correction was performed according to the manufacture’s protocol with the knee at 0
degrees of flexion. The dynamometer’s pre-load and minimal force values were set
at five Newton’s. The exercise intensity was set at 65% of the subjects’ concentric
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22
1-RM for both the eccentric and concentric exercise bouts. Each testing session
consisted of either concentric or eccentric exercise bouts of three sets of 10
repetitions for the three exercises. There was a 30 second rest period between sets of
exercises performed on the KinCom and a two minute rest period between the squat
exercises performed on the Smith rack. Subjects were given five minute rest periods
between sets for each o f the three different exercises.
Absolute VO2 (ml/min), relative VO2 (ml/kg/min), VCO2 (ml/min),
total expired ventilation (VE; [give units here]) were measured using a Medgraphics
Cardio II gas analysis module (Breeze Suite software version 6.0 A). Gases were
collected beginning five minutes before exercise to establish baseline measures,
during exercise and for five minutes after completion of exercise. Oxygen
consumption was also corrected for appendicular lean tissue as determined by dual
x-ray absorptiometry scanning (DEXA).
Specific Aim 2: Determine if the HR, BP, Cl and RPP responses are lower with
eccentric versus concentric contractions during a single eccentric and single
concentric resistance exercise bout at the same workload.
Blood pressure was measured during the resistance exercise bouts (every two
minutes) using a manual blood pressure cuff and stethoscope. Heart rate was
determined using a limb lead ECG monitor (Cardio Control accessory for the
Medgraphics, CardioII). The Cardio Control accessory for the metabolic cart
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23
recorded heart rate throughout the entire resistance exercise bout, including pre and
post exercise periods.
Specific Aim 3: Determine if ventilatory and cardiac responses are different in
younger subjects (21-30 years of age) than older subjects (60-80 years of age)
and according to gender during a single eccentric and single concentric
resistance exercise bout at the same workload.
Older subjects performed the same resistance exercises as for specific Aim #1
at the same intensity (65% of their 1-RMs) and were tested using the same protocol
as for the younger subjects. To assess the effects of differences in lean body mass
(LBM) in the extremities (primarily skeletal muscle) that may differ between age
groups, ventilatory measurements were corrected for appendicular LBM in the two
age groups. Similarly, because maximum voluntary strength (1-RM) was expected to
differ between age groups, ventilatory measures were corrected for 1-RM strength to
assess whether differences in forces used during exercise testing affected outcomes
in the two age groups.
Specific Aim 4: Obtain pilot data on the feasibility of determining if fewer
motor units are activated with eccentric contractions versus concentric
contractions at the same workload.
To obtain pilot data on the feasibility of determining motor unit activation during
the ECC and CON contractions during the vigorous parallel knee squat exercises,
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24
EMG signals were collected from a subset of four subjects during the parallel knee
squat exercises on the Smith rack. After skin preparation (shaving and scrubbing
with alcohol), surface EMG electrodes were placed over the rectus femoris, the
lateral hamstrings, and the gastrocnemius muscles of the dominant limb. A ground
electrode was placed over the acromion process of the scapula. Electrodes were
secured with tape and an elastic sleeve. The EMG telemetry unit was worn in a pack
secured to the subject’s back. Electrical activity was recorded at a sampling rate of
1560 Hz, using pre-amplified bipolar surface electrodes (Motion Control, Salt Lake
City, UT). EMG signals were transmitted by telemetry to a 12-bit analog-to-digital
converter using an FM-FM telemetry unit. Differential amplifiers were used to reject
the common noise and amplify the remaining signal (gain=1000).
All EMG pilot data were filtered with a band pass Butterworth filter, 20-500 Hz,
and a 60 Hz notch filter. Full wave rectification and smoothing of the EMG signal
was accomplished using average root-mean-square (RMS) over 100 ms intervals. In
order to compare EMG intensity between subjects and muscles, and to control for
variability induced by electrode placement, EMG during concentric and eccentric
phases of the squat activity was normalized using the peak EMG signal acquired
during a concentric 1RM parallel knee squat. The average squatting trials were then
expressed as a percentage of the EMG obtained during 1RM (% 1RM).
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25
Eligibility Criteria: All study subjects must have met the following eligibility
criteria:
Inclusion Criteria:
• Group I: Healthy men and women 21-30 years of age
• Group II: Healthy men and women 60-80 years of age
Exclusion Criteria:
• Anemia (serum hemoglobin <10 g/dL)
• Uncontrolled hypothyroidism or hyperthyroidism
• Rheumatoid arthritis, chronic hepatitis, renal failure or other illness
that could be catabolic
• Prior cancer other than squamous or basal cell carcinoma of the skin
• Blood pressure that could not be controlled with medication to
<180/95 mm Hg
• Failure to pass a modified Bruce exercise stress test on a cycle
ergometer
• Disability limiting strength or physical function testing
• Dementia or cognitive impairment affecting a subject’s ability to
provide informed consent
• Resistance training and/or heavy aerobic exercise in the preceding 12
months defined as more than one bout per week.
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26
Methods:
Eccentric and Concentric Resistance Exercise Bouts:
Subjects were tested for maximum voluntary force by the one repetition
maximum (1-RM) method (Johnson and Nelson 1974) for knee extension, knee
flexion and parallel knee squat (visit #1). The 1-RM for each exercise was re-tested
5 to 7 days later (visit #2) to minimize learning effects in setting the workload for the
testing bouts. In addition, a whole body DEXA scan was performed in order to
determine lean body mass (LBM) (visit #2). In the first exercise testing session
(visit #3), subjects were randomized to perform either the eccentric or concentric
exercise bout. The subsequent exercise session was performed using the opposite
type of muscle contraction (visit #4). The exercise sessions (visits #3 and #4)
consisted of three sets of 10 repetitions each at 65% of their respective concentric 1-
RM strength for each exercise whether performed in the concentric or eccentric
mode.
The Smith rack apparatus was modified with a pulley system to enable study
subjects to perform parallel knee squats using only eccentric or concentric muscle
actions. For example, after the subject performed an eccentric squat (lowering of the
weight), the pulley system allowed the investigator to raise the weight, thus
preventing the subject from performing the concentric muscle action. Likewise, after
the subject performed a concentric squat (lifting of the weight), the pulley system
allowed the investigator to lower the weight, thus preventing the subject from
performing the eccentric muscle action.
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27
The velocity of the eccentric and concentric movements performed during the
squat exercise was performed to the sound of a metronome in order to standardize
time of 2 seconds in the eccentric and 2 seconds in concentric movements. Subjects
rested for 30 seconds between sets for the knee flexion and extension exercises, two
minutes between sets for the parallel knee squat exercise and 5-minute rest periods
between each different exercise.
EKG Exercise Stress Test (Group II only):
To screen older subjects for increased risk of coronary ischemia during exercise
testing all Group II subjects without other contraindications to testing underwent an
exercise stress test on a cycle ergometer with electrocardiographic and blood
pressure monitoring (Pre-entry visit#2). Testing was performed in the LAC-USC
Medical Center General Clinical Research Center.
Body Composition Analysis:
DEXA Scanning: Appendicular and total LBM was determined by DEXA scanning
(Watkins, Roubenoff et al. 1992; Fuerst and Genant 1996; Adams 1998). Total
appendicular LBM was used to estimate total appendicular skeletal muscle mass
(TASM) in the extremities and total body muscle by the relationship: appendicular
LBM/0.75. TASM was be adjusted for height (TASM/m2) to correct for difference in
stature and ethnicity (Proctor, O'Brien et al. 1999). The DEXA scanner at the LAC-
USC Medical Center General Clinical Research Center is a Hologic QDR-4500
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28
(Waltham, MA) which provides CVs of 1.4% for total and 2.1% for appendicular
LBM, respectively (Fuerst and Genant 1996).
Laboratory Testing:
Blood Tests to Screen for Catabolic Disease and Safety Testing: Blood was
collected in the GCRC and analyzed in the LAC-USC Medical Center Clinical
Laboratory. This testing was used to screen potential subjects for eligibility to
exclude those with catabolic disease, anemia, uncontrolled diabetes, liver disease,
renal failure, etc which could confound assessment of outcome measures. These
disorders could also put subjects at increased risk for adverse outcomes during
exercise testing and thus it was important to exclude subjects with these disorders.
Schedule of Events:
Group I: Young Men and Women
Study
visit
Pre-entry Visit 1 Visit 2 Visit 3 Visit 4
O b ta in
I n fo r m e d
C o n s e n t
1- R e p e titio n
M a x im u m
( 1 - R M )
D E X A
R e p e a t
1 -R M
C o n c e n tr ic /
E c c e n tr ic
E x e r c is e
T e s t in g
E c c e n tr ic /
C o n c e n tr ic
E x e r c is e
T e s t in g
Group II: Older Men and Women:
Study
visit
Pre
entry 1
Pre-entry
■ B W M B
Visit 1 Visit 2 Visit 3 Visit 4
O b ta in
I n fo r m e d
C o n s e n t
E K G S tr e ss
T e s t a n d
P h y s ic a l
E x a m
1 -R M
D E X A
R e p e a t
1 -R M
C o n c e n tr ic /
E c c e n tr ic
E x e r c is e
T e s t in g
E c c e n tr ic /
C o n c e n tr ic
E x e r c is e
T e s tin g
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29
Statistical Considerations and Data Management
Statistical Considerations
Study Design: The investigation involved two different age groups. Group I
included young men and women 21-30 years of age and Group II included older
men and women 60-80 years of age who underwent single bouts of eccentric and
concentric resistance exercises. The primary outcome measures (V02, VC02,
VE, BP, HR, Cl and RPP) were assessed during eccentric or concentric
resistance exercise bouts (different visits as described above) to achieve the
specific aims of the proposal.
Primary Outcome Measures:
1. Ventilatory Measures: Absolute and relative oxygen consumption (V02),
carbon dioxide production (VC02), total expired ventilation (VE),
measures were also corrected for appendicular LBM and work.
2. Heart Rate: Heart rare was assessed using a limb lead (3-lead) ECG.
3. Blood Pressure: Blood pressure was assessed using a manual blood
pressure cuff and a stethoscope.
4 Cardiac Index: Cardiac index is based on cardiac output (Q), which is the
volume of blood ejected by the left ventricle into the systemic circulation
in one minute (L/min) based on body surface area (M) = (Q/Meters2 ).
5. Rate-Pressure Product: Rate pressure product is the product of systolic
blood pressure and heart rate divided by 100.
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30
Statistical Analyses:
Data were presented in the text and tables as mean ± 1 SD. Data presented
in tables show absolute values achieved at peak effort. To depict relative
changes (differences from baseline to peak), results are shown by histograms.
Demographics and baseline characteristics were compared between young
and older subjects using independent t-tests for means and Fishers exact test
procedures for proportions.
For the primary outcome measures, a repeated measures ANOVA (age,
gender for between-subject factors, resistance exercise mode for within-
subject factors) was performed for each exercise type (knee extension, knee
flexion, parallel knee squat, and unloaded squats). Within-subjects main
effects (exercise mode), between-subjects main effects (age, gender),
between-subjects interaction effects (age x gender), and within-subjects by
between-subjects interaction effects (exercise x age, exercise x gender,
exercise x age x gender) were tested. The a priori plan was that if gender did
not affect the outcomes, results would not be presented by gender. All post
hoc tests were performed with Bonferroni adjustment for the four
comparisons.
For each exercise type, mean strength and metabolic variables between
young and older subjects were compared using independent t-tests, stratified
by resistance exercise mode. The mean strength and metabolic variables
between eccentric and concentric exercise were compared using paired t-tests
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31
and stratified by age status. For each exercise type, mean baseline and
maximum levels of cardiovascular variables were compared between young
and older subjects using independent t-tests, stratified by resistance exercise
mode; changes in cardiopulmonary variables (maximum minus baseline) were
tested by paired t-tests within each age status, stratified by resistance exercise
mode.
All statistical testing was performed with a two-sided 5% level of
significance (1.25% for each post hoc t-test) using Statistical Analysis System
version 8.0 (SAS Institute, Inc., Cary, NC).
Statistical Power Calculations:
The following statistical power calculations were based on pilot data from the
prior studies performed in the Laboratory of the Clinical Exercise Research
Center of the University of Southern California.
Young Men and Women (Group I):
A sample size of seven subjects in each group would provide an 80% power
to detect a difference in absolute Y 02 of 400 ml of oxygen (the difference
between a concentric group mean of 1200 ml and an eccentric group mean of 800
ml) assuming a common standard deviation of change o f approximately 245 ml
with a 0.05 two-sided alpha significance level. To account for 15% attrition rate
10 men and 10 women were needed to assess the effects of exercise mode and
gender.
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32
Older Men and Women (Group II):
Due to the heterogeneity of older populations, power considerations were
determined using a more conservative approach in order to prevent a type II
(beta) error for Group II. A sample size of 14 subjects in each group would
provide a 85% power to detect a difference in absolute V 02 of 400 ml of oxygen
(the difference between a concentric group mean of 1000 ml and an eccentric
group mean of 600 ml.) assuming a common standard deviation of change of
approximately 300 ml with a 0.05 two-sided alpha significance level. To account
for 15% attrition, a total of 20 subjects were needed. There was no plan to
consider gender differences in this age group.
Data Management:
Data entry and management utilized a variety of methods, all of which have
been validated in previous clinical trials by our laboratory group at USC and the
GCRC. In brief,
1 Subjects were identified only by study identification numbers.
2 Visual checking was done on all files for outliers and logical inconsistencies.
3 Software scripts were used to scan all data files for values outside prescribed
ranges.
4 Data were re-keyed by an independent third party to verify all data entries.
5 An audit trial of data changes/modifications was maintained.
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33
Quality Control in Measurements and Standardization of Procedures and
Equipment
■ The GCRC DEXA Scanner was calibrated monthly with a wedge phantom.
■ KinCom dynamometer was calibrated before each testing session
(manufacturer’s instructions) by Mr. Vallejo.
■ Cycle EKG-Stress Testing was performed at the Los Angeles County General
Clinical Research Center by Mr. Vallejo and supervised by Dr. Fred Sattler
(board certified physician) using a modified Bruce Protocol in accordance to
American Heart Association and American College of Cardiology guidelines
for exercise stress testing.
■ Exercise testing of all exercise bouts was supervised by Alberto F. Vallejo.
Potential Limitations:
a. Use of DEXA scanning to assess appendicular LBM, although a validated
measure of body composition, provides only an estimate of appendicular
skeletal musculature. A further limitation of DEXA is that hydration effects
(such as edema in older subjects) may be measured as LBM.
b. The variability of outcomes was anticipated to be greater in older subjects,
since they may have variable impairments in cardiac and pulmonary function.
Moreover, local effects in muscle (quantity of connective tissue,
neuromuscular adaptations, etc) was expected to vary in the older individuals.
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34
Thus, the power calculations for sample size could not be confidently
estimated in the older subjects.
c. Comprehensive direct measures of pulmonary (e.g. FVC, FEV1) or cardiac
function (e.g. intra-arterial blood pressure, dye dilution for cardiac output)
were not obtained, which could greatly affect outcome measures in the older
subjects. However, this potential limitation should similarly affect bouts of
concentric or eccentric resistance exercise.
d. Although efforts were made to standardize the exercise stimulus, the
eccentric and concentric exercises were performed to the beat of a
metronome. There may be other variability between the eccentric and
concentric exercises such as the length-tension curve relationships between
the two modes.
e. Although subjects were randomized to first undergo bouts of either
concentric or eccentric resistance exercise, it is possible that there may have
been learning effects from one mode (eccentric versus concentric) of exercise
for example, due to familiarity with the equipment.
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35
Study Time Line:
Month 0-3 Month 4-6 Month 7-12
Year
1
Completion of
Proposal *
Recruitment
(Young &01der Subjects) Testing
Month 12-14 Month 13-20 Month 21-22 Month 23-24
Year — ——
^ Testing
>
Data Analysis 1. Data Analysis
2. Preparation of
Abstracts,
Manuscripts,
* 1 R B and G C R C a p p ro v a l, a n d p ro p o sa l
3. Completion of
Dissertation
Gender and Minority Considerations:
Subjects o f all ethnic and racial backgrounds were recruited for inclusion
(USC employees and students, clients utilizing our university health care
facilities as well as free living, community dwelling individuals responding to
local advertising) as has been our practice in other studies involving normal
volunteers and elderly subjects. The ethnic constituency for the University
Hospital in 2000-2001 was comprised of 79% white, non-Hispanics, 6.6%
Hispanics, 5.5% non-Hispanic blacks, 4.3% Asian-Pacific Islanders, 1.3% Native
Americans, and 2.3% unknown. By contrast, the constituency of the patient
population at the Los Angeles County-USC Hospital for the last several decades
has been comprised of 60-70% Hispanics and 10-15% non-Hispanic blacks.
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Since 1985 our laboratory group has successfully recruited persons of ethnic
minorities for studies and has consistently accrued in excess of 60% Hispanics
and non-Hispanic blacks for these trials. Although subjects were drawn from
both the private and public domain, the goal was to accrue a sizable portion of
subjects from ethnic minorities.
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CHAPTER IV
RESULTS
Study Subjects
Thirty eight volunteers were recruited for the study. Nineteen subjects were
enrolled in Group I (female= 10, male = 9). The mean age for the group was 25±2
years; their height was 145±7.5 cm and weight 70±15 kg. Nineteen subjects were
recruited for Group II (female= 15, male = 4). The mean age for the group was 64±4
years; their height was 139±6.0 cm and weight, 75±12 kg. The baseline
characteristics for the study subjects are shown in Table 2. O f note, there were a
greater number of Hispanic subjects enrolled in the older group and a greater number
of Asian Pacific Islanders enrolled in the younger group. In addition, the body mass
index (BMI) and trunk fat, total cholesterol, HDL, and triglycerides were
significantly higher in the older subjects.
Although there were more female subjects in the older group, there were no
significant differences for gender by ANOVA in Group I for any of the test
measures. Thus, the results by gender are not displayed in the subsequent tables as
predetermined in the statistical plan.
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Table 2: Study Population Characteristics
Young Older P-value
Subjects Subjects
N=19 N=19
25±2 64±4 <0.001
10 15 0.09
Age (range)
Gender
Female
Male
Ethnicity
Hispanic
Non-Hispanic White
Asian Pacific Islander
History of Diabetes
Hypertension
History of Smoking
Body Composition
Weight (kg)
BMI
Total LBM (kg)
Appendicular LBM (kg)
Trunk Fat (kg)
Blood Counts and Chemistries
Hgb (g/dl)
White Blood Count (M/cm3 )
BUN (mg/dl)
AST (U/L)
Total Cholesterol (mg/dl)
Triglycerides (mg/dl)
HDL-cholesterol (mg/dl)
LDL-cholesterol (mg/dl)
9 4
4 17
4 2 <0.0011
11 0
0 5
0 12
0 0
70±15 75±12 0.053
25±4 29±4 0.005
50±11 44±10 0.08
23±6 18±5 0.09
7±4 16±5 <0.001
M il M il 0.63
6.4±2 9 .8 il6 0.37
14i3 15i5 0.28
29i26 25i9 0.51
186i36 217i42 0.02
75i45 169i77 <0.001
62±15 5 0 ill 0.009
109i33 132i39 0.06
'p-value from Fisher’s exact test
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Maximal Force Measurements
Table 3 summarizes the maximal force measurements for the
concentric and eccentric knee extension, knee flexion, and knee squat
exercises for Group I and Group II subjects. As indicated earlier,
maximum force was determined using the 1 repetition maximum (1-RM)
method (Johnson and Nelson 1974), which was assessed twice, 5 to 7
days apart. The higher of the two values was recorded (Table 3) to
account for any learning effects that may have influenced maximal effort.
For the parallel knee squat, the maximal strength assessment could not be
safely performed in the eccentric mode thus, only the concentric mode
was assessed.
Eccentric 1 -RM measures for the knee extension and flexion
exercise were approximately 20% greater than the concentric 1 -RM
measures. Thus, during the eccentric resistance exercise bout, subjects
were tested at approximately 50% of their maximal eccentric force, which
was 65% of their maximal concentric force.
Finally, Table 3 shows that when comparing the differences in 1-
RM between young and older subjects, maximal eccentric forces were
significantly higher (approximately > 23%) in the young subjects, for the
three exercises (knee extension, knee flexion and parallel knee squat).
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Table 3: Maximal Force Measurements
Young
Subjects
N=19
Older
Subjects
N=19
P-value
Knee Extension Bouts
Left Leg
1-RM concentric (N2 )
440±87 325±85 <0.001
1-RM eccentric (N) 540±110 400±120 <0.001
p-value3 <0.001 <0.001
Right Leg
1-RM concentric (N) 447±90 288±81 <0.001
1 -RM eccentric (N) 551±117 380±162 <0.001
p-value <0.001 0.02
Knee Flexion Bouts
Left Leg
1-RM concentric (N) 274±64 211±49 0.002
1-RM eccentric (N) 326±94 270±78 0.050
p-value <0.001 <0.001
Right Leg
1-RM concentric (N) 295±68 213±53 <0.001
1-RM eccentric (N) 348±94 264±72 0.004
p-value <0.001 <0.001
Parallel Knee Squat Bouts
1-RM concentric (lbs) 207±81 149±35 0.008
1= difference between young and older subjects
2= Newtons
3= difference between concentric and eccentric modes
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41
Metabolic Outcomes
Knee Extension/ Flexion Exercise Bouts
The metabolic outcomes for knee extension and knee flexion bouts tested on
an isokinetic dynamometer are shown in Tables 4 and 5, respectively, and Figures 3
and 4, respectively. For both the older and younger and subjects, V 02 ml/min
(absolute), V 02 ml/min/kg (relative), YC02 L/min, and VE L/min btps were
significantly less for the eccentric resistance training bouts than the concentric
resistance training bout. These metabolic measures were significantly greater in the
younger subjects when compared to older subjects (Tables 4, 5 and Figure 3) for
both the ECC and CON exercise bouts, consistent with the greater maximal force
measures achieved by the young subjects (Table 3).
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Table 4: Metabolic Outcomes for Knee Extension
Eccentric
N=19
Concentric
N=19
P-value1
V 0 2 ml/min
Older 230±68 363±93 <0.001
Young 320±97 594±201 <0.001
p-value2 0.02 <0.001
VO2 ml/min/kg
Older 3.1±1.0 5.0±1.5 <0.001
Young 4.7±1.0 8.5±2.3 <0.001
p-value <0.001 <0.001
V C 02 L/min
Older 2.3±0.7 3.6±0.9 <0.001
Young 3.2±1.0 6.0±0.2 <0.001
p-value 0.004 <0.001
VE btps L/min
Older 8.0±2.0 11.9±3.2 <0.001
Young 11±3.5 20.3±6.8 <0.001
p-value 0.005 <0.001
1= difference between eccentric and concentric modes
2= difference between older and young subjects
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Table 5: Metabolic Outcomes for Knee Flexion
Eccentric
N=19
Concentric
N=19
P-value1
VO2 ml/min
Older 269±73 408±104 <0.001
Young 331±96 609±217 <0.001
p-value2 0.03 <0.001
VO2 ml/min/kg
Older 3.6±1.1 5.2±1.7 <0.001
Young 5.2±1.7 8.6±2.4 <0.001
p-value <0.001 <0.001
V C 02 L/min
Older 3.0±0.8 4.1±1.1 <0.001
Young 3.3±1.0 6.3±2.3 <0.001
p-value 0.06 <0.001
VE btps L/min
Older 9.0±2.4 12.6±4.0 <0.001
Young 11.5±3.1 20.2±7.0 <0.001
p-value 0.009 <0.001
1= difference between eccentric and concentric inodes
2= difference between older and young subjects
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44
1200i
Eccentric Q Concentric
Older
Young older
> 400-
Knee Extension
* p<0.05 different from eccentric exercise
f p<0.05 different from younger subjects in sam e exercise mode
Knee Flexion
Figure 3: Change in V 02 during Exercise Bouts
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45
Knee Extension and Flexion Exercise Bouts Corrected for Age Related
Appendicular LBM
Differences in metabolic measures in young and older subjects were
evaluated to determine if differences in muscle mass between the groups could
explain the effects of age. Therefore, skeletal muscle mass was assessed by DEXA
scanning to determine appendicular LBM, which is primarily comprised of muscle
tissue. As shown in Table 2, appendicular LBM mass was significantly less in older
than younger subjects. Figure 4 shows that after correcting for appendicular LBM,
V 02 measures for the knee extension and knee flexion remained significantly
different between the eccentric and concentric bouts. The relative magnitude of the
V 02 measures for the different bouts was very similar to the measures of absolute
V 02 without correction for appendicular LBM (compare Figures 3 and 4).
However, there were no significant differences between young and older subjects
after correcting for appendicular LBM, indicating that age differences, as shown in
Figure 3, may be accounted for by the differences in the amount of extremity muscle
mass in the two age groups.
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V02 ml/min/App. LBM
46
Eccentric [ | Concentric
Older
Older
Knee Extension K nee Flexion
p<0.05 different from eccentric exercise
Figure 4: Change in V 02 corrected for appendicular LBM
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47
Knee Extension and Flexion Exercise Bouts Corrected for Age Related
Work
In addition, differences in metabolic measures in young and older subjects
were evaluated to determine if differences in work (= force x distance) between the
age groups could explain the effects of age on the ventilatory measures. Work
during these exercises was tightly controlled by testing on an isokinetic
dynamometer, which controls force and distance. Thus, it was possible to preset
work performed during the eccentric and concentric bouts of the knee extension and
flexion on the dynamometer to be identical for a given subject.
Work performed during the testing bouts on the isokinetic dynamometer for
these two exercises was based on the measures of maximal force measurements,
namely the 65% of 1-RM (Table 3). Figure 5 shows that after correcting for work (at
65% of the 1-RM), V 02 measures for the knee extension and knee flexion remained
significantly different between the eccentric and concentric bouts. However, there
were no significant differences between young and older subjects after correcting for
work, indicating that the significant age differences in V 02, as shown in Figure 3,
may be in part be accounted for by the differences in the amount of work performed
in the two age groups. This data together with calculations as shown in Figure 4
indicate that differences in ventilatory measures between the age groups for both the
eccentric and concentric exercise bouts were to a large measure due to differences in
muscle mass and differences in the work performed in the two age groups.
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K n e e E x t e n s i o n K n e e F l e x i o n
* p<0.05 different from eccentric exercise
Figure 5: Change in V 02 corrected Work (65% of 1-RM)
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49
Parallel Knee Squat Bouts
Parallel knee squats were performed on a modified Smith rack. Similar to the
knee extension and knee flexion isokinetic exercises performed on the KinCom
dynamometer, V 02 ml/min, V 02 ml/min/kg, VC02 L/min, and VE btps L/min were
significantly less for the eccentric exercise bouts when compared to the concentric
exercise bouts during the parallel knee squats (Table 6 and Figure 6a). In addition,
as with the knee exercises, these metabolic outcomes were significantly greater in the
younger than older subjects.
To evaluate the metabolic measures needed to lift and lower the body weight
during the parallel knee squat exercise; subjects performed a squat exercise set using
both concentric and eccentric muscle actions without an external load. The
body weight “only” squats resulted in metabolic measures that were 77-91 % of the
eccentric and 58-65% concentric bouts with a fixed external load (Table 7). Thus,
body weight contributed a smaller portion of the metabolic response for the
concentric exercise bouts than the eccentric bouts.
In addition, similar to the knee extension and knee flexion exercises (Figure
6a), when the parallel knee squat measures were corrected for appendicular LBM,
there were no significant differences between young and older subjects for V 02
ml/min/App. LBM (Figure 6b). This suggests that the significant differences
between eccentric and concentric parallel knee squats were due to the amount of
extremity muscle mass and not the age of the subjects.
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Table 6: Metabolic Outcomes for Parallel Knee Squat
(Eccentric vs Concentric)
Eccentric
N=19
Concentric
N= 19
P-value1
VO2 ml/min
Older 452±131 588±147 <0.001
Young 642±193 881±224 <0.001
p-value2 <0.001 <0.001
VO2 ml/min/kg
Older 6.1±1.6 8.0±2.2 <0.001
Young 9.2±1.6 12.5±1.9 <0.001
p-value <0.001 <0.001
VC02 L/min
Older 4.6±1.3 6.1±1.5 <0.001
Young 6.2±1.9 8.9±2.6 <0.001
p-value 0.003 <0.001
VE btps L/min
Older 13.5±3.6 18.9±5.1 <0.001
Young 18.4±5.1 27.6±7.6 <0.001
p-value 0.002 <0.001
1= difference between eccentric and concentric modes
2= difference between young and older subjects
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Table 7: Metabolic Outcomes for Parallel Knee Squat
(Bodyweight only vs Load)
Bodyweight1 Eccentric Concentric
VO2 ml/min
Older 349±101 452±131 (77%)2 588±147 (58%)2
Young 546±162 642±193 (85%) 881±224 (60%)
p-value3 <0.001 <0.001 <0.001
VO2 ml/min/kg
Older 4.8±1.4 6.1±1.6 (79%) 8.0±2.2 (60%)
Young 8.4±1.9 9.2±1.6 (91%) 12.5±1.9 (65%)
p-value <0.001 <0.001 <0.001
VC 02 L/min
Older 3.8±1.1 4.6±1.3 (83%) 6.1±1.5 (62%)
Young 5.3±1.8 6.2±1.9 (85%) 8.9±2.6 (60%)
p-value 0.006 0.003 <0.001
VE btps L/min
Older 11.8±3.2 13.5±3.6 (87%) 18.9±5.1 (61%)
Young 16.0±4.5 18.4±5.1 (87%) 27.6±7.6 (58%)
p-value 0.006 0.002 <0.001
1= no added weight to Smith rack
2= percentage of metabolic measures comparing force from bodyweight to a fixed
external load (e.g. from eccentric and concentric)
3= difference between older and young subjects
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Eccentric □ Concentric
1400 ■
o o o -
f 800
9 600 -
Parallel Knee Squat
* p<0.05 different from eccentric exercise
*p<0.05 different from younger subjects
Figure 6a: Change in V 02 (absolute) during Parallel Knee Squats
8
Eccentric □ Concentric
m 5 ■
CL
t «•
E
CM
r
Young
_ A _
r
Older
A
Parallel Knee Squat
p<0.05 different from eccentric exercise
Figure 6b: Changes in V 02 during Parallel Knee Squats corrected for
appendicular LBM
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53
Cardiovascular Outcomes
Knee Extension Bouts:
Changes in heart rate for knee extension from rest to maximal measures were
significantly (p<0.05) lower for the eccentric and concentric modes (Table 8). In
addition, the older subjects had higher heart rates at both baseline and maximal
values. Changes in heart rate were significantly greater in the younger compared to
the older subjects (Figure 7).
Systolic BP, DBP, Cl, and RPP measures increased significantly from
baseline to maximal measures for both groups (Table 8). When comparing age,
these measures were greater for the older than young subjects with several
exceptions. Systolic BP’s at maximum concentric testing and at baseline for
eccentric testing were not different for the two age groups (Table 8). For Diastolic
BP’s, there were no age related differences for either exercise mode.
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Table 8: Cardiovascular Outcomes for Knee Extension
Young
Subjects
N= 19
Older
Subjects
N= 19
P-value1
Heart Rate2
Concentric
Baseline 67±16 82±14 0.003
Maximum 98±18 124±19 <0.001
- 3
p-value <0.001 <0.001
Eccentric
Baseline 64±8 72±11 0.01
Maximum 78±15 90±11 0.006
p-value <0.001 <0.001
SBP (minlig)
Concentric
Baseline 118±15 127±13 0.01
Maximum 145±9 147±13 0.60
p-value <0.001 <0.001
Eccentric
Baseline 113±7 118±15 0.2
Maximum 116±6 125±19 0.08
p-value <0.001 0.05
DBP (mmHg)
Concentric
Baseline 76±7 79±4 0.1
Maximum 80±7 81±4 0.73
p-value 0.004 0.003
Eccentric
Baseline 75±5 75±5 0.8
Maximum 76±5 77±5 0.95
p-value 0.005 0.02
1= difference between young and older subjects
2= beats per minute
3= within group change
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Table 8: Cardiovascular Outcomes for Knee Extension
(continued)
Young
Subjects
N=19
Older
Subjects
N=19
P-value1
Cardiac Index
Concentric
Baseline 5.1±1 4.6±0.3 0.003
Maximum 9.0±2 6.8±1 <0.001
p-value <0.001 <0.001
Eccentric
Baseline 4.8±0.4 5.0±0.3 0.004
Maximum 6.1±0.7 5.4±1.0 <0.001
p-value <0.001 <0.001
Rate Pressure Product
Concentric
Baseline 83±11 103±23 0.002
Maximum 146±32 183±35 0.002
p-value <0.001 <0.001
Eccentric
Baseline 75±13 79±12
Maximum 102±25 109±16
p-value <0.001 <0.001
1= difference between young and older subjects
2= within group change
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56
Knee Flexion Bouts:
Similar to the knee extension exercise, increases in heart rates from rest to
maximum measures were significantly lower (p<0.001, for each comparison) for the
eccentric and concentric modes for the knee flexion bouts (Table 9). In addition, the
older subjects had higher heart rates at both baseline and maximum values, although
p= 0.07 when comparing eccentric maximum values. Changes in heart rate were
significantly greater in the younger subjects compared to the older subjects (Figure
7).
Systolic BP, DBP, Cl and RPP increased significantly from baseline to
maximum measures for both groups (Table 9), although p= 0.08 for change in DBP
during the eccentric mode in young subjects. When comparing age, values for these
parameters were greater for the older than younger subjects with a few exceptions.
Systolic BP at maximum concentric testing, DBP for maximum concentric and both
time points for eccentric testing, Cl at maximum measures for the eccentric mode,
and RPP at both time points for the eccentric mode were similar for both age groups.
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Table 9: Cardiovascular Outcomes for Knee Flexion
Young Older P-value1
Subjects Subjects
N=19 N=19
Heart Rate2
Concentric
Baseline 67±17 82±23 0.03
Maximum 101±22 129±17 <0.001
p-value3 <0.001 <0.001
Eccentric
Baseline 64±7 73±11 0.005
Maximum 86±14 94±12 0.07
p-value <0.001 <0.001
SBP (mmHg)
Concentric
Baseline 123±9 131±4 0.04
Maximum 146±15 147±1 0.80
p-value <0.001 0.01
Eccentric
Baseline 113±6 124±19 0.03
Maximum 116±7 125±19 0.07
p-value <0.001 <0.001
DBP (mmHg)
Concentric
Baseline 75±8 80±4 0.02
Maximum 80±7 83±7 0.10
p-value <0.001 <0.001
Eccentric
Baseline 74±8 75±5 0.72
Maximum 76±5 79±11 0.45
p-value 0.08 <0.001
1= difference between young and older subjects
2= beats per minute
3= within group change
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Table 9: Cardiovascular Outcomes for Knee Flexion
(continued)
Young
Subjects
N= 19
Older
Subjects
N= 19
P-value
Cardiac Index
Concentric
Baseline 5.2±1 4.7±.3 0.001
Maximum 8.3±1
7.0±1 <0.001
p-value <0.001 <0.001
Eccentric
Baseline 4.8±.3 4.5±0.2 0.009
Maximum 6.4±0.7 6.0±0.7 0.06
p-value <0.001 <0.001
Rate Pressure Product
Concentric
Baseline 85±13 109±25 <0.001
Maximum 161±40 195±3 <0.001
p-value <0.001 <0.001
Eccentric
Baseline 80±17 83±13 0.56
Maximum 107±23 108±16 0.89
p-value <0.001 <0.001
1= difference between young and older subjects
2= within group change
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59
Parallel Knee Squat Bouts:
There were significant differences (p< 0.003) between baseline and maximal
measures for all cardiovascular measurements (Table 10). Both young and older
subjects had similar responses for the parallel knee squat exercise. However, the
older subjects had a greater response (p< 0.05) to the parallel knee squat than the
young subjects for all the cardiovascular measures. Similar to the knee extension
and knee flexion exercise, the BP responses were not significantly different between
the young and the older subjects.
Overview of Cardiovascular Changes for the Three Exercises:
For the three exercises, knee extension, knee flexion, and parallel knee
squats, there were significantly lower responses in the eccentric resistance exercise
bouts compared to the concentric resistance exercise bouts; however, the squat
exercise elicited the largest changes in response (Figures 7-10). The only significant
differences between young and older subjects occurred during the concentric
resistance exercise bouts for SBP and Cl for the three exercises (Figures 7-10).
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Table 10: Cardiovascular Outcomes for Parallel
Knee Squats
Young Old P-value
Subjects Subjects
N= 19 N= 19
Heart Rate2
Concentric
Baseline 62±26 68±22 0.004
Maximum 116±24 155±16 <0.001
p-value3 <0.001 <0.001
Eccentric
Baseline 68±6 68±10 0.02
Maximum 98±14 119±10 <0.001
p-value <0.001 <0.001
SBP (mmHg)
Concentric
Baseline 121±13 130±16 0.043
Maximum 157±14 152±12 0.21
p-value <0.001 <0.001
Eccentric
Baseline 116±8 120±10 0.37
Maximum 122±18 128±8 0.27
p-value <0.001 <0.001
DBP (mmHg)
Concentric
Baseline 74±9 78±4 0.06
Maximum 81±4 82±4 0.49
p-value <0.001 0.003
Eccentric
Baseline 75±5 76±5 0.70
Maximum 77±5 78±5 0.54
p-value <0.001 <0.001
1= difference between young and older subjects
2= beats per minute
3= within group change
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Table 10: Cardiovascular Outcomes for Parallel
Knee Squats (continued)
Young
Subjects
N= 19
Old
Subjects
N= 19
P-value
Cardiac Index
Concentric
Baseline 5.4±0.4 4.8±0.5 <0.001
Maximum 12±1.5 9.2±2.4 <0.001
p-value <0.001 <0.001
Eccentric
Baseline 5.0±0.3 5.0±0.3 <0.001
Maximum 10±2 7.8±2 <0.001
p-value <0.001 <0.001
Rate Pressure Product
Concentric
Baseline 78±25 111±28 <0.001
Maximum 178±38 235±35 <0.001
p-value <0.001 <0.001
Eccentric
Baseline 75±14 81±14 0.18
Maximum 133±32 149±17 0.06
p-value <0.001 <0.001
1= difference between young and older subjects
2= within group changes
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62
10Ch
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20-
10-
EccentricD C oncentricB
Young Older
Young Older Young Older
m i
Knee Extension Knee Flexion Knee Squat
' p<0.05 different from eccentric exercise
FIGURE 7: Change in Heart Rate
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
45i
40-
EccentricQ Concentric | Young Older
p
Young Older Young Older
D) 3 5
c 1 5
c 10
I I
Knee Extension Knee Flexion Knee Squat
p<0.05 different from eccentric exercise
t p<0.05 different from young subjects
FIGURE 8: Change in Systolic Blood Pressure
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Change i n D B P (mmHg)
64
10
Eccentric [ ] Concentric |
g . Young older Young Older
Young Older
, 1 1
Knee Extension
‘ p<0.05 different from eccentric exercise
Knee Flexion Knee Squat
FIGURE 9: Change in Diastolic Blood Pressure
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Change i n Cardiac In d ex (Q/ht2 )
65
10
9
8
7
6
5
4
3
2
1
0 - I —
Eccentric G Concentric
Young 0 |der
Young older
K _
Young 0 |der
< \r
■ i ■ i
Knee Extension Knee Flexion Knee Squat
p<0.05 different from eccentric exercise
tp<0.05 different from younger subjects in same exercise mode
FIGURE 10: Change in Cardiac Index
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140
120
Q.
O H
< D 0
O)
C
S O H
o
20 ■
Eccentric □ Concentric |
Young Older Young 0|der
Young Older
I I
Knee Extension
p<0.05 different from eccentric exercise
I I
Knee Flexion Knee Squat
FIGURE 11: Change in Rate Pressure Product
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67
Electromyography during Parallel Knee Squats
Electromyography (EMG) pilot data was collected for four subjects (2 male,
2 female) who performed parallel knee squats on the modified Smith rack. Figure 12
shows representative tracings from one of the four subjects. For the four subjects,
EMG tracings of the rectus femoris muscle illustrate (Figure 12) that there was 58%
less muscle motor unit activation for the eccentric squat (RMS = 1 lOpV) than the
concentric squat (RMS = 190pV) at the same work load for both bouts (65% of the
concentric 1-RM); (Figure 12).
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6 8
£
o
>
o
>
CONCENTRIC
ECCENTRIC
1 301 601 901 1201 1501 1801 2101 2401 2701 3001 3301
m illis e c o n d s FIGURE 12: Raw EMG during Parallel Knee Squat
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69
CHAPTER V
DISCUSSION
Significance of Outcomes
Prior studies have indicated that eccentric resistance training using an
overload model may be a more efficient method to increase skeletal muscle cross-
sectional area and volume, muscular strength and physical performance compared to
concentric resistance training (Bigland-Ritchie and Woods 1973; Bigland-Ritchie
and Woods 1976; Hesser, Linnarsson et al. 1977; Pahud, Ravussin et al. 1980;
Lindstedt, LaStayo et al. 2001; Meyer, Steiner et al. 2003). However, there is
limited information about the physiological and cardiovascular effects of an
eccentric resistance exercise bout compared to a traditional resistance exercise
(involving concentric contractions) bout. The current study was, therefore, designed
to investigate the measures of energy expenditure in single bouts of three different
eccentric resistance exercises (knee extension, knee flexion, and parallel knee squat)
compared to single bouts of the same concentric resistance exercises, which are
traditional components of progressive resistance training regimens. Moreover, this is
the first study to examine the effects of eccentric resistance exercises at a
submaximal workload (65% of concentric 1-RM). The importance and relevance of
the results of this project are discussed in this chapter according to the specific aims
of the proposal.
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70
Specific Aim 1: Determine if V 02, VC02, and VE are different during a single
eccentric and single concentric resistance exercise bout at the same workload.
In summary, for specific aim #1, the average volume of oxygen consumed
(V02), carbon dioxide produced (VC02), and total expired ventilation (VE) was
significantly less (p<0.001) for the eccentric than the concentric resistance exercise
bouts for the three exercises. For the knee extension, knee flexion and parallel knee
squat exercises, V 02 during the eccentric resistance exercise bouts were
approximately 30 to 50% lower than during the concentric resistance exercise bouts
in both young and older subjects. When these results were corrected for
appendicular lean body mass (LBM), which is primarily comprised of muscle mass,
there were no differences between age groups, suggesting that the difference in
appendicular LBM, which was lower in the older subjects, maybe responsible for the
significant differences observed for V 02 between the age groups.
The greater V 02 consumed during the concentric resistance exercise bout
indicates that more energy was required to perform the same amount of work as
during the eccentric resistance exercise bout. The concentric movements (active
shortening) of the muscle requires a larger number of actin-myosin cross-bridges to
be formed, which necessitates greater adenosine tri-phosphate (ATP) utilization
compared to eccentric movements at the same workload. In addition, elastic energy
is stored in the structural protein titin during eccentric contractions (Fry, Staron et al.
1997; Tskhovrebova and Trinick 1997; Tskhovrebova, Trinick et al. 1997). Thus, as
the muscle lengthens, the number of cross-bridges required is significantly less
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compared to the concentric contractions and likely explains the lower V 02 required
during the eccentric bouts.
Others studies have attempted to investigate the metabolic effects of eccentric
muscle contractions but have not directly measured the effects produced from pure
eccentric muscle actions during resistance exercise. Dudley et al. hypothesized that
the use of eccentric actions allows a person to double the resistance used during
training (compared to concentric actions alone), yet adds minimal additional energy
to the cost of the exercise (Dudley, Tesch et al. 1991). In brief, the investigators
randomized 17 subjects to perform either a combination concentric/eccentric
(CON/ECC) contractions (n=9) or a concentric only (CON) contractions (n= 8),
during supine knee squats, for 10-12 weeks. At the completion of training period,
caloric expenditure was similar for both the CON/ECC and CON exercise groups.
The investigators deduced that the contribution o f the eccentric actions to perform
the standard exercise movement (combination of eccentric and concentric muscle
actions) adds little to the energy expenditure of the resistance exercise compared to
the isolated concentric actions. These findings provide support for the hypotheses
that V 02 will be lower during the eccentric resistance exercise bout than during the
concentric resistance exercise bout. However, investigators did not measure
eccentric only contractions. Therefore, the eccentric muscle action was not directly
examined and was only hypothesized to contribute minimally to metabolic cost of
the combined muscle actions.
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72
The current study is the first to directly measure V 02, V C02 and VE before,
during and after exercise bouts of pure eccentric and pure concentric muscle
contractions. The eccentric and concentric muscle actions were separated by having
subjects perform eccentric only resistance exercise bouts and concentric only
resistance exercise bouts on different days. Moreover, subjects were randomized to
do either the eccentric or concentric exercise at the first session and the other type of
muscle contraction at the second bout. This was done to minimize the effects that
one type of muscle contraction may have on the response of the other type of muscle
contraction.
A number of studies that have examined the effects of a submaximal chronic
eccentric training stimulus during cycle ergometry. For example, LaStayo, et al.
studied the effects of low intensity training using locomotor muscles (Lastayo, Reich
et al. 1999; LaStayo, Pierotti et al. 2000). Fourteen male subjects (range 19-38 years
of age) were randomized to one of two groups; eccentric cycle ergometer group or a
concentric cycle ergometer group. Subjects trained five times a week for 30 minutes
at 65% of their peak heart rate. The subjects in both groups pedaled at the same
rpm’s (initially 50 and then 70 rpm’s by the 5 week of training) in order to achieve
and maintain the 65% peak heart rate (determined prior to study) for both the
eccentric and concentric groups. At the completion of the study, subjects training in
the eccentric mode were training at higher intensities than the concentric cycle
ergometer mode but were still training at the same relative heart rate percentage.
This study, which compared pure eccentric cycling to pure concentric cycling,
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73
showed that eccentric contractions were more metabolically efficient with lower
V02. However, this model was based on a modified cycle ergometer and “aerobic
exercise”, which is not an optimal exercise to augment muscle mass and strength as
is possible with the resistance exercises used in the current study.
The current study is based on the observation that aerobic eccentric exercises
are metabolically more efficient than concentric aerobic exercise (LaStayo, et al,
1998). The central premise of the current study was that the same principles would
hold true for eccentric and concentric resistance exercises. The submaximal
workloads for the two study groups were both set at 65% relative to the concentric 1-
RM so that the physiological effects could be examined at intensities previously
shown to improve muscle mass and function. The results showed that an eccentric
resistance exercise bout using typical resistance exercises is associated with
measures of lower energy expenditure compared to an identical bout of concentric
resistance exercise and consistent with the observations made by LaStayo on the
modified cycle-ergometer.
The classic eccentric exercise studies have used an overload model (exercise
intensities of 100% or greater relative to the concentric mode) for resistance training
(Higbie, Cureton et al. 1996; Hakkinen, Kallinen et al. 1998). This could raise
concern in the current study whether the exercise strategy was of sufficient intensity
to elicit favorable muscle adaptations for increased muscle strength, endurance, and
performance that could ultimately be used for training. The 65% load was based on
a body of literature that is summarized in Table 11, which illustrates the potential for
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74
muscle adaptations based on guidelines set forth by the American College of Sports
Medicine (Anonymous 1998; Kraemer, Adams et al. 2002). In the initial pilot study
before beginning the project, naive older subjects could not perform the proposed
bouts of three sequential sets at 70-80% of the 1-RM. Moreover, even younger,
naive exercise subjects could not perform the bouts at this level of intensity.
Because both groups were able to perform the bouts at 65% of the 1-RM and this
level of intensity has been validated to produce significant increases in muscle mass,
strength, and power (Table 11), this workload was selected for the current study.
Table 11: Summary of Resistance Training Recommendations by ACSM.
Mussle
Aetton S eM en Loading Volume
Strength
Nov.
Irrt.
A dv,
ECC & CON
E C C & C O N
ECC & CON
SJ&MJex,
SJ&MJex.
SJ & MJex, - emphasis: M J
60-70% of tffld
70-80% of 1RM
IBM - PER.
1-3 sets. 8-12 reps
M ult. Sets, 6-12 reps
Mult. Sets, 1-12 reps - PER .
Hypertrophy
N ov.
Int.
A dv.
ECCa CON
ECC a CON
ECC S CON
SJ & MJ ex,
SJ&MJex.
s j a mj
60-70% Of 1R M
70-80% Of 1R M
70-100% ol 1RM with emphasis on
70-85% - PE R
1-3 sets. 8-12 reps
M ult. Sets, 6-12 reps
Mult Sets, 1-12 reps with emphasis
on 6-12 reps - PE R
Poser
Nov.
int.
A dv.
ECC a CON
ECC a CON
ECC & CON
For Nov, Irrt. Adv:
Mostly M l
For Nov, Int. A dv:
Heavy toads (>80%) - strength;
Light (30*60%) - velocity - PER
Train for strength
1-3 sets, 3-6 reps
3-6 sets, 1-6 reps - PER
Endurance
Nov. ECC a CON SJ & MJ ex. m ~ n % of tRM 1-3 sets. 10-15 reps
Irtt.
A dv.
ECC a CON
ECC a CON
SJ & MJ ex.
s j a mj
50-70% Of 1R M
30-80% Of 1R M - PER
Mult, Sets. 10-15 reps or more
M ult. Sets, 10-25 reps or more - reft
ECC, eccentric; CON, concentric; Nov., novice; Int., intermediate; Adv., advanced; SJ, single
joint; MJ, multiple-joint; ex., exercises; HI, high intensity; LI, low intensity; 1RM, 1-repetition
maximum; PER., periodized.
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75
Contrary to the hypothesis of this study, some investigators have argued that
concentric training may produce greater adaptations than eccentric training
(Mayhew, Rothstein et al. 1995; Hakkinen, Kallinen et al. 1998). For example,
Mayhew et al., compared the effects of training with concentric and eccentric
contractions on fiber hypertrophy and isometric torque (Mayhew, Rothstein et al.
1995). Subjects were randomized to either perform concentric contractions of their
quadriceps at 90% of power output (near maximal intensity) relative to their
concentric maximal power output; the other groups performed eccentric contractions
at the same intensity thrice weekly for 12 weeks. At the completion of training, there
were significantly greater increases in type II fiber area and isometric torque
production in the concentric compared to the eccentric group. These results may be
expected since eccentric contractions produce 20-45% greater force than concentric
contractions when overload models are studied (Johnson, Adamczyk et al. 1976;
Dean 1988; Hather, Tesch et al. 1991; Mayhew, Rothstein et al. 1995; Higbie,
Cureton et al. 1996; Hortobagyi, Hill et al. 1996; Hakkinen, Kallinen et al. 1998;
Hortobagyi, Houmard et al. 1998; Hawkins, Schroeder et al. 1999; Lastayo, Reich et
al. 1999; Middleton and Montero 2004). The concentric groups may have had
greater adaptations based on the relatively greater stimulus in the concentric mode of
training when compared to the somewhat limited load in the eccentric group (under
loaded relative to potentially greater force capability with form of exercise), thereby
limiting the adaptations with eccentric training.
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76
The current study which investigated the effects of a load (65% relative to
concentric 1-RM) that is expected to elicit important functional adaptations
(Kraemer, Adams et al. 2002) and in fact showed eccentric resistance exercise was
metabolically more efficient based on lower values of V 02, V C02 and overall VE
compared to concentric bouts. Moreover, as will be discussed later, persons with
muscle wasting or sarcopenia may be able to train with less demands on the
cardiovascular system in the eccentric mode at this level of intensity but may not be
able to perform concentric based training regimens at the same intensity due to
increased cardiovascular risks.
Specific Aim 2: Determine if the HR, BP, Cl and RPP responses are lower with
eccentric versus concentric training during a single eccentric and single
concentric resistance exercise bout at the same workload.
The results showed that the cardiovascular responses (HR, BP, Cl and RPP)
to bouts of eccentric resistance exercises were significantly (p<0.05) less compared
to bouts of concentric resistance exercises for both the young and older subjects (the
same three exercises in the eccentric compared to the concentric modes). Similar
responses when comparing eccentric to concentric changes have been reported
following iso-kinetic testing. (Thompson 1971) For example, Thompson et al,
described HR, mean arterial BP and perceived exertion responses to submaximal iso
kinetic concentric and eccentric exercise at the same torque output. The subjects
(mean age 74.5±4.6yrs) performed two minute bouts of concentric and eccentric
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77
knee extensions at an intensity 50% of concentric peak torque. Their results showed
that mean arterial HR and RPP were significantly (p<0.01) greater after the
concentric bout than after than eccentric bout. However, in the current study the
changes in HR, DBP, and RPP response (Tables 9,11) were not different between
young and older subjects, while the changes in SBP was lower and Cl was higher in
the young group (Tables 7, 8,10) (P<0.05).
Similar changes in cardiovascular parameters in various age groups have
been attributed to the higher angular velocity (> 120 deg/s) during test modes.
(Horstmann, Martini et al. 1994) To account for this variable, the current study
employed a lower angular velocity (60 deg/s) for the isokinetic knee exercises. This
angular velocity was selected to allow subjects to perform equal number of sets and
repetitions in both the concentric and eccentric modes of training. A possible
explanation for the greater increases in SBP in the older subjects may be the result of
inherent peripheral vascular disease (PVD) that frequently occurs in this age group.
With aging, there is an increase in peripheral vascular pressure in response to
exercise causing greater increases in SBP compared to younger subjects (Schulman
1999). However, accurate BP measurements during dynamic exercise are
problematic when BP is measured manually (Griffin, Robergs et al. 1997) and,
therefore, intra-arterial measures of BP would be necessary to validate the
differences in BP responses that were observed during the current study.
The significance of this study is that at equal torques (relative to concentric 1-
RM) for both the eccentric and concentric modes of exercise, the eccentric bouts
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78
resulted in significantly less stress on the cardiovascular system as reflected by
smaller increases in HR, BP, Cl, and RPP.
Because existing evidence suggests that muscle adaptations are superior with
eccentric exercise with an overload compared to a standard concentric training mode
(Higbie, Cureton et al. 1996; Hakkinen, Kallinen et al. 1998; Hortobagyi, Houmard
et al. 1998; Hortobagyi 2003) and because workloads of 65% of the 1-RM produce
significant increases in muscle mass, strength, and power (Table 11) (Kraemer,
Adams et al. 2002), eccentric training at the same submaximal load evaluated in this
study should produce greater benefits and be less stressful to the cardiovascular
system in older than with concentric based exercise regimens. Thus, the results of
the current study suggest that eccentric training of populations with muscle wasting
or sarcopenia and who have cardiopulmonary limitations should produce greater
benefits in physical function and be safer for the cardiovascular system. Moreover,
because of the greater stresses placed on the cardiovascular system with concentric
exercise, it is possible that patients with serve cardiopulmonary limitations may not
be able to tolerate concentric based exercises even at 65% of the 1 -RM.
Meyer et al. tested the hypotheses that eccentric exercise could be an
attractive alternative to traditional resistance exercise for patients with limited
cardiovascular exercise tolerance. (Meyer, Steiner et al. 2003) These investigators
evaluated cardiovascular tolerance of eccentric exercise in 13 subjects with coronary
artery disease (ages 40-66 years) with mild in reduced left ventricular function.
Subjects were randomized to an eccentric training group or a concentric training
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79
group for eight weeks. One group trained on an eccentric cycle ergometer in the
sitting position. The concentric group trained concentrically on a standard cycle
ergometer. Both groups of subjects trained three times a week for 30-minutes at
intensities approximately 85% of peak HR determined at baseline. Central
hemodynamic measures (arteriovenuos oxygen difference, stroke volume) were
obtained during right heart catherization. Subjects were able to train at a higher
power output during the eccentric than the concentric modes of training (357± 96 W
versus 97± 21W, respectively; P<0.005). After eight weeks of training there was a
significant increase in left ventricular ejection fraction for the eccentric group
(P<0.05). These investigators showed that subjects who trained in the eccentric
mode were able to generate almost four times the exercise power output compared to
the concentric group, while at the same time demonstrating that there was a
significant lower oxygen requirement in the eccentric group. Although these
catheterization findings validate the metabolic and peripheral cardiovascular findings
of the current study, the method of exercise, namely, cycle ergometry, as indicated
earlier, is not optimal for rehabilitation where significant increases in muscle mass,
strength, and power are necessary. However, resistance exercise, especially the
eccentric component, may be better suited to achieve these rehabilitation goals.
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80
Specific Aim 3: Determine if ventilatory and cardiac responses are different in
younger subjects (21-30 years of age) than older subjects (60-80 years of age)
and according to gender during a single eccentric and single concentric
resistance exercise bout at the same workload.
In the current study, ventilation changes (V 02, VC02, and VE) were greater
in the young subjects than the older subjects’ for both the eccentric and concentric
bouts of the three resistance exercises (Tables 4-6) (P<0.05). However, the changes
in ventilation, as shown for V 02 in Figure 4, when corrected by appendicular LBM
(which is primarily composed of muscle) were not significantly different for the two
age groups. This suggested that differences in extremity muscle mass between the
two age groups were in part responsible for the absolute differences (p<0.05) of V 02
as shown in Tables 4 and 5.
In addition, the exercise bouts in the young group were performed at higher
levels of work since their maximal strength measurements were significantly greater
(p<0.05) than the older subjects for the three exercises (table 3). Thus, when
exercises were performed at 65% of the 1-RM for the exercises, subjects in the
younger group worked at a higher absolute workload. When V 02 measures were
corrected for absolute work (65% of 1-RM strength), there were no statistical
differences in V02 for both exercises for the two age groups, consistent with the
findings when V 02 was corrected for appendicular LBM. Therefore, greater muscle
mass and greater workload in the young group was largely responsible for
differences in oxygen utilization between the young and older subjects.
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81
In the current study, it was hypothesized (null hypothesis) that changes in
cardiac responses to eccentric versus concentric skeletal muscle contractions would
not vary by gender or age. The results showed that there were no gender differences
within the young and older subjects or for the 38 subjects in their entirety. Whereas,
the cardiovascular changes from baseline (HR, SBP, Cl, and RPP) were generally
greater in the older subjects compared to the younger subjects (Table 8-10) (P<0.05).
Differences in cardiovascular responses between age groups may have been
due to a number o f factors in the older subjects including cardiopulmonary
limitations, differences in skeletal muscle architecture, insulin resistance and
endothelial dysfunction. Age related changes that traditionally impair cardiac and
lung function in older subjects such as decreased cardiac stroke volume and
diminished pulmonary function may limit oxygenation as described in Chapter II.
These factors would require greater heart rate responses in older persons to deliver
similar oxygen content to tissues such as skeletal muscle to perform similar amounts
of work.
In addition, there were ethnic-racial differences between the age groups. In
particular, only four of 19 subjects in the young group were Hispanic compared to 17
of 19 in the older group. Hispanics traditionally are at increased risk for insulin
resistance (Bonoro, Kiechel et al. 1997). Indeed, five of the subjects in the older
group already had type II diabetes. In addition, 12 of the 19 had hypertension and
hypertension is closely linked to insulin resistance (Reaven 1991). Thus, at least 17
of the 19 subjects in the older group had clinical manifestations consistent with
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82
underlying insulin resistance. Moreover, insulin resistance is also tightly linked with
endothelial dysfunction, which manifests as decreased capacity of large arteries to
dilate (e.g. diminished brachial reactivity) and peripheral arteriolar resistance due to
diminished nitric oxide dependent and independent dilatation (Stein, Dobbins et al.
1997). Thus, even though hypertension may have been controlled in the older study
subjects, it is not surprising that blood pressure would increase greater in this group
if they indeed had endothelial dysfunction even though the workload was less than
for the younger group as the heart attempts to deliver oxygen to the tissues during
exercise.
Older individuals have greater intramyocellular lipid (IMCL), which is also
associated with increasing insulin resistance. O f importance, the quantity of IMCL
is linked with decreased transport of GLUT 4 to the muscle cell membrane (Ellis,
Poynten et al. 2000; McGarry 2002) thereby inhibiting transport of blood glucose to
the intracellular space, and thereby limiting this source of fuel during exercise in
older persons. How exactly this would affect heart rate and delivery of oxygen to
tissues is unknown but certainly would be expected to affect cardiovascular
measures. Other structural, biochemical, and genetic differences of older muscle
such as decreased type II muscle fibers (as may occur with de-innervation atrophy),
decreased capillary density, and changes in mitochondrial number, size and enzymes
may further contribute to the greater cardiovascular responses (refs). Future studies
will be necessary to understand the effects of each of these variables on the
metabolic response to eccentric resistance exercise in older persons.
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83
Previous investigators evaluating eccentric resistance training in healthy
older subjects and have demonstrated that the cardiovascular effects were relatively
safe in this population (Hakkinen, Kallinen et al. 1998; Hortobagyi and DeVita
2000). Hortobagyi, et al suggested that the importance of eccentric contractions
(overload model) is to achieve rapid strength gains at low cardiovascular stress in
elderly subjects. These investigators compared seven days of eccentric overload
training to standard resistance training on strength, cardiovascular stress and muscle
activation in 30 elderly women (ages 71 ±4.8 years) who had not exercised more than
once a week during the previous three years. Both training groups significantly
raised their HR, MAP (mean arterial pressure), RPP, and Rate of Perceived Exertion
(RPE). However, the standard exercise group had a 12-beat greater HR response to
exercise than the eccentric overload group (P<0.05) and their HR’s remained
elevated by nine beats/ minute after recovery (P<0.05). The MAP was also greater
in the standard exercise group by 15 mmHg (P<0.05) and remained higher by 11
mmHg in recovery (P<0.05) compared to the eccentric overload group. Both the
RPP and RPE were consistently higher in the standard groups (P<0.05); however,
RPE was similar in recovery. This latter Study further supports the hypotheses that
cardiac responses are lower during eccentric than concentric exercise.
The current study produced cardiovascular responses results similar to those
of Hortobagyi et al but those studies were conducted at a workload of 90% and XXX
% of the eccentric 1-RM for the eccentric and concentric exercise tests (Hortobagyi
and DeVita 2000). The primary differences are that the current project evaluated the
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84
response to submaximal workloads in the eccentric phase necessary to elicit muscle
adaptation (increases in hypertrophy, strength, and performance) (Schroeder,
Hawkins et al. 2004; Pachalis, Koutedakis et al. 2005) that should be better tolerated
by frail or impaired individuals compared to training at higher workloads.
Specific Aim 4: Obtain pilot data on the feasibility of determining if fewer
motor units are activated with eccentric contractions versus concentric
contractions at the same workload.
When a contracted muscle is stretched by an external force, potential energy
is temporarily stored in the series of elastic components of the activated muscle. The
large potential energy residing in the actin-myosin cross-bridges during eccentric
stretch are most likely responsible for this additional potential (elastic) energy
(Huxley, Reconditi et al. 2003). Studies utilizing overload models and exercise
cycles have demonstrated that this energy may be utilized to increase the mechanical
energy output during the subsequent muscle contractions (Cavangna, Dusman et al.
1968; Asmussen 1974). Thus, eccentric contractions are associated with
conceptually higher mechanical efficiency and submaximal resistance exercise
should produce lower EMG activity than concentric contractions as demonstrated
with these other forms of exercise (Davies and Barnes 1972; Asmussen 1974; Komi
1984).
Therefore, to assess the feasibility of measuring motor unit activation for
both pure eccentric and pure concentric muscle contractions during vigorous parallel
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85
knee squats, surface EMG was measured in a subset of four subjects (Figure 12).
The resulting EMG pilot data showed in each subject that during the eccentric
parallel knee squat, there was lower EMG activity compared to the concentric
parallel knee squat (Figures 12). This lower EMG response during the eccentric
mode supports the hypothesis that there is greater efficiency of the muscle
contraction as a result of the eccentric muscle actions during exercise bouts at
submaximal loads (65% concentric 1 -RM).
A number o f other studies that have demonstrated similar lower motor unit
activation during eccentric contractions for different types of exercises (Cavangna,
Dusman et al. 1968; Komi 1984; Higbie, Cureton et al. 1996; Hortobagyi, Hill et al.
1996; Hakkinen, Kallinen et al. 1998) but not resistance forms o f exercise at
submaximal loads. Moritani et al. investigated the motor unit activity of the biceps
brachii in 12 men during isokinetic eccentric and concentric contraction (Moritani,
Muramatsu et al. 1987). The purpose of that study was to determine the quantitative
and qualitative differences in motor unit recruitment and rate coding patterns during
a single elbow flexion (concentric) and extension (eccentric) contraction. Both
surface and intramuscular EMG tracings demonstrated greater electrical activity
during concentric contractions than during the eccentric contractions, e.g. 716±53.2
pV vs 439±40.2 pV, p<0.01 at a joint angle of 135 degrees. Also, mean motor unit
spike frequencies were significantly greater during concentric contractions at joint
angles of 45 degrees (12.7± 0.79 vs 10.4±0.68) and 135 degrees (16.1±1.1 vs
13.0±0.81 Hz, p<0.05), respectively. These observations are consistent with the pilot
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86
observations in this study of the larger lower extremity muscle groups that eccentric
contractions require substantially less motor unit activation to generate a given
tension compared to concentric contractions.
Perrey, et al., evaluated electromyographic activity from the vastus medialis,
rectus femoris, biceps femoris and medial gastrocnemius muscles during constant
load concentric and eccentric cycling (Perrey, Betik et al. 2001). In brief, to achieve
an equivocal EMG response with the eccentric and the concentric modes of exercise,
the eccentric mode needed a greater workload. Those results in concept are
consistent with the hypothesis that eccentric contractions allow greater economical
tension development than the concentric contractions, as supported by the very
preliminary observations of specific aim #4 in the current study.
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Clinical Implications
For physical therapists, exercise specialists, orthopedic surgeons, athletic
trainers and occupational therapists, the primary goal is to rehabilitate patients to
normal physical function or at the least to augment impaired function. Eccentric
resistance training may provide an optimal rehabilitation exercise modality. The
current study showed that eccentric contractions are metabolically more efficient and
less stressful to the cardiovascular system than concentric contractions at the same
workload. This is important since impaired patients often are only able to train at
very low intensities. This method of training may serve as the ideal modality for
populations with muscle wasting (i.e. from catabolic disease or aging) and frailty
who often also have cardiopulmonary disease (e.g. CHF, COPD). These individuals
should be able to train at submaximal intensities needed to stimulate improvements
in muscle mass and strength without the greater metabolic requirements typically
associated with traditional resistance training using primarily concentric muscle
contractions that could cause cardiopulmonary complications.
A major component to the rehabilitation process is motivation. Eccentric
training allows a patient to train at higher intensities, thereby enabling the patient to
perform more work and progress more rapidly. A patient’s mood and affect may
improve as a result of these improvements in function achieved even with low levels
of intensity that are possible with eccentric exercise, which may eventually result in
greater independence. Thus, training studies are needed to evaluate whether
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eccentric training is in fact associated with greater functional and psychological
benefits in frail persons and individuals with limited cardiopulmonary capacity.
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89
Potential Future Studies
Clinical Studies: Based on the results of this study, which showed that at equal
workloads, eccentric resistance bouts may be a better-suited mode of exercise for
physically impaired individuals (chronic lung disease, heart failure, HIV, cancer, and
the frail elderly etc.). However, before initiating a trial in these very impaired
patients, the next step, would be to conduct a prospective, longitudinal training study
in an ambulatory community dwelling population of relatively healthy men and
women greater than 65 years of age (Figure 13). The goal of such a study would be
to determine if, in fact, pure eccentric training at submaximal intensities produces
greater or at least comparable gains in muscle mass, strength, power, and function
and that the effects on the cardiovascular system are less stressful and therefore safer
than standard RT at the same workload. Such a study should be completed to
document the benefits for muscle adaptations and safety before a similar study is
performed in a more impaired population for example, older persons with CHF or
COPD. It would not be appropriate to expose these latter patients to risks until the
potential for clinically important muscle adaptations and benefits are established in
older subjects without disease or disability.
Subjects would be randomized to one of three groups: standard resistance
training that is based on concentric muscle contractions, eccentric only resistance
training or a control group (stretching only). The training intervention should be
conducted two or three times weekly for at least 12 weeks (Anonymous 1998;
Kraemer, Adams et al. 2002). The pre and post assessment measures would include
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90
dual x-ray absorptiometry (DEXA) or magnetic resonance imaging to assess lean
body mass, appendicular lean body mass, muscle mass and volume along with
measures of muscle strength, power measures and physical performance. In
addition, a number of functional tests such as sit to stand, six-minute walk, and the
Margaria power step test.
(Pre-Assessment)
Traditional Eccentric Controls
RT RT (Stretch Only)
12-16 wks
RT
t v
(Post -Assessment)
FIGURE 13: Potential Future Study
If such a study establishes that eccentric training produces greater benefits in muscle
mass, strength, and function in older, relatively healthy persons than traditional RT
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91
and is well tolerated, a similar study could be designed and performed in a more
impaired population with CHF or COPD.
Mechanistic Studies: Importantly, studies are also needed to investigate the
mechanisms whereby eccentric resistance exercise is metabolically more efficient
than concentric exercise. Existing data suggests that with eccentric skeletal muscle
contractions, V 02 requirements are less than with concentric contractions because
fewer actin-myosin cross bridges are generated due to the contribution of stored
potential energy in titin molecules during eccentric contractions. As a result of the
stored energy in titin molecules, mechano-energy efficiency is greater with eccentric
contractions. Preliminary data from this dissertation is consistent with the
hypothesis that activation o f fewer motor units are necessary to perform the same
workload with eccentric contractions, as shown in the surface EMG tracings in the
four subjects. If larger controlled studies confirm that there are in fact fewer motor
units activated during eccentric than concentric contractions at the same workload,
this will provide the justification for molecular studies of muscle tissue to explore
and better understand the mechanistic basis for the greater mechano-energy
efficiency with this form of exercise.
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92
Limitations
A major limitation of studies evaluating eccentric versus concentric
contractions of the same muscle groups are that there may not be equal forces
generated during the two different movements owing to different joint angles or
acceleration of the movements. Therefore, isokinetic dynamometry was selected to
assure equal forces and work during the knee extension and knee flexion exercises
for both the eccentric and concentric bouts. However, with the parallel knee squats,
forces (F = mass x acceleration) may not be similar if the speed (acceleration)
changed during the concentric versus eccentric bouts. However, attempts were made
to control for the speed (acceleration) of the movements by used of a metronome to
control the speed of the movements. The fact that the ventilatory and cardiovascular
outcomes showed comparable benefits for the eccentric bouts during the parallel
knee squat to those on the isokinetic dynamometer (where speed and workload
[mass] were constant) suggests that the findings for this exercise (where speed was
only partially controlled by the metronome) were most likely not seriously flawed by
potential differences in forces for the concentric and eccentric contractions.
Another potential limitation might be the racial and ethnic imbalances
between the young and older subject groups. It can be argued that the results should
not differ across different ethnic groups since ATP utilization and oxygen
consumption in skeletal muscle at the same relative workloads are expected to be
similar regardless of ethnicity (micro-array analyses of muscle tissue would be
necessary to confirm this speculation that ethnicity or race would not affect
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93
outcomes). However, it is possible that insulin resistance, which would affect energy
metabolism, is more common in Latinos and could have affected the outcomes in the
older subjects. Although subjects were screened for metabolic disorders such as
diabetes or hypo/hyperthyroidism, which may influence the metabolic outcomes,
future studies should control for differences in ethnicity. Finally, subjects were
screened for other underlying medical conditions that could have been associated up-
regulation of inflammatory cytokines. Thus, future studies should test subjects for
markers of inflammation, such as ultra sensitive C-reactive protein.
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CHAPTER VI
GLOSSARY OF TERMS
Appendicular LBM: sum of the lean body mass in the arms and legs (kg)
Baseline Measure: measurements at rest prior to the start of exercise
Bout: three sets of a particular exercise
EMG: motor unit activity o f the muscle (electromyography)
Group I: young subjects, age 21 to 30 years
Group II: older subjects, age 60 to 80 years
LBM: amount of total lean body mass (kg)
Maximal Measure: maximal measurements anytime during exercise bout
N: Newton of Force
Rpm: rotations per minute
Set: defined by the number o f repetitions (without rest period)
VC02: total amount of carbon dioxide produced in one minute
(ml/min)
V 02 (absolute): total amount of oxygen consumed in one minute (ml/min)
V 02 (relative): total amount of oxygen consumed in one minute (ml/min)
kilogram of bodyweight
W: Watts
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95
CHAPTER VII
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CHAPTER VIII
APPPENDIX A
HUMAN SUBJECTS
Description of Proposed Involvement of Human subjects
Source of Research Materials
Recruitment
Potential Risks
Procedures for Minimizing Potential Risks
Relation of Risks and Benefits to Participating Subjects
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102
APPENDIX A
HUMAN SUBJECTS
1. Description of the Involvement of Human subjects:
This proposed investigation evaluated the effects of two different types of
muscle contractions. The total sample size included 20 young and 20 older adults to
provide adequate statistical power to discriminate important significant differences in
oxygen consumption, C 02 production, total ventilation, heart rate, blood pressure,
cardiac index and rate-pressure product response.
Inclusion Criteria:
Group I: Healthy men and women 21-30 years of age
Group II: Healthy men and women 60-80 years of age
Exclusion criteria:
Anemia (serum hemoglobin <10 g/dL)
Uncontrolled hypothyroidism or hyperthyroidism
Rheumatoid arthritis, chronic hepatitis, renal failure or other illness
that could be catabolic
Prior cancer other than squamous or basal cell carcinoma of the skin
Blood pressure that could not be controlled with medication to
<180/95 mm Hg
Failure to pass a modified Bruce exercise stress test
Disability limiting strength or physical function testing
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103
• Dementia or cognitive impairment affecting a subject’s ability to
provide informed consent
• Resistance training and/or heavy aerobic exercise in the preceding 12
months defined as more than one bout per week.
2. Source of Research Materials:
a. Measurements of Maximal Muscle Force. Maximal voluntary skeletal muscle
strength was determined in the Clinical Exercise Research Center, room 149 of
the Center for the Health Professions,
b. Body Composition Imaging. DEXA scanning was done by licensed personnel
in the USC General Clinical Research Center.
c. Cvcle-Ergometer EKG-Stress Testing (Group ID. Tests were performed at the
USC General Clinical Research Center by Mr. Vallejo and supervised by Dr.
Fred R. Sattler (a board certified physician).
3. Recruitment:
a. Recruitment. Older subjects were recruited primarily by advertisements and a
registry o f older subjects who have participated in prior studies at USC and who
granted permission to be called about new studies. The younger subjects were
recruited by advertisements and were comprised largely of university students.
b. Informed Consent. Study subjects were only allowed to enter the study after they
had signed an informed consent, that had been approved by the USC Institutional
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104
Review Board (IRB), describing study procedures and potential risks. The study
and informed consent was explained to the subjects by one of the investigators
approved to obtain informed consent. Potential subjects were encouraged to bring
family, friends, health advocates, etc. to orientation sessions and to ask questions
about the study. Subjects were instructed to take the informed consent home and
to further consider and discuss the study with others before they made a final
decision whether to participate.
c. S c r e e n i n g . Study subjects were screened for underlying medical conditions that
would pose an increased risk for adverse events resulting from study procedures,
their ability to be tested for strength and physical function, and their ability to
understand the informed consent process.
4. Potential Risks: Potential risks of the study included the risks of DEXA
scanning, performing exercise bouts, and undergoing EKG-Stress Testing.
a. The radiation exposure risk of DEXA scanning is equivalent to about 1 millirem
or less, which is below the normal amount of radiation in the environment to
which people are exposed every month.
b. The risks of exercise included muscle soreness and injury. These risks were
minimized by following careful procedures (standardized protocols) for warm
ups, progressive increases in workload, and careful supervision of the subjects
during their exercise testing.
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105
c. The risks associated with the exercise stress test for the older subjects include
coronary ischemia, abnormal heart rhythms, stroke, fainting, and muscle
soreness.
5. Procedures for Minimizing Potential Risks:
a. Exercise Testing: A Smith Squat rack was used to determine bilateral leg
strength. During the testing, subjects were coached and closely monitored by
members of the research Team who are experienced in exercise science and
clinical evaluations.
b. Exercise Stress Testing: Prior to undergoing the cycle-ergometer EKG-stress test,
subjects were screened for evidence of heart disease with a complete history,
physical examination, electrocardiogram, and chest radiograph. EKG-Stress
testing was performed at the USC GCRC using a modified Bruce protocol and
was administered by a physician and qualified technician certified in
cardiopulmonary resuscitation.
c. Confidentiality. To assure confidentiality, data forms did not use personal
identifiers and were stored in a secured locked area at the USC Clinical Exercise
Research Center.
d. Occurrence of Physical Injury. In the event of physical injury resulting during the
conduct of this study at the USC General Clinical Research Centers (GCRC), the
informed consent indicated that appropriate medical care would be provided.
However, the duration and extent of any medical treatment would be determined
by the GCRC Advisory Committee. No monetary compensation for injury was
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106
offered. There was no medical care or financial compensation provided for
subjects injured during exercise testing in the USC Clinical Exercise Research
Center.
6. Relation of Risks and Benefits to Participating Subjects: Risks were deemed
minimal and subjects were informed that there were no direct benefits to
participating in the study. However, unsuspected underlying medical conditions
(e.g. anemia, diabetes, impaired renal function, elevated PSA, EKG or EKG-Stress
Test evidence of coronary heart disease, osteoporosis by DEXA scanning, etc.) were
detected during the screening process and these results were provided to the study
subjects and their primary doctors.
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Asset Metadata

Creator Vallejo, Alberto Francisco (author)

Core Title The physiological effects of a single bout of eccentric versus concentric resistance exercise

Contributor Digitized by ProQuest (provenance)

Degree Doctor of Philosophy

Degree Program Biokinesiology

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

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

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Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-461276

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