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THE 3D KINEMATICS OF THE SINGLE LEG
FLAT AND DECLINE SQUAT
Stephen Timms
Bachelor of Applied Science (Human Movements Studies)
Professor Keith Davids, Dr Anthony Shield, Dr Marc Portus
Submitted in fulfilment of the requirements for the degree of
Masters of Science (Research)
School of Human Movements
Faculty of Health
Queensland University of Technology
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The 3D kinematics of the single leg flat and decline squat i
Keywords
Kinematics, biomechanics, single leg squat, physiotherapy screening protocols,
lumbopelvic stability, intrinsic injury risk, malalignment, hip strength, ankle
dorsiflexion
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ii The 3D kinematics of the single leg flat and decline squat
Abstract
Background: Pre-participation screening is commonly used to measure and assess
potential intrinsic injury risk. The single leg squat is one such clinical screening
measure used to assess lumbopelvic stability and associated intrinsic injury risk.
With the addition of a decline board, the single leg decline squat (SLDS) has been
shown to reduce ankle dorsiflexion restrictions and allowed greater sagittal plane
movement of the hip and knee. On this basis, the SLDS has been employed in the
Cricket Australia physiotherapy screening protocols as a measure of lumbopelvic
control in the place of the more traditional single leg flat squat (SLFS). Previous
research has failed to demonstrate which squatting technique allows for a more
comprehensive assessment of lumbopelvic stability. Tenuous links are drawn
between kinematics and hip strength measures within the literature for the SLS.
Formal evaluation of subjective screening methods has also been suggested within
the literature.
Purpose: This study had several focal points namely 1) to compare the kinematic
differences between the two single leg squatting conditions, primarily the five key
kinematic variables fundamental to subjectively assess lumbopelvic stability; 2)
determine the effect of ankle dorsiflexion range of motion has on squat kinematics in
the two squat techniques; 3) examine the association between key kinematics and
subjective physiotherapists’ assessment; and finally 4) explore the association
between key kinematics and hip strength.
Methods: Nineteen (n=19) subjects performed five SLDS and five SLFS on each leg
while being filmed by an 8 camera motion analysis system. Four hip strength
measures (internal/external rotation and abd/adduction) and ankle dorsiflexion range
of motion were measured using a hand held dynamometer and a goniometer
respectively on 16 of these subjects. The same 16 participants were subjectively
assessed by an experienced physiotherapist for lumbopelvic stability. Paired samples
t-tests were performed on the five predetermined kinematic variables to assess the
differences between squat conditions. A Bonferroni correction for multiple
comparisons was used which adjusted the significance value to p = 0.005 for the
paired t-tests. Linear regressions were used to assess the relationship between
kinematics, ankle range of motion and hip strength measures. Bivariate correlations
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The 3D kinematics of the single leg flat and decline squat iii
between hip strength measures and kinematics and pelvic obliquity were employed to
investigate any possible relationships.
Results: 1) Significant kinematic differences between squats were observed in
dominant (D) and non-dominant (ND) end of range hip external rotation (ND p =
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iv The 3D kinematics of the single leg flat and decline squat
stability using the SLS. The association between kinematics and the subjective
measures of lumbopelvic stability also remain tenuous between and within SLS
screening protocols. More functional measures of hip strength are needed to further
investigate these relationships.
Conclusion: The type of SLS (flat or decline) should be taken into account when
screening for lumbopelvic stability. Changes to lower limb kinematics, especially
around the hip and pelvis, were observed with the introduction of a decline board
despite no difference in frontal plane knee movements. Differences in passive ankle
dorsiflexion range of motion yielded variations in knee and ankle kinematics during
a self-selected single leg squatting task. Clinical implications of removing posterior
ankle restraints and using the knee as a guide to illustrate changes at the hip may
result in inaccurate screening of lumbopelvic stability. The relationship between
sagittal plane lower limb kinematics and hip strength may illustrate that self-selected
squat depth may presumably be a useful predictor of the lumbopelvic stability.
Further research in this area is required.
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The 3D kinematics of the single leg flat and decline squat v
Table of Contents
Keywords .................................................................................................................................................i
Abstract .................................................................................................................................................. ii
Table of Contents .................................................................................................................................... v
List of Figures ...................................................................................................................................... vii
List of Tables ...................................................................................................................................... viii
List of Abbreviations ..............................................................................................................................ix
Statement of Original Authorship ........................................................................................................... x
Acknowledgments ..................................................................................................................................xi
CHAPTER 1: INTRODUCTION ....................................................................................................... 1
1.1 Background .................................................................................................................................. 1
1.2 Purposes ....................................................................................................................................... 4
1.3 Hypotheses ................................................................................................................................... 5
1.4 Thesis Outline .............................................................................................................................. 5
CHAPTER 2: LITERATURE REVIEW ........................................................................................... 7
2.1 Methodology ................................................................................................................................ 7
2.2 Sport and Exercise Related Injury................................................................................................ 7
2.3 Intrinsic Injury Risks of the Lower Limb .................................................................................... 9 2.3.1 Strength Deficiencies ........................................................................................................ 9 2.3.1.1 Strength Deficiencies and General Injury Incidence ...................................................... 10 2.3.1.2 Regionally Specific Injuries and Associated Strength Deficits ...................................... 12 2.3.2 Lower Limb Alignment - The ‘Medial Collapse’ ........................................................... 17 2.3.2.1 Clinical Implications of Medial Collapse ....................................................................... 19 2.3.3 Hip Strength, Lower Limb Malalignment and Force Attenuation .................................. 22 2.3.3.1 Running .......................................................................................................................... 22 2.3.3.2 Landing ........................................................................................................................... 23 2.3.3.3 Cricket Fast Bowling ...................................................................................................... 25 2.3.4 Ankle Dorsiflexion Range of Motion ............................................................................. 26
2.4 Exercise and Sport Related Epidemiology ................................................................................. 30 2.4.1 Cricket Epidemiology ..................................................................................................... 31
2.5 Screening Protocols Used To Assess Risk ................................................................................. 35
2.6 Functional Testing to Assess Intrinsic Risk: .............................................................................. 38 2.6.1 Trendelenburg Assessment ............................................................................................. 38 2.6.2 The Squat ........................................................................................................................ 39 2.6.3 The Single Leg Squat ...................................................................................................... 40 2.6.4 Single Leg Flat Squat Vs Single Leg Decline Squat. ..................................................... 46
2.7 Summary and Implications ........................................................................................................ 53
CHAPTER 3: RESEARCH DESIGN ............................................................................................... 55
3.1 Participants ................................................................................................................................. 55
3.2 Research Design......................................................................................................................... 55 3.2.1 Anthropometry ................................................................................................................ 55 3.2.2 Single Leg Squatting Protocol ........................................................................................ 55 3.2.3 Single Leg Squatting 3-Dimensional Motion Capture .................................................... 57
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vi The 3D kinematics of the single leg flat and decline squat
3.2.4 Anatomical Modelling .................................................................................................... 58 3.2.4.1 Kinematic Modelling and Data Output ........................................................................... 58 3.2.4.2 Data Filtering .................................................................................................................. 60 3.2.5 Strength Testing Protocol ............................................................................................... 60 3.2.6 Ankle Dorsiflexion Range of Motion ............................................................................. 63
3.3 Analysis ..................................................................................................................................... 64 3.3.1 Data Analysis.................................................................................................................. 64 3.3.2 Statistical Analysis ......................................................................................................... 65 3.3.2.1 Comparing SLDS and SLFS kinematics ........................................................................ 65 3.3.2.2 Ankle Dorsiflexion Range of Motion and Kinematics ................................................... 66 3.3.2.3 Subjective Lumbopelvic Screening and Kinematic Comparison.................................... 66 3.3.2.4 Strength Measures Vs Kinematics .................................................................................. 67
3.4 Ethics and Limitations ............................................................................................................... 68
CHAPTER 4: RESULTS ................................................................................................................... 70
4.1 Subjects ...................................................................................................................................... 70
4.2 Kinematics of the SLFS and SLDS ........................................................................................... 70 4.2.1 End of Range Angles ...................................................................................................... 70 4.2.2 Mean Angles ................................................................................................................... 71 4.2.3 Additional Kinematic Observations ............................................................................... 72
4.3 Ankle Dorsiflexion Range of Motion ........................................................................................ 75
4.4 Qualitative and Quantitative Assessment of Pelvic Obliquity and Hip Rotation ....................... 77
4.5 Strength Measures ..................................................................................................................... 81
CHAPTER 5: DISCUSSION ............................................................................................................. 84
5.1 3D Kinematics of the Single Leg Flat and Decline Squats ........................................................ 84 5.1.1 Pelvic Obliquity .............................................................................................................. 85 5.1.2 Weight Bearing Hip Rotation and Adduction ................................................................. 85 5.1.3 Lateral Flexion of the Lumbar Spine Relative to the Pelvis ........................................... 87 5.1.4 Frontal Plane Movement of the Knee ............................................................................. 87 5.1.5 Additional Kinematic Observations ............................................................................... 88
5.2 Ankle Dorsiflexion .................................................................................................................... 90
5.3 Kinematic and Subjective Clinical Assessment ......................................................................... 93
5.4 Kinematics and Strength Analysis ............................................................................................. 95
CHAPTER 6: CONCLUSIONS ........................................................................................................ 99
6.1 Direct Response To Study Hypotheses ...................................................................................... 99
6.2 Concluding Statements ............................................................................................................ 101
BIBLIOGRAPHY ............................................................................................................................. 105
CHAPTER 7: APPENDICES .......................................................................................................... 117
7.1 Appendix A: UWA Model outputs .......................................................................................... 117
7.2 Supplementary Results ............................................................................................................ 118
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The 3D kinematics of the single leg flat and decline squat vii
List of Figures
Figure 1 Illustration of the decline squat in the sagittal (left) and frontal (right) plane......................... 56
Figure 2 Anterior (a) posterior (b) and lower limb markers (c) complete with marker clusters
used to store the Joint Coordinate Systems (JCS) ................................................................ 57
Figure 3 Coronal and sagittal screenshots of a SLFS in VICON Nexus ............................................... 58
Figure 4 An example of the Anatomical Coordinate System for the entire lower limb model
[177] ..................................................................................................................................... 59
Figure 5 A) Illustration of the hip coordination system (XYZ), femoral coordinate system
(xyz), and the Joint Coordinate System (JCS) for the right hip [1]. 5 B) Graphical
representation of knee flexion in the sagittal plane. ............................................................. 60
Figure 6 Example of the abduction strength test conducted in lying supine during the study.
The dynamometer is held against the lateral malleolus and subjects are asked to
build up force against the dynamometer. ............................................................................. 61
Figure 7 Example of the internal rotation strength test. ........................................................................ 62
Figure 8 Example of the knee to wall test. The angle of the tibia relative to the vertical is
represented by “” and was reported as ankle dorsiflexion. The distance (mm) the
hallux was away from the wall is represented by “d”. ......................................................... 63
Figure 9 Sagittal plane representations of the SLDS and SLFS conditions at EOR (A and B
respectively) and a direct comparison of the squatting conditions (C) Frontal plane
representations of the SLDS and SLFS conditions at EOR (D and E respectively)
and a direct comparison of the squatting conditions (F). ...................................................... 74
Figure 10 A graphical representation of the ND ankle and knee kinematics with respect to the
clinical measure of ankle dorsiflexion. ................................................................................. 76
Figure 11 Kinematic scatter plot of the dominant hip rotation and frontal plane knee as
categorised by subjective physiotherapy rating. ................................................................... 79
Figure 12 Comparison of the hip external rotation kinematics for the SLFS and SLDS when
plotted against normalised hip external rotation strength. The shape “” represents
the SLFS ND hip rotation (º) whilst the shape “” represents the SLDS ND hip
rotation angles. ..................................................................................................................... 82
Figure 13 The pelvic obliquity kinematics for both squatting protocols compared with hip
abduction strength. The symbol “” represents the SLFS ND pelvic obliquity
angles (º) whilst the symbol “o” represents SLDS ND pelvic obliquity angles (º) .............. 83
file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859853file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859854file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859854file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859855file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859857file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859857file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859857file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859858file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859858file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859858file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859859file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859861file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859861file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859861file:///E:/MASTERS%20THESIS/TIMMS%20-%20Masters%20Thesis%20Final2.docx%23_Toc324859861
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List of Tables
Table 1 Reported incidence of cricketing injuries according to injured body region. ........................... 33
Table 2 Summary of the single leg squat literature. .............................................................................. 50
Table 3 Basic descriptive statistics of the joint angles at EOR and the results of the paired t-test
comparing squatting conditions. .......................................................................................... 71
Table 4 Basic descriptive statistics of the mean joint angles and the results of the paired t-test
comparing squatting conditions. .......................................................................................... 72
Table 5 Summary of the functional differences from the paired t-test of the SLS conditions .............. 73
Table 6 Correlations between the two measures of ankle dorsiflexion ROM and sagittal plane
movement of the knee and ankle. ......................................................................................... 75
Table 7 The average pelvic obliquity and relative lateral flexion measurements as categorised
by qualitative physiotherapy assessment (“Normal” vs. “Excessive” movement) for
the SLDS. ............................................................................................................................. 77
Table 8 The average pelvic obliquity and relative lateral flexion measurements as categorised
by qualitative physiotherapy assessment (“normal” and “excessive” movers) for the
SLFS .................................................................................................................................... 78
Table 9 Mean strength measurements as categorised by qualitative physiotherapy assessment
for each squat condition. ...................................................................................................... 80
Table 10 UWA model outputs and practical meanings ....................................................................... 117
Table 11 Non-dominant leg strength (in Newtons) and EOR kinematic correlation matrix ............... 118
Table 12 Non-dominant leg strength (normalised to body weight) and EOR kinematic
correlation matrix ............................................................................................................... 118
Table 13 Dominant leg strength (in Newtons) and EOR kinematic correlation matrix ...................... 119
Table 14 Dominant leg strength (normalised to body weight) and EOR kinematic correlation
matrix ................................................................................................................................. 119
Table 15 Results from independent t-tests comparing the strength measures of normal and
excessive movers in both squat conditions. ........................................................................ 120
Table 16 Linear regression modelling comparing the clinical measure of ankle dorsiflexion and
sagittal plane ...................................................................................................................... 120
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The 3D kinematics of the single leg flat and decline squat ix
List of Abbreviations
SLS Single Leg Squat
SLDS Single Leg Decline Squat
SLFS Single Leg Flat Squat
EOR End of Range
ND Non Dominant
D Dominant
WB Weight Bearing
NWB Non Weight Bearing
PO Pelvic Obliquity
LF Lateral Flexion
Var Varus
ER External Rotation
Add Adduction
WHO World Health Organisation
ISB International Society of Biomechanics
JCS Joint Coordinate system
ICC Intraclass Coefficient
MSE Mean Squared Error
3D Three Dimensional
ITBS Illiotibial Band Syndrome
PFPS Patellofemoral Pain Syndrome
QL Quadratus Lumborum
CA Cricket Australia
COE Centre of Excellence
SSSM Sport Science Sport Medicine
QUT Queensland University of Technology
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x The 3D kinematics of the single leg flat and decline squat
Statement of Original Authorship
The work contained in this thesis has not been previously submitted to meet
requirements for an award at this or any other higher education institution. To the
best of my knowledge and belief, the thesis contains no material previously
published or written by another person except where due reference is made.
Signature: _________________________
Date: _________________________
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The 3D kinematics of the single leg flat and decline squat xi
Acknowledgments
I would like to take this opportunity to thank the following organisations and people.
Without their help and support this project would have not been possible.
My three Supervisors – Dr Anthony Shield, Dr Marc Portus and Professor
Keith Davids, The Queensland University of Technology (QUT), The Cricket
Australia Centre of Excellence Sport Science Sport Medicine (SSSM) Unit, The
Australian Institute of Sport (AIS) Biomechanics Department, The Toombul District
Cricket Club (TDCC) and the associated players who participated in this study, Dr
Kevin Sims, Mr Patrick Farhart, Ms Elissa Phillips, Mr Rian Crowther, Mr Wayne
Spratford, Dr Michael McDonald and finally to all my family and friends.
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Chapter 1: Introduction 1
Chapter 1: Introduction
This chapter outlines the background (Section 1.1) of the research, and its
purposes (Section 1.2). Section 1.3 outlines the hypotheses of the study and finally
Section 1.4 outlines the remaining thesis chapters.
1.1 BACKGROUND
Whilst there has been an increased promotion of physically active lifestyles to
improve quality of life [2, 3] and reduce the risk of noncommunicable diseases [4],
there has been a reluctance to recognise the coupled risk of injury associated with
participation in physical activity [5]. A large proportion of the population engage in
sport and as such, sports injuries are relatively common in modern western societies
[6].
Sports injuries are a multifaceted phenomenon and are often difficult and time
consuming to treat resulting in serious financial ramifications such as the cost of
medical treatment and physiotherapy, loss of work time and the loss of physical
function [2, 3, 5-7]. It was estimated that the cost of sports injuries in Australia was
$1 billion annually in 1990 [8], $1.65 billion in 2002 [9], and still remains
significant [10]. Preventative strategies are therefore justified on medical as well as
economic grounds [9-12].
To fully appreciate the complexities of the multifaceted concept of injury; the
epidemiology, aetiology, risk factors and exact mechanisms associated with injury
need to be defined. Risk factors are typically differentiated into either extrinsic
(environmental) or intrinsic (internal) factors [5, 7, 13, 14]. Emphasis has been
placed on the role of the intrinsic risk factors [7] as these have been demonstrated to
be more predictive of injury than environmental related factors [15].
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Pre-participation (or baseline) screening is a commonly used method to assess
potential intrinsic injury risk factors by identifying characteristics of the
musculoskeletal system that may predispose an athlete to injury, or to identify
incomplete recovery from a previous injury [16, 17]. In addition to injury risk
management strategies, screening is concurrently promoted as part of a performance
enhancement strategy [18]. Screening tests are thought to highlight an athlete’s
predisposition to injury but the validity of a majority of the current protocols have
yet to fully established due to the paucity of quality injury risk factor studies [18, 19].
Moreover, there is almost no reliable evidence base to support the validity of these
tests in predicting injury risk [20, 21].
The ability to clearly identify injury risk or performance enhancing factors is
reliant on the accuracy with which measurements are made. Furthermore,
establishing the reliability and validity of commonly used clinical assessment tools is
a key issue encountered by studies of intrinsic injury risk factors [17]. Issues
surrounding screening reliability can be alleviated by biomechanically investigating
the accuracy of screening protocols. A level of formal evaluation such as motion
analysis clarifies the association between the clinical practices and the quantitative
methods [22]. Whilst research has been conducted in assessing the reliability of
lower extremity clinical screening tests [17, 19, 23], it focussed on inter-rater and
test-retest reliability. The reliability of functionally orientated tasks has been
investigated [18] but many of these are yet to be validated.
There is almost a universal agreement within the literature that a lack of
physical fitness is an intrinsic risk factor for musculoskeletal injury during physical
activity [5, 7, 24]. Nevertheless, the link between muscular strength and lower injury
risk is not fully understood [25]. Athletes must possess sufficient strength to provide
joint stability in all three planes of motion [26] to maximise athletic function [27] as
well as reducing the incidence of injury [14, 25, 26, 28-34].
Evidence is beginning to emerge that highlights a relationship between certain
screening tests and the incidence of lower limb injuries, particularly in the sporting
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Chapter 1: Introduction 3
demographic [35]. One such screening test that warrants further investigation is the
single leg squat (SLS) which replicates an athletic position commonly assumed in
sport requiring multi-plane control of the trunk and pelvis on the weight bearing
femur [25, 27, 36]. The SLS is used clinically as a functional measure of
lumbopelvic stability [25, 27, 36] as it is argued that this test has a greater ability to
highlight those with poor lumbopelvic stability [37] than the standard two legged
squat. With the addition of a decline board, the single leg decline squat (SLDS) is
also widely used as a targeted rehabilitation intervention for patellar tendinopathy
due to an increased loading of the patellar tendon [38-42]. Increased loading of the
patellar tendon is achieved by significantly reducing any posterior ankle constraints
allowing greater squat depth [43]. Greater squat depth is presumably the reason why
the SLDS has been employed in the Cricket Australia (CA) physiotherapy screening
protocols as a measure of lumbopelvic control in the place of the more traditional
single leg flat squat (SLFS). The greater squat depth conceivably promotes a more
challenging position for the participant and supposedly allows for a superior
lumbopelvic screening tool. However, the assumption of a deeper squat created by
the decline board promoting a more challenging position has yet to be tested.
Previous research has investigated the kinematic differences between the SLDS
and SLFS both in 2D [44] and 3D [43] focussing mainly on the differences in sagittal
plane knee kinematics. These researchers were unable to demonstrate clear
differences between the two conditions relating to the kinematics of the torso and
weight bearing hip [43, 44]. In particular, it is not known whether the two techniques
differ with regards to hip internal rotation and adduction, obliquity of the pelvis and
torso lateral flexion. A better understanding of the differences between the two
conditions around the weight bearing hip is an important aspect of interpreting the
SLDS in the CA physiotherapy protocol.
Investigating the relationship between the clinical and field based testing
procedures [23] and the more sophisticated 3D kinematic analysis is an important
step in validating the use of field based tests to predict injury. Understanding this
relationship would facilitate the development of standardised musculoskeletal
screening protocols. This standardisation would conceivably yield more reliable and
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accurate screening protocols allowing for appropriate musculoskeletal interventions
[18]. Appropriate interventions assist the management of any predispositions to
injury, which in turn may influence the incidence of lower limb musculoskeletal
injury in cricket.
1.2 PURPOSES
This study had numerous goals. The first was to compare the kinematic
differences between the flat and decline squatting conditions, primarily the five key
kinematic variables fundamental to subjectively assess lumbopelvic stability. These
variables were; 1) pelvic obliquity; 2) hip abduction/ adduction angles of the weight
bearing (WB) hip; 3) hip internal/external rotation angles of the WB hip; 4) the
degree of lateral flexion of lumbar spine relative to pelvis and 5) frontal plane
excursion of the knee on the weight bearing limb.
The second aspect was centred on the basis for the employment of a decline
board for the single leg squat. Determining the effect of ankle dorsiflexion range of
motion has on squat kinematics is vitally important in determining the future role that
that decline board has in screening for lumbopelvic stability with the single leg squat.
The third aspect was to examine the association between squat kinematics and
the associated subject clinical assessment. Understanding the terms of agreement
between qualitative and quantitative measurements of movement is an essential
element in validating such tests.
The fourth and final facet was to assess what relationship, if any, the
aforementioned key kinematic variables had with measures of hip strength. An
understanding of the relationship between kinematics and strength may provide
insight into pathomechanics patterns highlighted by functional screening tools such
as the single leg squat.
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Chapter 1: Introduction 5
So to summarise, the numerous focal points of this study were namely;
1. To compare the kinematic differences between the two single leg squatting
conditions, primarily the five key kinematic variables fundamental to
subjectively assess lumbopelvic stability;
2. Determine the effect of ankle dorsiflexion range of motion has on squat
kinematics;
3. Examine the association between key kinematics and subjective
physiotherapists’ assessment;
4. Explore the association between key kinematics and hip strength;
1.3 HYPOTHESES
Given the numerous aims of this study, various corresponding hypotheses were
founded prior to the commencement of this study. These were;
1. Greater levels of pelvic obliquity, WB hip adduction, WB hip internal
rotation, lateral flexion of the trunk relative to the pelvis and knee valgus will
be observed in the SLDS due to the greater depth of squat relative to the
SLFS.
2. Reduced ankle dorsiflexion range of motion will have a linear relationship
with kinematics of the hip, knee and ankle for the SLFS but not the SLDS.
3. Kinematics for pelvic obliquity, hip rotation and relative lumbar flexion will
correspond with the subjective clinical assessment of the same movements.
4. Hip abduction strength will correlate positively with the obliquity of the
pelvis in both squatting conditions for both weight bearing legs. External
rotation strength deficits would result in movements into internal rotation and
hip adduction. Some measure of hip strength will have a relationship with
self-selected squat depth.
1.4 THESIS OUTLINE
The subsequent chapters of this thesis reviews the literature (Chapter 2)
regarding sport and exercise related injury, intrinsic injury risks such as strength
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deficits, lower limb malalignment, associated biomechanical changes and clinical
implications of lower limb malalignment, force attenuation through the lower limb
and ankle dorsiflexion; cricket epidemiology, functional screening tools and their
association with assessing intrinsic injury risk and finally, the employment of the
single leg squat in screening protocols. Chapter 3 outlines the research design and
protocols employed in this study. Results from the study are outlined and discussed
in Chapters 4 and 5 respectively. Finally the implications and concluding statements
can be located in Chapter 6. Chapter 7 (Appendix) also contain a guide to the
kinematic terms used in this thesis that may assist the reader in understanding what
each of the kinematic terms represent. Supplementary tables from the results section
are also located here for the perusal of the reader.
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Chapter 2: Literature Review 7
Chapter 2: Literature Review
2.1 METHODOLOGY
The methodology employed for the collection of relevant literature pertaining
to this review was chiefly through papers available to QUT students through
electronic databases namely, Academic Search Elite, Mediline, Cinahl, SportDiscus
and Academic Search Premier which are all subsidiaries of EBSCOhost. Some
papers were obtained from within the bounds of the QUT library periodicals section
if not accessible electronically at the previously mentioned databases. All papers
were peer reviewed.
The key words that were predominantly used to search for journal articles
included: kinematics, biomechanics, single leg squat, physiotherapy screening
protocols, lumbopelvic stability, intrinsic injury risk, injury, malalignment, hip
strength and ankle dorsiflexion.
The reference list of this review was emailed to all members of the research
team as to ensure no prominent omissions from the literature review.
2.2 SPORT AND EXERCISE RELATED INJURY
Physical inactivity is among the leading causes of the major noncommunicable
diseases, including cardiovascular disease, type 2 diabetes and certain types of
cancer, contributing substantially to the global burden of disease, death, disability
and injury [4]. Previously, physically active lifestyles were linked with more
vigorous working and labour intensive domestic environments. Currently however,
technological advancements have reduced incidental physical activity and thus
yielded a more sedentary society. As a consequence, sport and exercise related
physical activity has been undertaken by a significant proportion of the population
either recreationally or competitively [5]. It has been well documented that physical
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8 Chapter 2: Literature Review
activities in the form of sport and exercise have positive effects on the physical and
psychological health and wellbeing of individuals [2-4, 45]. It is recognised
internationally that physical activity, such as sport, exercise and active travel, may
help to prevent a number of global public health problems [45] such as those
previously outlined [4]. This ethos has consequently encouraged the World Health
Organisation (WHO) as well as many governments to set formal physical activity
guidelines encouraging citizens to engage in physical activity through sport and
active travel [5].
Whilst there has been an increased promotion of physically active lifestyles to
improve quality of life [2, 3] and reduce the risk of noncommunicable diseases [4],
there has been a reluctance to recognise the coupled risk of injury associated with
participation in physical activity [5]. A large proportion of the population engage in
sport and as such sports injuries are relatively common in the modern western
societies [6]. In the US, sports-related injuries account for 2.6 million visits to the
emergency room made by children and young adults (aged 5–24 years) [46]. Injuries
sustained by high-school athletes currently result in 500 000 doctor visits, 30 000
hospitalisations and a total cost to the healthcare system of nearly $2 billion per year
[46]. In the UK, there are an estimated 19.3 million sport and exercise related injuries
annually [3] whilst one in five Australians are prevented from being more physically
active due to injury or disability [8]. Sports injuries are a multifaceted phenomenon
and as such are often difficult and time consuming to treat resulting in serious
financial ramifications such as the cost of medical treatment and physiotherapy, loss
of work time, and notwithstanding the loss of physical function [2, 3, 5-7]. It was
estimated that the cost of sports injuries in Australia was $1 billion annually in 1990
[8] $1.65 billion in 2002 [9], and still remains significant [10]. Preventative
strategies are therefore justified on medical as well as economic grounds.
To fully appreciate the complexities of the multifaceted concept of injury; the
epidemiology, aetiology, risk factors and exact mechanisms associated with injury
need to be defined. Risk factors for example are usually differentiated into either
extrinsic or intrinsic factors [5, 7, 13, 14]. Extrinsic risk factors are those that
originate external to the body. These are described within the literature as elements
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Chapter 2: Literature Review 9
such as level of competition and skill level, intensity and frequency of activity, shoe
type, playing surface, environmental conditions and external contact from equipment
and other players [5]. Conversely, intrinsic injury risk factors can be defined as those
that are internal to the body in forms such as age, gender, musculoskeletal alignment,
previous history of injury, somatotype, strength, range of motion and biomechanics
[13]. The varying aetiologies of lower limb injuries are typically a manifestation of
one or numerous risk factors interacting together at a given time. More recently,
emphasis has been placed on the role of the intrinsic risk factors [7] as these have
been demonstrated to be more predictive of injury than environmental related factors
[15]. As such, for the purposes of this literature review intrinsic risk factors such as
lower limb strength deficits, alignment, biomechanics, landing kinematics and ankle
dorsiflexion range of motion will be focussed on to illustrate their association with
lower limb injuries.
2.3 INTRINSIC INJURY RISKS OF THE LOWER LIMB
2.3.1 STRENGTH DEFICIENCIES
Considering the wide variety of movements associated with athletic function,
athletes must possess sufficient strength to provide joint stability in all three planes
of motion [26]. Whilst there is almost a universal agreement within the literature that
a lack of physical fitness is a risk factor for musculoskeletal injury during physical
activity [5, 7, 24], the link between muscular strength and lower injury risk is not
fully understood [25]. When the musculoskeletal system works effectively, the result
is the appropriate distribution of forces, optimal control and efficiency of movement,
adequate absorption of ground-impact forces and an absence of excessive
compressive, translational, or shearing forces on the joints of the kinetic chain [33].
Stability through the pelvis and hips, proximal lower limb, spine and abdominal
structures creates several advantages for integration of proximal and distal segments
in generating and controlling forces to maximise athletic function [27].
The gluteal muscles are stabilisers of the trunk over a planted leg which
generate a great deal of power for athletic activities [27]. Moreover, the hip
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abductors (gluteus maximus, posterior gluteus medius, biceps femoris) and external
rotators (piriformis, gemellus superior, obturator internus, gemellus inferior,
obturator externus and quadratus femoris) play an important role in lower extremity
alignment in ambulatory activities as they assist in the maintenance of a level pelvis
[47] and are involved in the prevention of hip adduction and internal rotation during
single limb support [26, 48, 49]. Conventional wisdom asserts that strength deficits
would presumably contribute to inadequacies in the aforementioned elements of an
effective system resulting in poor physical performance, elevated injury risk, or both.
An increase in injury risk varies depending on the anatomical location, as muscles of
the peri-pelvic region and lower limb have numerous individual and synergistic roles
in lower limb movements.
2.3.1.1 STRENGTH DEFICIENCIES AND GENERAL INJURY INCIDENCE
The association between weakness of the hip musculature and injuries of the
lower limb has been investigated by numerous studies [14, 25, 26, 28-34, 50]. An
early study by Nicholas, Strizak and Veras [34] attempted to define the existing
relationships between an injured part of the lower extremity and muscle groups far
removed anatomically from the site of injury. These researchers classified 134
injured patients into a seven categories according to the nature of their
musculoskeletal disease or injury. These injury groups were named ankle and foot-,
back-, knee ligamentous instability-, intraarticular defect-, patella-, arthritis- and
control-group [34]. The control group was derived from the all patients’ legs that
were uninvolved by the aforementioned injury processes and were matched against
the affected of symptomatic leg [34]. Generally speaking, the data revealed that the
more distal the injury site, the greater the total weakness in the affected limb.
Patients with ankle injuries revealed consistent weaknesses in their hip abductor and
adductor muscle group [34]. Ipsilateral quadriceps weakness was significantly
associated with ligamentous instability of the knee, patellar lesions, intraarticular
defects and back complaints (P < 0.025, 0.01, 0.005 and 0.05 respectively) [34]. The
researchers concluded that the strength of the lower body is an integrated unit, which
can be affected in many different areas, some quite remote form the site of
pathology, by a single pathological disorder [34]. A clear limitation of this study is
the retrospective aspect of data collection as it is difficult to ascertain whether
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Chapter 2: Literature Review 11
weakness contributed to the injury, exacerbated it symptoms, or is a product of the
injury.
An attempt was made by Lysens and colleagues [7] to understand the physical
and psychological profiles of the accident prone and overuse prone athletes. In a one
year prospective study, 185 physical education students (118 males; 67 females) of
the same age (18.3 ± 0.5 years) trained under the same conditions and were exposed
to similar extrinsic risk factors [7]. Numerous physical intrinsic risk factors were
profiled including anthropometric data, physical fitness parameters, flexibility
aspects and malalignments of the lower extremities in addition to 16 personality
traits [7]. Concerning the overuse proneness, a lack of static strength, ligamentous
laxity and muscle tightness predisposed students to injury, presumably due to the
compromised function of associated muscles and ligaments [7]. These effects were
amplified by large body weight and height, a high explosive strength and lower limb
malalignment [7]. Researchers also noted that psychosomatic factors such as a
degree of carefulness, dedication, vitality and hypochondria are prominent in the
pathogenesis and management of an overuse injury [7].
Leetun and colleagues [26] prospectively studied collegiate athletes who
participated in running and jumping sports comparing core stability measures
between genders in addition to comparing injured and uninjured athletes. Findings
unearthed that athletes who sustained an injury over the course of a season
demonstrated significantly lower measures of hip abduction and external rotation
strength [26]. Moreover, backwards logistic regression revealed that external rotation
strength was the sole variable that predicted injury status for the athletes in the study
[26]. Studies such as Lysens and colleagues [7], Nicholas, Strizak and Veras [25] as
well as Leetun and colleagues [26] demonstrated the relationship between proximal
strength deficiencies and the general incidence of injury in the lower limbs.
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2.3.1.2 REGIONALLY SPECIFIC INJURIES AND ASSOCIATED STRENGTH
DEFICITS
THE KNEE:
Additional studies have investigated the relationship between regionally
specific injuries of the lower limb and strength deficits in particular the pivotal role
of hip strength on the incidence of patellofemoral pain syndrome (PFPS) [31, 32, 50-
54]. Patellofemoral pain is a common orthopaedic complaint frequently seen in
physiotherapy practice [32, 51] and is characterised by retropatellar symptoms that
present insidiously and tend to be exacerbated with prolonged sitting or repetitive
weight bearing activities over a flexed knee [32]. It has also been reported that
females are more susceptible than their male counterparts to PFPS [31, 32, 50, 51]. A
number of contributing mechanisms have been proposed to explain this gender bias
centring on altered kinematics as a result of hip strength deficits.
A study by Cichanowski and colleagues [31] determined the strength
differences of hip muscle groups in collegiate female athletes diagnosed with
unilateral patellofemoral pain and subsequently compared the strength measures with
the unaffected leg and non-injured sport-matched controls. Results illustrated that hip
abductors and external rotators were significantly weaker between the injured and
unaffected legs of the injured athletes [31]. Moreover, injured collegiate female
athletes exhibited global hip weakness compared with age- and sport-matched
asymptomatic controls [31]. Ireland and colleagues [32] also measured a number of
hip strength measures using hand held dynamometry and demonstrated that
participants with PFPS demonstrated 26% less hip abduction strength (p
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Chapter 2: Literature Review 13
Overuse knee injuries such as illiotibial band syndrome (ITBS) have also been
investigated. The causative mechanisms of injury for ITBS include extrinsic factors
such as spikes in workload and downhill running in addition to intrinsic risk factors
such as illiotibial band (ITB) tightness [56] and abnormal biomechanics [57]. In
addition, Fredericson and colleagues [28] observed that distance runners with ITBS
had weaker hip abduction strength in the affected leg compared with their unaffected
leg and with unaffected long distance runners [28]. Their findings surrounding the
relationship between hip abduction strength and ITBS were augmented when a six-
week stretching and strengthening intervention program prescribed to all injured
runners reduced the symptoms of ITBS [28]. The researchers concluded that
symptom improvement in addition to a successful return to the pre-injury training
program, accompanied improvement in hip abductor strength [28]. The suggestion
that symptom improvement reflected improvements in hip abductor strength is
congruent with a more recent study by Arab and Nourbakhsh [56] which reported
that lower back pain participants with and without ITB tightness had significantly
lower hip abductor muscle strength compared to participants without lower back pain
[56].
Whilst the relationship between hip strength weakness and injury has been
examined, Niemuth and colleagues [29] have proposed that a relationship exists
between hip muscle imbalance and injury patterns. Their study demonstrated that
injured runners exhibited significant side-to-side differences in muscle strength in
three hip groups (hip abduction, adduction and flexion), compared to non-injured
counterparts [29]. The injured runners’ side hip flexors and abductors were
significantly weaker whilst their adductors were significantly stronger than their
uninjured side muscles [29]. As a point of comparison, non-injured runners did not
show any side-to-side differences in hip strength. This was the first study to show an
association between hip abductor, adductor, and flexor muscle group strength
imbalance and lower extremity overuse injuries in runners [29]. Although no cause
and effect relationship between weakness and injury was established, this study
identified an association not widely recognised in the contemporary literature for the
analysis and treatment of running injuries. This study in conjunction with those
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previously mentioned emphasized the substantive role of the hip external rotators and
abductors in healthy and pathological knee function.
THE HAMSTRINGS:
Moving distally from the stabilising proximal hip musculature, the hamstring
muscle group plays a more significant role during activities such as running and
jumping [58]. The hamstrings contract eccentrically when they slow the forward
swing of the leg to prevent overextension of the knee and flexion of the hips typical
of such movements as sprinting and when kicking a ball [59]. Not surprisingly,
hamstring strains are a common injury in sports that demand high intensity sprinting
efforts such as athletics or numerous football codes [30, 60, 61]. The total amount of
missed playing time as a result of a hamstring injury has accounted for 16% in the
Australian Football League (AFL) [62], between 10 and 23% in soccer [63] and
almost 18% in cricket [64]. There appears to be a consensus within the literature that
a vicious circle of recurrent hamstring injuries is not uncommon, resulting in a
chronic problem with significant morbidity in terms of symptoms, reduced
performance, and time loss from sports [15, 60, 61, 63, 65, 66]. Additional causative
factors for hamstring muscle strains have been studied extensively revealing that
muscle fatigue, age and muscle weakness are the most commonly postulated intrinsic
risk factors [19, 59, 60, 63, 65, 66]. Studies have also shown that the addition of
specific preseason strength training for the hamstrings – including eccentric
overloading – would be beneficial for elite soccer players, both from an injury
prevention and from performance enhancement perspectives [67].
THE LUMBAR SPINE
The dysfunction of the lumbar spine musculature plays a significant role in the
aetiology of lower back pain in general population [68]. The osteo-ligamentous
lumbar spine is inherently unstable since, in vitro, it buckles under compressional
loading of only 90N or 20lbs [69]. The lumbar vertebrae tend to be most susceptible
given their load dissipating attributes during trunk motion which in turn requires
stabilization via the coordination of a number of mechanisms [27]. This critical role
is undertaken by the complex interplay of both superficial and deep muscles around
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Chapter 2: Literature Review 15
the spine and demonstrates how vital core musculature is for generation and
attenuation of energy during movement [27, 69]. Deeper muscles primarily provide
postural stability and consist of the quadratus lumborum (QL), iliocostalis
lumborum, longissimus lumborum and the lumbar multifidus. These muscles can
have a direct influence on segmental stability and control of the lumbar spine due to
their attachments to the spinal column [70]. Coordinated, co-contraction of the
lumbar paraspinal muscles with the abdominal wall muscles such as transversus
abdominus is suggested to provide single joint stabilization that in turn allows multi-
joint muscles to work more efficiently to control spine movements [27, 69].
Consequently, this mechanism is assumed to provide a stable and safe platform for
trunk and limb movement in addition to load dissipation [71].
Muscles of the lumbar region are reported to be major stabiliser of the lumbar
spine [55] with a prime example being the QL. The QL has been described as a
major stabilizer of the lumbar spine by working dynamically in union with more
passive structures such as bone and ligament [27, 69] in addition to being active
during activities that require lateral flexion, axial rotation and extension of the trunk
such as javelin throwing and fast bowling in cricket [72, 73]. Understandably, any
mechanisms that alter the functionality of any of the structures of the lumbar spine
such as muscular asymmetry or weakness are likely to have detrimental effects on
the loading characteristics and thus likelihood of injury [72-74]. Muscular
asymmetry in side-to-side strength of the hip extensors and abductors was found in
athletes with a previous history of lower extremity injury or lower back pain in a
study by Nadler and colleagues [74], implying a lateral dominance effect.
Furthermore, these same injured athletes were shown to have decrements in hip
strength as compared with athletes without injury [74].
The notion of muscular asymmetry and weakness has been illustrated in
numerous cricket studies investigating the force attenuation role of the QL in relation
to stress fractures of the pars interarticularis. In a mechanical sense the pars acts as a
fulcrum for the facet joints which lie to the posterior and are vital in preventing
excessive lumbar spine movement [75, 76]. Without the sufficient strength and
activation of the lumbar musculature in symphony with numerous other lumbopelvic
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mechanisms, the likelihood of a defect or fracture in this narrow portion of bone is
elevated [73]. Such fractures are referred to as a spondylolysis [77].
Engstrom and co-workers [72] have previously prospectively linked
asymmetry of the QL muscle to lumbar spondylolysis in 51 adolescent bowlers. They
used MRI annually to measure and quantify QL asymmetry and for also identifying
spondylolysis and compared QL asymmetry to that of a control group of swimmers
(n=18). It was concluded that there was a strong association between QL asymmetry
and the development of symptomatic unilateral spondylolysis [72]. An appealing
association was evident between the mechanical couplings of repetitive forces
associated with symptomatic spondylolysis and the substantial asymmetry of QL in
the injured fast bowlers [72]. Asymmetry of the QL conceivably reflected an
adaptive preferential hypertrophy of QL in response to the loading milieu and thus
escalating susceptibility for pathogenesis of spondylolysis [72]. This viewpoint is
congruent with a study conducted by Visser and colleagues [73] who hypothesized
that that the bowling technique of some cricketers caused unilateral hypertrophy of
the QL indicating a technique that transmits abnormal stresses upon the lumbar
musculature. According to this study, the longer a cricketer has been exposed to a
compromised technique that produces high stresses in the pars, the more likely the
establishment of a cause-effect relationship between an bowling specific large
asymmetry and a fracture [73]. The discrimination between bowlers with and without
symptomatic pars lesions provides a rational basis for using QL asymmetry as a
potential clinical screening tool for investigating suspected spondylolysis [73].
THE ANKLE
The link between muscular strength, imbalance, and flexibility of the muscles
acting on the ankle are frequently mentioned in the literature as possible intrinsic risk
factors [78]. However, due to the lack of quality prospective studies, the conclusions
that can be drawn regarding the possible injuries are tenuous [78]. Mahieu and
colleagues [78] however, have prospectively investigated numerous intrinsic injury
risk factors on the rate of Achilles overuse injuries in a military recruit population.
Almost 15% of the studied population suffered an injury with the analysis revealing
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Chapter 2: Literature Review 17
that male recruits with lower plantar flexor strength and increased dorsiflexion
excursion were at a greater risk of Achilles tendon overuse injury [78]. An isometric
plantar flexor strength of lower than 50 Nm and dorsiflexion range of motion higher
than 9.0° were possible thresholds for developing an Achilles tendon overuse injury
[78]. It was concluded by the research team that greater muscle strength produced
stronger tendons that could deal better with high loads [78]. These results reiterate
how adequate muscular strength facilitates force attenuation and the associated
reduction of injury risk.
When all of the aforementioned literature is integrated, it indicates that
movements of the lower limb involve a series of synergistic muscular contributions
of the entire kinetic chain to achieve the desired locomotor or performance outcome.
Any disruptions to this system manifest themselves in the form of an injury and can
be accredited to intrinsic and/or extrinsic injury risk factors. Intrinsic risk factors
such as deficits in muscular strength and balance have consistently been associated
with the aetiology of lower limb injuries throughout all parts of the lower limbs and
lumbopelvic region. The literature in this area particularly demonstrates the
importance of proximal stabilization for lower extremity injury prevention [26]
particularly the knee [31, 32, 34, 51, 79]. It appears that adequate lumbopelvic-femur
muscle function may conceivably reduce exposure to other intrinsic risk factors such
as inefficient force attenuation, unstable movement patterns and lower limb
malalignments [25, 80].
2.3.2 LOWER LIMB ALIGNMENT - THE ‘MEDIAL COLLAPSE’
The intersegmental joint forces and the structures that resist them, such as
articular surfaces, ligaments and musculature, are associated through the anatomical
alignment of the joints and skeletal system [14]. Lower limb skeletal malalignments
have been proposed as a risk factor for acute and chronic lower extremity injuries [5,
81] and may even be the primary cause of musculoskeletal patient problems [82].
Biomechanical abnormalities associated with malalignments of the lower limb have
frequently been implicated as a causative factor for lower limb injuries as a result of
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intensive exercise [5], in addition to exacerbating the presence of a musculoskeletal
injury that have some other causal mechanism [82].
The quadriceps angle or Q-angle is defined as the angle formed by a line from
the anterior superior iliac spine to the patella centre and a line from the patella centre
to the tibial tuberosity and is often associated with malalignments of the lower limb
[81, 83]. Numerous studies have postulated that it is this structural difference
between males and females that may contribute to an altered lower extremity
movement pattern [84], and in turn, contribute to a gender injury bias [25, 26, 84,
85]. Non-contact anterior cruciate ligament (ACL) injury rates, for example, have
been reported to be six times higher in women especially in jumping sports [85-87].
Whilst the aetiology of this type of injury is multifactorial [88], the most common
mechanism of injury has been proposed to involve rapid deceleration of the lower
extremity such as when landing from a jump or a rapid change in direction whilst
running [87, 88]. During activities such as rapid changes in direction or landing, the
greater Q-angle in the female athlete may predispose the knee to more vulnerable
positions which in turn places greater strain on the ACL [86, 88, 89].
Excessive frontal- or transverse-plane hip motion during single-limb weight
bearing may be associated with excessive femoral adduction, an internal rotation
leading to knee valgus, tibial internal rotation and excessive foot pronation. This
series of postural malalignments has been described as medial collapse [90, 91].
Such alignments have been associated with insufficient muscular control and can
alter the joint load distribution and, consequently, joint contact pressure of adjacent
or distant joints [92]. Accounting for the alignment of the entire extremity in this
context, rather than a single segment, may more accurately describe the relationship
between anatomic alignment and the risk of lower extremity injury, since one
alignment characteristic may interact with or cause compensations at the other bony
segments [81, 82]. Whilst this viewpoint remains largely theoretical [91], it appears
more plausible when clinical interventions are designed and successfully
implemented to reduce symptoms by addressing the underlying pathological
malalignment and biomechanics [82].
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Chapter 2: Literature Review 19
The potential for an interactive effect between joint segments has been
explored by Nguyen and Shultz [81]. A factor analysis approach was employed in
attempt to use a number of lower extremity alignment variables (femoral anteversion,
quadriceps angle, tibiofemoral angle, genu recurvatum, tibial torsion and pelvic angle
– the angle formed by a line between ASIS and PSIS relative to the horizontal plane)
to examine whether relationships could be identified among these variables [81]. The
analysis identified three distinct lower extremity alignment factors namely a valgus
(greater anterior pelvic, quadriceps, and tibiofemoral angles), pronated (greater genu
recurvatum and navicular drop and less outward tibial torsion) and femoral
anteversion factor which demonstrated the potential interaction among lower
extremity alignment variables [81]. A factor of particular relevance to this review
was the relative valgus alignment characterised by increased pelvic angle, quadriceps
angle and tibiofemoral angle as this collective posture insinuates a medial collapse of
the knee. The medial collapse alignment may reflect an interaction between the
pelvis and knee angles as increased anterior pelvic tilt has been associated with
internal rotation at the hip [93].
2.3.2.1 CLINICAL IMPLICATIONS OF MEDIAL COLLAPSE
The clinical implications of a medial collapse of the knee on lower limb
injuries have been investigated with numerous plausible explanations. Numerous
studies [31, 32, 50-54, 94] have theorised that deficits in hip musculature strength
contribute to the mechanisms of patellofemoral pain, particularly through alteration
of lower limb kinematics. Specifically, deficiencies in hip external rotation and
abduction strength presumably contribute to excessive femoral adduction and
internal rotation during weight bearing activities [25, 31, 32], which has been shown
to promote increased lateral retropatellar contact pressure in cadaveric studies [32].
Riegger-Kruch and Keysor [92] rationalised that skeletal malalignments can alter
soft tissue loading of adjacent or distal joints. Altered loading can be demonstrated
by using excessive genu valgus as an example. In this instance, the quadriceps group
may become less effective as a knee extensor if the quadriceps tendon is altered in a
direction with more of the resultant force pulling the patella laterally and less of the
force pulling the patella proximally [92]. By altering the line of pull of the
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quadriceps muscle, there would be a tendency for the patellar to be more laterally
displaced resulting in a reduction of knee extension force [92].
The relationship between knee valgus and hip muscle function is of particular
importance. Hollman and colleagues [90] explored the relationships among frontal
plane hip and knee angles such as knee valgus, hip muscle strength, and
electromyographic (EMG) recruitment in women during a step-down. Strong
correlations were found between knee valgus and hip adduction angles (r = .755, P <
.001) further demonstrating the findings of collective kinematic alignments. Gluteus
maximus recruitment was moderately and negatively correlated (r = -.451) with knee
valgus, accounting for 20% of the variance in knee valgus [90]. An unexpected
finding was that there was a significant positive relationship between abduction
isometric force-production values and greater knee valgus angles during the step
down task [90]. These findings were explained in part by the secondary role of the
gluteus medius. Though primarily a hip abductor, gluteus medius also functionally
assists in internal rotation due to its increased moment arm during greater levels of
hip flexion [95]. This observation is in line with the theory of Gottashalk and
colleagues [49] who have postulated that the gluteus medius functions primarily as a
hip stabiliser and pelvic rotator, rather than a hip abductor when the hip is less
flexed.
The hip abductors and external rotators play an important role in lower
extremity alignment and ambulatory activities as they assist in the maintenance of a
level pelvis [47] and are involved in the prevention of hip adduction and internal
rotation during single limb support [26, 48, 49, 95]. Consequently, movements into
hip internal rotation and adduction may be due to weakness in the muscles
controlling eccentric hip internal rotation [25, 26]. This notion was supported by the
findings of Willson and colleagues [25] in a study which evaluated the association
between core strength (trunk, hip and knee) and the orientation of the lower
extremity during a single leg squat among male and female athletes. The findings
indicated that females generated lower trunk, hip and knee torques than males which
was coupled with greater frontal plane projection angles, or knee valgus [25].
Additionally, the association between external rotation strength and frontal plane
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Chapter 2: Literature Review 21
projection angles was both statistically and clinically significant [25]. Participants
with greater hip external rotation strength may be better suited to resist internal
rotation moments [25].
When investigating excessive movements of internal rotation of the hip, Delp
and colleagues [95] noted that rotational moment arms of the hip musculature should
be considered, especially when the hip is flexed. Through the development of a
three-dimensional computer model of the hip muscles, they were able to compare the
rotational moment arms of the hip musculature during varying stages of hip flexion.
Their experimental results demonstrated that the internal rotation moment arms of
some muscle increased; the external rotation moment arms of other muscles
decreased, and some muscles switched from external rotators to internal rotators as
hip flexion increased [95]. The trend toward internal rotation with hip flexion was
apparent in 15 of the 18 muscle compartments, suggesting that internal rotation is
exacerbated by hip flexion [95]. This observation has obvious implications for
activities that involve elevated hip flexion angles such as in landing and other shock
absorbing activities as there may be a tendency for medial collapse.
Whilst lower limb alignment has been shown to alter the joint load distribution
and, therefore, contact pressure of adjacent and/or distant joints [5, 81], lower
extremity malalignment may be secondary to inferior proximal hip musculature
function [25, 26, 32, 88]. Inadequate musculoskeletal strength, malalignment and
biomechanics of the lower limb have all been associated as an intrinsic injury risk
and may additionally cause an inability to efficiently attenuate the forces associated
with ground impact. Consequently, it is also pertinent to review any literature that
describes the interrelated aspects of hip strength and lower limb malalignment to
ascertain the influence these factors have on force attenuation in the lower limb.
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2.3.3 HIP STRENGTH, LOWER LIMB MALALIGNMENT AND FORCE ATTENUATION
2.3.3.1 RUNNING
Most recreational sporting enthusiasts engage in running based sports which
involve repetitive high magnitude foot impacts with the ground [96]. These athletic
activities can impose extreme loads on the musculoskeletal system and may
contribute to musculoskeletal injury development [97, 98]. Deficits in hip
musculature have been shown to play a role in postural malalignments and injury
aetiology [25]. The ability of the lower limb musculature to resist medial collapse
presumably allows the lower limb to attenuate forces through the kinetic chain with
greater efficacy. Numerous studies have explored the relationship between lower
limb alignment [99], strength of the hip musculature and the force attenuation
properties of the lower limb during weight bearing activity.
McClean and colleagues [99] examined the relationship between peak knee
valgus moment and lower extremity postures for men and women at impact during a
sidestep cutting task. Results of this study revealed that females had significantly
larger normalised peak valgus moments and a greater initial contact hip flexion and
internal rotation position than males during the sidestepping movements [99]. The
authors hypothesised that increased hip internal rotation and/or flexion at initial
contact therefore, may compromise the ability of hip internal rotators and other
medial muscles to adequately support resultant knee valgus loads [99]. Greater levels
of hip flexion has been shown, theoretically to exacerbate movements into hip
internal rotation as a consequence of altered hip musculature moment arms [95]. As a
result, hip neuromuscular training has been suggested to increase control at the hip
joint as this may ultimately reduce the likelihood of lower limb injury via a valgus
loading mechanism during sidestepping, especially in females [36, 99].
The hip muscles are capable in balancing a number of biomechanical forces in
the body [29]. During running activities the trunk laterally flexes towards the same
side as the foot strike and the pelvis is upwardly oblique primarily as a shock
absorption mechanism [29, 100] which is in turn stabilised by an equalising
contraction of the hip abductors [100]. A study by Snyder and colleagues [101]
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Chapter 2: Literature Review 23
illustrated that strength training of the hip abductors and external rotators favourably
altered the lower extremity biomechanics and joint loading in running [101]. This
study revealed that rear foot eversion range of motion, hip internal rotation range of
motion, knee abduction and rear foot inversion joint moments were reduced
following six weeks of hip muscle strengthening [101]. The authors suggested that
the hip strengthening intervention employed in this study may alter knee joint and
ankle joint loading and thus be useful in treating patients with lower extremity
injuries [101].
2.3.3.2 LANDING
During landing, the lower extremity joints function to reduce and control the
downward momentum acquired during the flight phase through joint flexion [102].
Different landing strategies have been shown to exist between genders with females
having larger frontal plane movements of the knee [85, 88, 89], more erect landing
posture, utilising more hip and ankle joint range of motion and joint angular
velocities compared to males [102]. It has been argued that females may choose
these kinematic characteristics to maximise the energy absorption from the joints
most proximal to ground contact [102].
A force attenuation strategy based around increased knee valgus and greater
lower limb stiffness is considered to be a contributing factor to the aetiology of
noncontact ACL injuries for females [85, 89, 103]. Hewett and colleagues [89]
prospectively screened 205 female adolescent soccer, basketball, and volleyball
players via three-dimensional biomechanical analyses in a jump-landing task before
their respective seasons. Joint angles and moments were measured to help delineate
whether lower limb neuromuscular control parameters could be used to predict ACL
injury risk in female athletes [89]. Of these 205 athletes, nine had confirmed ACL
rupture and exhibited significantly different knee posture than the 196 that did not
have an ACL rupture. Knee abduction angle (P < .05) at landing was 8° greater in
ACL-injured than in uninjured athletes. The ACL-injured athletes also had 2.5 times
greater knee abduction moment (P < .001) and 20% higher ground reaction force (P
< .05), whereas stance time was 16% shorter [89]. As a consequence, the ACL-
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injured participants were characterised as having increased motion, force, and
moments occurring in a smaller amount of time than the non-injured [89]. The
findings of this study elude to increased valgus motion and valgus moments at the
knee joint during the impact phase of jump-landing tasks being key predictors of the
increased potential for ACL injury in females [89].
The influence of hip-muscle function on knee joint kinematics during landing
and the influence of fatigue has been investigated by Carcia and colleagues [103].
Frontal plane tibiofemoral landing angle, excursion and vertical ground reaction
forces were recorded from a drop jump under prefatigue, postfatigue and recovery
conditions on twenty recreationally active college aged students. A bilateral fatiguing
protocol was employed which involved a maximal voluntary isometric contraction
against a dynamometer. Bilaterally fatiguing the hip abductors elicited larger knee
valgus but no differences in frontal plane excursion or vertical ground reaction forces
in double leg drop landings when compared to the non-fatigued state [103]. The
results from this study further illustrate that proximal hip musculature influences the
kinematics at the tibiofemoral joint. Moreover, fatigue in the proximal musculature
might increase the injury risk to the knee during landing [103].
A recent study was conducted to evaluate the relationship between ankle
dorsiflexion and landing biomechanics by Fong and colleagues [104]. Thirty five
healthy volunteers (17 male and 18 female) were recruited. Landing biomechanics
were measured by an optical motion-capture system interfaced with a force plate.
Results observed significant correlation between ankle dorsiflexion and knee flexion
displacement (r = 0.646, P = 0.029) and vertical (r = -0.411, P = 0.014) and posterior
(r = -0.412, P = 0.014) ground reaction forces. The researchers suggested that greater
knee displacement and smaller ground reaction forces during landing were indicative
of a landing posture consistent with reduced ACL injury risk by limiting the forces
the lower limb must absorb.
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Chapter 2: Literature Review 25
2.3.3.3 CRICKET FAST BOWLING
Fast bowling, by its very nature is a dynamic, multi-planar and forceful activity
that produces considerable mechanical loads to the spine which can be repeated as
often as 300 to 500 times per week [72, 77, 105]. Amongst cricketers, fast bowlers
have consistently been identified as having the greatest risk of injury due to the
characteristic chronic loading of the musculoskeletal system [106]. The enormous
intensity of the activity can overwhelm the normal repair process of the soft tissue
and bone alike and cause microscopic defects to form and propagate resulting in
lower extremity injuries [107]. The absorption of these forces is significant in the
aetiology and pathogenesis of injuries to the lower limb and vertebral spine as they
can reach four to nine times body weight during delivery [108, 109]. Excessively
frequent exposure to large forces in combination with predisposing factors that
include poor technique [110, 111], substandard physical preparation [112],
musculoskeletal immaturity [75, 105, 113] and muscular asymmetries [72, 106, 112]
consequently demarcates a multifactorial pathogenesis, observed in such injuries
such as stress fractures in fast bowlers [72, 75, 77, 106, 108, 109].
The ground reaction forces that are observed during bowling are high
magnitude and high frequency forces. The coupling of these mechanical components
is instrumental in the development of lower extremity injuries. The magnitude of
force generated and absorbed in the fast bowlers delivery stride is substantial and
transmitted and dissipated through the various loading mechanisms of the lower
limbs [105]. The process of force attenuation places immense levels of stress upon
the osseous structures of the lower limb, hip, pelvis and spine [114, 115]. These
forces are all generally lower than the critical limit of the specific tissue and combine
to produce a fatigue effect over time, predisposing the tissue to overuse pathologies
such as tendonitis, bursitis, fasciitis, fracture or neuritis and cricket specific injuries
such as vertebral disk degeneration [105] and spondylolysis [77, 106, 107].
Certain factors contribute to the differences in ground reaction forces. Hurrion
and colleagues [108] simultaneously measured the back and front foot ground
reaction forces of fast bowlers during a delivery stride. Results suggested that the
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26 Chapter 2: Literature Review
stride length and alignment influence ground force in the delivery stride [108]. These
factors where described as dependent upon the velocity at which the bowler impacts
the crease with the front foot, which also determines the magnitude of force [116].
Results also concluded that the highest front foot strike forces are a by-product of a
fully extended, or even hyper-extended knee however there is less conclusive
evidence to link the straight front leg technique to injury [108].
Previous sections have highlighted the interrelation of proximal strength,
malalignment, force attenuation and the resultant genesis of injury. However, the
more distal ankle joint, particularly range of motion deficits, also contribute
significantly to the pathogenesis of lower limb injuries. Consequently, reviewing the
literature relevant to the ankle dorsiflexion range of motion will add further
understanding of the multifaceted nature of intrinsic injury risk.
2.3.4 ANKLE DORSIFLEXION RANGE OF MOTION
The flexibility of a joint is determined by the geometry of the articular surfaces
and by muscle, tendon, ligament and joint capsule laxity [82]. The literature is
divided on the influence of range of motion (ROM) has on injury [14]. However,
decreases in ankle ROM, particularly dorsiflexion, have been implicated in several
studies to impaired function and injury [5, 17, 65, 66, 78, 82, 117-122]. Adequate
dorsiflexion of the talocrural joint is required for the normal performance of
functional activities such as walking, running, stair climbing and squatting [119] in
addition to adequate force development and attenuation during foot contact [117,
123]. The point of maximal ankle dorsiflexion during human gait is approximately
10° and occurs during stance phase just prior to heel rise [124]. For this reason,
numerous studies advocate testing ankle dorsiflexion range of motion and associated
restrictions during full knee extension to accurately assess functional dorsiflexion
range of motion [5, 82]. Restrictions of ankle dorsiflexion may be caused by a tight
gastrocnemius, soleous, capsular tissue or abnormal ossesous formation of the ankle
[82, 117] or prolonged immobilization due to injury [117, 118, 122].
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Chapter 2: Literature Review 27
Ankle