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Whole body mechanics of running turn maneuvers: relationship to injury and performance

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Whole body mechanics of running turn maneuvers: relationship to injury and performance

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Content Running head: MECHANICS OF MANEUVERS i

WHOLE BODY MECHANICS OF RUNNING TURN MANEUVERS:
RELATIONSHIP TO INJURY AND PERFORMANCE

by

Kathryn L. Havens

A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTEHRN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(BIOKINESIOLOGY)

August 2013

MECHANICS OF MANEUVERS ii

DEDICATION

I dedicate this dissertation to my family:

By blood,
Through marriage,
Urban, and
Furry.

I am grateful for all of you.

MECHANICS OF MANEUVERS iii

ACKNOWLEDGEMENTS

I have had the privilege of spending the last five years doing something that I love, and I
am so grateful to have had this opportunity. I’m not suggesting that getting my PhD was easy, or
that there weren’t major struggles (personal as well as academic), but I know that I chose the
right path. I have spent these years developing and asking clinically-based scientific questions,
working with high-level athletes, collaborating with very intelligent people who challenged me
daily, and thinking critically. This would not have been possible without the support and
assistance from numerous people. First, I would like to acknowledge the Division of
Biokinesiology and Physical Therapy for financially supporting me, as well as the generous
endowment from Dr. Jacqueline Perry.
I may have entered this program as an engineer, but I’m leaving with a well-rounded
appreciation for clinical physical therapy. That is in no small part to my dissertation committee,
all experts in the fields of biomechanics, motor control, and statistics who have significantly
contributed to my knowledge and viewpoint. First and foremost, I’d like to express my deepest
gratitude and appreciation for my Ph.D. advisor, Dr. Susan Sigward. As Dr. Sigward’s first Ph.D.
student, I have had a unique experience. We built a laboratory from the ground up (literally); lab
meetings grew from just the two of us to half a dozen; and I think that we’ve witnessed each
other’s growth—as she evolved as an advisor and I learned to be an independent researcher and
anatomy teacher. I’m grateful that we both took a leap of faith. I would like to thank my co-
chair, Dr. Salem, who has pushed me to question methodology and provided an exercise and
sports perspective. Dr. Gregor’s knowledge bridges biomechanics and motor control, and I am
very grateful for his ability to challenge my thinking to a systems and neural control point of
view. I greatly benefited from conversations with Dr. Fisher, whose expertise in postural control
MECHANICS OF MANEUVERS iv

and anticipatory adjustment significantly contributed to the depth of my dissertation. Thank you
to Dr. Keim, who graciously answered even my most basic statistics questions and always
provided a different perspective and encouragement. While he wasn’t on my dissertation
committee, I have always felt invaluably supported by Dr. Gordon. I am so grateful for those
post-workout coffee conversations, and for his genuine concern for not only my research by my
health and wellbeing during my time in the division.
Twenty-five athletes allowed me to tape 79 markers on them, then ran their absolute
hardest, repeatedly, until I had the data that I needed. I am grateful to those individuals, and the
LA Strikers and Chivas USA teams in particular. Thank you especially to Jim Liston for
recruitment, also to Robert DeLeon, Matt Janusz, Dan Calichman and everyone else at CATZ for
their patience and support. Rich Peterson, Daniela Roark, and Annabelle Maman made data
collections go smoothly and kept me level-headed when they didn’t- thanks!
My peers have provided amazing support, advice, words of encouragement, and the
always-necessary chat breaks about anything from balance control to wedding plans. Thank you
HPL members—Gui, Kristamarie, Matt, and Paige; MBRL past and present members—Kristen,
Marks, Ching, John, Shawn, Jenny, Rachi, Jo, Eugene, Kai-Yu, Hsiang-Ling, Michelle, and
Allie; and Neuro BKNers—Barbara, Alice, and Matt.
I would like to thank the faculty and staff in the Division of Biokinesiology and Physical
Therapy, who have significantly contributed to my professional development. In particular, I
have greatly benefited from the classes and conversations with Drs Kulig, Powers, Yu, Dieli-
Conwright, Bradley, and Winstein. Not only have they given me a great foundation of
understanding in the field of Biokinesiology but also challenged me and provided important
MECHANICS OF MANEUVERS v

feedback. I would also like to thank Janet, Weslie, Lydia, Matt, Chad and David for their
organizational, technical, and supportive roles.
Finally, this dissertation and certainly my life as I know it would not be possible without
the love and support from my family and friends. Mom and Dad, your pride in me and constant
encouragement have kept me striving to do and be better. Thank you for hundreds of cards,
thousands of phone calls, and trips across the country. I couldn’t have done this without your
belief in me. Robin, your creative spirit and unending love has kept me believing in life’s
mysteries and taking my life less seriously. I am thankful every single day for you, for the life
that we have together, and for the adventures yet to come. You really are a dream come true.
Betsy, you’ve taught me so much about perseverance and having an open and courageous heart.
Thank you for your pearls of wisdom, your laughter, and for always helping me see the sunshine.
Grandma Kakabaker, thank you for teaching me so much about life and love—how to sew, bake,
garden, remain positive, and have a life-long boyfriend. Grandma Havens, thank you for sharing
your intelligence, opinions, and strength—I see a piece of you in me every day. Mama B. and
Mikey, I’m so lucky to have such affectionate and strong parents in-law; thank you for always
being there for me, cooking special veggie dishes just for me, and finding your own happiness.
Aijia and Andy, the way that you both go for your dreams is so inspiring—thanks for reminding
me to both keep my head up and learn to let go. To my wonderful family in Michigan, my
fabulous friends in California and around the world, and my adorable doggies: thank you for
your love and support. I did it!!!

MECHANICS OF MANEUVERS vi

TABLE OF CONTENTS

DEDICATION ............................................................................................................................................ ii

ACKNOWLEDGEMENTS ........................................................................................................................ iii

LIST OF TABLES .................................................................................................................................... viii

LIST OF FIGURES .................................................................................................................................... ix

ABSTRACT ................................................................................................................................................ xi

CHAPTER I: OVERVIEW .......................................................................................................................... 1

CHAPTER II: BACKGROUND & SIGNIFICANCE ................................................................................. 4
I. Statement of the Problem ............................................................................................................ 4
II. Anterior Cruciate Ligament Injuries: Mechanism and Risk Factors ........................................... 4
III. Quick Changes of Direction: Agility .......................................................................................... 6
IV. Posture and Mechanics of Turning ............................................................................................. 9
V. Cutting Performance and Anterior Cruciate Ligament Injury Prevention ................................ 15
VI. Summary ................................................................................................................................... 19

CHAPTER III: WHOLE BODY POSTURAL MECHANICS OF RUNNING TURN MANEUVERS . 20
INTRODUCTION ................................................................................................................................. 20
METHODS ............................................................................................................................................ 25
Subjects ......................................................................................................................................... 25
Instrumentation ............................................................................................................................. 26
Procedures .................................................................................................................................... 26
Data Analysis ................................................................................................................................ 28
Statistical Analysis ........................................................................................................................ 30
RESULTS .............................................................................................................................................. 31
DISCUSSION ........................................................................................................................................ 36

CHAPTER IV: JOINT AND SEGMENTAL MECHANICS OF RUNNING TURN MANEUVERS..... 43
INTRODUCTION ................................................................................................................................. 43
METHODS ............................................................................................................................................ 47
Subjects ......................................................................................................................................... 47
Instrumentation ............................................................................................................................. 48
Procedures ..................................................................................................................................... 48
Data Analysis ................................................................................................................................ 49
Statistical Analysis ........................................................................................................................ 51
MECHANICS OF MANEUVERS vii

RESULTS .............................................................................................................................................. 51
DISCUSSION ........................................................................................................................................ 56

CHAPTER V: CUTTING MECHANICS: RELATIONSHIP TO PERFORMANCE AND ACL INJURY
RISK ......................................................................................................................................................... 62
INTRODUCTION ................................................................................................................................. 62
METHODS ............................................................................................................................................. 67
Subjects ......................................................................................................................................... 67
Instrumentation ............................................................................................................................. 68
Procedures ..................................................................................................................................... 68
Data Analysis ................................................................................................................................ 70
Statistical Analysis ........................................................................................................................ 72
RESULTS .............................................................................................................................................. 72
DISCUSSION ........................................................................................................................................ 77

CHAPTER VI: SUMMARY & CONCLUSIONS .................................................................................... 83

REFERENCES ........................................................................................................................................... 90

MECHANICS OF MANEUVERS viii

LIST OF TABLES

Table 4.1 Subject demographics (mean ± standard deviation) 47
Table 4.2

Kinematics and kinetics of cutting maneuvers
52
Table 5.1 Descriptive statistics for CUT45 and CUT90 tasks 75
Table 5.2 Regression statistics for completion time and knee adductor
moment for CUT45 and CUT90 tasks
76

MECHANICS OF MANEUVERS ix

LIST OF FIGURES

Figure 2.1 Overhead view of the comparison of COM and COP
trajectories. Axes unit: meters; long line: COM; R & L: right
and left foot COP traces, respectively; RFC1 & RFC2: right
foot contact 1 & 2; LFC: left foot contact. Plots taken from Xu
et al., 2004.
10
Figure 2.2 Translation and rotation of the body during turning, adapted
from Patla et al., 1991.
12
Figure 3.1 Experimental set up for right-foot dominant subject. Open
arrow indicates original direction of progression.
27
Figure 3.2 COM horizontal velocity at initial contact (left) and stance time
(right). Gray diamonds represent approach step; black squares
represent execution step. Error bars represent standard
deviation. * represent differences between tasks during the
execution step; + represent differences between tasks during the
approach step; ^ represent within-task differences between
steps.
32
Figure 3.3 Ground reaction force impulse (left column) and peak ground
reaction force (GRF) (left column). Gray diamonds represent
approach step; black squares represent execution step. Error
bars represent standard deviation. * represent differences
between tasks during the execution step; + represent differences
between tasks during the approach step; ^ represents within task
differences between steps.
34
Figure 3.4 Representative graphs of center of mass (long light gray lines)
and center of pressure (short dark gray lines) position for a right
foot dominant subject: (A) RUN, (B) CUT45, (C) CUT90 (L
and R = left and right foot COP; Lon = left foot contact:
approach step; Loff = end of left stance; Ron = right foot
contact: execution step; Roff = end of right stance) The vertical
axis represents forward displacement (m); the horizontal axis
represents lateral displacement (m).
35
Figure 3.5 Peak separation distance of COM and COP in AP (left) and ML
(right) directions. Gray diamonds represent approach step;
black squares represent execution step. Error bars represent
standard deviation. < represent differences between tasks when
collapsed across steps; * represent differences between tasks
during the execution step; + represent differences between tasks
36
MECHANICS OF MANEUVERS x

during the approach step; ^ represents within task differences
between steps.
Figure 4.1 Ensemble averages of angles and moments during the stance
phase CUT45 (gray line) and CUT90 (black line). X-axis is
percentage of stance phase. Standard deviation (SD) bars either
+1 SD (bars above line) for that task or -1 SD (bars below line)
for that task.
54
Figure 4.2 Average and standard deviations of joint powers across the first
half of stance during CUT45 (white) and CUT90 (gray).
54
Figure 5.1 Layout of the agility t-test. Subjects started behind laser timing
gates at point A. They ran through the timing gates to point B
and touched a 9 inch cone with their hand. They side-shuffled
left and touched the cone at C. Next, they shuffled right and
touched the cone at D, then shuffled left back to B. After
touching the cone at B a second time, they back-pedaled
through the timing gates at A.

70

MECHANICS OF MANEUVERS xi

ABSTRACT

Anterior cruciate ligament (ACL) injuries are serious knee joint injuries that often occur
during cutting, or running turn maneuvers. These maneuvers are frequently performed in
multidirectional sports and are required for successful participation. Numerous studies have
analyzed cutting movements in order to identify the mechanics related to potentially injurious
knee joint loading and inform injury prevention training programs. However, the mechanics
necessary to perform these turns has not yet been systematically characterized. It is not known
how ACL injury prevention recommendations aimed at improving limb mechanics relate to the
demands of cutting tasks. The specific aims of this dissertation were developed in order to better
understand the whole body postural and joint/segmental strategies used by skilled individuals to
perform running turn maneuvers and identify their relationships to performance and knee
mechanics related to injury risk.
The purpose of Chapter III was to investigate the influence of cut angle on whole body
postural adjustments prior to and during the cut’s execution. To do this, whole body measures of
center of mass velocity and position were compared across three tasks with varied deceleration
and translation demands (straight running, and 45 and 90 degree sidestep cuts performed as fast
as possible) in twenty-five healthy athletes. Ground reaction forces and impulse, and center of
mass position relative to center of pressure were assessed in the anterior-posterior and medial-
lateral directions during the approach and execution steps using separate two-way repeated
measures ANOVA. When compared to straight running, cutting required greater deceleration
and translation. Disproportionately greater braking but proportionately greater translation was
observed with increased cut angle. The adjustments made in the approach step indicated that
MECHANICS OF MANEUVERS xii

deceleration was prioritized over translation for the 90 degree cut but individuals distributed
these demands more evenly during the 45 degree condition.
The purpose of Chapter IV was to investigate the influence of cut angle on joint and
segmental mechanics. Twenty-five healthy athletes completed 45 and 90 degree cuts as fast as
possible. Sagittal plane hip, knee, and ankle kinematics and kinetics were evaluated to determine
the deceleration mechanics. Frontal plane hip and trunk and transverse plane hip kinematics and
kinetics were assessed to determine redirection mechanics. A two-way multi-variate analysis of
covariance (MANCOVA) determined that differences existed between task directions when
considering all dependent variables and covarying for approach velocity (α ≤0.05). Post-hoc
analyses were then examined with paired t-tests. Systematic increases in joint and segmental
variables were not found with increased cut angle. In particular, the role of the hip differed
between tasks. It worked to stabilize the body in the sagittal and frontal planes during the 90
degree cut but propel and translate the body during the 45 degree cut.
The purpose of Chapter V was to identify and quantify the whole body postural and/or
joint/segmental variables that were related to performance of cutting tasks, and to determine
whether these variables also related to potentially injurious knee loading. To do this, correlation
analysis was run between the completion time of the 45 and 90 degree cutting tasks (analyzed
separately) and the dependent variables of interest. The correlated variables were then analyzed
with two regression models, with completion time and peak knee adductor moment as the
independent variables. During the 45 degree cut, sagittal plane hip mechanics were the strongest
predictors of performance and were not predictive of knee loading. Only separation of the center
of mass from the center of pressure in the medial-lateral direction during the 45 degree cut
predicted both performance and knee loading, but it was a relatively weak predictor for both.
MECHANICS OF MANEUVERS xiii

During the 90 degree cut, primarily frontal plane mechanics predicted performance but did not
predict knee loading. In general, the results indicated that different mechanics predicted
performance for the two cutting tasks, and few variables were predictive of both performance
and knee loading.
Taken together, the results of this dissertation indicate that individuals use different
whole body postural and joint/segmental mechanics to accomplish cutting tasks performed to
different angles. Accordingly, the mechanics predictive of cut performance and knee joint
loading differed between cutting tasks. In particular, when individuals performed 45 and 90
degree cuts at their own maximal velocity, deceleration and translation demands differed and
were accomplished with differences in whole body postural adjustments during and prior to the
cut, and in joint/segmental mechanics. Furthermore, mechanics that were important to
performance and knee joint loading differed between the cutting tasks. Results from this
dissertation provide essential insight into quick change of direction tasks and have important
implications for training programs aimed at reducing ACL injury risk.

MECHANICS OF MANEUVERS 1

CHAPTER I
OVERVIEW

The ability to change directions quickly is essential for participation in multi-direction
sports (Alentorn-Geli et al., 2009; Bloomfield, Polman, & O'Donoghue, 2007a; Brughelli,
Cronin, Levin, & Chaouachi, 2008; Krustrup, Mohr, Ellingsgaard, & Bangsbo, 2005; Orendurff
et al., 2010), but running change of direction tasks (i.e., cutting) are associated with non-contact
anterior cruciate (ACL) ligament injury (Boden, Dean, Feagin, & Garrett, 2000; Cochrane,
Lloyd, Buttfield, Seward, & McGivern, 2007; Krosshaug et al., 2007; Olsen, Myklebust,
Engebretsen, & Bahr, 2004). ACL injury prevention programs have been designed to improve
lower extremity mechanics based on the current understanding of the injury mechanism
(Alentorn-Geli, et al., 2009; Gilchrist et al., 2008; Hewett, Lindenfeld, Riccobene, & Noyes,
1999; Mandelbaum et al., 2005; Myer, Ford, McLean, & Hewett, 2006; Myklebust et al., 2003).
However, it is not clear how these recommendations relate to successful performance of athletic
cutting tasks.
Changing direction involves deceleration of the body’s center of mass (COM) in the
original direction, as well as translation and rotation into the new direction (Hase & Stein, 1999;
Hollands, Sorensen, & Patla, 2001). Gait and turning literature suggests that adjustments to the
COM position and velocity are needed to accomplish deceleration, translation and rotation
(Glaister, Orendurff, Schoen, Bernatz, & Klute, 2008; Patla, Prentice, Robinson, & Neufeld,
1991; Xu, Rosengren, & Carlton, 2004). An association between COM position and velocity
during gait termination (Pai & Patton, 1997) suggests that these COM adjustments would scale
during turns performed at faster velocities; however, these relationships have not been
MECHANICS OF MANEUVERS 2

established during running turns. Whole body posture necessary to accomplish athletic turns has
not yet been systematically studied. Limb abduction and ipsilateral trunk lean are thought to
facilitate changes in COM position during walking turns (Patla, Adkin, & Ballard, 1999), but
there is evidence that these kinematics result in potentially injurious loading of the knee during
cutting (Dempsey et al., 2007; Jamison, Pan, & Chaudhari, 2012; Sigward & Powers, 2007).
Our current understanding of the ACL injury mechanism is limited, as there is no
knowledge of how knee loading and adjacent joint mechanics relate to the postural adjustments
needed for task performance. As athletes’ behavior is driven by performance, it is important to
understand how training for injury prevention relates to performance. Thus, understanding the
relationship between mechanics required for optimal performance and those needed to reduce
injury risk is essential for the development of successful ACL injury prevention programs.
Therefore, the overall goal of this dissertation was to characterize whole body mechanics
during cutting maneuvers in skilled individuals. Specifically, this dissertation aimed to compare
the whole body postural adjustments as well as joint and segmental mechanics used during
running change of direction tasks performed to varied angles and to determine whether the
mechanics that predict cutting performance are also related to knee joint loading. To accomplish
these objectives, three studies with the following specific aims were completed:
Specific Aim 1: To evaluate the postural strategies necessary for cutting by comparing whole
body measures of center of mass velocity and position during the approach and execution steps
across tasks with different direction demands (straight run, 45 degree sidestep cut, and 90 degree
sidestep cut). (Chapter III)
Specific Aim 2: To determine how differences in whole body deceleration and redirection
demands affect joint and segmental mechanics by evaluating lower limb and trunk kinematics
MECHANICS OF MANEUVERS 3

and kinetics during the execution of two sidestep cutting maneuvers to 45 and 90 degrees.
(Chapter IV)
Specific Aim 3: To identify whole body postural and/or segmental mechanics that are related to
good performance (i.e., fast completion times) of 45 and 90 degree cuts, and from these
variables, determine which variables are significant predictors of performance and/or ACL injury
risk (i.e., peak knee adductor moment). (Chapter V)
MECHANICS OF MANEUVERS 4

CHAPTER II
BACKGROUND & SIGNIFICANCE

Statement of the Problem
Quick changes of direction during running (cutting) are associated with non-contact
anterior cruciate ligament injury risk (Boden, et al., 2000; Cochrane, et al., 2007; Krosshaug, et
al., 2007; Olsen, et al., 2004), yet are required for successful participation in many sports
(Alentorn-Geli, et al., 2009; Bloomfield, et al., 2007a; Brughelli, et al., 2008; Krustrup, et al.,
2005; Orendurff, et al., 2010). Research has identified lower extremity movement patterns
thought to place individuals at risk for injury during cutting (Hewett et al., 2005; McLean,
Huang, & van den Bogert, 2005; Sigward & Powers, 2007). However, less is known about
mechanics necessary for optimal performance of cutting tasks and how they relate to injury risk.
This is important because athletes’ success depends on their performance, and they are unlikely
to adopt movement patterns that decrease risk for injury if they do not relate to good
performance. An understanding of mechanics necessary for performance of change of direction
tasks and their relationship to potentially injurious knee loading is thus needed to develop
training programs that reduce the risk for ACL injury and enhance performance. Therefore, the
primary objective of this dissertation is to characterize the whole body and segmental movement
strategies during running turns and to determine the relationship between these strategies and
task performance as well as patterns thought to contribute to ACL injury risk.
Anterior Cruciate Ligament Injuries: Mechanism and Risk Factors
Non-contact anterior cruciate ligament (ACL) tears are one of the most common knee
injuries in sports (Agel, Arendt, & Bershadsky, 2005). It has been estimated that 50,000 to
MECHANICS OF MANEUVERS 5

250,000 ACL injuries occur annually, with females sustaining injuries at a rate of 3-6 times that
of their male counterparts (Agel, et al., 2005; Arendt & Dick, 1995; L. Y. Griffin et al., 2006).
In 2000, the financial impact of ACL reconstructions alone (not including initial care,
rehabilitation, etc.) was estimated to be just under a billion dollars (Letha Y. Griffin et al., 2000).
This type of injury also has serious consequences to the long-term health of the athlete, including
knee instability, pain, loss of range of motion, secondary disruption of the menisci and chondral
surfaces, and early onset osteoarthritis of the joint (Lohmander, Englund, Dahl, & Roos, 2007).
Video analysis and self-report indicate that ACL injuries generally occur just after foot
contact with the ground during tasks that involve deceleration and change of direction,
specifically during forceful cutting maneuvers or when landing from a jump (Boden, et al., 2000;
Cochrane, et al., 2007; Krosshaug, et al., 2007; Olsen, et al., 2004). Thus, injuries often occur in
sports such as soccer and basketball, both of which involve frequent cutting and landing
maneuvers (Agel, et al., 2005). Videotape analyses suggest that at the time of injury, the trunk is
erect and the knee is in a relatively extended position with knee valgus and tibial rotation
(Boden, et al., 2000; Cochrane, et al., 2007; Hewett, Torg, & Boden, 2009; Krosshaug, et al.,
2007; Olsen, et al., 2004). Support for this observed mechanism comes from in vitro (Fukuda et
al., 2003; Markolf et al., 1995; Markolf, Gorek, Kabo, & Shapiro, 1990), in vivo (Beynnon et al.,
1995), computer simulation (Chaudhari & Andriacchi, 2006; McLean, Huang, & van den Bogert,
2008), and modeling studies (Shin, Chaudhari, & Andriacchi, 2011) that have shown that knee
joint positions including relative extension, excessive abduction, and tibial rotation, with large
adductor (valgus) moments contribute to increased loading of the ACL.
One of the primary roles of the ACL is to restrict anterior tibial translation in the sagittal
plane. As such, cadaveric studies have demonstrated greater ACL loading when an anterior
MECHANICS OF MANEUVERS 6

shear force was applied to the tibia with the knee in relative extension (Berns, Hull, & Patterson,
1992; Markolf, et al., 1995). Biomechanical studies indicate that anterior shear forces increase
during the deceleration phase of dynamic tasks (Yu, Lin, & Garrett, 2006). During deceleration,
anterior tibia shear force has been related to peak knee extensor moments, large posteriorly-
directed GRF, as well as large quadriceps contraction (Sell et al., 2007; Yu, et al., 2006).
Additionally, in vivo and modeling studies have shown a significant effect of sagittal plane knee
position (relative extension), as well as kinetics including knee extensor moment on ACL strain
(Fleming et al., 2003; Shelburne, Pandy, Anderson, & Torry, 2004).
Compelling evidence points to frontal plane knee mechanics playing a role in the
mechanism of ACL injuries. Combining a valgus moment with anterior shear force has been
shown to load the ACL more than anterior shear force alone (Markolf, et al., 1995). In a
prospective study, increased knee frontal plane loading during a drop land task was found to be a
predictor of ACL injury. Female athletes who sustained an ACL injury (9/205) exhibited greater
knee adductor moments and angles during a drop land task than non-injured individuals. The
results of this important study also showed that peak knee valgus moment predicted ACL injury
status with high specificity and sensitivity, and a predictive R
2
of 0.88 (Hewett, et al., 2005).
Thus, while sagittal plane biomechanics during deceleration are thought to play a role in the
injury mechanism, only knee abduction angles and knee adductor moments have been
prospectively related to risk for ACL injury.
Quick Changes of Direction: Agility
Agility in Sports
Agility is required for many field sports. It can be defined as a rapid whole body
movement with change in direction and/or velocity (Sheppard & Young, 2006). Running
MECHANICS OF MANEUVERS 7

changes of direction, or cuts, are hallmarks of agility. Athletes may change direction in response
to an object (e.g. the moving ball, boundary line, etc.), the movements of their teammates, or to
evade or pursue an opponent (J. Hewit, Cronin, Button, & Hume, 2010; W. Young & Farrow,
2006; WB. Young, McDowell, & Scarlett, 2001). Work bout analysis suggests that cutting,
acceleration and deceleration are very frequent occurrences in soccer matches (Krustrup, et al.,
2005; Orendurff, et al., 2010). A recent video analysis study of soccer showed that players
perform an average of 727 turns/swerves during a 90-minute game (Bloomfield, et al., 2007a).
High and low intensity movements were interspersed throughout the match, indicating a range of
speeds at which running turns are performed (Orendurff, et al., 2010). Running speed may
depend on the turn angle, as players turning to less sharp angles more often perform jogging,
running or shuffling before and after the change of direction, while turns to more severe degrees
were more often preceded and followed by slowing, stopping or skipping (Bloomfield, Polman,
& O'Donoghue, 2007b). Changes of direction have also been shown to be made to different
angles during game situations; about 85% of these were turns of 0-90 degrees to the right or left,
and another 10% were 90-180 degrees (Bloomfield, et al., 2007b). Clearly, multi-directional
sports require turns to various directions, which are performed at different speeds.
The role of agility in distinguishing between levels of sports participation, identifying
talent, and influencing player selection in teams underscores its importance in sports. The ability
to change direction is thought to be a prerequisite for successful participation in multi-directional
field sports (Brughelli, et al., 2008; Sheppard & Young, 2006). In fact, time to complete an
agility test can discriminate between intercollegiate athletes, recreational athletes and non-
athletes (Pauole, Madole, Garhammer, Lacourse, & Rozenek, 2000), as well as between elite and
sub-elite basketball (Delextrat & Cohen, 2008) and soccer players (Kaplan, Erkmen, & Taskin,
MECHANICS OF MANEUVERS 8

2009; Reilly, Williams, Nevill, & Franks, 2000). Higher level athletes outperform their less-
skilled counterparts. Talent-identification and team selection literature further support the
importance of change of direction ability in athletes (Gil, Ruiz, Irazusta, Gil, & Irazusta, 2007 ;
McGee & Burkett, 2003; Reilly, et al., 2000). Out of 28 tests that included anthropometric,
psychological and sport-specific skills tests, Reilly et al. (2000) found agility to be the most
important indication of talent in soccer. It is also an important determinant of player selection in
youth soccer teams (Gil, et al., 2007) and the NFL (McGee & Burkett, 2003).
Agility and Sports Performance
Tests used to assess agility generally include short sprints combined with multiple
changes in direction (Brughelli, et al., 2008). They vary considerably in number and type of
direction changes, length of test (in distance and time), and force application throughout the test
(Brughelli, et al., 2008). However, for all tests of agility, performance is measured by the time to
complete the test (Brughelli, et al., 2008; Little & Williams, 2005; Oliver & Meyers, 2009;
Pauole, et al., 2000; WB. Young, James, & Montgomery, 2002).
Strength and conditioning coaches, athletic training practitioners, and sports medicine
researchers have sought to identify trainable qualities that may optimize change of direction
performance. Young and colleagues (2002) proposed a deterministic model of agility, describing
potential factors that may influence the ability of an individual to perform changes of direction
quickly. Among the components proposed to contribute to change of direction speed are straight
running speed, anthropometrics, leg muscle qualities, and technique (WB. Young, et al., 2002).
Despite extensive examination, the relationship between many of these trainable qualities and
change of direction speed has not been empirically supported (Brughelli, et al., 2008; Little &
Williams, 2005; Markovic, 2007; WB. Young, et al., 2002; WB. Young, et al., 2001).
MECHANICS OF MANEUVERS 9

Importantly, change of direction performance is not related to straight running speed (Buttifant,
Graham, & Cross, 1995; Little & Williams, 2005; W. Young & Farrow, 2006; WB. Young, et
al., 2002). This indicates that agility is a specific skill separate from speed. Athletes cannot just
be fast to be agile; they must be able to quickly redirect the horizontal position of the body.
The technique required for successful performance of agility tasks is not fully
understood. Specific quantitative research of technique, including foot placement, and body lean
and posture, as it relates to change of direction performance is very limited (Sheppard & Young,
2006). That is, running change of direction posture and mechanics and how they are adapted to
different tests or demands is not known. Much of what we know about the mechanics of turning
comes from the walking turn literature; it provides important insight into the biomechanical
components necessary for changing direction.
Posture and Mechanics of Turning
Walking Turns
Like cutting, walking turns involve redirection of the body during ongoing movement.
The body decelerates in the original direction of forward progression, then translates, rotates and
accelerates into the intended direction (Hase & Stein, 1999; Hollands, et al., 2001). Each of
these components, deceleration, translation and rotation are necessary for turning. These
elements are evident in the postural strategies used, including manipulations to loads and body
position, which are accomplished through changes in segmental biomechanics. While
deceleration, translation, and rotation are required to successfully complete a turn, the angular
magnitude at which walking turns are performed influence both the postural strategies and
kinematics.
MECHANICS OF MANEUVERS 10

Deceleration. Deceleration of the body is necessary during turning. It is hypothesized
that the body would over-rotate if deceleration is not accomplished. Specifically, without
braking forces, body rotations of 1.4-3 times the desired change of direction angle have been
calculated using a mathematical model (Jindrich, Besier, & Lloyd, 2006). Braking causes large,
posteriorly-directed ground reaction forces (GRF), as the body directs force into the ground to
slow anterior velocity. When compared to straight walking, both posteriorly-directed GRF and
ground reaction force impulse (GRI), the area under the GRF-time curve, have been shown to be
significantly greater during turns, underscoring the importance of deceleration during turning
(Glaister, et al., 2008; Patla, et al., 1991; Strike & Taylor, 2009). Further, braking GRI is larger
when turns are made to a greater angular magnitude (Xu, et al., 2004). In order to generate these
braking forces, the position of the body is also manipulated. During straight walking, the center
of mass (COM) is initially posterior to the base of support (or the center of pressure (COP)) then
crosses over and continues anterior during late stance. In contrast, during deceleration, the COM
remains posterior to the base of support longer (Orendurff, Bernatz, Schoen, & Klute, 2008).
Greater deceleration requires that the center of mass be more posterior to the base of support
(Jian, Winter, Ishac, & Gilchrist, 1993; Orendurff, et al., 2008; Pai & Patton, 1997).

Figure 2.1 Overhead view of the comparison of COM and COP trajectories. Axes unit: meters;
long line: COM; R & L: right and left foot COP traces, respectively; RFC1 & RFC2: right foot
contact 1 & 2; LFC: left foot contact. Plots taken from Xu et al., 2004.
MECHANICS OF MANEUVERS 11

Translation. During turning, the body must translate towards the new direction. This
change in the direction of the horizontal velocity vector is reflected in the medial ground reaction
force impulse. When compared to straight walking, the medial GRI has also been shown to be
greater during the initiation of a turn (Glaister, et al., 2008; Patla, et al., 1991; Strike & Taylor,
2009; Xu, et al., 2004). Whole body translation is accomplished through medial-lateral
separation of the COM and center of pressure. This is seen in the Figure 2.1. From left to right,
the plots show the COM and COP trajectories during straight walking, and 45 and 90 degree step
turns (the left foot plants while turning to the right). During the execution of the turns, the
medial-lateral COM-COP separation increases when compared to straight walking and scales
with turn magnitude (Xu, et al., 2004).
Translation of the COM into the new direction is facilitated by lateral foot placement and
trunk lean away from the direction of the turn (Fuller, Adkin, & Vallis, 2007; J. R. Houck,
Duncan, & De Haven, 2006; Patla, et al., 1999; Strike & Taylor, 2009; Taylor, Dabnichki, &
Strike, 2005). Lateral foot placement is accomplished segmentally through abduction at the hip
(Taylor, et al., 2005), and the gluteus medius muscle contributes to the hip abductor moment
(Hase & Stein, 1999; Taylor, et al., 2005).
Rotation. Rotation into the new direction is also necessary in order to align the body with
the new travel path (Figure 2.2) (Besier, Lloyd, Cochrane, & Ackland, 2001; Patla, et al., 1991).
Rotational moments about the vertical axis must be generated for whole body rotation (Jindrich
& Qiao, 2009; Patla, et al., 1991). This is accomplished by a consistent top-down transverse
plane segment reorientation sequence (Akram, Frank, & Fraser, 2010). The order of head,
shoulder, and pelvic rotation always preceded mediolateral foot displacement, while task
condition (turn velocity or magnitude) affect the relative timing (Akram, et al., 2010).
MECHANICS OF MANEUVERS 12

Figure 2.2 Translation and rotation of the body during turning, adapted from Patla et al.,1991

Turning literature indicates that the necessary features of changes of direction during
walking include deceleration in the original direction of forward progression with lateral
translation and rotation of the body to move towards the intended new direction. These are
accomplished by whole body postural strategies including specific loading patterns, body
position, and changes to segmental kinematics. It is not yet clear whether these same strategies
are used when turns are made at faster velocities (i.e., cutting). With a shorter time to complete
these necessary components, greater loads and greater changes in body momentum must be
managed by the neuromuscular system.
Running Turns
Cutting research also provides insight into the mechanics of turning, though much of the
cutting research to date focuses on biomechanics as they relate to ACL injury. Specifically, the
kinematics, kinetics, and muscle activity of lower extremity (Beaulieu, Lamontagne, & Xu,
2009; Besier, Lloyd, & Ackland, 2003; Besier, Lloyd, Ackland, & Cochrane, 2001; Chan,
Huang, Chang, & Kernozek, 2009; Fedie, Carlstedt, Willson, & Kernozek, 2010; Hanson, Padua,
Blackburn, Prentice, & Hirth, 2008; Landry, McKean, Hubley-Kozey, Stanish, & Deluzio, 2007;
Malinzak, Colby, Kirkendall, Yu, & Garrett, 2001; McLean, Lipfert, & Van Den Bogert, 2004;
MECHANICS OF MANEUVERS 13

Pollard, Davis, & Hamill, 2004; Pollard, Sigward, & Powers, 2007; S. Sigward & C. M. Powers,
2006), and more recently of the trunk (Dempsey, Lloyd, Elliott, Steele, & Munro, 2009; J. R.
Houck, et al., 2006) have been examined. Comparisons in cutting mechanics have been made
between sexes (Beaulieu, et al., 2009; Hanson, et al., 2008; Landry, et al., 2007; Malinzak, et al.,
2001; McLean, et al., 2005; Pollard, et al., 2004; Pollard, et al., 2007), levels of experience (S.
Sigward & C. M. Powers, 2006), and with different environmental (Besier, et al., 2003; Besier,
Lloyd, Ackland, et al., 2001; Dowling, Corazza, Chaudhari, & Andriacchi, 2010; McLean, et al.,
2004) or attention (Chan, et al., 2009; Fedie, et al., 2010) demands. However, our current
understanding of cutting is limited to segmental and joint mechanics. To date, no study has
evaluated the whole body postural strategies necessary for cutting. This limits our understanding
of the cutting tasks, as whole body postures account for the mechanics of all segments/joints.
While differences found in lower extremity mechanics between task demands suggest that whole
body postures is altered to accomplish changes of direction, this has not yet been researched.
Besier et al. (2001) showed that when compared to straight running, individuals
performed cutting tasks to 30 and 60 degrees with greater external knee moments, and these
moments increased with greater cut magnitude. Only the knee joint was analyzed, but this study
provides support that mechanics differ based on task demand. Other studies have collected
running trials (Beaulieu, et al., 2009; Besier, et al., 2003; Malinzak, et al., 2001; Pollard, et al.,
2004; Rand & Ohtsuki, 2000), but direct comparisons between cutting and running were not
made. A better understanding of how individuals alter their whole body posture to change
direction during running may provide better insight into the relationship between task demands
and knee loading.

MECHANICS OF MANEUVERS 14

Anticipatory Adjustments
Motor control literature has demonstrated that alterations in body posture or muscle
activation are made in advance of voluntary movements (Adkin, Frank, Carpenter, & Peysar,
2002; Hines, 1997; Le Pellec & Maton, 1999; Massion, 1992). These anticipatory adjustments
are thought to play several roles. They may contribute to minimizing the postural disturbance
created by the movement, providing a stable, egocentric reference system, and/or initiating the
disequilibrium that is necessary to produce momentum (Le Pellec & Maton, 1999; Massion,
1992). Anticipatory adjustments are adapted to task conditions (Adkin, et al., 2002; Benvenuti,
Stanhope, Thomas, Panzer, & Hallett, 1997) and are acquired through learning or practice
(Pedotti, Crenna, Deat, Frigo, & Massion, 1989).
During walking, adjustments have been shown prior to circumvention of an obstacle
(Vallis & McFadyen, 2003), as well as turning (Xu, et al., 2004). Patla et al. (1991) found that
subjects were unable to make a turn when the cue was presented during the ongoing step,
indicating that planning was required in order to be successful. Another study (Xu, et al., 2004)
investigated the postural adjustments made in the step before a walking turn. They found greater
medial-lateral separation of the COM and under-foot center of pressure (COP) and greater
posterior and medial ground reaction force impulse when compared to straight walking. This
suggests that the central nervous system predicts the consequences of this perturbation from
steady state locomotion and provides feed-forward planning to keep the body stable (Xu, et al.,
2004).
During cutting, altered lower extremity mechanics have been found when cuts are
unanticipated, or cued during the approach, compared to when they are anticipated, or cued in
advance (Besier, Lloyd, Ackland, et al., 2001; J. R. Houck, et al., 2006). Specifically, reduced
MECHANICS OF MANEUVERS 15

knee joint loading has been shown during preplanned cuts (Besier et al., 2001a). This suggests
that when given time to plan their movements, individuals are able to make adjustments to their
mechanics in advance of the cut’s execution that result in reduced knee loading. However, the
nature of these anticipatory adjustments has not yet been characterized. It is therefore not known
how they are adapted to task demands or what roles they may play to accomplish the task goals.
Cutting Performance and Anterior Cruciate Ligament Injury Prevention
Movement Strategies for Cutting Performance
The maximal speed at which athletes can change direction likely differs between
individuals, as indicated by the varied time it takes individuals to complete a series of change of
direction tasks (Kaplan, et al., 2009; Pauole, et al., 2000). This presents a problem when
interpreting the current cutting literature, as velocity is commonly constrained across subjects.
That is, individuals of different ages, sexes, heights, with different training or fitness levels are
all instructed to perform cuts at the same speed (Beaulieu, et al., 2009; Fedie, et al., 2010;
Hanson, et al., 2008; Landry, et al., 2007; McLean, et al., 2005; Pollard, et al., 2004; Sigward &
Powers, 2007). While there are reasons to constrain velocity, it limits our ability to determine
how the strategies identified in these studies relate to the individual athletes’ abilities. In
addition, we gain little insight into the strategies needed for optimal performance if subjects are
not providing a maximal effort. Studies that assess maximal effort and allow for variability in
individual performance are needed to address how mechanics and performance are related.
To date, very few studies have examined the relationship between biomechanics and
cutting task performance. A recently published study (J. K. Hewit, Cronin, & Hume, 2013)
attempted to identify kinematic factors that differed between fast and slow performers of a 180
degree change of direction task. While the researchers estimated torso and hip sagittal angles
MECHANICS OF MANEUVERS 16

using 2D video analysis, the results indicated that only step frequency differed between the
groups. In another study (Sasaki, Nagano, Kaneko, Sakurai, & Fukubayashi, 2011), sagittal and
frontal plane trunk angle and angular displacement were analyzed at several time points during a
180 degree cut. Only one of the ten variables analyzed, forward trunk angular displacement from
initial foot contact to maximal inclination, was significantly correlated with time to complete the
cutting task. Greater forward trunk displacements were moderately related to longer cutting
times. Clearly, more systematic research is needed to understand the relationship between
movement strategies and performance outcome in a variety of cutting tasks.
As described, it is well accepted that cutting mechanics that include high knee abduction
moments are associated with ACL injury risk. During cutting, trunk lean opposite the direction
of cut (Dempsey, et al., 2007), lateral limb placement (Golden, Pavol, & Hoffman, 2009;
Imwalle, Myer, Ford, & Hewett, 2009; Sigward & Powers, 2007), and rotation (McLean, et al.,
2005; Sigward & Powers, 2007) have been shown to be associated with increased knee
abduction angles and moments. These combined mechanics are thus thought to put individuals at
risk of knee injury (Dempsey, et al., 2009; Dempsey, et al., 2007; Dowling, et al., 2010; Golden,
et al., 2009; McLean, et al., 2005; Sigward & Powers, 2007), and are discouraged with ACL
injury prevention programs (Dempsey, et al., 2007; Mandelbaum, et al., 2005). However, these
strategies may be necessary for optimal change of direction performance. In fact, walking turn
literature suggests that trunk lean and leg abduction facilitate redirection of the body’s center of
mass (Fuller, et al., 2007; Hollands, et al., 2001; Patla, et al., 1999; Taylor, et al., 2005). This is
a major gap in our understanding of effective prevention of ACL injuries.

MECHANICS OF MANEUVERS 17

Anterior Cruciate Ligament Injury Prevention
Numerous ACL injury prevention programs aimed at altering potentially injurious
movement strategies have been created, with varied success (Alentorn-Geli, et al., 2009).
Successful programs have incorporated multiple types of exercises, though many emphasize
plyometrics, jumping and landing (Alentorn-Geli, et al., 2009; Gilchrist, et al., 2008; Hewett, et
al., 1999; Mandelbaum, et al., 2005; Myer, et al., 2006; Myklebust, et al., 2003). In particular,
these programs instruct athletes to maintain proper technique when performing landing and
jumping exercises, emphasizing increased sagittal plane motion (Gilchrist, et al., 2008; Hewett,
et al., 1999; Mandelbaum, et al., 2005; Myer, Chu, Brent, & Hewett, 2008; Myer, et al., 2006)
and discouraging frontal and transverse plane motion of the lower extremity and trunk
(Dempsey, et al., 2007; Mandelbaum, et al., 2005; Myer, et al., 2006). These guidelines are
based on ACL injury mechanisms as they apply to landing, but may not be appropriate for
cutting.
While poor lower extremity movement patterns are thought to contribute to frontal plane
knee loads (L. Y. Griffin, et al., 2006), the mechanism of loading differs between landing and
cutting tasks. Hip adduction and internal rotation contribute to greater knee abduction angle and
adductor moments during landing (Powers, 2010; Sigward, Havens, & Powers, 2011). In
contrast, hip abduction and internal rotation are associated with increased knee abduction and
adductor moments during cutting (Imwalle, et al., 2009; McLean, et al., 2005; Sigward &
Powers, 2007). These differences are likely due to the distinct demands of each task. Landing
requires primarily vertical deceleration and acceleration of the body using both limbs, while
cutting is executed primarily in the horizontal plane on one limb. Accomplishing these task
demands likely requires different whole body postural strategies. In jumping and landing,
MECHANICS OF MANEUVERS 18

improving limb mechanics by increasing sagittal plane motion of the lower extremity reduces
frontal plane loads (Pollard, Sigward, & Powers, 2010; Tsai, Pollard, Salem, & Powers, 2012)
and likely improves jumping performance. In fact, several studies have reported improvements
in performance of jumping tasks following injury prevention training (Chappell & Limpisvasti,
2008; Myer, Ford, Palumbo, & Hewett, 2005; Zebis et al., 2008). However, some research
suggests that improving limb mechanics to reduce frontal plane loading during cutting is not
beneficial to performance.
Following an injury prevention training program, agility performance has been shown to
decline (Vescovi & VanHeest, 2010). In this study, 58 adolescent female soccer players
participated in an ACL injury prevention program for 12 weeks. The program, the Santa Monica
Prevent Injury Enhance Performance program (Gilchrist, et al., 2008; Mandelbaum, et al., 2005),
emphasized technique as described above and included strengthening, plyometrics, agility drills
(Gilchrist, et al., 2008; Mandelbaum, et al., 2005). Because these components are used routinely
by sports performance professionals to enhance athletic performance (Brughelli, et al., 2008;
Simenz, Dugan, & Ebben, 2005), it may be expected that participation would improve measures
of performance. However, agility performance in the trained subjects dropped. Time to
complete two agility tests (both the pro-agility and Illinois agility tests) increased following
training (Vescovi & VanHeest, 2010). It was thought that improvements in performance were
not seen in part because of the lack of specificity for agility performance in the training program.
However, it is also possible that the techniques trained for landing and jumping resulted in
inefficient biomechanics for cutting. As this was not a biomechanical study, it remains unclear
how the techniques emphasized in ACL injury prevention programs relate to the mechanics
necessary for successful performance of cutting tasks.
MECHANICS OF MANEUVERS 19

Coaches’ willingness to implement prevention programs that results in diminished agility
performance may be limited. Further, athletes’ behavior is driven by performance. They are
likely to choose strategies that allow them to succeed in their game. That is, if these
recommended body postures are necessary for successful performance of turning maneuvers,
athletes are unlikely to alter their mechanics at the detriment of their agility performance. In
order to effectively inform injury prevention training, we must first understand the whole body
movement strategies used to perform running change of direction maneuvers.
Summary
Cutting presents a paradox to athletes: it is associated with a debilitating injury yet is
essential for sports performance. While lower extremity mechanics of cutting related to ACL
injury have been identified, whole body postural strategies have not, and even less is known
about mechanics necessary for successful performance of cutting tasks. This information may
assist in the eventual recognition of new risk factors for lower extremity injury in the general
athletic population. It may also guide athletes, trainers, clinicians, and coaches in the
development of training techniques to lower the risk of injury as well as improve performance
during athletic tasks that include deceleration and change of direction.

MECHANICS OF MANEUVERS 20

CHAPTER III
WHOLE BODY POSTURAL MECHANICS OF RUNNING TURN MANEUVERS

Abstract
Quick changes of direction during running (cutting) represent a challenge to the postural
control system, as they require deceleration and translation of the whole body during ongoing
movement. In this study, the whole body postural and anticipatory adjustments necessary for
cutting were evaluated. Whole body measures of center of mass velocity and position during the
approach and execution steps of three tasks (straight running, 45˚ sidestep cut, and 90˚ sidestep
cut) performed as fast as possible were compared in twenty-five healthy soccer athletes.
Repeated measure ANOVA was used to evaluate the effect of task direction during approach and
execution steps on the variables of interest, including ground reaction forces and separation of
the center of mass and center of pressure. Overall, greater braking and translation were found
during the cuts compared to the straight run. With increased cut angle, disproportionately greater
braking but proportionately greater translation was observed. Anticipatory adjustments suggested
that individuals evenly distributed the deceleration and redirection demands across steps of the
45˚ cut but prioritized deceleration over translation during the approach step of the 90˚ cut.
Introduction
The ability to change direction quickly is a prerequisite for participation in multi-
directional sports (Brughelli, et al., 2008). In soccer, running change of direction, or cutting, is a
very frequent occurrence (Krustrup, et al., 2005; Orendurff, et al., 2010), with players
performing an average of 727 turns/swerves during a 90-minute game (Bloomfield, et al.,
2007a). Cutting is the hallmark of agility, a rapid whole body movement with change in
MECHANICS OF MANEUVERS 21

direction and/or velocity (Sheppard & Young, 2006). The importance of agility performance in
sports is underscored by its role in distinguishing between elite and sub-elite players (Kaplan, et
al., 2009; Pauole, et al., 2000; Reilly, et al., 2000), identifying talent (Reilly, et al., 2000), and
influencing player selection in teams (Gil, et al., 2007; McGee & Burkett, 2003).
Unfortunately, cutting is frequently associated with lower extremity injuries such as ankle
sprains (Garrick, 1977) and anterior cruciate ligament (ACL) tears (Boden, et al., 2000;
Cochrane, et al., 2007). These injuries have been attributed to poor technique or mechanics, as
they often occur without contact from another player or object. Specifically, altered sagittal and
frontal plane loading mechanics during deceleration of cutting tasks are thought to place athletes
at greater risk for ACL injuries (Cochrane, et al., 2007; L. Y. Griffin, et al., 2006; Markolf, et al.,
1995; Yu & Garrett, 2007). As a result, investigations of cutting mechanics have focused on
identifying and ameliorating potentially injurious lower extremity and trunk kinematics and
kinetics (Besier, Lloyd, Cochrane, et al., 2001; Myklebust, et al., 2003; Sigward & Powers,
2007).
Despite the importance of cutting in sports performance and its relevance to injury, little
research has focused on the mechanics of cutting from a whole body postural perspective. While
movement at individual joints is important, center of mass (COM) position or velocity variables
account for the movement of all body segments. For example, hip abduction and trunk lean
away from the stance limb are together reflected in a center of mass position lateral to the center
of pressure. Consideration of both the position of the whole body and the magnitude and
direction of its velocity is necessary in order to assess postural control during dynamic tasks
(Hof, Gazendam, & Sinke, 2005; Pai & Patton, 1997). Further, whole body position and velocity
measures provide an understanding of the mechanical demands of the task and how the body
MECHANICS OF MANEUVERS 22

segments work together to achieve these demands. In order to develop effective athlete training
and injury prevention programs, this whole body postural approach is needed.
Changing directions represents a complex challenge to the postural control system.
Turning involves braking in the original direction of forward progression, and translation,
reorientation and acceleration into the new intended direction, all without stopping ongoing
locomotion (Hase & Stein, 1999; Hollands, et al., 2001). In order to accomplish these subtasks,
whole body adjustments to the position and velocity of the body’s COM are required. Moreover,
requirements for deceleration overlap in time with those for translation, further challenging the
postural system. Whole body postural adjustments necessary for braking and translation during
walking turns are well documented. However, it is not clear whether the same strategies are used
during sidestep cutting performed at faster velocities.
Larger posteriorly-directed ground reaction force (GRF) and ground reaction force
impulse (GRI) during turning, compared to walking, indicate that a greater decrease in anterior
velocity of the COM is necessary to successfully complete a turn (Glaister, et al., 2008; J.
Houck, 2003; Patla, et al., 1991; Strike & Taylor, 2009). During the deceleration of gait, the
position of the body’s COM is tightly coupled with anterior velocity, in that the COM must be
positioned posterior to the stance limb or center of pressure (COP, i.e., the 2-dimensional
position of the ground reaction force vector). Faster anterior velocities require this posterior
position to be even greater in order to decelerate the COM to zero (Jian, et al., 1993; Pai &
Patton, 1997). During turning, these postural adjustments to the body’s COM scale with
increased angle of turn (Xu, et al., 2004), indicating that greater deceleration is required when
turning to greater angles.
MECHANICS OF MANEUVERS 23

Compared to gait, less information is available with respect to deceleration during
cutting. Observational analysis during competition indicates that deceleration is necessary
during cutting, as athletes appear to slow their speed more when subsequent cuts are made to
greater angular magnitudes (Bloomfield, et al., 2007b). Deceleration is thought to prevent over-
rotation of the whole body about the vertical axis during cutting. Using a mathematical model,
Jindrich and colleagues (2006) determined that without braking forces, the body would over-
rotate 1.4-3 times more that the desired change of direction. However, greater posterior
(braking) GRF have been related to increased anterior tibial shear force, which is considered a
risk factor for ACL injury (Sell, et al., 2007; Yu, et al., 2006). A better understanding of the
extent to which deceleration is necessary for cutting tasks performed at speeds and angles
experienced in sports and the whole body adjustment required to accomplish deceleration is
needed to inform training programs for injury prevention and agility performance.
Translation of the body’s COM towards the new direction occurs throughout much of
stance during turning. Specifically, when compared to straight walking, medial-lateral (ML) GRI
and peak GRFs have been shown to be greater during the initiation and execution of a turn
(Glaister, et al., 2008; J. Houck, 2003; Patla, et al., 1991; Strike & Taylor, 2009; Xu, et al.,
2004). ML GRI was shown to be approximately 3.5-4.5 times greater during 90˚ turns when
compared to straight walking (Glaister, et al., 2008; Strike & Taylor, 2009). A laterally placed
limb (Patla, et al., 1999) and a larger step width (Strike & Taylor, 2009) are used to separate the
COM and COP laterally. While not measured directly, this lateral separation is thought to
contribute to acceleration of the body’s COM in the opposite direction (i.e., the direction of the
turn) (Patla, et al., 1999). As center of mass acceleration direction and magnitude are dictated by
separation of the COM from the center of pressure (Winter, 1995a), it stands to reason that larger
MECHANICS OF MANEUVERS 24

separation distances are needed for larger magnitude turns. It is not known to what extent these
adjustments to force, impulse, or COM position are necessary during cutting.
Whole body translation has not been studied during cutting. However, the presence of a
laterally placed limb or abducted hip at initial contact of cutting (Dempsey, et al., 2007; McLean,
et al., 2004; Sigward & Powers, 2007) is consistent with the lower limb posture described during
walking turns, suggesting that individuals may use medial-lateral separation of the COM and
COP to facilitate acceleration of the COM into the new direction. In addition, some studies have
reported that while the cutting tasks performed in the laboratory setting were accurate on visual
inspection, the calculated angles were smaller than the desired target cut angles (Besier, Lloyd,
Cochrane, et al., 2001; Dowling, et al., 2010; Vanrenterghem, Venables, Pataky, & Robinson,
2012). This suggests that the COM is positioned medial to the stance limb during the cut.
However, it is not clear to what extent medial-lateral separation is utilized during cutting or how
cutting angle affects the magnitude of the separation.
Differences observed in lower extremity loading during cutting tasks performed in
unanticipated (cued during the approach) and anticipated (cued in advance) conditions suggest
that whole body adjustments are made prior to executing the cut. The lower loads observed in
anticipated conditions indicate that when adequate planning time is available, individuals make
anticipatory adjustments (Besier, Lloyd, Ackland, et al., 2001; J. R. Houck, et al., 2006). This is
consistent with turning literature, where Xu et al. (2004) showed that postural adjustments for
braking and translation are made in the step before turns, and these adjustments scaled with turn
magnitude. Motor control literature has demonstrated that alterations in body posture or muscle
activation are made in advance of voluntary movements (Adkin, et al., 2002; Hines, 1997; Le
Pellec & Maton, 1999; Massion, 1992) and are adapted to task conditions (Adkin, et al., 2002;
MECHANICS OF MANEUVERS 25

Benvenuti, et al., 1997). However, the extent to which these anticipatory postural adjustments
are employed during cutting tasks and the effects of cutting angle on these adjustments is not
known.
The purpose of this study was to evaluate the postural strategies necessary for cutting by
comparing whole body measures of COM velocity and position during the approach and
execution steps across tasks with different direction demands (straight run, 45˚ sidestep cut, and
90˚ sidestep cut). We hypothesize that with greater cut angle, more braking and translation will
be required and will be accomplished through larger peak ground reaction forces and greater
separation of the COM and COP. Further, we expect that braking and translation will begin prior
to the execution of the cut.
Methods
Participants
Twenty-five healthy soccer players participated (12 females, mean age = 22.4 ± 3.9 yr,
height = 1.74 ± 0.1 m, mass = 70.9 ± 9.3 kg). An a-priori power analysis based on pilot data
determined that with 25 subjects, the study would be adequately powered to detect differences in
GRI and COM-COP separation distance between task conditions with an alpha of 0.05 and 95%
power. Athletes were considered experienced, high-level soccer players (college, semi-
professional, professional), with an average of 16.7 ± 4.3 years of soccer experience. Twenty-
two participants reported that they were right-limb dominant, when asked which foot they would
kick a ball with.
All subjects were healthy without complaints associated with lower extremity injuries.
Subjects were excluded from the study if they had: 1) history of previous lower extremity
surgery, 2) recent lower extremity injury resulting in persistent pain and/or inability to participate
MECHANICS OF MANEUVERS 26

in sport (greater than 3 weeks) in the last six months, 3) concurrent pathology or morphology
that could cause pain or discomfort during physical activity; or 4) any physical, cognitive or
other condition that would impair their ability to perform the tasks in this study. Prior to
participation, all subjects were explained the testing procedures, and informed consent was
obtained as approved by the Investigational Review Board at the University of Southern
California Health Science Campus.
Instrumentation
Three-dimensional motion analysis was performed using a marker-based, 11-camera
digital motion capturing system (Qualisys, Gothenburg, Sweden) at 250 Hz. Ground reaction
force data were obtained at 1500 Hz using two 1.20 x 0.60 m
2
force platforms (AMTI, Newton,
MA, USA) embedded into the floor surface. Kinematic and kinetic data were collected
synchronously using the motion capture software (Qualisys Track Manger, version 2.6).
Reflective markers (25 mm spheres) placed on specific bony landmarks were used to define body
segments in three-dimensional space. Laser timing gates (Brower IRD-T175; Brower Timing
Systems, Draper, UT, USA) were used to demine the time to complete the task.
Procedures
All testing took place at the Human Performance Laboratory at the University of
Southern California, located within Competitive Athlete Training Zone (CATZ). Participants
wore shorts, tank tops, and their own running/athletic shoes (not cleats). Tracking marker
clusters mounted on semi-rigid plastic plates were secured to nylon/lycra bands on the subject’s
arms, forearms, thighs, shanks, and shoes. Reflective markers were placed over 45 anatomical
landmarks, similar to that used by Song et al. (2012). Following a static calibration trial, the
tracking marker clusters as well as the markers on the end of the second toes, posterior superior
MECHANICS OF MANEUVERS 27

iliac spines, iliac crests, L5-S1 junction, acromions, radial and ulnar styloid processes, third
metacarpal heads, clavicle, cervical process of C7, and head remained on the subject.

Figure 3.1 Experimental set up for right-foot dominant subject. Open arrow indicates original
direction of progression.

Prior to testing, subjects were led through a 15 minute warm-up and were given time to
stretch. Participants were then instructed to perform three tasks: straight running (RUN), and
sidestep cutting maneuvers to 45˚ (CUT45) and 90˚ (CUT90) at their fastest speed. For RUN,
subjects ran as fast as possible across a 15 meter path. For both cutting tasks, subjects ran as fast
as possible 7.5 meters, planted their dominant foot and changed direction away from their plant
foot at the designated angle (45 or 90 degrees), and continued running as fast as possible for 7.5
meters (Figure 3.1). The cutting angles were marked on the floor with tape. Laser timing gates
were placed at the beginning and end of the 15 meter path to measure task completion time. The
45˚ and 90˚ cut order was counter-balanced between subjects to prevent effects related to testing
MECHANICS OF MANEUVERS 28

order. Trials were accepted if the subject’s task completion time was within a ± 2.5% interval as
measured by the timing gates and if the non-dominant foot made complete contact with the first
force platform and the dominant foot fully contacted the second force platform.
Data analysis
Qualisys Tracking Manager was used to reconstruct the three-dimensional marker
coordinates. Visual 3D software (Version 4.8, C-Motion, Inc., Rockville, MD, USA) was used
to process the raw coordinate and force data and compute segmental kinematics and kinetics.
Force data and coordinate data were low-pass filtered using a fourth-order zero-lag Butterworth
filter with a 200 Hz and 12 Hz cutoff frequency, respectively. Lower and upper extremity
segments and the thorax were modeled as frustra of cones, while the pelvis was modeled as a
cylinder and the head as a sphere. The whole body center of mass position was calculated as the
weighted average of the center of mass positions of each of the 15 modeled segments. Data
obtained from Visual3D was exported and analyzed using a customized Matlab program
(Version R2011b, The MathWorks, Natick, MA, USA). Foot contact events were defined using
a 30 N vertical force threshold. Stance time was calculated by dividing the number of frames that
the foot contacted the force plate by the frame rate.
Rotation into the new direction during cutting orients the body to the new path of travel
(Besier, Lloyd, Cochrane, et al., 2001; Patla, et al., 1991). As a result, the local coordinate
system of the body is no longer aligned with GRF and COP variables, referenced in the global
coordinate system of the lab. Thus, in order to understand these data with respect to the planes
of the body, GRF data and COM-COP variables were rotated to align with the local coordinate
system following the methods described by Glaister et al. (2007).
MECHANICS OF MANEUVERS 29

Briefly, using the COM as the origin of the local coordinate system, axis alignment was
determined using a finite-difference method with a two-point interval. This determined the
COM orientation relative to the global coordinate system and is reported in this study as
progression angle, calculated in Equation 1:

, (1)
where x
2
, x
1
, y
2
, and y
1
are the x and y positions of the COM in global coordinates at
individual time frames (x is medial-lateral (ML) and y is anterior-posterior (AP)).
Horizontal GRFs were rotated to align with the local coordinate system using a rotation
matrix (Equation 2).
[

] [

] [

], (2)
where F
x
and F
y
are the horizontal force outputs from the force plates, F’
x
and F’
y
are the
rotated GRF, and θ is the axis alignment angle calculated in Equation 1.
All GRF data were normalized by body weight. Negative AP (braking) GRFs were
defined as those opposing forward progression; positive ML (medial) GRFs were defined as
those pushing the body towards the direction of the cut. To quantify deceleration and translation
demands, the change in AP and ML whole body linear momentum was quantified in each plane
by calculating ground reaction force impulse (GRI) as the integration of GRF over time using
reoriented posterior and medial-lateral GRF data (Zatsiosky, 2002).
Separation distance between the COM and COP was calculated in the AP and ML
directions by subtracting their positions in the global coordinate system. These distances were
rotated into a local coordinate system, using a rotation matrix for vector rotation (Equation 3).

MECHANICS OF MANEUVERS 30

[

] [

] [

] , (3)
where COM-COP
x
and COM-COP
y
are the global separation distances in the ML and AP
directions, respectively, COM-COP’
x
and COM-COP’
y
are the rotated anatomical separation
distances, and θ is the axis alignment angle calculated in Equation 1.
All COM-COP variables were normalized to body height, to account for the
anthropometrics of body segments. Negative AP (posterior) separation indicates that the COM is
posterior to the COP. Positive (medial) separation indicates that the COM is separated from the
COP towards the direction of the cut.
Deceleration demands were quantified using AP ground reaction force impulse during the
braking phase, the time during which the AP ground reaction force vector remained posterior;
translation demands were quantified using ML ground reaction force impulse during the entire
stance phase. To understand deceleration mechanics, peak COM-COP posterior separation
distance and peak posterior GRF were calculated. To understand translation mechanics, peak
COM-COP ML separation distance and peak medial GRF were calculated. Other dependent
variables for this study included 2D horizontal resultant COM velocity at initial contact with
each force plate, stance time, and peak progression angle. All dependent variables were
calculated during the cut (execution) step and one step prior to the cut step (approach). For all
dependent variables, the average of 4 trials for each subject for each task was used for analysis.
Statistical Analysis
Descriptive statistics were used to describe peak progression angle for each task.
Separate two-way repeated measure ANOVAs (direction x step) were used to determine if
differences exist between task directions (RUN, CUT45 and CUT90) or steps (approach and
MECHANICS OF MANEUVERS 31

execution) for all other dependent variable. Greenhouse-Geisser adjustments were used to
correct for violations of sphericity, when appropriate. Significance was set at α≤ 0.05. Post-hoc
analyses were then examined with t-tests, using a Bonferroni correction, α ≤ 0.0056 (0.05/9
paired comparisons). Statistical analyses were performed using PASW software (version 18,
SPSS, Inc., Chicago, IL).
Results
Velocity
Subjects performed all tasks at their maximum effort. A significant direction x step
interaction (F(2, 48) = 565.973, p<0.001) was observed for horizontal COM velocity at initial
contact (Figure 3.2). During both steps, when compared to RUN, velocity was smaller during
CUT45 and CUT90 (p<0.001), and velocity was greater during CUT45 than CUT90 (p<0.001).
When compared to the execution step, velocity was greater during the approach step of CUT90
(p<0.001) but smaller during RUN and CUT45 (p<0.005).
Stance Time
A significant direction x step interaction (F(1.293, 31.032) = 58.404, p<0.001) was
observed for stance time (Figure 3.2). During both steps, stance time was larger in CUT45 and
CUT90 compared to RUN (p≤0.001), and stance time was greater in CUT90 compared to
CUT45 (p<0.001). When compared to the execution step, stance time was smaller during the
approach step of CUT90 (p<0.001).
Progression angle
Peak progression angle for the RUN condition was 1.2 ± 0.6 degrees, for the CUT45
condition was 30.6 ± 3.1 degrees, and for CUT90 was 63.4 ± 8.2 degrees.
MECHANICS OF MANEUVERS 32

Figure 3.2 COM horizontal velocity at initial contact (left) and stance time (right). Gray
diamonds represent approach step; black squares represent execution step. Error bars represent
standard deviation. * represent differences between tasks during the execution step; + represent
differences between tasks during the approach step; ^ represent within-task differences between
steps.
Braking
Ground reaction force impulse. A significant direction x step interaction (F(1.335,
32.042) = 25.693, p<0.001) was observed in AP GRI (Figure 3.3). During both steps, when
compared to RUN, posterior GRI was greater during CUT45 and CUT90 (p<0.001), and
posterior GRI was greater during CUT90 than CUT45 (p<0.001). When compared to the
execution step, a smaller braking impulse was found in approach step of RUN (p<0.001), and a
larger impulse was found in the approach step of CUT90 (p<0.001). No differences were
observed between the approach and execution steps of CUT45.
Peak ground reaction force. A significant direction x step interaction (F(2, 48) =
52.852, p<0.001) was found in peak posterior GRF (Figure 3.3). During both steps, posterior
GRF was greater during CUT90 than CUT45 and RUN (p<0.001). During the execution step,
when compared to the RUN condition, posterior GRF was greater in the CUT45 condition
(p<0.001). When compared to the execution step, a greater peak GRF was found in the approach
step of CUT90 (p<0.001).
MECHANICS OF MANEUVERS 33

COM-COP separation distance. The peak posterior COM-COP separation was
observed at the beginning of stance for all tasks (Figure 3.4). A significant main effect of
direction (F(2, 48) = 348.555, p<0.001) was observed (Figure 3.5). When collapsed across step,
separation distance was greater in the CUT45 and CUT90 conditions compared to the RUN
condition (p<0.001). Posterior COM-COP separation was greater during CUT90 compared to
CUT45 (p<0.001).
Translation
Ground reaction force impulse. A significant direction x step interaction was found
(F(2, 48) = 168.358, p<0.001) in ML GRI (Figure 3.3). During both steps, medial GRI was
greater in CUT45 and CUT90 compared to RUN (p<0.001). Medial GRI was greater in CUT90
compared to CUT45 during the execution step (p<0.001) but smaller during the approach step
(p<0.001). When compared to the execution step, a smaller GRI was found in the approach step
of all tasks (p<0.001).
Peak ground reaction force. A significant direction x step interaction was found (F(2,
48) = 16.380, p<0.001) in peak medial GRF (Figure 3.3). During both steps, a greater peak
medial GRF was found during the CUT45 and CUT90 conditions compared to the RUN
condition (p<0.001). No differences were found between CUT45 and CUT90 during either step.
When compared to the execution step, a smaller GRF was found in the approach step of all tasks
(p<0.001).
COM-COP separation distance. The center of mass was positioned medial to the stance
foot during the execution step of all tasks. For the approach step, subjects’ COM was medial to
the stance foot during CUT45 and CUT90 and lateral to the stance foot during the run (Figure
3.4). Generally, peak ML separation distance occurred during mid-stance. A significant
MECHANICS OF MANEUVERS 34

direction x step interaction was found (F(2, 48) = 208.052, p<0.001) in peak medial COM-COP
separation (Figure 3.5). During both steps, ML separation distance was greater during the
CUT45 and CUT90 conditions than the RUN condition (p<0.001). ML distance was also greater
during CUT90 compared to CUT45 in the execution step (p<0.001) but smaller in the approach
step (p<0.001). When compared to the execution step, a smaller separation distance was found
in the approach step of all tasks (p<0.001).

Figure 3.3 Ground reaction force impulse (left column) and peak ground reaction force (GRF)
(left column). Gray diamonds represent approach step; black squares represent execution step.
Error bars represent standard deviation. * represent differences between tasks during the
execution step; + represent differences between tasks during the approach step; ^ represents
within task differences between steps.

MECHANICS OF MANEUVERS 35

Figure 3.4 Representative graphs of center of mass (long light gray lines) and center of pressure
(short dark gray lines) position for a right foot dominant subject: (A) RUN, (B) CUT45, (C)
CUT90 (L and R = left and right foot COP; Lon = left foot contact: approach step; Loff = end of
left stance; Ron = right foot contact: execution step; Roff = end of right stance) The vertical axis
represents forward displacement (m); the horizontal axis represents lateral displacement (m).

MECHANICS OF MANEUVERS 36

Figure 3.5 Peak separation distance of COM and COP in AP (left) and ML (right) directions.
Gray diamonds represent approach step; black squares represent execution step. Error bars
represent standard deviation. < represent differences between tasks when collapsed across steps;
* represent differences between tasks during the execution step; + represent differences between
tasks during the approach step; ^ represents within task differences between steps.

Discussion
These data support the hypothesis that cutting requires greater braking and translation
than running and that these demands increase when cutting to a larger angle. Greater posterior
and medial ground reaction force impulses during cutting compared to running and during
CUT90 compared to CUT45 indicate that greater changes in whole body momentum or velocity
were required for cutting to larger angles. While individuals adjusted the position of their center
of mass, the magnitude of the ground reaction forces, and stance time to meet these braking and
translation demands, the extent of these adjustments varied across tasks.
The braking demands, as indicated by the posterior GRI, were greater during cutting than
running, but disproportionately larger braking demands were observed during CUT90. As
expected, when cuts were performed at maximal effort, individuals had to decelerate more when
compared to straight running. This was accomplished during the execution step with a reduction
in velocity at initial contact, longer stance time, larger peak posterior GRFs, and a more posterior
MECHANICS OF MANEUVERS 37

position of the COM. Interestingly, these data indicate that with systematically increased cut
angle, the deceleration demands did not also linearly increase: CUT90 required
disproportionately greater braking. During the execution step, the difference in posterior GRI
between CUT45 and CUT90 was almost four times the difference observed between RUN and
CUT45. GRI can be modulated by altering the magnitude of the GRF or the duration of force
application or both. Across tasks, disproportionately slower velocity and greater stance time was
observed, while a more proportional increase in peak posterior GRFs was observed. The data
from this study indicate that both the magnitude of the posterior GRF and time of force
application were altered to accomplish the greater decrease in linear momentum during CUT90.
However, stance time may have played a larger role in meeting deceleration demands during the
execution step of CUT90.
Greater braking was accomplished with a more posteriorly positioned COM during
cutting to 45 and 90 degrees. The position-velocity relationship modeled during gait termination
suggests that the faster the anterior velocity at initial contact, the more posterior the COM must
be positioned relative to the terminating foot in order to successfully decelerate the COM (Pai &
Patton, 1997). In the current study, the COM was positioned most posteriorly during the task
with the slowest approach velocity (CUT90). In fact, the trend in posterior position across tasks
was similar to the trend observed in GRI. These data suggest that while posterior COM position
may be coupled with anterior velocity during deceleration, it is more likely related to the change
in anterior velocity demands of the task as opposed to the initial contact velocity during tasks
that require ongoing motion.
Greater translation demands during cutting were found compared to running, and these
demands proportionately increased with greater cut angle. These observations are based on the
MECHANICS OF MANEUVERS 38

differences in ML GRI during the execution step: unlike the posterior GRI, the medial GRI
linearly scaled across tasks. This suggests that CUT90 required proportionately greater
translation. Also unlike braking, no difference in peak GRF was observed in this plane between
CUT45 and CUT90. It appears that the larger translation demands of CUT90 were accomplished
by increasing stance time but not GRF magnitude.
Greater translation during cutting was accomplished with greater ML separation of the
COM and COP. During the execution step of both cuts, subjects’ separated their COM from the
COP in the ML direction by more than 25% of their body height, which may have allowed for
increased cut speed but resulted in a decreased progression angle. This is the first study in which
individuals attempted cuts at their fastest speed, and their COM trajectory followed a curved path
(Figure 3.4). Upon visual inspection, subjects completed the required change of direction,
following the taped lines on the floor; however, peak progression angles of the COM were
approximately 70% of the desired cut angle for both CUT45 and CUT90. A recent study
(Vanrenterghem, et al., 2012) demonstrated decreased progression angle during cutting at 45˚ as
cutting speed increased incrementally from 2 to 5 m/s. At the fastest speed (5 m/s), they found a
smaller progression angle (25.5˚) than was shown in this study (Vanrenterghem, et al., 2012).
While this supports the notion that the body follows a curved path during cutting, the larger
progression angle for CUT45 at a faster speed found in this study may be attributed to the fact
that subjects were cutting at a speed reflective of their athletic abilities rather than a target speed.
Whole body postures during cutting may have implications for ACL injury. Greater
posterior GRFs were found during cutting, which has been related to increased anterior tibial
shear force during dynamic tasks (Sell, et al., 2007; Yu, et al., 2006), a risk factor for ACL
injury. Along with loading, the position of the COM during the cuts, posterior and medial to the
MECHANICS OF MANEUVERS 39

COP, is similar to the body position described during the time of ACL injuries (Teitz, 2001). In
fact, hip abduction during cutting, which may contribute to separation of the COM from COP
medially, has been correlated with potentially injurious knee joint loading (Sigward & Powers,
2007). The segmental mechanics that contribute to these whole body postures were not
considered in this study; thus, more research is needed to determine the lower extremity and
trunk kinematics and kinetics associated to these whole body postures and how they are related
to risk of injury.
Results from this study provide insight into the anticipatory adjustments necessary to
decelerate and translate the body during cutting. Posterior and ML GRI were greater during the
approach step of both cutting tasks compared to running, indicating that deceleration and
translation began prior to the execution step. During the approach step of both cuts, the ML
GRF was oriented into the direction of the cut, unlike RUN. Thus, the ML GRF acted to
accelerate the COM into the direction of the cut during both steps, similar to turning (Glaister, et
al., 2008). Interestingly, individuals prioritized deceleration and translation differently across
steps, depending on the cut angle. During CUT45, GRI and peak GRFs suggest that both
braking and translation were somewhat evenly distributed over the approach and execution steps.
In contrast, greater braking (i.e., greater posterior GRI and peak GRFs) was observed during the
approach step of CUT90 compared to the execution step. Less translation was accomplished
during the approach step of CUT90 however, despite the greater translation demands. ML
impulse during the approach step was 3.2 smaller than the execution, indicating that translation
was accomplished primarily during the execution step. Thus, these data suggest that individuals
evenly distributed the deceleration and redirection demands across the approach and execution
steps of CUT45 but prioritized deceleration over translation during the approach step of CUT90.
MECHANICS OF MANEUVERS 40

In this study, two steps were analyzed, but the results suggest that adjustments from steady state
locomotion may have been initiated prior to the approach step and continued after the execution
step.
These anticipatory adjustments may play different roles based on the stability-mobility
requirements that different cut angles present. Based on previous research, LePellec and Matton
(1999) summarized multiple roles that anticipatory postural adjustments could serve, including
minimizing the postural disturbance, and/or initiating the disequilibrium that is necessary to
produce momentum. When cutting to a greater angle, greater translation was required and more
braking began prior to the execution step. This suggests that a certain degree of stability may be
needed in the plane of progression in order to initiate the disequilibrium necessary to translate
the body into the new direction. When cutting to a larger angle, deceleration during the approach
step may provide a more controlled, stable position of the body, thereby reducing the postural
disturbance caused by the movement to allow successful translation. When cutting to a less
severe angle, braking and translation were more evenly distributed across steps. In this case,
deceleration did not appear to be prioritized, and initiation of disequilibrium into the new
direction was occurring in the approach step. This indicates that less stability in the plane of
progression is needed in order to initiate the disequilibrium necessary for translation to smaller
cut angles. Taken together, these data suggest that the stability demands for redirection differ
based on the degree of the cut angle. It is not clear from the tasks chosen for this study whether
this stability-redirection tradeoff shifts at a particular cut angle within the 45 to 90 degree range.
The whole body adjustments made in anticipation of the cutting tasks have important
implications for athletes. Compared to the execution step, smaller ML separation distance as well
as impulse in the approach steps of both cuts suggests that translation began before and was
MECHANICS OF MANEUVERS 41

completed during the execution step. Braking was evenly distributed over both steps during
CUT45 but was accomplished to a greater degree during the approach step of CUT90. In a game
situation, if athletes do not have adequate time to plan their change in direction, these subtasks
would have to be superimposed into a single step. This could lead to unsuccessful cutting
attempts, particularly when changing direction to more acute angles as adequate deceleration
may not be feasible. Alternatively, if lower extremity muscles are not prepared to counter the
increase in external load, high forces during the cutting step could lead to strain in passive
structures of lower extremity joints, thus potentially resulting in injury.
This study provides important insight into the whole body adjustments made during cuts
performed at maximal effort to different angles. However, interpretation of these data is limited.
First, only high level soccer players were studied, as these types of athletes have experience
changing direction quickly. It is assumed that these mechanics represent strategies that optimize
performance, but further work is needed to understand the relationship between postural
variables and task performance. In addition, it is not known whether these same strategies would
be used by athletes that participate in different sports or in less skilled individuals. Furthermore,
the variables assessed in this study related to whole body posture. While some of these variables
have been implicated in lower extremity injury mechanisms, interpretation of injury risk is not
valid without understanding the joint or segmental mechanics used to accomplish these whole
body postures.
This was the first study to analyze whole body postural adjustments during cutting.
Overall, braking and translation were greater in the cuts compared to the straight run. With
systematically increased cut angle, disproportionately greater braking but proportionately greater
translation was found. Anticipatory adjustments were made prior to the execution of the cuts,
MECHANICS OF MANEUVERS 42

and these provided important insight into task demands. Future work is needed to understand
how these postural strategies relate to joint mechanics or how they are related to agility
performance or injury.

MECHANICS OF MANEUVERS 43

CHAPTER IV
JOINT AND SEGMENTAL MECHANICS OF RUNNING TURN MANEUVERS

Abstract
Cutting is necessary for participation in many sports but is also associated with non-
contact ACL injury. Whole body demands of deceleration and redirection increase with greater
cut angles. However, the influence of cut angle on joint and segmental mechanics has not been
systematically studied. The purpose of this study is to determine how increases in deceleration
and redirection demands affect joint and segmental mechanics. To do this, lower limb and trunk
kinematics and kinetics were evaluated during the execution of two sidestep cutting maneuvers
(to 45 and 90 degrees) in twenty-five healthy soccer players. A two-way multi-variate analysis of
covariance (MANCOVA) determined that differences existed between task directions but not
sexes when considering all dependent segmental variables and covarying for approach velocity
(α ≤0.05). Post-hoc analyses were then examined with paired t-tests. Generally, the larger
deceleration and redirection demands of the CUT90 did not translate into systematic increases
across all kinematic and kinetic variables. While differences in joint and segmental mechanics
were found between tasks, they were not simply systematically scaled differences. Individuals
emphasized different joints to decelerate the body and exhibiting different patterns at the hip to
redirect.
Introduction
Quick changes of direction during running (i.e., cutting) are required for successful
participation in many sports (Alentorn-Geli, et al., 2009; Bloomfield, et al., 2007a; Brughelli, et
al., 2008; Krustrup, et al., 2005; Orendurff, et al., 2010), yet are associated with non-contact
MECHANICS OF MANEUVERS 44

anterior cruciate ligament (ACL) injury risk (Boden, et al., 2000; Cochrane, et al., 2007;
Krosshaug, et al., 2007; Olsen, et al., 2004). Successful performance of cutting tasks requires
athletes to make whole body postural adjustments in order to decelerate and redirect their body
(Chapter III). Joint and segmental mechanics during cutting have been studied in detail with
respect to ACL injury mechanisms but have not been considered in the context of the
deceleration and redirection demands of the task. Understanding the relationship between whole
body and joint mechanics necessary for cutting and those related to increased risk for injury is
important for the development of injury prevention training programs. Training
recommendations aimed at modifying segmental mechanics to reduce injury risk may not be
adopted by athletes if they are in opposition to the demands of the task.
Whole body adjustments for deceleration and redirection are characterized by the
position and velocity of the center of mass (COM), specifically the position of the COM with
respect to the center of pressure (COP) as well as ground reaction forces and ground reaction
force impulse. Deceleration during cutting is accomplished by positioning the COM posterior to
the COP and generating posteriorly-directed (braking) ground reaction forces (GRF) (Chapter
III). Redirection of the body is accomplished by generating medial ground reaction forces,
separating the COM from the COP towards the new direction, and rotating the body to align with
the new travel path. The extent of the separation between the COM and COP and the magnitude
of ground reaction forces have been found to increase with increasing deceleration and
redirection demands. Specifically, greater posterior and medial-lateral (ML) separation distances
between the COM and COP and greater posterior and medial ground reaction forces were
observed during a sidestep cut performed to 90 degrees compared to 45 degrees (Chapter III).
MECHANICS OF MANEUVERS 45

Based on previous biomechanics research of sidestep cutting tasks, it appears that the
whole body postural requirements for deceleration and redirection are accomplished through
adjustments at the joint or segment level. In the sagittal plane, the ankle and knee are in relative
extension at initial contact during cutting (Neptune, Wright, & Van den Bogert, 1999; Pollard, et
al., 2004; S. Sigward & C. M. Powers, 2006), which may allow positioning the COM posterior to
the COP. Additionally, the presence of hip and knee extensor and ankle plantar flexor moments
and increased electromyographic (EMG) activity of the gluteus maximus, quadriceps and
plantarflexor muscles during the deceleration phase of stance suggest that the lower extremity
extensors work to decelerate the body during cutting (Andrews, McLeod, Ward, & Howard,
1977; Besier, Lloyd, Cochrane, et al., 2001; Colby et al., 2000; Landry, et al., 2007; Neptune, et
al., 1999; Rand & Ohtsuki, 2000; S. Sigward & C. M. Powers, 2006; S. M. Sigward & C. M.
Powers, 2006). Frontal and transverse plane hip and trunk position may facilitate redirection. A
laterally-placed limb or hip abduction (Dempsey, et al., 2007; Sigward & Powers, 2007)
observed during cutting is consistent with separation of the COM from the COP in the ML
direction. Trunk lean over the plant foot, observed in turning (Patla, et al., 1999) and cutting
(Jamison, et al., 2012), may facilitate acceleration of the COM into the new direction. Finally,
pre-rotation of the limb at initial contact and rotational movement (external) of the hip are
thought to contribute to rotation of the body toward the new direction (McLean, et al., 2005;
Sigward & Powers, 2007).
While joint and segmental mechanics observed during cutting appear to contribute to the
whole body postural adjustments, much of what we know about these mechanics comes from
assessments of sidestep cutting tasks performed at smaller angles (i.e., 30-45 degrees). It is
therefore not known how these joint and segmental mechanics change with increased whole
MECHANICS OF MANEUVERS 46

body deceleration and redirection demands, though this may have implications for ACL injury.
Individuals may be at greater risk for ACL injury during tasks that have greater deceleration
demands if greater lower extremity extension and larger quadriceps contraction are needed to
position the COM more posteriorly and accommodate the larger posteriorly-directed GRF.
Together, these mechanics are thought to contribute to excessive anterior tibial shear (Yu &
Garrett, 2007), resulting in increased loads to the ACL (Berns, et al., 1992; Beynnon, et al.,
1995; Markolf, et al., 1995). Similarly, greater trunk lean (Dempsey, et al., 2009; Jamison, et al.,
2012), more hip abduction (Golden, et al., 2009; Sigward & Powers, 2007), and greater hip and
limb internal rotation (McLean, et al., 2005; Sigward & Powers, 2007) have been related to
potentially injurious frontal plane knee loading.
Therefore, the purpose of this study was to determine how increases in whole body
deceleration and redirection demands affect joint and segmental mechanics by evaluating lower
limb and trunk kinematics and kinetics during the execution of two sidestep cutting maneuvers
(to 45 and 90 degrees). Whole body COM position and GRF variables have been reported during
sidestep cuts performed to 45 and 90 degrees as fast as possible in this subject population
(Chapter III). We hypothesized that subjects would exhibit lower extremity extension, extensor
moments and power absorption at the ankle, knee, and hip during both cutting tasks and that
these variables would be greater during cuts performed to 90˚ when compared to cuts to 45˚. In
addition, during both cutting tasks, we hypothesized that subjects would exhibit trunk lean and
hip abduction, external rotation, as well as abductor and external rotator moments, and power
generation at the hip in the frontal and transverse planes. We hypothesized that these variables
would also scale with cut angle (i.e., be greater during cuts performed to 90 when compared to
cuts to 45 degrees).
MECHANICS OF MANEUVERS 47

Methods
Participants
Twenty-five healthy soccer players between the ages of 18-30 participated in this study
(Table 4.1). A power analysis determined that with 25 subjects, the study is adequately powered
to detect differences between task conditions with an alpha of 0.05 and 85% power. Athletes
were considered experienced, high-level soccer players (college, semi-professional,
professional). Twenty-two participants reported that they were right-limb dominant, when asked
which foot they would kick a ball with.
Table 4.1
Subject demographics (mean ± standard deviation)
Males (n=13) Females (n=12)
Age (years)
20.23 ± 2.8
24.8 ± 3.6
Height (m) 1.8 ± 0.1 1.7 ± 0.1
Weight (kg) 76.2 ± 8.0 65.3 ± 7.0
Soccer experience (years) 14.5 ± 4.1 19.1 ± 3.4
Soccer experience (% age) 71.21 ± 12.9 76.9 ± 5.8

All subjects were healthy without complaints of lower extremity injuries. Subjects were
excluded from the study if they had: 1) history of previous lower extremity surgery, 2) recent
lower extremity injury resulting in persistent pain and/or inability to participate in sport (greater
than 3 weeks) in the last six months, 3) concurrent pathology or morphology that could cause
pain or discomfort during physical activity; or 4) any physical, cognitive or other condition that
would impair their ability to perform the tasks in this study. Prior to participation, all subjects
MECHANICS OF MANEUVERS 48

were explained the testing procedures, and informed consent was obtained as approved by the
Investigational Review Board at the University of Southern California Health Science Campus.
Instrumentation
Three-dimensional motion analysis was performed using a marker-based, 11-camera
digital motion capturing system (Qualisys, Gothenburg, Sweden) at 250 Hz. Ground reaction
force data were obtained at 1500 Hz using a 1.20 x 0.60 m
2
force platforms (AMTI, Newton,
MA, USA) embedded into the floor surface. Kinematic and kinetic data were collected
synchronously using the motion capture software (Qualisys Track Manger, version 2.6).
Reflective markers (25 mm spheres) placed on specific bony landmarks were used to define body
segments in three-dimensional space. Laser timing gates (Brower IRD-T175; Brower Timing
Systems, Draper, UT, USA) were used to demine the time to complete the task.
Procedures
All testing took place at the Human Performance Laboratory at the University of
Southern California, located within Competitive Athlete Training Zone (CATZ). Participants
wore shorts, tank tops, and their own running/athletic shoes (not cleats). Tracking marker
clusters mounted on semi-rigid plastic plates were secured to nylon/lycra bands on the subject’s
arms, forearms, thighs, shanks, and shoes. Using a full-body marker set, reflective markers were
placed over 45 anatomical landmarks, similar to that used by Song et al. (2012). Following a
static calibration trial, the tracking marker clusters as well as the markers on the end of the
second toes, posterior superior iliac spines, iliac crests, L5-S1 junction, acromions, radial and
ulnar styloid processes, third metacarpal heads, clavicle, cervical process of C7, and head
remained on the subject.
MECHANICS OF MANEUVERS 49

Prior to testing, subjects were led through a 15 minute warm-up and were given time to
stretch. Participants were then instructed to perform two sidestep cutting maneuvers to 45˚
(CUT45) and 90˚ (CUT90) at their fastest speed. For both cutting tasks, subjects ran as fast as
possible 7.5 meters, planted their dominant foot and changed direction away from their plant foot
at the designated angle (45 or 90 degrees), and continued running as fast as possible for 7.5
meters (Figure 3.1). The cutting angles were marked on the floor with tape. Laser timing gates
were placed at the beginning and end of the 15 meter path to measure task completion time. The
cut order was counter-balanced between subjects to prevent effects related to testing order.
Trials were accepted if the subject’s task completion time was within a ± 2.5% interval as
measured by the timing gates and if the foot fully contacted the force platform.
Data analysis
Qualisys Tracking Manager was used to reconstruct the three-dimensional marker
coordinates. Visual 3D software (Version 4.8, C-Motion, Inc., Rockville, MD, USA) was used
to process the raw coordinate and force data and compute segmental kinematics and kinetics.
Force data and coordinate data were low-pass filtered using a fourth-order zero-lag Butterworth
filter with a 200 Hz and 12 Hz cutoff frequency, respectively. The whole body center of mass
position was calculated as the weighted average of the center of mass positions of each of the 15
modeled segments. The local coordinate systems of the body segments were derived from the
standing calibration trial. Lower and upper extremity segments and the thorax were modeled as
frustra of cones, while the pelvis was modeled as a cylinder and the head as a sphere. Joint
kinematics were calculated by determining the transformation from the triad of markers to the
position and orientation of each segment determined from the standing calibration trial. Euler
angles with the following order of rotations were used to calculate joint kinematics:
MECHANICS OF MANEUVERS 50

flexion/extension, abduction/adduction, and internal/external rotation. Three-dimensional net
joint moments were calculated using inverse dynamics equations. Joint power was calculated as
the product of joint moment and angular velocity in each plane. All kinetic data were
normalized to body mass. Data obtained from Visual3D was exported and analyzed using a
customized Matlab program (Version R2011b, The MathWorks, Natick, MA, USA). Foot
contact events were defined using a 30N vertical force threshold. Approach velocity was
calculated using the COM position. The average velocity of the COM in the original direction of
progression over a 1.5 meter distance before initial contact with the force plate was calculated
(i.e., approach velocity).
All dependent variables were analyzed during the deceleration phase, defined as the time
from initial contact with the force plate to maximal knee flexion. This generally occurred at 50%
of stance, and has been used in previous studies to define the deceleration phase during cutting
(Chaudhari, Hearn, & Andriacchi, 2005; Jamison, et al., 2012). The deceleration phase was of
particular interest because non-contact ACL injuries often occur within this period of stance
(Boden, et al., 2000). Joint kinematics were calculated at initial contact, and the change in joint
angle over the deceleration phase (i.e., joint excursion) was also calculated. Peak net joint
moments during deceleration and average joint power throughout the deceleration phase were
also determined. In order to assess the joint and segmental mechanics that contributed to
deceleration of the body’s COM, sagittal plane kinematics and kinetics were analyzed at the
ankle, knee and hip. Hip frontal and transverse plane kinematics and kinetics were analyzed to
assess the joint and segmental mechanics involved in redirection. Also, the angle that the trunk
deviated from global vertical in the frontal plane was analyzed (trunk lean). For all dependent
variables, the average of 4 trials for each subject for each task was used for analysis.
MECHANICS OF MANEUVERS 51

Statistical Analysis
Previous work has reported sex differences in mechanics during cutting (McLean, et al.,
2005; Pollard, et al., 2004; Pollard, et al., 2007; S. M. Sigward & C. M. Powers, 2006). In
addition, the magnitude of ground reaction forces used to calculate joint kinetics is influenced by
velocity (Brughelli, Cronin, & Chaouachi, 2011). Therefore, sex and approach velocity were
considered statistically in this analysis. A two-way multi-variate analysis of covariance
(MANCOVA) was used to determine if differences exist between task directions (CUT45 and
CUT90) or sexes (male and female) when considering all dependent segmental variables and
covarying for approach velocity (α ≤0.05). Post-hoc analyses were then examined with paired t-
tests, using a Bonferroni correction, α ≤ 0.002 (0.05/22 comparisons). Statistical analyses were
performed using PASW software (version 18, SPSS, Inc., Chicago, IL).
Results
The results of the MANCOVA revealed a significant main effect of direction (F(22,24) =
2.054, p=0.044) but not sex (p=0.096). No significant interaction between sex and direction was
found (p=0.415) when all of the dependent variables were considered; therefore data were
collapsed across sex, and comparisons were made between CUT45 and CUT90 (Table 4.2).
Approach velocity
When compared to CUT45, approach velocity was slower during CUT90 (4.15 ± 0.32
m/s versus 5.73 ± 0.45 m/s, p<0.001).

MECHANICS OF MANEUVERS 52

Table 4.2
Kinematics and kinetics of cutting maneuvers
Variable CUT45 CUT90 p-value
Kinematics

Hip flexion angle

IC 46.06 ± 6.82 32.08 ± 11.05 <0.001*

Excursion -18.50 ± 5.07 -6.02 ± 9.19 <0.001*
Hip abduction angle

IC 3.90 ± 7.07 23.94 ± 4.85 <0.001*

Excursion 3.12 ± 4.69 -7.27 ± 4.88 <0.001*
Hip internal rotation angle

IC 12.96 ± 6.23 10.14 ± 7.88 0.098

Excursion -11.64 ± 6.79 -11.49 ± 8.83 0.928
Knee flexion angle

IC 25.21 ± 6.97 14.67 ± 6.35 <0.001*

Excursion 16.58 ± 9.42 34.85 ± 9.62 <0.001*
Ankle plantarflexion angle

IC -4.48 ± 8.86 -12.86 ± 11.85 <0.001*

Excursion 23.49 ± 9.25 36.71 ± 15.59 <0.001*
Trunk lean into direction of cut

IC 9.25 ± 4.78 15.18 ± 6.71 <0.001*

Excursion 4.79 ± 1.96 8.92 ± 4.08 <0.001*

Moments

Peak hip extensor moment 4.65 ± 1.41 3.11 ± 1.10 <0.001*
Peak hip adductor moment 1.40 ± 1.46 3.20 ± 1.27 <0.001*
Peak hip external rotator moment 1.64 ± 0.90 1.60 ± 0.56 0.772
Peak knee extensor moment 2.67 ± 0.73 3.06 ± 0.60 0.030
Peak ankle plantarflexor moment 3.04 ± 0.53 2.58 ± 0.58 <0.001*

Power

Average hip sagittal power 6.66 ± 3.50 -0.13 ± 0.85 <0.001*
Average hip frontal power 0.09 ± 1.05 0.37 ± 0.99 0.400
Average hip transverse power 1.27 ± 1.00 0.40 ± 0.70 <0.001*
Average knee sagittal power -4.15 ± 3.11 -6.80 ± 2.16 0.001*
Average ankle sagittal power -10.08 ± 3.28 -6.87 ± 2.91 <0.001*

Note: Comparisons (mean ± SD) of hip, knee, ankle and trunk angles (degrees), moments
(Nm/kg), power (Watts/kg) of sidestep cutting maneuvers (CUT45 and CUT90). Positive power
indicates generation, negative power indicates absorption. * indicates a statistically significant
pairwise difference (p≤ 0.002).
MECHANICS OF MANEUVERS 53

MECHANICS OF MANEUVERS 54

Figure 4.1 Ensemble averages of angles and moments during the stance phase CUT45 (gray
line) and CUT90 (black line). X-axis is percentage of stance phase. Standard deviation (SD) bars
either +1 SD (bars above line) for that task or -1 SD (bars below line) for that task.

Figure 4.2 Average and standard deviations of joint powers across the first half of stance during
CUT45 (white) and CUT90 (gray).
MECHANICS OF MANEUVERS 55

Deceleration: Sagittal plane mechanics
When compared to CUT45, subjects exhibited smaller hip and knee flexion and greater
ankle plantarflexion angles at initial contact during CUT90 (p<0.001) (Figure 4.1). Less hip
sagittal plane angular excursion but greater knee and ankle excursions were found during CUT90
compared to CUT45 (p<0.001). Significantly smaller peak hip extensor and ankle plantarflexor
moments were found during CUT90 (p<0.001), but there was a trend towards a significantly
greater knee extensor moment during CUT90 compared to CUT45 (p=0.030). During the
deceleration phase, subjects exhibited average hip power absorption during CUT90 but average
power generation during CUT45 (Figure 4.2). Compared to CUT45, subjects exhibited
significantly less ankle power absorption but greater knee power absorption in the sagittal plane
during CUT90 (p≤0.001).
Redirection: Frontal and Transverse plane mechanics
When compared to CUT45, CUT90 was performed with significantly greater hip
abduction and trunk lean angles at initial contact (p<0.001). During CUT45, subjects moved into
a more hip abducted position during the deceleration phase. However, during CUT90, they
moved into less hip abduction and exhibited greater trunk frontal plane angular excursion into
the cut (i.e., away from their plant foot) (p<0.001). Peak hip adductor moments were noted
during early stance of both tasks (Figure 4.1). A significantly greater peak hip adductor moment
was found during CUT90 (p<0.001) but hip frontal plane power was not different between tasks
(p=0.400) (Figure 4.2).
In the transverse plane, only hip power differed between tasks: less hip power generation
was found during CUT90 compared to CUT45 (p<0.001). Differences were not found in
kinematics or joint moments.
MECHANICS OF MANEUVERS 56

Discussion
These data illustrate that different joint and segmental mechanics were used to meet the
whole body postural demands of sidestep cuts performed to 45 and 90 degrees. In contrast to our
hypotheses, the larger deceleration and redirection demands of the CUT90 did not translate into
systematic increases across all kinematic and kinetic variables. While differences in joint and
segmental mechanics were found between tasks, they were not simply scaled versions of one
another.
In the sagittal plane, joint position data were consistent with whole body postural data,
though the kinematic and kinetic data at the knee indicated that this joint may have played a
more critical role during CUT90. Consistent with the COM position data, all lower extremity
joints were in more extended positions at initial contact during CUT90 compared to CUT45.
This suggests that lower extremity sagittal plane kinematics assisted in positioning the COM
more posteriorly during deceleration. While the knee and ankle contributed to deceleration
during both cutting tasks, the larger deceleration requirements of CUT90 appeared to place
disproportionately greater demands on the knee. During both cuts, knee flexion and ankle
plantarflexion excursion and sagittal plane power absorption at the knee and ankle were found.
However, greater flexion excursion, power absorption, and a trend towards larger peak extensor
moments were found at the knee during the CUT90 compared to CUT45. This is of concern, as
previous studies suggest that during dynamic tasks, peak knee extensor moments, peak posterior
GRF, as well as EMG activity of the quadriceps is related to anterior tibial shear force (Sell, et
al., 2007; Yu, et al., 2006). This shear force at small degrees of knee flexion results in increased
ACL loading (Berns, et al., 1992; Markolf, et al., 1995). Thus, these data suggest that the greater
deceleration demands observed in the 90 degree cut were not distributed across the lower
MECHANICS OF MANEUVERS 57

extremity joints but instead were accommodated primarily at the knee joint, with mechanics that
are thought to increase ACL loading.
In contrast to the ankle and knee, the role of the hip extensors appeared to vary between
task conditions. Peak hip extensor moments were observed during both cutting tasks. However,
average hip sagittal plane power during CUT90 was close to zero, suggesting that the hip
extensors stabilized rather than decelerated the body. Moreover, power generation, not
absorption, was observed at the hip during deceleration of CUT45, indicating that subjects used
their hip extensors to propel their body forward. This pattern is similar to the one observed
during straight running (Novacheck, 1998; Zatsiorsky, 2008). It is also consistent with the whole
body postural differences observed between cutting to 45 degrees and straight running (Chapter
III). Compared to running, a small decrease (9%) in initial contact velocity during the cut step
along with relatively small increases in posterior impulse and peak posterior GRFs, during
CUT45 suggests that the deceleration demands of CUT45 are not much greater than those of a
straight run.
Differences in frontal plane hip mechanics were observed between cutting tasks,
suggesting that the hip functions differently to accomplish whole body redirection. It was
expected that hip abduction would be necessary to separate the COM and COP medially and
propel the body into the new direction. Further, greater hip abductor moments, abduction
excursion and power generation were expected during CUT90 to meet the larger redirection
demands compared to CUT45. While greater hip abduction was observed at initial contact of
CUT90, it was followed by movement into less abduction rather than more. This appears
counterintuitive to whole body mechanics, as ML COM-COP separation peaks at mid-stance.
This suggests that hip abduction must not be the only contributor to separation the COM from
MECHANICS OF MANEUVERS 58

the COP in the ML direction. Kinetic data suggests that during CUT90, the hip may work to
stabilize in the frontal plane rather than contribute to propulsion into the new direction. Initial
peak adductor moments were observed during both cuts, consistent with previous studies
(Pollard, et al., 2004; Pollard, et al., 2007); however, frontal plane moment patterns following
this peak differed between tasks. While not statistically analyzed, Figure 4.1 illustrates that the
initial adductor moment during CUT45 was followed by a peak abductor moment, similar to
previous studies assessing cutting to smaller angles (i.e., 30-45 degrees) (McLean, et al., 2004;
Neptune, et al., 1999; Pollard, et al., 2004). In contrast, individuals continued to exhibit a hip
adductor moment through most of deceleration during CUT90, with small power generation at
the hip. This suggests that cutting to greater angles may require greater hip frontal plane
stabilization.
Trunk lean into the direction of the cut was observed during both tasks. This is in
contrast to what is reported during walking turns (J. R. Houck, et al., 2006; Patla, et al., 1999)
and cutting (Jamison, et al., 2012), where trunk lean over the stance limb (i.e., away from that
turn) is thought to propel the COM into the new direction. The difference between the trunk
position in this study and Jamison et al. (2012) may be attributed to task demands; in this study,
cuts were preplanned and performed as fast as possible to greater cut angles. Trunk frontal plane
mechanics must also be considered in light of differences in hip mechanics between the tasks.
Along with hip frontal plane position, trunk lean into the cut likely contributed to ML COM-
COP separation. In fact, trunk lean into the cut may have been more critical during CUT90, as it
likely counteracted the hip movement into less abduction and allowed for the greater ML
separation distance. The increased stability afforded by this hip frontal plane position and the
large hip adductor moment may have facilitated the larger trunk lean into the cut during CUT90.
MECHANICS OF MANEUVERS 59

Despite the distinct rotation demands of the tasks, no differences in transverse plane
kinematics or kinetics were observed at the hip. While external rotation motion and external
rotator moments observed in both tasks suggest that the hip contributes to body rotation into the
new direction, greater excursion and peak moments were not observed during CUT90. In fact,
greater power generation was observed during CUT45. Together, these data suggest that the
greater rotational demands of CUT90 may have been accomplished by mechanics other than
those assessed in this study. Previous research has reported that during preplanned cutting tasks,
individuals pre-rotate their limb in anticipation of the rotational demands (Sigward & Powers,
2007). To further explore the extent to which individuals prepared themselves for the rotational
demands of the CUT90, a post-hoc analysis was performed on the magnitude of pelvic rotation
relative to the laboratory at initial contact. During CUT90, individuals rotated their pelvis
toward the new direction almost 35 degrees more compared to CUT45 (14.2 ± 5.5 versus 48.7 ±
2.4 degrees, p<0.001). Together, these data suggest that subjects may have met the greater
redirection demands of the CUT90 task by rotating the whole body and not just the lower limb.
Frontal and transverse plane hip and trunk mechanics described during the task with
greater redirection requirements (CUT90) may be considered potentially injurious. Greater hip
abduction and internal rotation has been associated with increase peak knee adductor moment
(McLean, et al., 2005; Sigward & Powers, 2007), and decreased trunk control has been shown to
predict ACL injury risk (Zazulak, Hewett, Reeves, Goldberg, & Cholewicki, 2007). As such,
injury prevention programs discourage excessive motion of the trunk and lower extremities in
the frontal and transverse planes (Dempsey, et al., 2007; Mandelbaum, et al., 2005; Myer, et al.,
2006). However, these mechanics increased with cut magnitude, suggesting that they may be
necessary for task success.
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These data provide important insight into how athletes achieve the whole body postures
that are required to complete side step cutting tasks performed at maximum effort. Not only do
these data suggest that the hip may play a different role during cutting to smaller and larger
angles, but they also illustrate a pattern of engagement in the sagittal and frontal planes that has
not been described previously. Instead of working to decelerate the body and attenuate impact
forces during cutting, it appears that the hip extensors work as stabilizers (CUT90) or power
generators (CUT45). During landing, increased engagement of the hip extensors has been
associated with decreased sagittal and frontal plane loading of the knee (Pollard, et al., 2010;
Sigward, Pollard, & Powers, 2012). However, it is not clear how increasing the engagement of
the hip extensors during cutting would influence task performance or potentially injurious
loading of the knee. Limb abduction and trunk lean into the cut appeared to contribute to the ML
separation of the COM and COP, and the presence of hip and pelvis internal rotation suggests
that pre-rotation of the body is necessary for redirection. Similarly, it is not known if limiting
frontal and transverse plane motion would affect task performance or potentially injurious
loading of the knee. Thus, future research should investigate relationships between these lower
extremity and trunk mechanics and both injury risk (i.e., knee valgus loading) and task
performance in order to effectively inform injury prevention training.
These data should be interpreted within the context of the experimental design. The
athletes in this study would be considered highly skilled as they performed at a high level
(profession, semi-professional or collegiate) and had been playing soccer for over 70% of their
life without incurring an ACL injury. This may account for the absence of sex differences in the
variables assessed. The tasks were performed at the athlete’s maximum effort and were
preplanned. Differences in joint mechanics would be expected during performance of randomly
MECHANICS OF MANEUVERS 61

cued tasks. Characterizations of potentially injurious mechanics were made based on previous
literature in this field and described in the context of changing cut demands (angles); therefore,
these mechanics cannot be related specifically to injury risk.

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CHAPTER V
CUTTING MECHANICS: RELATIONSHIP TO PERFORMANCE AND ACL INJURY
RISK

Abstract
Quick changes of direction during running (cutting) are necessary for successful
performance of many sports but are associated with non-contact ACL injuries. Currently, little is
known about the biomechanics associated with successful, fast performance of cutting tasks.
Without this knowledge, the technique emphasized in injury prevention programs may be at odds
with the demands of cutting tasks. The purpose of this study was to: 1) identify whole body
and/or segmental mechanics that are related to fast completion times of a 45 and 90 degree cut,
and from these variables, 2) determine which variables are significant predictors of performance
and/or ACL injury risk (i.e., peak knee adductor moment). Twenty-five healthy soccer players
performed sidestep cutting maneuvers to 45 and 90 degrees as fast as possible. Pearson’s
correlation coefficients and stepwise multiple regression were used to analyze relationships
between variables. The variables predictive of 45 degree cut performance included hip extensor
moment and hip sagittal plane power generation as well as ML COM-COP separation. ML
separation distance was also predictive of peak knee adductor moment. During the 90 degree
cut, ML GRI and hip frontal plane power generation were predictive of performance, while hip
internal rotation and knee extensor moment were predictive of peak knee adductor moment.
Introduction
Agility, a rapid whole body movement with change in direction and/or velocity,
(Sheppard & Young, 2006), is required for many field sports. Running change of direction
MECHANICS OF MANEUVERS 63

(cutting) maneuvers are hallmarks of agility but are unfortunately associated with anterior
cruciate ligament (ACL) injury (Boden, et al., 2000; Cochrane, et al., 2007; Krosshaug, et al.,
2007; Olsen, et al., 2004). Manipulations to whole body and segmental mechanics used to
complete cutting tasks as fast as possible, including greater horizontal ground reaction forces,
whole body position posterior and medial to the foot, and hip abduction and trunk lean, have also
been considered to be potentially injurious (Jamison, et al., 2012; Markolf, et al., 1995; McLean,
et al., 2005; Sigward & Powers, 2007; Teitz, 2001; Yu & Garrett, 2007). However, these
mechanics may be necessary (Chapter III, IV) and related to fast, successful performance of
these tasks. As athletes are driven by performance, they are unlikely to adopt movement patterns
that decrease risk for injury if they do not result in effective performance. Thus, an
understanding of the relationship between whole body and joint/segmental mechanics of cutting
maneuvers and both task performance and knee frontal plane loading is needed.
Athletes’ success in many sports relies on their ability to quickly change direction—to be
agile. They may perform a cutting maneuver in response to an object (e.g., the moving ball,
boundary line, etc.) or the actions of their teammates, or in order to evade or pursue an opponent.
During a 90-minute soccer game, players make an average of 727 turns/swerves: about eight
every minute (Bloomfield, et al., 2007a). The role of agility in distinguishing between levels of
sports participation, identifying talent, and influencing player selection in teams underscores its
importance in sports. Time to complete an agility test can discriminate between intercollegiate
athletes, recreational athletes and non-athletes, (Pauole, et al., 2000) as well as between elite and
sub-elite basketball (Delextrat & Cohen, 2008) and soccer players (Kaplan, et al., 2009; Reilly,
et al., 2000). Agility has been shown to be the most important indicator of talent in soccer, over
sport-specific skills, anthropometric, or psychological tests (Reilly, et al., 2000). It is also an
MECHANICS OF MANEUVERS 64

important determinant of player selection in youth soccer teams (Gil, et al., 2007) and the NFL
(McGee & Burkett, 2003).
Given its importance in sports, strength and conditioning coaches, athletic trainers, and
sports medicine researchers have sought to identify trainable qualities that may optimize change
of direction performance. Despite extensive examination, the relationship between many of the
trainable qualities thought to contribute to agility performance (e.g., leg muscle qualities, straight
running speed, leg power) and test completion time has not been empirically supported
(Brughelli, et al., 2008; Little & Williams, 2005; Markovic, 2007; WB. Young, et al., 2002; WB.
Young, et al., 2001). Importantly, change of direction performance is not related to straight
running speed (Buttifant, et al., 1995; Little & Williams, 2005; W. Young & Farrow, 2006; WB.
Young, et al., 2002), indicating that agility is a specific skill separate from speed. As
quantitative biomechanics research focused on change of direction performance is very limited
(Sheppard & Young, 2006), optimal technique for cutting is not well understood.
In order to change direction, individuals must decelerate in the original direction and
redirect their body into the intended direction (Hase & Stein, 1999). While whole body center of
mass position and velocity variables indicate that deceleration and translation of the body
increase with increased cut angle (Chapter III), joint and segmental mechanics reveal that these
sub-tasks are accomplished through different patterns when cuts are made to 45 and 90 degrees
(Chapter IV). It is therefore likely that different mechanics would be related to faster
performance times during a 45 and 90 degree cut.
Sagittal plane mechanics at the hip are likely to be related to performance of a 45 degree
cut, while frontal plane mechanics of the whole body may be related to performance of a 90
degree cut. During a 45 degree cut, the hip extensors act to propel the body forward in early
MECHANICS OF MANEUVERS 65

stance. This is contrast to a 90 degree cut, where the hip extensors stabilize and contribute to
deceleration (Chapter IV). Further, as this sagittal plane pattern at the hip is attributed to faster
straight running speeds (Belli, Kyrolainen, & Komi, 2002; Kyrolainen, Komi, & Belli, 1999), hip
extensor moments and power generation at the hip likely contributes to completion time during a
45 degree cutting task also. During the 90 degree cut, propulsion into the new direction does not
seem to be accomplished through hip abductors or rotators muscles, as small joint power was
observed in these planes (Chapter IV). Performance of the 90 degree cut may therefore be more
related to the whole body postural mechanics. While whole body deceleration is unlikely to
relate to fast completion times, translation of the whole body into the new direction is required to
a greater extent in this task compared to a 45 degree cut (Chapter III). Thus, during a 90 degree
cut, whole body postural mechanics for translation (i.e., medial-lateral center of mass (COM)
position relative to the center of pressure (COP) and medial-lateral ground reaction force impulse
(GRI)) are expected to relate to completion time.
As the relationship between non-contact ACL injury risk factors and cutting performance
remains unknown, it is possible that these variables hypothesized to relate to 45 and 90 degree
cutting performance also relate to knee joint loading. Altered frontal plane loading of the knee
during deceleration of landing and cutting tasks is thought to increase risk for injury.
Specifically, increased loads to the ACL are associated with relative knee extension and knee
abduction combined with large knee adductor (valgus) moments (Chaudhari & Andriacchi, 2006;
Markolf, et al., 1995; McLean, et al., 2008). In a prospective study, knee adductor moment
during a drop-land task was shown to predict ACL injury risk (Hewett, et al., 2005). High knee
adductor moments during cutting tasks are associated with joint positions at initial contact
including increased hip flexion, abduction and internal rotation angles (McLean, et al., 2005;
MECHANICS OF MANEUVERS 66

Sigward & Powers, 2007) and trunk lean (Jamison, et al., 2012). As these movement patterns
are thought to increase knee adductor moment, and thus the risk of ACL injury, they are
discouraged in prevention programs (Dempsey, et al., 2007; Mandelbaum, et al., 2005; Myer, et
al., 2006). However, they may be necessary for cutting success and performance. Limb
abduction and trunk lean are thought to facilitate redirection of the body during walking turns
(Patla, et al., 1999). Further, trunk displacement was shown to be a predictor of 180 degree
cutting performance (Sasaki, et al., 2011). It is therefore possible that these movements may be
necessary for successful completion of the task yet may also result in potentially injurious knee
joint loading.
ACL injury prevention programs have been designed to improve lower extremity
mechanics based on the current understanding of the injury mechanism, which may not relate to
the demands of cutting tasks. In a recent study, an injury prevention programs aimed at
improving limb mechanics in order to reduce frontal plane knee loading resulted in decreased
agility performance (Vescovi & VanHeest, 2010). Fifty-eight adolescent female soccer players
participated in a 12-week program, which emphasized maintaining proper biomechanical
technique during the exercises, particularly focusing on increasing sagittal plane motion of the
lower extremity (Mandelbaum, et al., 2005). Following training, time to complete two agility
tests increased (Vescovi & VanHeest, 2010). While this was not a biomechanical study, it is
possible that optimal biomechanics for agility performance were contrary to the trained
technique aimed at reducing knee valgus loading. This is a problem, as coaches’ willingness to
implement ACL prevention programs that result in diminished agility performance is likely to be
limited. Further, athletes’ behavior is driven by their performance, and they are likely to choose
strategies that allow them to succeed in their game.
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The purpose of this study was to: 1) identify whole body postural and/or segmental
mechanics that are related to good performance (i.e., fast completion times) of 45 and 90 degree
cuts, and from these variables, 2) determine which variables predict performance and/or ACL
injury risk (i.e., peak knee adductor moment). Based on research demonstrating differences in
mechanic between cutting tasks, we propose that different mechanics will be related to cutting
performance for a 45 and 90 degree cut. Further, we hypothesize that during a 45 degree cut, hip
extensor moment and power will contribute to completion time. During a 90 degree cut, we
hypothesize that medial-lateral COM position relative to the COP and medial-lateral GRI will be
related to completion time. We also hypothesize that these mechanics will also be related to peak
knee adductor moment.
Methods
Participants
Twenty-five healthy soccer players participated in this study (12 females, mean age =
22.4 ± 3.9 yr, height = 1.74 ± 0.1 m, mass = 70.9 ± 9.3 kg). A power analysis determined that
with 25 subjects, the study is adequately powered to detect correlations with an alpha of 0.05 and
85% power. Athletes were considered experienced, high-level soccer players (college, semi-
professional, professional). Twenty-two participants reported that they were right-limb
dominant, when asked which foot they would kick a ball with.
All subjects were healthy without complaints of lower extremity injuries. Subjects were
excluded from the study if they had: 1) history of previous lower extremity surgery, 2) recent
lower extremity injury resulting in persistent pain and/or inability to participate in sport (greater
than 3 weeks) in the last six months, 3) concurrent pathology or morphology that could cause
pain or discomfort during physical activity; or 4) any physical, cognitive or other condition that
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would impair their ability to perform the tasks in this study. Prior to participation, all subjects
were explained the testing procedures, and informed consent was obtained as approved by the
Investigational Review Board at the University of Southern California Health Science Campus.
Instrumentation
Three-dimensional motion analysis was performed using a marker-based, 11-camera
digital motion capturing system (Qualisys, Gothenburg, Sweden) at 250 Hz. Ground reaction
force data were obtained at 1500 Hz using a 1.20 x 0.60 m
2
force platforms (AMTI, Newton,
MA, USA) embedded into the floor surface. Kinematic and kinetic data were collected
synchronously using the motion capture software (Qualisys Track Manger, version 2.6).
Reflective markers (25 mm spheres) placed on specific bony landmarks were used to define body
segments in three-dimensional space. Laser timing gates (Brower IRD-T175; Brower Timing
Systems, Draper, UT, USA) were used to determine the time to complete the tasks.
Procedures
All testing took place at the Human Performance Laboratory at the University of
Southern California, located within Competitive Athlete Training Zone (CATZ). Participants
wore shorts, tank tops, and their own running/athletic shoes (not cleats). Tracking marker
clusters mounted on semi-rigid plastic plates were secured to nylon/lycra bands on the subject’s
arms, forearms, thighs, shanks, and shoes. Reflective markers were placed over 45 anatomical
landmarks, similar to that used by Song et al. (2012). Following a static calibration trial, the
tracking marker clusters as well as the markers on the end of the second toes, posterior superior
iliac spines, iliac crests, L5-S1 junction, acromions, radial and ulnar styloid processes, third
metacarpal heads, clavicle, cervical process of C7, and head remained on the subject.
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Prior to testing, subjects were led through a 15 minute warm-up and were given time to
stretch. Participants performed two sidestep cutting maneuvers to 45˚ (CUT45) and 90˚
(CUT90) at their fastest speed. For both cutting tasks, subjects ran as fast as possible 7.5 meters,
planted their dominant foot and changed direction away from their plant foot at the designated
angle (45 or 90 degrees), and continued running for 7.5 meters as fast as possible (Figure 3.1).
The cutting angles were marked on the floor with tape. Laser timing gates were placed at the
beginning and end of the 15 meter path to measure task completion time. The cut order was
counter-balanced between subjects to prevent effects related to testing order. Trials were
accepted if the subject’s task completion time was within a ± 2.5% interval as measured by the
timing gates and if the dominant foot fully contacted the force platform.
In order to determine if cutting tasks (CUT45 and CUT90) analyzed for this study were
representative of the subjects’ abilities to perform change of direction tasks, subjects also
completed an agility T-test as fast as possible (Figure 5.1). The T-test was performed outside the
biomechanics laboratory on artificial turf and was chosen because it is a reliable (Pauole, et al.,
2000) and frequently used assessment of agility performance (Brughelli, et al., 2008). The
agility T-test involved forward run, side shuffle and back pedal movements, with four changes of
direction over a forty yard distance (Figure 5.1). Trials were accepted only if subjects touched
each cone and faced forward the entire time.
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Figure 5.1 Layout of the agility t-test. Subjects started behind laser timing gates at point A.
They ran through the timing gates to point B and touched a 9 inch cone with their hand. They
side-shuffled left and touched the cone at C. Next, they shuffled right and touched the cone at D,
then shuffled left back to B. After touching the cone at B a second time, they back-pedaled
through the timing gates at A.

Data analysis
Qualisys Tracking Manager was used to reconstruct the three-dimensional marker
coordinates. Visual 3D software (Version 4.8, C-Motion, Inc., Rockville, MD, USA) was used
to process the raw coordinate and force data and compute segmental kinematics and kinetics.
Force data and coordinate data were low-pass filtered using a fourth-order zero-lag Butterworth
filter with a 200 Hz and 12 Hz cutoff frequency, respectively. The local coordinate systems of
the body segments were derived from the standing calibration trial. Lower and upper extremity
segments and the thorax were modeled as frustra of cones, while the pelvis was modeled as a
cylinder and the head as a sphere. The whole body center of mass position was calculated as the
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weighted average of the center of mass positions of each of the 15 modeled segments. Joint
kinematics were calculated by determining the transformation from the triad of markers to the
position and orientation of each segment determined from the standing calibration trial. Euler
angles with the following order of rotations were used to calculate joint kinematics:
flexion/extension, abduction/adduction, and internal/external rotation. Three-dimensional net
joint moments were calculated using inverse dynamics equations, and joint power was calculated
as the product of joint moment and angular velocity. All kinetic data were normalized to body
mass. Data obtained from Visual3D was exported and analyzed using a customized Matlab
program (Version R2011b, The MathWorks, Natick, MA, USA). Foot contact events were
defined using a 30N vertical force threshold.
Completion time for the cutting tasks and agility T-test was recorded from laser timing
gates to the nearest one-hundredth of a second. For the agility T-test, the fastest completion time
out of three trials performed was used for analysis.
Horizontal ground reaction force (GRF), and separation of the center of mass (COM) and
center of pressure (COP) were rotated to align with the anatomical reference frame as described
previously (Chapter III). Peak posterior and medial GRF, braking and medial-lateral (ML) GRI,
and peak anterior-posterior (AP) and ML distance between the COM and COP were calculated.
All segmental (joint) variables were analyzed during the deceleration phase, defined as the time
from initial contact with the force plate to maximal knee flexion. This generally occurred at 50%
of stance, and has been used in previous studies to define the deceleration phase (Chaudhari, et
al., 2005; Jamison, et al., 2012). The deceleration phase was of particular interest because non-
contact ACL injuries often occur during this period of stance (Boden, et al., 2000). Joint
kinematics were calculated at initial contact. Peak net joint moments and average joint power
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over the deceleration phase were also determined. Sagittal plane kinematics and kinetics were
analyzed at the ankle, knee and hip. Hip frontal and transverse plane kinematics and kinetics
were analyzed; also, the angle that the trunk deviated in the frontal plane from global vertical
was analyzed (trunk lean). For all cutting dependent variables, the average of 4 trials for each
subject for each task was used for analysis.
Statistical Analysis
The two cutting tasks were analyzed separately. To determine if relationships existed
between cutting task completion time (CT) and agility T-test CT as well as the biomechanical
dependent variables of interest, Pearson’s product-moment correlations were used (α ≤ 0.05). In
order to determine the best predictors of CT during the cutting tasks, the variables that were
correlated to CT (with α < 0.075) were considered in a stepwise multiple linear regression model
(entry and removal thresholds p≤0.05 and p≤0.10, respectively). In order to determine whether
the variables that were significantly correlated with CT were also predictive of peak knee
abductor moment, these variables were considered in a second stepwise multiple linear
regression model. Significance was set at α ≤ 0.05. Statistical analyses were performed using
PASW software (version 18, SPSS, Inc., Chicago, IL).
Results
Average (± standard deviation) completion time for the agility T-test was 10.1 ± 0.7
seconds, for CUT45 was 2.7 ± 0.2 seconds, and for CUT90 was 3.2 ± 0.2 seconds. Completion
time for the agility T-test was significantly correlated with CT of both CUT45 (r=0.816,
p<0.001) and CUT90 (r=0.788, p<0.001). Smaller (faster) times for the T-test were associated
with faster times for the cutting tasks.
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Average (± standard deviation) peak knee adductor moment for CUT45 was -1.07 ± 0.99
Nm/kg and for CUT90 was -1.83 ± 0.77 Nm/kg.
CUT45
Completion time for CUT45 was significantly correlated with hip power generation in the
sagittal plane, and peak ankle plantarflexor moment (p<0.05). There was also a trend towards a
relationship between completion time and hip extensor moment (p=0.056) and peak medial-
lateral COM-COP separation distance (p=0.052; Table 5.1). Better performance (i.e., shorter
CT) was associated with greater hip power generation and greater plantarflexor moments, as well
as greater hip extensor moments and larger separation distances. When these four variables were
considered in a stepwise multiple regression, hip sagittal power generation, ML COM-COP
separation, and hip extensor moment entered the model and together explained 73% of the
variance in completion time (r= 0.854, p<0.001). Hip sagittal power entered the model first
explaining 23% of the variance (p=0.016), followed by peak hip extensor moment explaining
and additional 38% of the variance in CT (p<0.001). ML COM-COP separation was the last
predictor to enter the model explaining an additional 12% of variance in CT (p=0.006; Table
5.2).
When the four variables that were correlated with CUT45 completion time were
considered in a stepwise multiple regression with peak knee adductor moment as the independent
variable, the ML COM-COP separation distance was the only predictor of peak knee adductor
moment, explaining 22% of the variance (r= 0.472, p=0.017; Table 5.2). Larger ML distances
between the COM and COP were associated with greater knee adductor moments.

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CUT90
Completion time of CUT90 was significantly correlated with medial-lateral ground
reaction force impulse, hip internal rotation angle at initial contact, hip frontal plane power
generation, and peak knee sagittal plane moment (p<0.05; Table 5.1). Faster CTs were
associated with greater ML GRI, greater internal rotation angles, greater hip power generation,
and greater knee extensor moments. When these variables were considered in a stepwise multiple
regression, ML GRI and hip frontal plane power generation were the only predictors of CT,
explaining 62% of the variance (r=0.790, p<0.001). Hip frontal plane power entered the model
first explaining 34% of the variance in knee adductor moment (p=0.002), followed by ML GRI
explaining an additional 28% of the variance (p=0.001; Table 5.2).
When the variables that were significantly correlated with CUT90 CT were considered in
a stepwise multiple regression model with peak knee adductor moment as the independent
variable, peak knee extensor moment and hip internal rotation angles at initial contact were the
best predictors of peak knee adductor moment, explaining 42% of the variance (r= 0.651,
p=0.002). Peak knee extensor moments entered the model first and explained 17% of the
variance (p=0.041). Hip internal rotation angle at initial contact explained an additional 25% of
the variance in peak knee adductor moment (p=0.005; Table 5.2). Greater knee adductor
moments were associated with greater knee extensor moments and less hip internal rotation.

MECHANICS OF MANEUVERS 75

Table 5.1
Descriptive statistics for CUT45 and CUT90 tasks
Completion time Knee adductor moment

Average ± SD Range
Correlation
coefficient p-value
Correlation
coefficient p-value
CUT45
Peak medial-lateral
COM-COP separation 0.26 ± 0.02 0.22 to 0.30 -0.387 0.056 0.472 0.017
Hip extensor moment -4.65 ± 1.41 -8.47 to -2.75 0.393 0.052

Hip sagittal power
generation 6.66 ± 3.50 0.76 to 13.75 -0.475 0.016

Ankle plantarflexor
moment -3.04 ± 0.53 -1.73 to -4.11 0.450 0.024

CUT90

Medial-lateral ground
reaction force impulse 0.21 ± 0.03 0.13 to 0.26 -0.489 0.013

Hip internal rotation
angle 10.14 ± 7.89 -3.74 to 23.53 -0.471 0.018 0.374 0.066
Hip frontal power
generation 0.37 ± 0.99 -1.44 to 2.30 -0.586 0.002

Knee extensor moment -3.06 ± 0.61 -4.33 to -1.98 0.499 0.024 0.412 0.041

Note. COM-COP separation distance (m/m), ground reaction force impulse (Ns/N), moment (Nm/kg), power (Watts/kg), angle
(degrees)

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Table 5.2
Regression statistics for completion time and knee adductor moment for CUT45 and CUT90
tasks
Completion time R
2
change p-value
CUT45
Hip sagittal power 0.23 0.016
Hip extensor moment 0.38 <0.001
Medial-lateral COM-COP separation 0.12 0.006
Total 0.73 <0.001
CUT90

Hip frontal power 0.34 0.002
Medial-lateral ground reaction force impulse 0.28 0.001
Total 0.62 <0.001

Knee adductor moment R
2
change p-value
CUT45

Medial-lateral COM-COP separation 0.22 0.017
CUT90

Peak knee extensor moment 0.17 0.041
Hip internal rotation angle 0.25 0.005
Total 0.42 0.002

Note. COM-COP separation distance (m/m), ground reaction force impulse (Ns/N), moment
(Nm/kg), power (Watts/kg), angle (degrees)

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Discussion
This study aimed to determine if the mechanics that are related to performance of athletic
cutting tasks (i.e., fast completion times) are also related to potentially injurious frontal plane
knee loading. The analysis focused on the deceleration phase of cutting, as this is the time
during which non-contact ACL injuries commonly occur (Boden, et al., 2000). Not surprisingly,
the variables that predicted faster cutting performance differed between cutting tasks performed
to 45 and 90 degrees. Primarily sagittal plane mechanics predicted performance of the CUT45
task, while frontal plane mechanics predicted performance of CUT90. Of the variables that
predicted performance, few were also predictive of potentially injurious knee joint loading.
The use of time to complete sidestep cutting tasks as a metric for agility performance was
supported by the significant positive correlations between time to complete the agility T-test and
the completion time for both of the cutting tasks. The average agility T-test time in this study
was the same as that found for collegiate athletes in a previous study (Pauole, et al., 2000).
Despite the differences in the distance to complete the tasks (36.6 versus 15 meters) and type of
direction change involved in each task, the significant correlation between completion times of
the three tasks is consistent with previous studies showing significant intercorrelations between
performance of various test of agility (Pauole, et al., 2000).
Hip mechanics in the sagittal plane were related to completion time of the CUT45 task, as
hypothesized. Greater hip extensor moments and power generation at the hip were associated
with faster completion times. Peak hip extensor moment and sagittal plane hip power generation
both entered the prediction equation, together explaining 61% of the variance in completion
time. This is not surprising, as hip extensors have been found to generate power during
deceleration of 45 degree cuts (Chapter IV). Moreover, similar relationships have been noted
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between hip extensor joint power and muscle activity and straight running speed (Belli, et al.,
2002; Kyrolainen, et al., 1999). Together, these data highlight the importance of sagittal plane
hip mechanics during ongoing tasks that require minimal deceleration. Greater medial-lateral
COM-COP separation distance was also found to be associated with faster performance of
CUT45, explaining an additional 12% of the variance in completion time. COM positioning into
the direction of the cut allows for acceleration and momentum generation towards the new
direction (Winter, 1995b). While ankle plantarflexor moments were correlated with completion
times, they did not enter into the prediction model. This may be due to the fact that the ankle
plantarflexors act to absorb energy during deceleration, and the peak moment occurred at the end
of the phase. Their contribution to performance may have been bigger had the entire stance
phase been considered.
Of the variables that correlated with CUT45 completion time, only ML COM-COP
separation distance was found to predict peak knee adductor moment. A more medial whole
body position with respect to the foot could contribute to a larger valgus moment at the knee by
positioning the COP more lateral to the COM of the body and the tibia. This could create a large
moment arm, the perpendicular distance from the axis of rotation to the force, for the vertical
GRF about the knee joint. However, a recent forward simulation modeling study indicated that
COM acceleration into the direction of the cut reduces peak knee valgus loading (Donnelly,
Lloyd, Elliott, & Reinbolt, 2012). Accelerating the COM medially while the foot is stationary
would increase its ML separation from the COP but redirect the GRF with respect to the knee.
Thus, while this current study indicates that large separation distance could be considered
potentially injurious during a 45 degree cutting maneuver, the magnitude and direction of the
GRF also play a role. As GRFs were not significantly correlated to completion time, they were
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not considered in the stepwise multiple regression but should be considered in future studies, as
they contribute to knee joint loading.
As hypothesized, completion time of CUT90 was associated with a medial-lateral whole
body parameter. Medial ground reaction force impulse and frontal plane hip power were the
only predictors of completion time. Frontal plane power was the first variable to enter the
prediction equation, explaining 34% of the variance. Interestingly, during the deceleration phase
of CUT90, a peak hip adductor (not abductor) moment is present; thus, the power generation at
the hip is associated with movement of the hip into less abduction and an adductor moment.
Ground reaction force impulse explained an additional 28% of the variance in completion time
during CUT90. GRI is proportional to the change in whole body velocity; thus, the greater
change in velocity into the direction of the cut during stance was important for faster
performance. While it makes sense that greater change in body velocity into the cut would be a
predictor of completion time, its relationship to power generation of the hip adductors is less
intuitive. The hip moves into less abduction during stance and is countered by trunk lean into the
cut during the CUT90 task. A large hip adductor moment is thought to allow for greater trunk
lean. The inclusion of power generation of the hip adductors into the prediction model suggests
that this mechanism is important for performance.
Larger knee extensor moments and greater hip internal rotation angles were correlated
with faster completion time during CUT90 but did not enter the regression equation. The knee
extensors have been found to play an important role in deceleration during CUT90 (Chapter IV).
While more effective deceleration of the body during this task (i.e., greater knee extensor
moments) may allow for a rapid transition to redirection and acceleration of the body and
therefore faster performance, knee extensor moment did into enter the prediction model. Hip
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internal rotation was also correlated to completion time during CUT90. Greater internal rotation
at the hip may be indicative of a pre-positioning of the limb into the direction of the cut.
When the variables that were significantly correlated to CUT90 completion time were
considered, hip internal rotation at initial contact and knee extensor moment were found to be
significant predictors of peak knee adductor moment, explaining 17% and 25% of the variance,
respectively. It is not clear how larger knee extensor moments would related to greater frontal
plane loading at the knee. It is possible that larger knee extensor moments reflect greater overall
loading of the knee during CUT90 across planes. Smaller degrees of hip internal rotation at
initial contact were related to larger peak knee adductor moments. This relationship is in contrast
to that found for completion time and is also in contrast to previous studies that found larger
degrees of hip internal rotation are related to greater peak knee adductor moments during cuts
performed to 45 degrees (McLean, et al., 2005; Sigward & Powers, 2007). However, when
compared to cuts performed to 45 degrees, the pelvis is more rotated into the new direction
during cuts performed to 90 degrees (Chapter IV). It is therefore possible that the relationship
between the femur and pelvis at initial contact would be different during a 90 degree cutting task,
resulting in a different relationship to loading at the knee joint.
In general, the predictors of completion time for the cutting tasks did not correspond to
the predictors of peak knee adductor moments. None of the predictors of completion time during
CUT90 also predicted knee adductor moments. For CUT45, the ML separation distance between
COM and COP was the only predictor of peak knee adductor moment but accounted for only
12% of the variance in completion time.
These data have important implications for ACL injury prevention programs. Current
programs generally focus on maintaining proper technique when performing landing and
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jumping exercises, emphasizing increased sagittal plane motion (Gilchrist, et al., 2008; Hewett,
et al., 1999; Mandelbaum, et al., 2005; Myer, et al., 2008; Myer, et al., 2006) and discouraging
frontal and transverse plane motion of the lower extremity and trunk (Dempsey, et al., 2007;
Mandelbaum, et al., 2005; Myer, et al., 2006). The current data suggest that these instructions
may be applicable to technique for cutting to 45 degrees as well as landing. While lower
extremity and trunk frontal plane motion did not predict knee loading, ML separation between
the COM and COP did. As this distance likely results from a combination of trunk and lower
extremity positioning, limiting these motions may result in decreased frontal plane loading of the
knee during CUT45. It is not clear to what extent these frontal plane recommendations would
influence performance, considering that separation distance explained only 12% of the variance
in completion time. In the sagittal plane, increased engagement of the hip may be more
advantageous for performance of a 45 degree cut. A relationship between sagittal plane hip
mechanics and knee frontal plane loading was not found in this study. However, previous
studies suggest that increasing engagement of the hip in the sagittal plane may decrease knee
adductor moments by reducing frontal and transverses plane motion of the hip (Pollard, et al.,
2007). Further investigation of the effects of increasing sagittal plane hip engagement during
cutting to small angles is needed.
The implications of current technique training on performance and injury risk during
CUT90 are less clear. Performing tasks in a more flexed posture may result in increased knee
extensor moments, which were predictive of greater knee frontal plane loading. In addition,
limiting transverse plane motion of the lower extremity may result in smaller degrees of hip
rotation, which was also predictive of frontal plane knee loading. Interestingly, the medial-
lateral variables related to and predictive of CUT90 performance, hip frontal plane power
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generation and ML GRI, were not predictive of knee adductor moment. This was not expected,
as frontal plane mechanics have been related to knee adductor moment during cutting in previous
studies (Jamison, et al., 2012; Sigward & Powers, 2007). However, this suggests that injury
prevention programs that discourage frontal plane movements of the lower extremity and trunk
may limit performance and may not improve injury risk factors during a 90 degree cutting task.
This is the first study to analyze the relationships between cutting performance and whole
body and segmental biomechanics. While these data provide some insight into the relationship
between cutting mechanics related to performance and injury risk, caution must be taken before
applying these data to injury prevention training. These predictors were assessed in highly
trained, healthy athletes during preplanned cutting tasks. It is not known if similar results would
be found in other athlete populations or under different task conditions. Moreover, it is not
known if altering these factors would affect performance or injury risk. In order to relate
performance variables to knee adductor moments and injury risk, only the deceleration phase of
stance was considered. It is likely that whole body or segmental mechanics associated with the
second half of stance (i.e., the propulsion phase) could provide additional insight into cutting
performance. Future research should consider the entire stance phase, and possibly the
mechanics of the approach steps before the cut’s execution.

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CHAPTER VI
SUMMARY AND CONCLUSIONS

Cutting presents a paradox to athletes. On one hand, quick changes of direction are
necessary for successful participation in multidirectional sports (Alentorn-Geli, et al., 2009;
Bloomfield, et al., 2007a; Brughelli, et al., 2008; Krustrup, et al., 2005; Orendurff, et al., 2010).
On the other hand, cutting maneuvers are associated with anterior cruciate ligament (ACL) injury
risk (Boden, et al., 2000; Cochrane, et al., 2007; Krosshaug, et al., 2007; Olsen, et al., 2004).
Much of the research on cutting maneuvers to date has focused on ACL injury (Beaulieu, et al.,
2009; Besier, et al., 2003; Besier, Lloyd, Ackland, et al., 2001; Chan, et al., 2009; Fedie, et al.,
2010; Hanson, et al., 2008; Landry, et al., 2007; Malinzak, et al., 2001; McLean, et al., 2004;
Pollard, et al., 2004; Pollard, et al., 2007; S. Sigward & C. M. Powers, 2006). However, without
knowledge of the whole body postural and joint/segmental mechanics needed for task
performance, or how these mechanics relate to performance and/or injury risk, our current
understanding of the ACL injury mechanism is limited.
Prevention is the cure. In order to mitigate the poor long-term consequences of ACL
tears and reconstruction, such as knee instability, pain, and early onset osteoarthritis of the joint
(Lohmander, et al., 2007), this injury must be prevented from happening in the first place.
However, movement patterns thought to decrease the risk for injury are unlikely to be adopted by
athletes if these movements hinder performance. In order to develop training programs that
reduce the risk for injury and enhance performance, an understanding of mechanics necessary for
performance of change of direction tasks and their relationship to injurious knee loading is
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needed. Therefore, the overall purpose of this dissertation was to characterize whole body
postural and joint/segmental mechanics during running turn maneuvers in skilled individuals and
identify relationships between these mechanics and both performance and injury risk.
The purpose of Chapter III was to evaluate the postural strategies necessary for cutting by
comparing whole body measures of COM velocity and position during the approach and
execution steps across tasks with different direction demands (straight run, 45˚ sidestep cut, and
90˚ sidestep cut). Consistent with our hypotheses, the deceleration and translation demands,
quantified as ground reaction force impulse in the AP and ML directions, respectively, were
greater in the cuts compared to the straight run. These demands were met by adjusting the
position of the center of mass, magnitude of the ground reaction forces and stance time during
the approach and execution steps, but the extent of these adjustments varied between tasks.
Though the cut angle was systematically scaled (0, 45 and 90 degrees), the demands of the tasks
were not. The 90 degree cut required disproportionately greater deceleration and proportionately
greater translation. Deceleration was prioritized in the approach step of the 90 degree cut, and
most of the translation occurred in the execution step. In contrast, deceleration and translation
were more evenly distributed across steps during the 45 degree cut. This chapter provided
important insight into the whole body postural demands and adjustments necessary to complete
cuts to various angles.
Without understanding the joint or segmental mechanics used to accomplish the whole
body postural requirements for deceleration and redirection, interpretation of how these postures
relate to ACL injury risk is difficult. Lower extremity injury mechanisms have not been related
to whole body postural mechanics. While previous cutting research suggests that whole body
postural requirements may be accomplished through adjustments at the joint or segment level,
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these observations are drawn from assessments of sidestep cutting tasks performed at smaller
angles (i.e., 30-45 degrees). Therefore, the purpose of Chapter IV was to determine how
increases in whole body deceleration and redirection demands affect joint and segmental
mechanics by evaluating lower limb and trunk kinematics and kinetics during the execution of
two sidestep cutting maneuvers (45 and 90 degree cuts). Contrary to our hypotheses, the larger
demands of the 90 degree cut did not translate into systematic increases across all kinematic and
kinetic variables. Individuals’ knee extensors were primarily used to meet the greater
deceleration demands of the 90 degree cut, while the hip was used to stabilize the trunk in the
sagittal and frontal planes. In contrast, subjects’ knee extensors and ankle plantarflexors were
used to decelerate during the 45 degree cut, while propulsion of the body was accomplished with
the hip extensors.
Chapter IV showed that redirection mechanics differed between tasks as well. During the
90 degree cut, the hip appeared to primarily stabilize the body, possibly allowing for greater
trunk lean into the cut and rotation into the new direction. During the 45 degree cut, individuals
exhibited movement into hip abduction and a peak hip abductor moment, as well as a greater hip
rotator power generation, suggesting that the hip played a larger role in active propulsion into the
new direction. The greater redirection demands of the 90 degree cut may therefore have been
accomplished by mechanics other than those assessed in this chapter. Together these results
suggest that the hip may play a different role during cutting to smaller and larger angles. These
data also illustrate a pattern of engagement in the sagittal and frontal planes that provide
important insight into how athletes achieve the whole body postures that are required to complete
side step cutting tasks performed at maximum effort.
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Despite its importance in sports, little is known about the technique or mechanics
necessary for successful, enhanced, performance of cutting tasks. Further, it is not known
whether these mechanics are also related to potentially injurious knee joint loading, which could
be critical information to injury prevention programs. The purpose of Chapter V was to 1)
identify whole body and/or segmental mechanics that are related to good performance (i.e., fast
completion times) of 45 and 90 degree cuts, and from these variables, 2) determine which
variables predict performance and/or ACL injury risk (i.e., peak knee adductor moment).
Consistent with the segmental differences across tasks observed in Chapter IV, we found that the
mechanics that are predictive of fast completion times for the 45 degree cut and 90 degree cut
differed. For the 45 degree cut, hip sagittal power, peak hip extensor moment, and ML COM-
COP separation were the best predictors of completion time, explaining 73% of the variance.
For the 90 degree cut, hip frontal plane power generation and ML GRI together explained 62%
of the variance in completion time. Of these mechanics, only ML COM-COP separation
distance during the 45 degree cut also predicted peak knee adductor moments (R
2
= 0.22). Peak
knee extensor moment and hip internal rotation angle during the 90 degree cut were the best
predictors of peak knee adductor moment (R
2
= 0.42). The results from this study demonstrated
that different mechanics are important for successful performance of cutting maneuvers and that
few of these mechanics are also related to knee frontal plane loading.
The results from this dissertation provide a more thorough understanding of the
mechanics necessary for 45 and 90 degree cuts. Chapter III revealed that the deceleration and
translation demands of cutting to smaller and larger angles differ. When compared to straight
running, greater braking and translation demands during the both cuts were accomplished
through adjustments in GRF, velocity and whole body position. However, when cutting to the
MECHANICS OF MANEUVERS 87

larger angle, disproportionately greater braking and proportionately greater translational
demands were required, and these were accomplished in different steps. Not only were the
whole body postural mechanics of these two cutting tasks found to be different, the way in which
segmental and joint mechanics contribute to whole body postures differed between the cutting
tasks (Chapter IV). Braking during the 45 degree cut was accomplished with the ankle and knee;
however, during the 90 degree cut, the knee primarily contributed to deceleration. During the 45
degree cut, subjects used their hip to propel the body forward but stabilize their body in the
sagittal plane during the 90 degree cut. In order to redirect the body, individuals used the hip in
the frontal plane during the 45 degree cut, moving into more abduction during stance, and
leaning their trunk into the cut. In contrast, the hip was used to in the frontal plane to stabilize
the body during the 90 degree cut and allow for even greater trunk lean into the cut. The
differences between task demands and the contribution of segmental and joint mechanics to
whole body posture were further supported in Chapter V. Here, it was revealed that sagittal
plane hip mechanics used to propel the body during the 45 degree cut was an important
movement pattern for good performance (i.e., fast completion times). In contrast, frontal plane
mechanics predicted performance during the 90 degree cut. Further, the mechanics that were
predictive of knee frontal plane loading differed between the tasks. Together, the results of this
dissertation show that increasing cut angle affects whole body and joint/segmental mechanics in
interesting ways: the mechanics necessary to cut to 90 degree are not simply scaled versions of
those necessary for cutting to 45 degrees.
In light of the findings of this dissertation, current cutting research should be interpreted
with several methodological factors in mind. First, this dissertation has clearly shown that the
angle at which a cut is performed affects the whole body and joint/segmental mechanics that are
MECHANICS OF MANEUVERS 88

adopted to complete them. It is therefore important to consider the angle at which cuts are made
when interpreting the results of other studies. Second, these are the first series of studies to have
subjects perform cutting tasks at their maximal effort. Perhaps as a result of the movement
speed, some of the joint/segmental mechanics qualitatively seem to differ from previously
published studies, when comparing the same cut angular magnitude. In particular, subjects in
this dissertation leaned their trunk into the direction of the cut, unlike other studies (Jamison, et
al., 2012). Individuals also appear to exhibit greater range of motion during stance at the hip in
the sagittal plane but less knee sagittal plane motion compared to a previous study (Pollard, et
al., 2004). A different movement pattern of the hip in the transverse plane is also observed
(McLean, et al., 2004; Pollard, et al., 2004). Third, the athletes in this dissertation would be
considered highly skilled and had never incurred an ACL injury. This may account for the
absence of sex differences in the variables assessed. However, other studies have found sex
differences in cutting mechanics (McLean, et al., 2005; Pollard, et al., 2004; Pollard, et al., 2007;
S. M. Sigward & C. M. Powers, 2006). Thus, caution must be taken when comparing cutting
literature, as this dissertation has pointed to several methodological factors that can influence
mechanics.
The results of this dissertation further suggest that current ACL injury prevention training
recommendations may be appropriate for cutting to 45 degrees but their relevancy to 90 degree
cuts remains unclear. Current injury prevention programs emphasize sagittal plane movements of
the lower extremity (Gilchrist, et al., 2008; Hewett, et al., 1999; Mandelbaum, et al., 2005; Myer,
et al., 2008; Myer, et al., 2006) and discourage frontal and transverse plane movements of the
lower extremity and trunk (Dempsey, et al., 2007; Mandelbaum, et al., 2005; Myer, et al., 2006).
During a 45 degree cut, emphasizing sagittal plane movements may be beneficial to performance
MECHANICS OF MANEUVERS 89

while limiting frontal plane movements of the body may reduce knee loading (Chapter V). The
same may not be true for a 90 degree cut. Sagittal plane movement patterns do not seem to be as
important to performance for this task. Also, the predictors of peak knee adductor moment (knee
extensor moment and hip internal rotation) found in Chapter V were contrary to expected
mechanics. The relevancy of ACL injury prevention programs to performance or injury risk for
the 90 degree cut is therefore unclear. Further work is needed to understand how specific training
recommendations would affect knee joint loading and performance during various cutting
maneuvers.
The movement patterns described in this dissertation should be interpreted with the
experimental design in mind. The tasks chosen for this dissertation were preplanned, which
allowed subjects to make anticipatory adjustments. Healthy, experienced soccer players, who had
never incurred an ACL injury or had any lower extremity surgery, performed these tasks at their
own fastest speed. If these tasks were performed under unanticipated conditions or at
submaximal speeds or in less trained individuals, conditions under which ACL injuries are
reported to occur (Boden, et al., 2000; Cochrane, et al., 2007), different movement patterns
would likely have been observed. In this dissertation, characterizations of potentially injurious
mechanics were made based on previous literature in this field, and these mechanics cannot be
related specifically to injury risk. More research is needed to characterize different types of
cutting movements in order to better understand the development of motor control strategies
used to complete them.

MECHANICS OF MANEUVERS 90

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Creator Havens, Kathryn L. (author)

Core Title Whole body mechanics of running turn maneuvers: relationship to injury and performance

School School of Dentistry

Degree Doctor of Philosophy

Degree Program Biokinesiology

Publication Date 07/30/2013

Defense Date 06/14/2013

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

Tag ACL injury,agility,anterior cruciage ligament,anticipatory postural adjustments,biomechanics,center of mass,cutting,injury prevention,knee loading,maneuverability,OAI-PMH Harvest,postural control,Running,sports performance,turning,whole body

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Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Salem, George J. (committee chair), Sigward, Susan (committee chair), Fisher, Beth E. (committee member), Keim, Robert G. (committee member)

Creator Email kate.havens@gmail.com,khavens@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-307838

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Legacy Identifier etd-HavensKath-1899.pdf

Dmrecord 307838

Document Type Dissertation

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Rights Havens, Kathryn L.

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