t 3d kinematics of the single leg flat and...

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 =

<0.001; D p = 0.004) and hip adduction kinematics (ND p = <0.001; D p = <0.001).

With the mean angle, only the non-dominant leg observed significant differences in

hip adduction (p = 0.001) and hip external rotation (p = <0.001); 2) Significant linear

relationships were observed between clinical measures of ankle dorsiflexion and

sagittal plane kinematic namely SLFS dominant ankle (p = 0.006; R2 = .429), SLFS

non-dominant knee (p = 0.015; R2 = .352) and SLFS non-dominant ankle (p = 0.027;

R2 = .305) kinematics. Only the dominant ankle (p = 0.020; R

2 = .331) was found to

have a relationship with the decline squat. 3) Strength measures had tenuous

associations with the subjective assessments of lumbopelvic stability with no

significant relationships being observed. 4) For the non-dominant leg, external

rotation strength and abduction strength were found to be significantly correlated

with hip rotation kinematics (Newtons r = 0.458 p = 0.049; Normalised for

bodyweight: r = 0.469; p = 0.043) and pelvic obliquity (normalised for bodyweight: r

= 0.498 p = 0.030) respectively for the SLFS only. No significant relationships were

observed in the dominant leg for either squat condition. Some elements of the hip

strength screening protocols had linear relationships with kinematics of the lower

limb, particularly the sagittal plane movements of the knee and ankle. Strength

measures had tenuous associations with the subjective assessments of lumbopelvic

stability with no significant relationships being observed;

Discussion: The key finding of this study illustrated that kinematic differences can

occur at the hip without significant kinematic differences at the knee as a result of the

introduction of a decline board. Further observations reinforce the role of limited

ankle dorsiflexion range of motion on sagittal plane movement of the hip and knee

and in turn multiplanar kinematics of the lower limb. The kinematic differences

between conditions have clinical implications for screening protocols that employ

frontal plane movement of the knee as a guide for femoral adduction and rotation.

Subjects who returned stronger hip strength measurements also appeared to squat

deeper as characterised by differences in sagittal plane kinematics of the knee and

ankle. Despite the aforementioned findings, the relationship between hip strength and

lower limb kinematics remains largely tenuous in the assessment of the lumbopelvic

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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

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viii The 3D kinematics of the single leg flat and decline squat

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.

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].

2

2 Chapter 1: Introduction

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

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

4


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.

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

6


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.

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

8

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


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

10


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


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.

12


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<.001) and

36% less external rotation strength (P<.001) than similar age-matched controls.

Baldon and colleagues [50] observed females with PFPS had higher hip adduction to

abduction torque ratio in addition to a diminished capacity to generate eccentric hip

abduction torque. The greater incidence of PFPS in these studies was presumably due

to insufficient muscular strength to protect the knee from excessive internal rotation

and knee valgus moments which may predispose to the further development of PFPS

[31, 32, 51, 55]


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

14


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


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

16


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


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

18


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].


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

20


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


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.

22


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]


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-

24


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.


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

26


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].


Ankle injuries are common in a number of populations from athletes [17, 65,

66, 120], dancers [122], soldiers [121], general active population [24] and even

children [117]. Despite the frequency of such injuries, little is known about

prevention, particularly in children [117]. Tabrizi and colleagues [117] investigated

whether decreased dorsiflexion predisposes children to such fractures and sprains. A

goniometer was used to assess dorsiflexion in an injured (n=82) and non-injured

control group (n=85). Findings showed that limited ankle dorsiflexion predisposes to

ankle injury [117]. These investigators hypothesized that a twisting fall produces a

torsional and dorsiflexion moment on the foot [117]. Gradual absorption of energy

by controlled dorsiflexion through a flexible gastrocnemius-soleus complex may

prevent injury, whereas sudden loading in the presence of a tight calf muscle may

result in a sprain or fracture [117]. Suggestions from this study included that children

with tight calf muscles should undergo a regimen of stretching exercises to improve

their ankle range of motion and resultant risk of ankle injury [117].

Decreased ankle dorsiflexion range of motion has been suggested as a risk

factor for inversion sprains in a prospective study by Willems and co-workers [24].

A total of 241 male physical education students were evaluated for possible intrinsic

risk factors for inversion sprains at the beginning of their academic study. The

evaluated intrinsic risk factors included anthropometric characteristics, functional

motor performances, ankle joint position sense, isokinetic ankle muscle strength,

lower leg alignment characteristics, postural control, and muscle reaction time during

a sudden inversion perturbation [24]. Running speed, cardiorespiratory endurance,

balance, dorsiflexion strength, coordination, muscle reaction, and dorsiflexion range

of motion at the ankle were associated with the risk of ankle inversion sprains in the

44 (18%) of male participants [24]. Based on the findings of this study, the authors

concluded that poor physical conditioning enhances the risk of a sports injury [24].

In a study attempting to identify intrinsic risk factors for hamstring injury at the

elite level of Australian football, a musculoskeletal screen was employed during the

preseason period of the 2002 Australian football season. Ankle dorsiflexion range, as

measured by the dorsiflexion lunge test, was found to be an independent, although

not significant, predictor of hamstring injury risk [66]. These results were supported

28


by a similar study identifying risk factors for general lower extremity injuries at the

community level of Australian football, with only ankle dorsiflexion ROM being

significantly associated with a player sustaining a lower extremity injury [65].

Commonly used tests of hip joint range of movement, hamstring flexibility, iliopsoas

flexibility and neural mobility were not associated with hamstring injury risk [66].

With respect to cricket, Dennis and colleagues [17] investigated the reliability

of a field-based musculoskeletal screening protocol for fast bowlers to measure

potential risk factors for injury. Restricted ankle dorsiflexion was again mentioned

with bowlers with an ankle dorsiflexion lunge of 12.1–14.0 cm on the leg

contralateral to the bowling arm being at a significantly increased risk than bowlers

with a lunge of >14 cm [17]. Bowlers with a lunge of ≤ 12 cm were also at an

increased risk, but not significantly so [17]. Dennis and colleagues hypothesised that

a lack of ankle dorsiflexion on the front foot impact leg could relate to injuries in fast

bowlers in a number of ways. Tight calf musculature with a lack of ankle

dorsiflexion may contribute to higher ground reaction forces at front foot impact as

there is less displacement available to attenuate the impact [17]. Resultant force

increases coupled with the compromised function of the calf muscle could increase

load up the kinetic chain on to the knee and patellar tendon, hip and even lumbar

spine [48, 108, 120, 125]. It may also be possible that greater ankle dorsiflexion

ROM may contribute to an improved force attenuating alignment of the tibia and

femur when the ankle joint is fully flexed, which has been speculated to cause

changes in optimal pelvis and lumbar spine alignment in weight bearing [91].

The influence of reduced ankle dorsiflexion range on patellar tendon injuries

has been explored. Milliaris and colleagues [120] investigated whether factors

relating to muscle and joint flexibility (sit and reach flexibility, dorsiflexion range),

strength (jump height, ankle plantar flexor strength) and activity level (years of

volleyball competition, activity level) are associated with patellar tendon injury

among volleyball players. They observed that only ankle dorsiflexion range was

associated with patellar tendinopathy [120]. It was considered that reduced ankle

dorsiflexion range may be a risk for the development of patellar tendinopathy due to

its contribution to lower limb shock absorption. Findings such as those described


previously from Dennis and colleagues [17] reinforce the hypothesis of higher front

foot ground reaction forces as a result of ankle dorsiflexion limitations.

Reduced ankle dorsiflexion results in a variety of compensatory changes within

the lower limb mechanics [82]. Gross [82] has reported that one type of

compensation involves decreasing step length of the contralateral lower extremity,

whilst others have a symmetrical and normal step length but have a hyper-mobile

dorsiflexion of the forefoot or the rear foot. These patients typically present with

midfoot pain during terminal stance phase of gait [82]. An additional compensation

outlined by Gross [82] is an increase in toe-out placement angle so that dorsiflexion

demands during terminal stance phase of gait are decreased. Patients who utilized

this toe-out compensation rely more on movements that occur within the foot about

the anterior posterior axes of rotation (e.g. subtalar joint) as they accomplish weight

bearing over the stance foot [82]. This theoretically results in greater ground reaction

forces as there is more of an eversion moment than a plantar flexion moment during

the loading phase of the gait cycle [82]. A tendency to exhibit eversion moments has

been shown to cause excessive and prolonged pronation [82, 121], defined as the

movement of abduction, dorsiflexion and eversion [124].

Pronation unlocks the mid tarsal joint of the foot which becomes more flexible

in order to adapt to the underlying surface. Pronation also acts as a shock absorber,

assists in maintaining balance, improves efficiency of muscle contraction and assists

in the distribution of normal forces the lower kinetic chain [126]. Compensatory

pronation has been said to be the most common cause of foot pathology and has been

linked to numerous lower limb injuries including tibial and metatarsal stress

fractures, plantar fasciitis, patellofemoral pain syndrome and anterior cruciate

ligament injuries [127].

Hughes [121] investigated the predisposing factors of metatarsal stress

fractures in two groups of soldiers with and without radiographic diagnosis.

Biomechanical analysis of the foot and ankle were included in the investigation to

help explain forefoot varus, abnormal rear foot valgus and dorsiflexion as

30


intervening variables in metatarsal stress fracture development. Ankle dorsiflexion

was measured with a goniometer with the knee fully extended and concluded that

participants with decreased dorsiflexion were 4.6 times more likely to develop a

metatarsal stress fracture than those with normal measurements [121]. The

relationship between decreased dorsiflexion and a higher rate of stress fractures are

supported by a similar study by Montgomery and colleagues [128], but this trend was

statistically insignificant.

The evidence pertaining to ankle dorsiflexion ROM and the link to injury

within the literature is limited. The available information suggests that constraints

associated with ankle dorsiflexion appear to influence lower limb pathologies,

particularly overuse. It may be that ankle dorsiflexion ROM itself is not an

independent risk factor, but rather injury incidence is the product of the

compensatory biomechanics previously outlined [129]. As such, ankle dorsiflexion

may simply be one of a number of variables that interrelate to contribute to injury.

In conclusion, by integrating the previously outlined literature in this section, it

can be argued that numerous intrinsic risk factors contribute to lower limb

pathogenesis. The contribution of intrinsic risk factors to lower limb pathogenesis is

an important notion to recognise as an increased understanding of these intrinsic risk

factors may provide insight in to the exercise and sport related epidemiology of the

lower limbs.

2.4 EXERCISE AND SPORT RELATED EPIDEMIOLOGY

Injury prevention and intervention have become focal points for researchers

and clinicians alike. Successful injury surveillance and preventions requires valid

pre- and post- intervention data on the extent of the problem [6]. Unfortunately,

inconsistencies within the methods of data collection, definitions of injury types and

severity and population samples have made comparison between studies a

complicated process [5, 6]. This weakness can be exemplified when observing the

reported incidence of injuries in the recreational running population. The rates of


injury incidence have been reported to be 25 to 75% [130], 24% [131], 37 to 56%

[132], 33 to 85% [133]. However, these rates are reported and influenced in a variety

of ways due to elements such as what the study defines as an injury, required

workloads to be a study participant and also the level of running experience. As a

result, the baseline population for these studies are often unidentifiable [5, 65]. These

issues are often alleviated when epidemiological data from sports are used, given the

population is already defined. Numerous sports have used injury surveillance to

ascertain the type and frequencies of injury in addition to any sport specific injuries.

One such sport that has done so is cricket.

2.4.1 CRICKET EPIDEMIOLOGY

Cricket is a seasonal sport played in a number of countries throughout the

world, primarily in the British Commonwealth. Domestic cricket in the Southern

hemisphere spans from September to March of each year while in the Northern

hemisphere it spans from April to August. Given cricket’s global audience, its

maturation has seen the scheduling of international matches increase dramatically

over time [134]. Today elite cricketers are expected to train longer, harder and

achieve success earlier in life and this commitment results in concurrent increases in

physical demands and the pace of the game [22, 134]. With the continually

escalating demands placed on players, cricket has moved from a sport of relatively

low injury incidence [22, 35] to a sport where players are now susceptible to a wide

variety of injuries at vital stages of the season [64]. Nevertheless, the reported injury

incidence in cricket is low when compared to those rates found in other professional

sports [22, 35, 135]. For example the injury prevalence of 9% observed in cricket

[22, 135] is less than that of the football codes (15% AFL, 16% first grade rugby

league, 13% state rugby union), suggesting that cricket is relatively safe [22].

Although strictly a non-contact sport, injuries in cricket are caused by a number of

mechanisms. However, most injuries result from cumulative micro trauma due to

chronic loading [22]. Epidemiological studies focusing on cricket suggest that injury

patterns for male cricketers at an elite level are fairly consistent and predictable, with

fast bowlers being injured far more often than other players [35, 135-137].

Consequently, much research has been conducted on this subgroup focussing

32


particularly on bowling technique [72, 111, 138], bowling workload [106, 139] and

physical characteristics [138, 140]

As of 2005, cricket was the first sport to publish a consensus regarding

international injury definitions [141, 142] with data being collected from some of the

major cricket playing countries such as Australia, England, South Africa and the

West Indies. The current internationally recognised definition of a cricket injury for

surveillance purposes has been outlined by Orchard [35] which states:

“Any injury or other medical condition that either: (1)

Prevents a player from being fully available for selection in

a match or (2) during a major match, causes a player to be

unable to bat, bowl, or keep wicket when required by either

the rules or team’s captain.”

It is hoped that in the near future all nations will publish similar comparable

data [35]. From the current epidemiological literature however, a number of trends

can be identified. Such trends revolve around the anatomical sites, the player’s

primary skill and playing position in addition to their age and time of the season the

injury occurred.

All studies that have focussed on injury surveillance have analysed the injuries

pertaining to differing anatomical sites. The body is divided with the head, trunk,

upper and lower extremities all heading a sub-group. The incidence of lower limb

and trunk injuries dominate the injury data with spans of 15.5% - 49.8% and 3.2% –

38.9% respectively [22, 35]. Upper extremity injuries accounted for between 16.5%

– 33.9% with the fingers being the most vulnerable site [136, 137]. The incidence of

injury to the head, neck and/or face had the greatest range varying from 1% in the

elite population to 44.2% [35] in a younger population [22]. Each study is outlined in

Table 1.


Table 1 Reported incidence of cricketing injuries according to injured body region.

Study Population Time Frame

Injured Area (%)

Head Upper

Extremity

Lower

Extremity Trunk Other

Stretch

(1995)[143]

116 (School boy

cricketers)

Cricket

Seasons 19.3 24.6 22.8 33.3

Orchard et al

(2006)[35]

Elite male Australian

cricketers (886 injuries)

10 years - 3

retrospective,

7 prospective

1 16.5 37.7 23.6 3.5

Stretch 2001

[136]

183 (South African Club

and provincial players) One season 5.6 22.2 33.3 38.9

Finch et al 1998

[12]

3846 injuries, 3408

players (Adults) 16.6 32.6 22.8 4.2 4.1

Finch et al

1998[12]

2345 injuries, 1945

(children) 44.2 33.9 15.5 3.2 3.2

Mansingh et al

(2006)[137]

Elite male West Indian

Cricketers 2003-2004 12 28 28 28 4

Leary & White

(2000)*[144]

English Country Club

Cricket (54 Club

Cricketers)

1985-1995 5.7 29.4 44.9 20

Stretch 2003

[64] 436 elite cricketers 3 seasons 4.1 23.3 49.8 22.8

*Acute injury only

Lower quarter injuries, defined as injuries occurring to either the lumbar spine

or lower extremities, dominated the injury list for all players irrespective of game

format [35, 64, 136]. The body of surveillance data identified workload as a

contributing factor to injury attributable mainly due to repetitive micro trauma where

a number of forces, each lower than the critical limit of the specific tissue, combine

to produce a fatigue effect over time [109]. Whilst there is a consensus within the

literature that overuse injuries are a major component of cricketing epidemiology,

particularly in fast bowlers [35, 64, 136, 137, 139, 144], the way in which these

issues should be addressed is a topic of debate. Consequently, there are a number of

standpoints which offer solutions. These include workload monitoring [106],

reduction in international scheduling [35], training diaries [137], rule changes [35],

modifications to training and recovery methods [137], conditioning [22], risk

assessment [18], tactical changes [35], enhanced management of injury and return to

play protocols [145], appropriate footwear [22], analysis of bowling technique [111]

and validation of pre-participation screening protocols [17, 19, 22, 23]. It is well

accepted that these preventative modalities should be incorporated into a multi-

dimensional, multi-disciplinary approach to injury prevention [22].

34


Injury to fast bowlers remains the priority area for prevention efforts at all

levels of the game [76, 106, 141]. The literature clearly illustrates a relationship

between the overall bowler workload and risk of injury in both junior and adult

cricket [106, 139]. Fast bowlers miss 16% of all potential playing time, whereas the

prevalence for batting and fielding injuries is less than 5% [35]. These findings

illustrate the demands of fast bowling and the associated injury risk. Again, lower

quarter injury dominates this aspect of the cricketing demographic.

Whilst the literature focuses on a global measure of injury prevalence, a more

accurate assessment would be injury rates per exposure time – that is, player

exposure in each category [137]. Whilst overuse and bowling workloads are major

contributors to injury, Mansingh and colleagues [137] have noted that half of the

batsmen’s injuries were sustained during fielding and catching. These results are

comparable to the findings of injuries to elite male cricketers in Australia over a 10-

year period with 45% of injuries occurring in matches whilst bowling, 23% whilst

fielding and 20% whilst batting [35]. These figures further highlight the relative

injury rates for each player category but, as mentioned, they fail to assess relative

risk per exposure time. Whilst this risk has failed to be assessed per player category,

it has been assessed within the varying match formats. Mean match injury incidence

in the West Indies for the season 2003-2004 was 48.7 per 10 000 player hours in Test

Cricket and 40.6 per 10 000 player-hours in one day international cricket [137].

These figures are not dramatically different to those presented by Orchard and

colleagues [35] from the Australian cricket seasons of 1995-1996 and 2004-2005.

These studies illustrate the coupling of increased workload with increased injury risk

per exposure time further augmenting the notion that the monitoring of athletes is

vital for preventing injury.

From the aforementioned analysis of epidemiological data, it can be seen that

methodical injury surveillance is now being employed within most of the 10 test

playing nations. The years of data already accumulated have illustrated that players,

in particular bowlers, are most prone to a lower quarter injury. Realising that lower


quarter injuries are most prevalent, suggest that musculoskeletal screening protocols

should play a role in the prediction and prevention of injuries in the cricketing

population.

2.5 SCREENING PROTOCOLS USED TO ASSESS RISK

Pre-participation (or baseline) screening is a common method for measuring

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 [16-18]. In addition to injury risk

management strategies, screening is concurrently promoted as part of a performance

enhancement strategy [18]. These tests are thought to highlight an athlete’s

predisposition to injury but the majority of the current protocols have yet to fully

illustrate this link to sporting injuries 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]. However, evidence is

beginning to emerge that highlights a relationship between certain screening tests and

injury incidence within the elite and recreational athlete demographics [35].

Screening tests are designed to assess all factors that are thought to be

associated with increased injury risk such as muscular strength, flexibility and

balance. Unfortunately, not all such tests have been validated as the development of

successful sports injury prevention strategies relies on a firm evidence base [23,

146]. Pre-participation screening underpins the evidence base as it is commonly

used to measure 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]. Moreover, for a pre-

participation screen to be effective as an element of an injury prevention strategy, it

is imperative that the tests are reliable, valid and can be easily reproduced across a

range of participants [19, 23, 146]. When measurements are not reliable, it is

difficult to distinguish between participants with or without risk factors because of

the large measurement errors [146]. Moreover, if a test is not valid it fails to measure

that which it is designed to measure.

36


A number of studies have investigated the reliability of common lower

extremity musculoskeletal screening tests. Gabbe and colleagues [19] have

investigated the inter-tester and test-retest reliability of clinical assessment tools

commonly used in the pre-season musculoskeletal screening protocols of elite

Australian football clubs. The tests of interest were Sit and Reach, Active Knee

Extension, Passive Straight Leg Raise, slump, active hip internal rotation range of

movement (ROM), active hip external rotation ROM, lumbar spine extension ROM

and the Modified Thomas Test [19]. They indicated that these simple, clinical

measures of flexibility and ROM had very good to excellent test-retest and inter-rater

reliability. The results support the use of these tests as pre-participation screening

tools for sports participants.

With respect to cricket, Dennis and colleagues [17] investigated the reliability

of a field-based musculoskeletal screening protocol for fast bowlers to measure

potential risk factors for injury. The protocol was comprised of knee extensions,

modified Thomas test (hip extension and abduction), hip internal and external

rotation ROM, combined elevation of the shoulders, ankle dorsiflexion lunge,

bridging hold, prone four point hold and calf heel raises. Their findings run counter

to those previously mentioned as they found inter-observer reliability to be generally

poor, with only four of 10 tests having an ICC greater than 0.80. The intra-observer

reliability of the tests was considerably higher however, with nine of the test having

an ICC greater than 0.80.

Whilst there has been research pertaining to pre-participation screening, only

one study has attempted to utilise pre-participation screening to identify risk factors

for injury in a cricketing demographic [23]. Dennis and colleagues [23] conducted a

prospective cohort study of fast bowlers over a single cricket season and measured a

broad range of musculoskeletal, fitness, anthropometric and technique variables

through pre-participation screening. Two measures were identified as independent

predictors of injury. Reduced internal hip rotation on the back foot impact leg of the

fast bowling action was associated with a significant decrease in injury risk, whilst


reduced ankle dorsiflexion on the front foot impact leg was associated with a

significantly increased risk of injury. Biomechanical research was proposed to

investigate how these two intrinsic risk factors increase injury risk so that the

appropriate interventions could be developed [17].

Biomechanical analysis of fast bowler’s actions is also used heavily to identify

predisposition to injury [109]. Technique analysis of the fast bowling action in

particular has allowed the identification of players with a predisposition to injury

[111] and addresses one of the elements of injury aetiology. The implementation of

functional screening measures focuses on other elements of this aetiology but is not

as well understood as the clearer links to injury observed in technique screening.

The ability to clearly identify injury risk or performance enhancing factors is

reliant on the accuracy with which measurements are made. 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 of reliability

surrounding subjective screening protocols may be alleviated by biomechanically

investigating the accuracy of such protocols. This level of formal evaluation 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.

A greater understanding of functional screening tests such as the single leg

squat is needed if they are to be fully utilised as useful screening tools for those

predisposed to injury. Consequently, 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 which would conceivably yield

more accurate, reliable and appropriate musculoskeletal interventions [18]. This

38


knowledge in turn would assist the management of any intrinsic injury risk factors

which would presumably influence the incidence of lower limb musculoskeletal

injury in cricket, as well as other physical activities.

2.6 FUNCTIONAL TESTING TO ASSESS INTRINSIC RISK:

Functional testing has been defined as the performance of an activity or series

of activities designed to assess (indirectly) muscular strength and power and to

quantify function [147-149]. The key purposes of functional testing are to: (1) reveal

asymmetries that may predispose an individual to injury, (2) measure progress in

rehabilitation objectively, and (3), assess the ability of a body segment to tolerate

external forces [147, 148]. Scientists and clinicians alike are widening their focus to

include assessments of joint mechanics proximal and distal to the sites where injuries

tend to occur [26] due largely to the closed chain nature of athletic activities. When

the distal end of a segment is relatively fixed such as in a planted foot during a squat

or cutting manoeuvre, motion at one segment will influence that of all other

segments in the chain [26, 125]. This notion is exemplified by the biarticular

muscles of the lower extremity during simultaneous movement of the hip, knee, and

ankle rising from a squatting position [148, 150]. These phenomena do not occur in

open chain exercise and as such the concurrent muscular shift is a hallmark of closed

kinetic chain exercise [148, 150].

2.6.1 TRENDELENBURG ASSESSMENT

The Trendelenburg test is a simple clinical test developed by Frederich

Trendelenburg in 1895 [151] to determine the integrity of hip abductor musculature,

with specific reference to congenital dislocation of the hip [151, 152]. Originally,

Trendelenburg described his test as standing on the treated (affected) leg and raising

the buttock of the other side up to or above the horizontal line. He stated that the test

result was considered ‘positive’ for hip abductor instability if the patient was unable

to stand on the treated (affected) leg and raise the buttock of the other side up to or

above the horizontal line [151, 152]. More recently it has been adapted to evaluate

hip abduction strength [149], assist in the identification of abnormal gait patterns and


as a diagnostic test for gluteus medius tears [153]. The test is considered ‘positive’,

or a sign of hip abduction weakness, when the pelvis on the non-weight bearing side

lowers in single leg stance due to the inability of the hip abductors to support the

weight of the body [154]. A judgment of hip abduction weakness is significant as

during the single-limb support phase of gait, the gluteus medius muscle on the stance

hip provides a force that contributes to the stability of the pelvis in the frontal plane

[48]. This muscular force, acting through a moment arm, creates an internal moment

about the stance hip that neutralizes and counteracts an opposing external moment

created by the person's body weight [154]. It has been shown in Section 2.2 that

insufficient muscular control of the frontal- or transverse-plane hip motion during

single-limb weight bearing can be associated with excessive femoral adduction an

internal rotation leading to knee, valgus, tibial internal rotation and excessive foot

pronation, a series of postural malalignments described as medial collapse [90, 91].

2.6.2 THE SQUAT

The dynamic squat exercise is an integral part of strength and conditioning

programs for many sports that require high levels of strength and power [155, 156].

The squat is a closed kinetic chain movement that begins with the individual in the

upright position with the knees and hips fully extended. The individual then squats

down in a continuous motion until a desired squat depth is achieved and then in a

continuous motion returns to the upright position [26, 155]. Extensor muscles of the

trunk, hip and knee, those primarily strengthened during the squat exercise, are

important muscles used in a number of common athletic manoeuvres such as running

and jumping [27, 155]. These muscles also influence the orientation of the lower

extremity during weight bearing activities [25]. The squat is, therefore, considered a

useful tool in the functional rehabilitation [156, 157], preservation of physical

function [158] and screening of athletes [25, 26].

The squat discriminates between those with poor lumbopelvic stability who are

unable to control multiplane motion at the spine, pelvis and hip [25, 26, 37]. Mitchel

and colleagues [37] have described three elements of lumbopelvic stability. These

are intrapelvic stability, peripelvic stability and functional stability [37]. Intrapelvic

40


stability is dependent on the transversus abdominus contracting with intact posterior

sacroiliac joint ligaments and essentially provides the platform for a firm and stable

pelvic foundation [37] . Peripelvic stability is simply an athletic extension of

intrapelvic stability which allows force transfer through the pelvis via muscle

strength and activation patterns. Assessments of peripelvic stability are concerned

with the relationship between the pelvis and the rest of the body during functional

movements [37]. Peripelvic stability and the resultant force transfer is reliant on the

ability of the deep multifidus to contract and control the lumbar segments and the

superficial multifidus to orientate the spine on the pelvis [159]. Finally, functional

stability is simply an ‘on field’ extension of peripelvic stability. Muscle strength,

activation patterns and force transfer are being assessed in typical athletic conditions

to maintain all the necessary components of intrapelvic and peripelvic stability to

hold the pelvis stable on the femur and lumbar spine [37, 159]. Technique, coaching,

conditioning, coordination and fatigue all play a role in the ability of an athlete to

maintain a stable pelvis during the functional phase of lumbopelvic stability.

Decreased lumbopelvic stability has been suggested to contribute to the aetiology of

lower extremity injuries due to the inability of the hip and lower extremity to avoid

abnormal loading patterns [26].

2.6.3 THE SINGLE LEG SQUAT

The single leg squat (SLS) incorporates elements of both the two legged squat

and the Trendelenburg test. However, the SLS is performed dynamically and as such

increases the demands particularly on the gluteus medius [36, 160] but also on the

musculature of the torso, lumbar region, pelvis, knees and ankles [155]. As a patient

or athlete performs an SLS test, the investigator visually observes the task and

assesses the patient’s ability to control the motion using on a number of subjective

observations. This assessment is proposed to indirectly assess the patient’s strength

and muscle function; however there has been no standardisation of the assessment

criteria. Observational practices are common clinically, but have rarely been

scrutinized scientifically [149].


The SLS is commonly used by clinicians as a functional measure of dynamic

lumbopelvic stability [25-27, 36, 37] because it has a greater ability to highlight

those with poor lumbopelvic stability [37] than the standard two legged squat. The

SLS in some ways replicates an athletic position commonly assumed in sport such as

cutting (powerful change in direction while running made from one leg), jumping

and balancing which all require the control of the trunk and pelvis on the weight

bearing femur in all three planes of movement [25, 27, 36]. The ability of an athlete

to control these multi-plane movements at the spine, pelvis and hip in single leg

stance may play a pivotal role in avoiding abnormal patterns of loading [91]. These

patterns include excessive femoral internal rotation, femoral adduction, knee valgus,

tibial internal rotation and foot pronation of the weight-bearing limb with resultant

excursion of the contralateral non weight bearing ilium and excessive lateral flexion

of the trunk [25, 27, 36, 37, 40].

Whilst it has been acknowledged that there is a relationship between muscular

strength and lower quarter injury risk, it is not fully understood [25]. However, there

is evidence to suggest that those with decreased musculoskeletal strength are at an

increased injury risk [5]. For example, knee flexion weakness is considered to be a

risk factor for hamstring strains in Australian Rules footballers [60, 66]. With respect

to the hip, Leetun [26] demonstrated prospectively that athletes who experienced an

injury over the course of an athletics season displayed significantly decreased levels

of hip abduction and external rotation strength. Leetun and colleagues [26] also

proposed that these strength deficits resulted in decreased lumbopelvic stability

contributing to the aetiology of the athletes lower extremity injuries. The literature

suggests that any lower extremity injury prevention should include measurements of

hip and knee strength [25], which has particular relevance for the SLS role as an

injury predictor.

Using the SLS, Willson and colleagues [25] conducted a study to: 1) compare

the orientation of the lower extremity between male and female athletes as

characterised by frontal plane projection angles (FPPA); 2) compare the strength of

muscle groups in the trunk, hips and knees between these groups; and 3), to evaluate

the association between aforementioned strength measures and the orientation of the

42


knee joint during this activity [25]. Results indicated that women consistently

generated less torque in all muscle groups, with the exception of trunk extension.

Women also tended to move in the opposite direction to men during the SLS with

females moving towards a more extreme frontal plane projection angle (FPPA),

whilst males remain more neutral. The more neutral knee and stronger hip external

rotators in men may result in a greater capacity to resist internal rotation moments

and consequently exhibit smaller hip internal rotation angles during the SLS [25].

Similar results were observed in a study by Zeller and colleagues [36]. Increased

knee valgus and increased quadriceps muscle activity were observed in females when

compared to males [36]. The authors concluded that the increased quadriceps activity

was not as effective at preventing frontal plane movement [36]. Instead, the authors

suggest that the females in this study demonstrated increased knee valgus due to

decreased hip muscle control [36]. The single leg squat may be effective for

screening athletes for knee valgus during weight bearing due to decreased hip

stability during athletic tasks. However, the contribution of muscles that may

influence knee valgus angles during weight bearing, including muscles of the trunk,

hip and knee has yet to be determined [25].

Yamazaki and colleagues [161] recently completed a study comparing the

differences in 3D kinematics of single leg squatting between ACL injured patients

and healthy controls. Sixty three (32 male, 31 female) ACL injured patients

performed half squats the day before ACL reconstruction and were compared to 26

healthy control subjects with no knee injuries. When comparing the injured and

uninjured legs within subjects, the injured leg of both the male and female subjects

illustrated more knee varus than the uninjured leg [161]. Gender differences

illustrated that more external hip rotation (M = 4.5º ± 8.6º F = 9.1º ± 8.0º p = 0.0019)

and knee varus (M = 19.8º ± 11.3º F = 8.2º ± 12.5º p < 0.0001) were present in the

female subjects compared to males for both the injured and uninjured legs. The male

subjects demonstrated less external knee and hip rotation, less knee flexion and more

knee varus than that of the uninjured leg of the male subjects [161]. It was concluded

that single leg squatting was a simple, safe and reproducible clinical test in

comparison to a single leg landing test. Moreover, the examination of a subject’s

kinematics during the SLS would presumably highlight those with pathomechanic


patterns. As such, training and correctional interventions could be employed to

reduce the injury and reinjury rate of ACL’s, particularly in females [161].

Limited information exists on the relationship between hip abduction

movement and gluteus medius strength [149]. DiMattia and colleagues [149] found a

weak positive correlation between hip-abduction strength and hip-abduction angle

during both the Trendelenburg and SLS tests. They concluded that the usefulness of

these tests for assessing hip abduction strength in a healthy physically active

population was limited. Zeller and colleagues [36] used three dimensional (3D)

motion analysis system to investigate the kinematic differences between males and

females during the SLS. Women had approximately 4° more hip adduction than men

when performing an SLS and the authors postulated that increased knee values in

women during SLS might occur because of decreased neuromuscular control in the

hip muscles [36]. Evidence suggests that increased knee valgus might also be

associated reduced hip abduction and external rotation strength [90]

Hip muscle activation during a number of functional tasks has previously been

investigated with the use of EMG. The lunge, SLS and step up and over exercises

were all used to assess the activation levels for muscles acting on the hip joint[160].

Boudreayu and colleagues [160] documented that mean gluteus medius activation

was highest during the SLS. Moreover, the SLS was documented to have the highest

overall hip muscle activation and therefore should be the final stage of functional

rehabilitation [160]. It is important to realise this when assessing lumbopelvic

stability using the SLS, as the gluteus medius muscle functions to stabilise the hip

joint during weight bearing [49]. Without adequate gluteus medius strength and/or

activation during single leg support, lumbopelvic stability is lost along with the

ability to control multi-plane movements at the spine, pelvis and hip in single leg

stance [49]. This inability results in the aforementioned abnormal patterns of loading

and movement and is thus thought to increase injury risk [37]. This observation

further consolidates the role of the SLS as both a functional screening tool and

potential injury predictor.

44


The SLDS is considered an effective rehabilitation exercise, particularly in

targeting patellar tendinopathy [38-42, 162]. This condition, a chronic overuse injury

characterised by pain during tendon loading, is characterised by anterior knee pain

[40, 120]. The efficacy of the SLDS as a rehabilitation intervention is due to its

greater ability to isolate and load the knee extensor muscles and associated tendinous

structures in an eccentric manner [42, 162] when compared to the SLFS [38]. When

a flat squat is performed, several mechanisms may unload the knee extensors and

potentially reduce the eccentric load through the patellar tendon [40, 162].

Conversely, it has been hypothesised that the increased loading of the SLDS may be

attributable to a concurrent coupling of decreased ankle dorsiflexion and increased

knee flexion not possible in the SLFS [43]. Both Young and colleagues [39] and

Purdam and colleagues [38] explained that this may be a result of reducing the

limitations caused by the calf muscles that constrain the extent of dorsiflexion in the

SLFS [42].

Increased patellar tendon loading in the SLDS has been supported by

quadriceps electromyography (EMG) research by both Richards and colleagues [41]

and Kongsgaard and colleagues [44]. These studies aimed to compare lower limb

EMG activity, patellar tendon strain and joint angle kinematics during standard and

decline eccentric squats [41, 44]. Richards and colleagues [41] used an adjustable

decline board able to be set to angles of 0°, 8° , 16° and 24° and measured the

aforementioned variables whilst Kongsgaard and colleagues [44] simply compared

platform angles of 0° and 25° . Both studies concluded that with greater decline

angles, increased load was placed on the patellar tendon during unilateral eccentric

squats. This was evidenced by greater quadriceps EMG activity and knee moments.

Additionally, both studies acknowledged a decrease in ankle plantar-flexor moments

with the greater decline angle [41, 44]. However, there is still debate regarding the

increase in quadriceps activation being explained by a decrease in the triceps surea

contribution. Kongsgaard and colleagues [44] reported that hamstring and calf

muscle mean EMG activity did not differ between standard and decline squats. This

standpoint was not shared by Richards and colleagues [41] and Frohm and

colleagues [43] who concluded that EMG activity for the gastrocnemius increased as

the decline was introduced.


A study by Young and colleagues [39] investigating the short term (12 weeks)

and long term (12 months) efficacy of two eccentric exercise programs (step and

decline squats) for the treatment of patellar tendinopathy in the adult volleyball

population. Participants were separated into either a SLDS group or a step down

group. Those in the SLDS group completed the downward component (eccentric

phase) of the squat on the symptomatic leg, and the upward component (concentric

phase) on the asymptomatic leg. Participants in the step group used a 10 cm step to

perform their squats. They completed both components of the squat on the

symptomatic leg. Both groups were instructed to exercise in the presence of tendon

pain and to progressively increase the load as pain decreased. Both the decline and

step protocols were effective in the treatment of tendon pain and corresponding

increases sporting function in athletes with patellar tendinopathy. Young and

colleagues [39] observed no difference in pain ratings between the two eccentric

protocols at the 12 week point. At 12 months, however, the decline squat group

displayed considerable beneficial differences in pain levels and sporting function.

This study shows that the decline squat protocol presents a much greater chance of

clinical improvement over a 12 month season than the step protocol [39], presumably

due to an increase in patellar tendon load and knee extensor mechanism involvement.

The SLDS has also been recommended by Purdam and colleagues [163] for the

physical assessment of adolescent jumper’s knee. Jumper’s knee is defined as

symptoms at the insertion point of the patellar or quadriceps tendon into the proximal

or distal pole of the patella and tibia [79]. The SLDS and single leg decline hop were

the tests that best detected a change in pain due to a bout of intense workload

however it was concluded that the SLDS was the best clinical test as it was easier to

standardise performance [163]. This further reinforces that the SLDS loads the

patellar tendon more that the flat squat due to greater knee flexion kinematics.

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 SLFS. The movement patterns of athletes can be analysed equally well

46


with the two squat techniques. However, it was hypothesised that the restraints of the

ankle and calf musculature in the SLFS would prevent athletes from assuming deeper

and more challenging squat positions and therefore prevents physiotherapists from

distinguishing between the hip, pelvis and trunk movement patterns of clinically

stronger and weaker players. Thus, it was thought that the SLDS would be more

sensitive in identifying those individuals with lumbopelvic and single leg stance

control issues. Experienced physiotherapists judge performance of the single leg

squat using a rating system whereby each athlete is scored on a competent (1

mark)/non-competent (0 marks) scale as per the following guidelines:

Rear Score: Assessment/observation of whether the pelvis is level, drops

down, hitches up or rotates (1mark)

Front Score: Assessment/observation of weight bearing limb, using the

knee as a reference for degree of internal rotation and adduction of the

femur (1 mark)

Interestingly, however, unpublished results from three years of Cricket

Australia SLDS data have indicated that those who have performed better in this test

have a higher incidence of injury compared to those who did not perform as well

clinically. This observation may indicate that the SLDS does indeed discriminate

between injured and the non-injured, but calls into question the rationale for the

SLDS test. Furthermore, further investigation is needed to assess the legitimacy of

the subjective assessment criteria used to assess players such as using the frontal

plane knee movement as a guide to infer what is happening at the hip and lumbar

spine. Additionally, a greater understanding is needed of how to accurately identify

and define pathomechanic patterns that appear both in the squatting assessment and

more task representative activities such as bowling technique.

2.6.4 SINGLE LEG FLAT SQUAT VS SINGLE LEG DECLINE SQUAT.

Very few studies have investigated the biomechanical differences between the

decline and flat variations of the SLS directly. Purdam and colleagues [38]


investigated the effect of eccentric quadriceps training on 17 patients (22 tendons)

with painful chronic patellar tendinopathy. Two different eccentric exercises regimes

were used by the participants who had chronic (greater than 6 months) patella tendon

pain with activity. Patients either performed eccentric training for 12 weeks standing

on a 25º decline board or with the ankle in the standard flat foot position. The results

illustrated that the standard single leg flat squat appeared to be a less effective form

of rehabilitation as determined by pain ratings and return to sport. This was probably

due to the declines ability to better isolate the knee extensor mechanism in the squat

exercise [38].

A study by Frohm and colleagues [43] focussed on comparing the magnitude

of the mechanical load on the patellar tendon in four differing experimental

variations of the eccentric squat on 14 habitually healthy active male fire-fighters. A

sub maximal free weight condition and a maximal effort in a device for eccentric

overloading (Bromsman®) were conducted on both a horizontal and decline surface.

The variations of interest to this review are the free weight conditions where a 10kg

free-weight (barbell disk) was held across the chest while squatting both bilaterally

and unilaterally on both a flat and horizontal surface [43]. During the unilateral

squats the participants descended on a single leg, with the contralateral foot touching

the floor or decline board, but bearing minimal weight [43]. Once participants had

reached a position where the weight bearing femur was parallel with the floor they

then ascended using both legs. Kinematics, reaction forces, EMG and knee joint

kinetics were all measured for both conditions but of most relevance to this review

are the kinematic results. Results comparing the flat and decline squats indicated that

movement started at a more flexed knee and a more plantar flexed ankle joint and

stopped at a less flexed hip, more flexed knee and more plantar flexed ankle joint as

compared to the free-weight condition [43]. Put simply, these differences resulted in

smaller range of motion at the hip, and larger range of motions at the knee and ankle

joints in the decline condition. This resulted in a more flexed stop angle (118° v

103°) of the knee joint in the decline squat which also produced 25-30% higher peak

patellar tendon forces [43]. These results add to the consensus that there is greater

load on the knee extensor mechanisms during the decline squat [38, 39, 42, 44] as

discussed previously.

48


The Frohm and colleagues [43] study focussed solely on the sagittal angles of

the hip, knee and ankle but failed to mention comparisons of these joints in any other

planes. This omission is understandable given that the paper focussed on patellar

loading during the aforementioned conditions however this additional information

could have given a deeper insight into the functional comparisons between the two

squatting conditions. For example, reporting the valgus and/or varus movement of

the knee during the different squatting conditions could have illustrated the ability of

the participants to control their pelvis during the descent. Frontal plane movement of

the knee has been shown in cadaveric studies to increase lateral retropatallar contact

pressure [32] as well as altering the line of pull of the quadriceps muscle

consequently displacing the patellar laterally resulting in a reduction of knee

extension force [92]. Reporting pelvic obliquity during the two conditions could have

provided similar insight into the activation of the stabilising pelvic musculature [37].

Non-reporting of the pelvic obliquity data may have been due to the squat technique

in which the participant had the non-weight bearing leg touching the ground in turn

providing balance and therefore not a true representation of a single leg squat.

Additionally, no trunk measurements were reported which could have potentially

shown if a lack of ankle flexion from the constraints previously outlined from ankle

dorsiflexion was compensated for with strategies such as increased trunk flexion,

lateral flexion or axial rotation of the trunk relative to the pelvis.

There has only been one study of the SLDS and injury incidence in cricket, as

yet unpublished by Farhart and colleagues [164] in collaboration with Cricket

Australia. This study prospectively assessed the SLDS as a predictor of lumbar spine

and lower limb injury in fast bowlers in cricket. Twenty four adult and 40 adolescent

fast bowlers performed two SLDS to a self-selected maximal hip flexion angle on a

20 decline board while being filmed by an 8 camera motion analysis system. These

were categorised as a back leg or a front leg SLDS depending on a bowler’s

dominant hand. Nineteen bowlers from the pooled cohort sustained an injury and

bowlers with low hip adduction angles at the commencement of the back leg SLDS

had reduced injury risk, whilst bowlers with greater hip external rotation during the

front leg SLDS were at increased injury risk. When performance of adults and


adolescents was analysed separately, greater hip external rotation during the front leg

SLDS was associated with injury in adult fast bowlers only. It was hypothesised that

the relationships of SLDS hip kinematics to injury may be a consequence of

prolonged exposure to the repetitive high impact forces of fast bowling and

subsequent motor control interactions that may occur in the lumbopelvic-hip

complex. However, the use of the decline board was criticised by reviewers since it

may have changed the normal kinematics of the squat, making it difficult to compare

to functional sport movement conducted on flat ground. Further comparison of the

SLFS and the SLDS kinematics is required to assess what effect a decline board has

on changing squat kinematics at the hip.

As mentioned, the SLS protocols are used clinically as both functional

measures of lumbopelvic stability [25, 27, 36] and as a rehabilitation tool [38-42] as

it replicates an athletic position commonly assumed in sport which requires multi-

plane control of the trunk and pelvis on the weight bearing femur [25, 27, 36].

However, a paucity of information directly comparing the 3D biomechanical

differences between the SLDS and SLFS has resulted in glaring omissions from the

literature. It is difficult to determine whether clinically significant aspects of the SLS

movement pattern such as knee valgus/varus, pelvic obliquity, hip rotation and

adduction or lateral flexion of the torso are altered due to the type of SLS protocol

being employed. Will the movement patterns that are related to intrinsic risk factors

mentioned be consistent in both squatting protocols or do the ankle constraints in the

SLFS alter the movements of the weight bearing knee, hip and pelvis? This question

has yet to be conclusively answered within the literature. Whilst the SLS has yet to

be described as a predictor of injury within the cricketing demographic, it remains

important to investigate the 3D kinematics of two SLS protocols. Unearthing any

kinematic differences between the SLFS and SLDS may provide insight into what is

assumed in functional screening protocols, intrinsic risk factors and the collated

epidemiological data [35, 64, 136, 137, 143, 144]. Investigation of the two squat

protocols may shape future screening protocols by determining which test is best for

assessing lumbopelvic stability.


Table 2 Summary of the single leg squat literature.

Authors Year Design Setting Population Study Focus Outcome

Crossley et al [165]

2011 Cohort Study Clinical 34 asymptomatic subjects

To evaluate the clinical relevance and effectiveness of using the SLS as an assessment tool of hip function in asymptomatic patients.

Subjects who were assessed as performing well during the SLS demonstrated significantly higher hip abduction torques, trunk side flexion forces and onset of anterior gluteal muscles. Clinical assessment of performance on the SLS is a reliable tool that may be used to identify people with hip muscle dysfunction.

Munkh et al [166]

2011 Descriptive Biomechanics Laboratory

12 healthy women

To determine the relationship between hip muscle strength and kinematics of the knee joint during SLS and dropping.

Muscle strength of hip external rotators was associated with knee medial displacement during both single leg squatting and dropping. The hip musculature, particularly the hip external rotators are closely related to the medial displacement of the knee

Yamazaki et al [161]

2010 Comparative Cross-Sectional

Laboratory 63 (32M 31F) ACL injured subjects

To evaluate the relative angles between the body, thigh, and lower leg using an electromagnetic device during SLS.

The uninjured leg of ACL-injured female subjects demonstrated significantly more external hip rotation and knee flexion and less hip flexion than that of the dominant leg of the female control. Comparing injured and uninjured legs, the injured leg of male subjects demonstrated significantly less external knee and hip rotation, less knee flexion, and more knee varus than that of the uninjured leg of male subjects.

Ageberg et al [167]

2010 Comparative Biomechanics Laboratory

25 (8M 17F) Healthy Subjects

To validate the single leg squat as an assessment of medio-lateral movement of the knee by comparing 2D and 3D metrics

Medio-lateral motion of the knee can reliably be assessed during a SLS. The test is valid in 2-D, while the actual movement, in 3-D, is mainly exhibited as increased internal hip rotation.

Boudrea et al [160]

2009 Intervention Laboratory 44 (22M 22F) healthy individuals

To document the progression of hip-muscle activation levels during 3 lower extremity functional exercises (step up, lunge and SLS).

The rectus femoris, gluteus maximus, and gluteus medius were activated least to most during the step up and over, lunge and single leg squat. Understanding this activation is vital for clinical progression.

Souza & Powers [54]

2009 Cross-sectional comparative

Laboratory 41 (20 control, 21 PFPS)

To determine whether females with PFPS demonstrate differences in hip kinematics, hip muscles strength and activation compared to controls.

Females with PFPS demonstrated greater peak hip internal rotation and diminished hip torque production. Gluteus maximus recruitment was greater in PFPS group during running and step down (SLS) task.

Hollman et al [90]

2009 Exploratory Laboratory 20 healthy women

To describe the relationships among frontal-plane hip and knee angles, hip-muscle strength, and EMG recruitment in women during a single leg step-down

Hip adduction angles/strength and gluteus maximus EMG all correlated with increased knee frontal plane projection angles. Gluteus medius strength might be associated with increased knee valgus. Gluteus maximus recruitment may have greater association with reduced knee valgus in women than does ER strength during step-down tasks.

Madhaven et al [168]

2009 Prospective Training Study

University Research Setting

10 health female participants

To examine the muscle activation patterns (using EMG) employed by female subjects in learning a novel SLS task under visual and non-visual conditions pre and post training interventions.

Quadriceps to hamstring coactivation ratio increased with improved accuracy and learning of movement. Muscle synergy around the knee changes as the accuracy of the task improves during a resisted SLS. Visual feedback should be considered when using the SLS to rehabilitate female patients with neuromuscular deficits.

Richards et al [41]

2008 Repeated Measures

Laboratory 10 physically active people

To determine the involvement of the gastrocnemius and rectus femoris muscles and the external ankle and knee joint movements at 60 knee flexion during a SLS at different angles.

As the decline angle increased, the knee extensor moment and EMG activity increased. However, as the decline angle increased the ankle plantor flexor moments decreased. SLDS at angles greater may not reduce passive calf tension and may provide no mechanical advantage for the knee.


Zwerver et al [42]

2007 Repeated Measures comparison

Laboratory

5 (2M 3 F) healthy subjects (mean 22 years)

To investigate knee moment and patellofemoral contact force for the SLDS performed at 0°, 5°, 10°, 15°, 20°and 25° (with/without a backpack of 10 kg), and 30°.

Knee moment increased by 40% at decline angles of 15° and higher, whereas hip and ankle moment decreased. Patellofemoral forces increase more than patellar tendon forces

Frohm et al [43]

2007

Repeated Measures, Descriptive Comparison

Laboratory 14 male firefighters (healthy)

The aim was to compare kinematics of lower limb and mechanical load the patellar tendon during four types of eccentric squat (Free weight (flat & decline) and with maximal effort in a device for eccentric overloading (flat & decline)).

Sagittal plane kinematics (free weight) suggested a greater flexed knee, and ankle but less flexed hip for the decline squat compared to the flat squat. No significant differences in kinematics for the eccentric overload machine. Eccentric work, mean and peak patellar tendon force, and angle at peak force were greater (25–30%) for squats on decline board compared to horizontal surface with free weight,

Youdas et al [169]

2007 Repeated Measures Comparative

Laboratory 30 (15M 15F)

To determine if women are quadriceps dominant and men are hamstring dominant during the performance of a SLS on both a stable and labile ground surface against body weight resistance.

Women are quadriceps dominant and men are hamstring dominant during the SLS on either a stable or labile surface. Men appear to be more efficient at hamstring activation during the SLS. The SLS may not be the ideal exercise for women without neuromuscular training.

Levinger et al [170]

2007 Cross Sectional Comparative

Laboratory 25 Females (13 healthy 12 with PFPS)

To investigate the medial collapse of the knee during a SLS in females with PFPS.

Females with PFPS had significantly larger femoral frontal angles (the angle projected between the long axis of the thigh and the foot) but no differences for femoral deviation (knee movement in the frontal plane). The SLS may be a useful tool for PFPS.

Willson et al [25]

2006 Descriptive Comparison

Clinical Laboratory

46 (24M 22F) Compare frontal plane projection angles of M & F. Compare hip and trunk strength in these individuals. Evaluate association between strength & kinematics.

The females were found to have greater frontal plane projection angles and generally decreased trunk, hip, and knee isometric torque. Hip external rotation strength was most closely associated with the frontal plane projection angle

Kongsgaard et al [44]


Laboratory 13 (7M 6F) To compare EMG activity, patellar tendon strain and joint angle kinematics during standard and SLDS.

The SLDS increases the load and the strain of the patellar tendon than standard SLFS. Greater strain likely explains superior clinical efficacy

Claibourne et al [171]

2006 Descriptive Comparative

Laboratory 30 Health adults (15M 15F)

Investigate the relationship between hip and knee strength and knee valgus during a single leg squat.

When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension.

Negrete et al [125]

2006 Correlational Laboratory 60 (29M 31F) college aged students

To determine the correlations between isokinetic lower extremity strength and functional performance. Secondly, the correlations among different modes of isokinetic testing.

The single leg squat correlated with all a single leg hop for distance, single leg vertical jump, leg press, knee extension and a lower extremity function task (running agility task)

DiMattia et al [149]

2005

Single measure concurrent validity

Laboratory 50 uninjured participants

To evaluate the validity of the SLS and Trendelenburg assessments and their relationship to hip strength.

The usefulness of the Trendelenburg and SLS test in screening hip-abductor strength in a healthy physically active population is limited.

Pantano et al [172]

2005 Comparative Laboratory 20 (11M 9F) College students

Investigating the differences in peak valgus angles between individuals with high and low Q-angles during a SLS.

Dynamic knee valgus during SLS was not greater in higher in Q-angle group. Pelvic width to femoral length ratios, rather than Q-angles, may be better structural predictors of knee valgus during dynamic movement.

52


Young et al [39]

2005

Prospective Longitudinal Comparison study

Clinical

17 elite volleyballers with patellar tendinopathy

To investigate the immediate (12 weeks) and long term (12 months) efficacy of two eccentric exercise programmes (SLDS and 'step downs') for the treatment of patellar tendinopathy.

Both exercise protocols improved pain and sporting function over the long term (12 months). The SLDS protocol offers greater clinical gains during a rehabilitation programme for patellar tendinopathy in athletes who continue to train and play with pain when compared to the single leg step down protocol.

McCurdy & Langford [173]


Laboratory 42 (17M 25F) apparently healthy

To compare unilateral squat strength of the dominant and non-dominant leg in young adult men and women using a modified unilateral squat 1RM protocol.

No significant differences were observed between dominant and non-dominant leg for apparently healthy young men and women.

Shields et al [174]

2005` Descriptive Laboratory 15 (8M 7F) Healthy subjects

To investigate the neuromuscular control of the knee using surface EMG during a SLS task with 3 increasing levels of resistance.

The normal SLS fails to typically control for bidirectional resistance and knee joint excursion. Performing controlled resistance SLS may help to simultaneously strengthen the quadriceps and facilitate coactivation of the hamstrings, thus reducing anterior tibial sheer force. Coactivation of the hamstring muscles is required for optimal neuromuscular control of the knee during the SLS.

Zeller et al [36]


Laboratory 18 Collegiate athletes (9M, 9F)

Investigating the differences in kinematics and EMG activity between men and women during the SLS.

Women tend to position their entire lower extremity and activate muscles in a manner that could increase strain on the anterior cruciate ligament

Purdam et al [163]

2003

Cross-Sectional Intervention Study

Clinical

56 Elite adolescent basketball players

To investigate the reliability/validity of 5 squat-based loading tests that are clinically appropriate for jumper’s knee (step up, double leg squat, decline double leg squat, SLDS, and SL decline hop).

The tests that best detected a change in pain due to intensive workload were the SLDS and SL decline hop. The SLDS is recommended in the physical assessment of adolescent jumper’s knee.

Beutler et al [157]

2002 Descriptive Laboratory 18 (11M 7F) apparently healthy

Purpose was to characterize single leg, closed chain exercises in young, healthy adults.

The SLS returned high and sustained levels of quadriceps activation, which would be effective in strength building and muscle rehabilitation. Moreover, they may also be protective of anterior cruciate ligament grafts.

Munich et al [175]

1997 Test-retest Reliability

Research 35 (18M 17F) Tertiary Students

To assess the test-retest reliability of a single leg squatting protocol on an inclined sliding squat rack. The number of squats performed in 20 seconds and time to complete 50 squats was the measure. Protocol re-tested one week post and analysed for reliability.

The single leg squat on an inclined sliding apparatus returns acceptable test-retest reliability and could be employed for the purpose of evaluating functional ability during the early stages of rehabilitation of lower extremity condition.

Farhart et al [164]

- Prospective Injury study

Laboratory

24 Adult and 40 Adolescent Male fast bowlers

To screen senior and junior fast bowlers using 3D analysis of a single leg decline squat. To analyse what characteristics of the SLDS differed between injured and non-injured fast bowlers.

19 bowlers from the pooled cohort sustained an injury. Bowlers with low hip adduction angles at the commencement of the back leg SLDS had reduced injury risk, whilst bowlers with greater hip external rotation during the front leg SLDS were at increased injury risk. SLDS hip kinematics to injury may be a consequence of prolonged exposure to the repetitive high impact forces of fast bowling and subsequent motor control interactions that may occur in the lumbopelvic-hip complex


2.7 SUMMARY AND IMPLICATIONS

Whilst the benefits of exercise and physical activity are well known, there is a

significant risk of injury when undertaking physical activity. The interplay between known

intrinsic risks factors such as strength and range of motion deficiencies, the ‘medial

collapse’ and abnormal biomechanics in particular have been identified as contributing risk

factors for injuries of the lower extremity specifically in the general physically active

population. With respect to cricket, epidemiological data from the past 10 years from a

number of different countries illustrates that the incidence of lower quarter injuries is high

and of concern to cricket players and coaches, particularly to fast bowlers [35, 64, 135-137,

143, 144]. There is also data from prospective intrinsic risk factor studies [5, 17, 23] to

suggest that certain tests and physical characteristics, such as decreased ankle dorsiflexion

range of motion, correlate significantly with injury. Moreover, functional screening tests

such as the SLFS and SLDS have also shown a correlation to injury presumably due to a

symphony of intrinsic risk factors within injury prone athletes [36, 38, 39, 163, 176].

The validity of the SLS tests, in particular the disparity between SLFS and the SLDS

has yet to be established. For instance, are there biomechanical discrepancies between the

two manoeuvres in the weight bearing knee, hip, pelvis or torso that is only attributable to

the decline or lack thereof? Is the presumption that the SLDS is a more demanding test of

lumbopelvic stability sound? Does it therefore allow better capacity to identify instability?

As a result of these questions, it is therefore necessary to employ biomechanical kinematic

analysis, hip strength profiling and subjective movement assessment to explore the

interrelationships between the differing SLS protocols associated profiling tools.

Investigation may provide a greater understanding of the discrepancies of movement

during differing SLS screening protocols. In addition, the results may also provide insight

into the physical characteristics and potential pathomechanics of the injured demographic

in a clinical environment.

Chapter 5: Research Design 55

Chapter 3: Research Design

In their single visit to the laboratory, the participants performed single leg flat

squats and single leg decline squats on both legs in a randomised order. A number of

hip strength tests were also undertaken in addition to an ankle flexibility measure. An

experienced physiotherapist qualitatively assessed each of the participants.

Qualitative ratings were subsequently compared with key hip and knee kinematics in

addition to hip strength variables to assess the qualitative and quantitative data. Each

of these stages is discussed in detail in the research design.

3.1 PARTICIPANTS

This study was undertaken in collaboration with Cricket Australia’s Centre of

Excellence (COE) and the Queensland University of Technology (QUT). The

recruited participants (n = 19) were cricketers who had played at least one game of

first grade club cricket or at a higher level in the previous season and were at least 18

years of age. Ethical clearance was granted by QUT prior to undergoing data

collection and written informed consent from each participant was obtained. Testing

was performed during the first month of a new season (September).

3.2 RESEARCH DESIGN

3.2.1 ANTHROPOMETRY

A height, weight and shoe length of each of the subjects was conducted. These

measures were necessary for data processing in VICON Nexus and were undertaken

by a single member of the research team.

3.2.2 SINGLE LEG SQUATTING PROTOCOL

The single leg squatting manoeuvres were explained and demonstrated to each

of the subjects in both the flat and decline positions. A decline board with a slope of

56

56 Chapter 5: Research Design

20° and the floor of the testing laboratory were used to satisfy the decline and flat

scenarios of the testing procedures respectively. Subjects were given two practice

squats on each leg for both types of squats to familiarize themselves with the activity.

During the decline squatting procedure (Figure 1) the subject’s weight bearing foot

was placed squarely on the decline board with the knee and hip slightly flexed. The

non-weight bearing limb was flexed at the knee and positioned posterior to the

weight bearing limb. The trunk remained in an upright position with arms folded

across the stomach so as not to obscure the line of sight between the reflective

markers and the cameras. Subjects were then asked to complete five continuous and

controlled squats with a self-selected depth but with instruction to squat as deeply as

they were comfortably able whilst attempting to maintain the original upright trunk

position. A metronome was used to ensure a standardized rate of movement though

the descending and ascending phase of the squats. Successful trials were those in

which the subject did not need to ground the non-weight bearing limb. The subject

then repeated this process for the contralateral leg and then on both legs for the flat

squat.

Figure 1 Illustration of the decline squat in the sagittal (left) and frontal (right) plane


3.2.3 SINGLE LEG SQUATTING 3-DIMENSIONAL MOTION CAPTURE

Kinematic measurements of the pelvis, knee and ankle during the performance

of the SLDS and SLFS protocols were assessed with an 8 camera 3-Dimensional

Vicon® motion analysis system at a sampling rate of 120 Hz. As per Besier and

colleagues [177], reflective kinematic markers were secured with double-sided tape

and placed on the C7 and T10 spinous processes, the sternal notch, the xiphoid

process of the sternum, the anterior superior iliac spines, the posterior superior iliac

spines, the medial and lateral joint lines of the knees, the lateral malleoli, the medial

malleoli, the calcanei, the first and second metatarsophalangeal joints and the heads

of the fifth metatarsals. A 3-marker cluster was placed over the lateral aspect of both

femurs and on the anterior midline of the tibias (Figure 2). As with the

anthropometric and hip measures the marker placement was carried out by one

researcher to prevent inter-rater variability.

Figure 2 Anterior (a) posterior (b) and lower limb markers (c) complete with marker clusters used to

store the Joint Coordinate Systems (JCS)

2c

c

2b 2a

58


3.2.4 ANATOMICAL MODELLING

3.2.4.1 KINEMATIC MODELLING AND DATA OUTPUT

A custom written kinematic model developed at the University of Western

Australia (UWA), using Bodybuilder for Biomechanics software (Oxford Metrics

Group, UK), was used for kinematic measures (Figure 3). The UWA model has been

validated by Besier and colleagues [177] and has been used in numerous kinematic

studies [178-182]. Joint coordinate systems at the knee and hip and the pelvic

coordinate system were defined from the anatomical placement of markers using the

methods of Besier and colleagues [177]. The origin for the thorax was based at the

midpoint between C7 and T10 (ThorOrig). The first defining line and x-axis runs

from ThorOrig to the midpoint between the sternal notch and the xiphoid process of

the sternum (MidStrn). The second defining line runs from C7 to T10; the cross

product of this vector with the x-axis gives the left to right running z-axis vector. The

cross product of the z-axis by the x-axis provides the vertically oriented y-axis

vector.

Figure 3 Coronal and sagittal screenshots of a SLFS in VICON Nexus


As per International Society of Biomechanics (ISB) standards [1], the Euler rotation

sequence was used to calculate global pelvis and thorax angles, and the relative

angles between the femur and the pelvis - the hip joint angle – and the relative angles

between the tibia and femur – the knee joint angle. Global pelvis (Figure 4) and

thorax angles were sequenced as flexion-extension (“tilt” for pelvis) about the

laboratory (medio-lateral) z-axis, lateral flexion (“obliquity” for pelvis) about the

laboratory (antero-posterior) x-axis and rotation about the laboratory (vertical) y-

axis. Hip (joint angles were sequenced as flexion-extension about the x-axis of the

proximal segment, abduction-adduction about a floating y-axis and then internal-

external rotation about the z-axis of the distal segment (Figure 5) [1, 177].Refer to

Table 10 on page 117 for a full description of the UWA model kinematic outputs.

Figure 4 An example of the Anatomical Coordinate System for the entire lower limb model [177]

60


3.2.4.2 DATA FILTERING

Kinematic data was filtered using a Woltring 10MSE (Mean Squared Error)

filter. The MSE method allows selection of the noise level and the spline is fitted to

the data points allowing the given level of tolerance and as such has been described

as a double Butterworth filter [183]. The differences are that with splines it is

possible to process data with unequal sampling intervals and the boundary conditions

are well defined [183]. The constant value of 10MSE was selected to due to the slow

speed of movement being performed during the investigation. Qualitative inspection

of smoothed and raw data during pilot testing indicated this to be an appropriate

value. All data was then exported to Microsoft Excel (2007) for further formatting.

3.2.5 STRENGTH TESTING PROTOCOL

Four hip strength measures were quantified using a hand-held dynamometer by

a trained physiotherapist. These were internal and external hip rotation strength in

addition to hip abduction (Figure 6) and adduction strength. These tests are employed

in the current Cricket Australia physiotherapy screening protocols. While

recognising that hand-held dynamometry does not represent the ‘gold-standard’ in

A B

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.


strength measurements, these tests were included because this technique is readily

available to physiotherapists who conduct these types of field based screening tests

[82]. As such, hand held dynamometry has been used in numerous field based studies

to measure assess strength of the lower limb [25, 26, 28, 31, 32].

The strength testing protocol followed the CA physiotherapy screening

protocol. For the hip abduction strength, the hand held dynamometer was placed on

the lower leg just proximal to the lateral malleoli (see Figure 6). Subjects were in

lying supine and pushed against the dynamometer gradually building up to their

maximal force over 2-3 seconds. The same procedure was used for hip adduction

strength except that the hand held dynamometer was placed just proximal to the

medial malleoli and the subject forcefully adducted from the hip.

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.

62


For the internal and external strength measures of the hip, subjects were asked

to lie prone and flex their knee 90°. Placement of the dynamometer was the same as

abduction/adduction testing (Figure 7). Similar instructions were given regarding the

build-up of force but directions were also given to ensure hip rotation movements as

opposed to contributions of abductors/adductors. The promotion of rotation based

movement was also facilitated by the restraining of the subject’s knee by the

physiotherapist.

All strength measures were recorded in Newtons (N). The raw strength

measures for all were then divided by the subject bodyweight in N to provide a

relative strength measure. For example, subject one has an abduction strength of

160N and a body weight of 75kg. This resulted in a relative strength measure of

0.218 (160N ÷ (75 *9.8)). The validity and reliability of hand held dynamometry has

been recorded previously, with a range of studies showing intraclass coefficients

(ICC’s) of >0.84 [184-186] and good agreement with isokinetic dynamometry [187].

Figure 7 Example of the internal rotation strength test.


3.2.6 ANKLE DORSIFLEXION RANGE OF MOTION

The rationale for including ankle range of motion data was to assess what role,

if any, it played on squat kinematics and the assessment of lumbopelvic stability.

Two methods of measuring ankle dorsiflexion were employed during the testing

protocols. The first was the knee to wall test commonly employed by

physiotherapists to assess ankle dorsiflexion [118]. For this test, the subject faces the

wall with their feet perpendicular to each other and lunge their front knee towards the

wall. The heel remained in full contact with the ground whilst the foot was

progressively moved away from the wall until the maximum range of dorsiflexion

was reached [118]. The physiotherapist conducting the test held the heel of the

subject to prevent lifting off the floor. Subjects were allowed to place their hands on

the wall for balance but were not allowed to skew their hips in order to exacerbate

their lunge towards the wall. The distance the hallux was from the wall (mm) at the

maximum point of dorsiflexion was the first measure of ankle dorsiflexion range.

The second measure was also recorded at the maximal point of ankle dorsiflexion

using a goniometer. The goniometer measured the angle (°) of the tibial shaft from

the vertical when placed on the tibia just distal to the tibial tuberosity as shown in

Figure 8.

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”.

d

ϴ°

64


3.3 ANALYSIS

3.3.1 DATA ANALYSIS

The mean (mean angle throughout the descent phase and return to upright

stance during the squatting protocol), the mean end of range (EOR - mean angles for

all kinematic variables when the knee was at maximal flexion) and range (maximal

knee flexion point – minimum knee flexion point) angles were calculated for the

weight bearing knee over four trials. All kinematic measures were deduced from an

average of the last four squats from each set of five. The first squat was excluded

from analysis due to concerns that it involved movements associated with the

transfer to unilateral stance.

The EOR was essentially a snapshot of the position each kinematic variable

was in at the deepest part of the squat as indicated by maximal knee flexion. The

basis for including the mean angle measure as a part of this analysis was to include

kinematic data that was not solely at the EOR position. It was theorised that

incorporating that the mean angle may offer additional information that may

differentiate similar EOR positions with contrasting preceding kinematics. Frontal

plane movement of the knee is an example. Two subjects may have similar neutral

EOR position but may arrive at this position from an adducted or abducted knee

position.

The following key variables were selected, to address the key omissions from

the literature and finally to address the criteria used to clinically assess lumbopelvic

stability. These variables were; 1) pelvic obliquity; 2) hip abduction/ adduction

angles of the WB hip/femur; 3) hip internal/external rotation angles of the WB

hip/femur; 4) the degree of lateral flexion of lumbar spine relative to pelvis and 5)

valgus/varus movements of the knee on the weight bearing limb. These variables are

used to clinically assess subjects during the Cricket Australia physiotherapy

screening protocols. Kinematic data from each subject was categorized with

reference to a dominant leg. Dominance was determined using the leg the participant

would use to kick a ball the greatest distance [85, 90].


The strength measures in this study were employed to investigate what affect,

if any, the force generated in the strength screening movements had on variation of

the SLS kinematics as well as the physiotherapist’s qualitative assessment. In

general, hip abductors and external rotators play an important role in lower extremity

alignment [26] as they assist in the maintenance of a level pelvis and in the

prevention of movement into hip adduction and internal rotation during single limb

support [48]. However, as mentioned previously, the findings within the literature

investigating the strength of this relationship is tenuous. Moreover, to our knowledge

there are no studies that have investigated how subjective assessment during a

functional task such as a single leg squat relates to hip strength profiling.

3.3.2 STATISTICAL ANALYSIS

3.3.2.1 COMPARING SLDS AND SLFS KINEMATICS

All data analysis was conducted in IBM SPSS statistics 18. For the kinematic

comparison of the SLFS and SLDS, paired samples t-tests were performed on the

five predetermined variables to investigate the differences between squat conditions.

The EOR and mean angle kinematic data for both the dominant (D) and non-

dominant (ND) leg was used to compare the conditions. A significance level of <.05

was originally set and a Bonferroni correction for multiple comparisons was

employed by dividing the p value by the number of paired t-tests performed

consequently resulting in a new significance value.

New p = Desired α for entire study (p .05)

Number of tests

= 0.05 / 10

p = 0.005

Descriptive statistics for all significant differences were displayed for each

variable however, due to the Bonferroni correction these relationships should not be

considered statistically significant and have only been reported to illustrate some of

the further differences between squatting conditions.

66


3.3.2.2 ANKLE DORSIFLEXION RANGE OF MOTION AND KINEMATICS

Ankle dorsiflexion was measured and recorded with two differing measures as

previously outlined in section 3.2.6. Bivariate correlations and linear regressions

were utilised to model the relationships between ankle dorsiflexion range of motion

and the sagittal plane kinematics of the knee and ankle. These statistical methods

were employed for both the dominant and non-dominant leg for both squatting

manoeuvres.

3.3.2.3 SUBJECTIVE LUMBOPELVIC SCREENING AND KINEMATIC COMPARISON

Further analyses centred on investigating the association, or lack thereof,

between the quantitative kinematic and strength data with that of the more qualitative

physiotherapist screening. Each subject was assessed by an experienced

physiotherapist with over 20 years of clinical experience during each of the squatting

conditions for both dominant and non-dominant legs. Subjects were assessed as

having either normal or excessive pelvic/lumbar spine motion as well as hip rotation.

The assessment of pelvic/lumbar spine motion and hip rotation as separate variables

is congruent with that of Cricket Australia’s screening protocols. The separation of

the two movements conceivably allows a subject to be more accurately categorised

by the aspects in which they are not competent during the screening protocol. A

rating of “1” was given to subjects who were assessed as maintaining normal

pelvic/lumbar spine motion, where as “0” was for those who were not. Each

physiotherapist’s subjective assessments were completed individually and were kept

blinded from each other. This was to ensure the individual subjective assessments

were not influenced.

For the second aspect of the physiotherapist’s qualitative assessment, hip

rotation was rated as either excessive internal, normal or excessive external.

Typically, a rating of normal would result in a “+1” score and excessive rotation

(either internal or external) would result in “0”, but for the purposes of this analysis

ratings were scaled to reflect the changes in kinematics and allow provide a

directional differentiation between excessive movement. Consequently, excessive


internal rotation was given a score of “+1”, normal was adjudicated as “0” and

excessive external rotation was scored as “-1”. This scoring system also matched

reporting convention of the kinematic data which expresses adduction angles as

positive whilst abduction angles were expressed as negative.

The collated scores were used in a bivariate analysis to investigate the presence

of any relationships between the subjective measures of movement from the

physiotherapist and the objective kinematic and strength data. Excessive femoral

rotation may happen at different stages of the decent or ascent and not necessarily at

the deepest point of the squat and as such the mean angle and range (minimal knee

flexion – maximal knee flexion) kinematic data was also used to comprehensively

investigate any potential relationships.

A one-way ANOVA was employed to investigate kinematic differences

between those deemed to have normal pelvic obliquity and/or hip rotation and those

without. This analysis was employed for both squat conditions and for both the

dominant and non-dominant limbs. A Cohen’s d was also calculated to report the

effect size differences between the means of the kinematic measures in each group.

An independent samples t-test was used to compare the strength measures of normal

and excessive movers in both squat conditions. Strength calculations were in the

form of Newtons and normalised to take into account absolute and relative strength

of the subjects. Effect sizes were also reported and a significance level of p<.05 was

set.

3.3.2.4 STRENGTH MEASURES VS KINEMATICS

As the rationale for the decline squat is to screen for lumbopelvic instability,

this study also investigated what influence strength had on EOR and mean angle

kinematics during the single leg squat. A Pearson bivariate correlation was employed

to investigate the relationships between all individual strength measures and

numerous EOR and mean angle kinematic variables within the data set. Factor

analysis was also employed to reduce the number of strength variables to a single

factor for each leg and squat condition (D SLFS; D SLDS; ND SLFS; ND SLDS)

68


with a directive to then compare to the same kinematic variables. An effect size was

also calculated to assess the size of all relationships. A significance level of p <.05

was set. This form of investigation was employed to provide insight into what

relationships, if any, existed between hip strength measures and the kinematics of the

squatting protocols within a laboratory environment.

3.4 ETHICS AND LIMITATIONS

Low risk ethical approval was granted by QUT for this study in accordance to

the requirements of the National Statement on Ethical Conduct in Human Research.

No foreseeable risks were associated with this project. Participants were

exposed to a sub maximal test that was well within their scope of physical

conditioning. Participants were excluded on the basis of lower limb injuries.

An additional limitation was the use of self-selected squatting depth. As a

result, it may have been possible that the two squatting techniques were performed at

different velocities, despite the attempts to monitor this with the use of a metronome.

The method however replicates the procedures used by Cricket Australia in their

field based physiotherapy screening protocols. Whilst this may potentially be a

limitation, the advantages were that this may also provide a greater insight into what

is classified as a satisfactory and unsatisfactory squat performance.

The use of hand held dynamometry is not the gold standard for measuring

strength and is still questioned within the literature. This is due in part due to

conflicting findings, low ICC as well as differences in testing protocols. However,

hand held dynamometry has been used in previous clinical research [32, 184].The

use of hand held dynamometry was decided as it provided continuity between the

current study and the same testing protocols that are employed by Cricket Australia.


The number of participants in the present study reflected a sample size of

convenience. A prerequisite to inclusion was that the subject had to be at a proficient

level of cricket ability thereby limiting the available participants. A power analysis

[188] has indicated that to demonstrate a 5˚ ± 8˚ difference of external rotation at the

hip with a statistical power of 0.9, the subject numbers needed to be in the vicinity of

40-45. Greater subject numbers may have allowed the incorporation of more

comprehensive statistical methods. Multinomial logistic regression for example,

would have been useful for the hip rotation data analysis as it allows the

classification of subjects based on the values of a set of predictor variables such as

kinematics, strength and range of motion data.

70

70 Chapter 5: Results

Chapter 4: Results

4.1 SUBJECTS

Nineteen volunteers participated in this study though only sixteen subjects had

ankle dorsiflexion range of motion and hip strength profiling conducted. The

subjects’ mean age was 23.8 ± 3.7 years, height was 184.5 ± 5.5cm and weight was

83.1 ± 7.1kg. All were free of injuries at the time of testing. All played first grade

cricket or higher in the previous season. There were no omissions of a subject’s data

from the study.

4.2 KINEMATICS OF THE SLFS AND SLDS

Mean joint angles and standard deviations of the five discussed variables for

the EOR and mean angles are outlined in Table 3 and Table 4 respectively. Results

from the paired t-tests are included which illustrate a number of significant

differences between the squatting conditions. Significant differences are observed

bilaterally in both the mean angles and EOR angles in the five key variables. These

differences have been shown diagrammatically in the sagittal and frontal plane views

(Figure 9). The average angles from each of the joint segments have also been

included to quantify and help illustrate the differences between SLS conditions.

4.2.1 END OF RANGE ANGLES

Pelvic obliquity and lumbar lateral flexion relative to the pelvis were not

significantly different (p ≥ 0.160) for the EOR angles between the SLFS and SLDS

on either leg. Statistically significant differences in hip adduction and external

rotation angles between the SLS conditions were observed bilaterally (p ≤ 0.004)

with the greatest differences observed in hip adduction angles. The significant

differences at the hip were not in addition to differences in the frontal plane

movement of the knee in either the descriptive or significance statistics. The

descriptive statistics for both squatting techniques indicated that the knee was in

generally in a neutral or slight varus position at the EOR point of the squat.

Chapter 5: Results 71

Table 3 Basic descriptive statistics of the joint angles at EOR and the results of the paired t-test

comparing squatting conditions.

SLFS with respect to

SLDS

Paired Differences

t

Sig.

(2-tailed) ∆ Mean

Std.

Deviation

Std.

Error Mean

95% Confidence Interval of

the Difference

Lower Upper

Non Dominant

Pelvic Obliquity -1.0 4.0 .9094 -2.9111 .9099 -1.100 .286

Relative Lateral Lumbar Flexion 0.5 1.4 .3490 -.2273 1.2605 1.480 .160

Hip Adduction 3.9 3.1 .7064 2.3806 5.3488 5.471 <.001*

Hip External Rotation 2.4 1.8 .4200 1.5606 3.3255 5.817 <.001*

Frontal Plane Knee Excursion -0.4 2.4 .5399 -1.5804 .6882 -.826 .420

Dominant

Pelvic Obliquity -0.5 8.3 1.8994 -4.4861 3.4950 -.261 .797

Relative Lateral Lumbar Flexion -0.5 1.9 .4739 -1.4734 .5466 -.978 .344

Hip Adduction 4.4 3.5 .8090 2.7188 6.1183 5.461 <.001*

Hip External Rotation 2.0 2.7 .6215 .7225 3.3342 3.263 .004*

Frontal Plane Knee Excursion -0.1 1.7 .3842 -.9422 .6719 -.352 .729

*Denotes statistical significance

Adjusted p value = 0.005

4.2.2 MEAN ANGLES

Similar results were observed in the mean angles analysis in Table 4. Pelvic

obliquity and lumbar lateral flexion relative to the pelvis were not significantly

different between the SLFS and SLDS for either squatting leg. Statistically

significant differences in femoral adduction (p = 0.001) and external rotation (p =

<.001) angles were observed in the non-dominant leg. No statistical differences were

observed in the dominant leg. However, results from the hip rotation (p = 0.006) and

hip adduction (p = 0.022) analysis indicated that there is the potential for differences

with low, but not significant, p values.. As with the EOR results, the differences at

the hip were not combined with differences in the frontal plane movement of the

knee in the either the mean descriptive statistics or significance statistics (p ≥ 0.268).

72


Table 4 Basic descriptive statistics of the mean joint angles and the results of the paired t-test

comparing squatting conditions.

SLFS with respect to SLDS

Paired Differences

t

Sig.

(2-tailed) ∆ Mean

Std.

Deviation

Std.

Error Mean

95% Confidence Interval of

the Difference

Lower Upper

Non Dominant

Pelvic Obliquity 0.4 2.6616 .6106 -.9117 1.6540 .608 .551

Relative Lateral Lumbar Flexion 0.3 .7809 .1952 -.1429 .6893 1.400 .182

Hip Adduction 1.6 1.7770 .4077 .6908 2.4038 3.795 .001*

Hip External Rotation 1.5 1.1966 .2745 .8849 2.0384 5.324 <.001*

Frontal Plane Knee Excursion -0.2 1.3662 .3134 -.8145 .5025 -.498 .625

Dominant

Pelvic Obliquity 1.6 7.7234 1.7719 -2.1690 5.2761 .877 .392

Relative Lateral Lumbar Flexion 0.1 1.2333 .3083 -.5290 .7853 .416 .684

Hip Adduction 1.2 2.0078 .4606 .1893 2.1247 2.512 .022

Hip External Rotation 1.2 1.7190 .3944 .3933 2.0503 3.098 .006

Frontal Plane Knee Excursion -0.5 1.8376 .4216 -1.3673 .4041 -1.142 .268

*Denotes statistical significance

Adjusted p value = 0.005

4.2.3 ADDITIONAL KINEMATIC OBSERVATIONS

Within the kinematic results, there were also some discrepancies between

dominant and non-dominant limb kinematics for the same squatting protocol. Of

particular note were the kinematics associated with hip rotation and lumbar lateral

flexion angles. External rotation values appear to be larger in the non-dominant

(SLFS 7.1° ± 7.6°; SLDS 8.6° ± 7.1°) when compared to the dominant (SLFS 4.2° ±

6.5°; SLDS 5.5° ± 6.3°). Relative lumbar lateral flexion was also different between

the non-dominant (SLFS -1° ± 2.2°; SLDS 1.3° ± 2.3°) and dominant limbs (SLFS

2.5° ± 2.1°; SLDS 2.4° ± 2.4°). However, neither of these results were found to be

statistically significant. Table 5 and Figure 9 illustrate the differences between the


SLS conditions particularly around the weight bearing hip and relative angles

between the pelvis and thorax.

Table 5 Summary of the functional differences from the paired t-test of the SLS conditions

Joint/Segment SLFS relative to SLDS

Thorax/Torso ↓ Flexion

↓ Lateral flexion

Pelvis ↑ Axial rotation toward WB limb

Pelvis relative to Thorax ↓ Flexion

↑ Axial rotation away from WB limb

WB Hip

↓Flexion

↑Adduction

↑ Internal femoral rotation

NWB Hip ↑Flexion

↑Adduction

Knee

↓Flexion

= Frontal Plane Knee Excursion

↓ Tibial internal rotation (at EOR)

Ankle ↓Flexion

74


Further differences were observed at most segments of the body, especially the weight bearing hip

which are summarized in

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).


4.3 ANKLE DORSIFLEXION RANGE OF MOTION

Clinically measured ankle dorsiflexion appeared to have a relationship with

some of the knee and ankle kinematics. More relationships were observed with the

flat squat than with the decline squat. The bivariate correlations (Table 6) for the

knee to wall distance (mm) had a significant positive relationship with the dominant

ankle EOR position on both the flat and decline squats. However, this was not

replicated with the goniometer (°) readings in the dominant leg. With respect to the

non-dominant leg, the knee to wall distance measure didn’t have a significant

relationship with either knee or ankle EOR kinematics. However, the goniometer

readings yielded a significant positive relationship with the EOR range kinematics of

the knee and ankle flexion angles.

Table 6 Correlations between the two measures of ankle dorsiflexion ROM and sagittal plane

movement of the knee and ankle.

Condition KTW (mm) KTW (Deg)

SLFS ND Knee EOR

Flexion Angle

Pearson Correlation .462 .593

Sig. (2-tailed) .072 .015*

SLFS ND EOR Ankle

Dorsiflexion Angle


Sig. (2-tailed) .240 .027*

SLDS ND Knee EOR

Flexion Angle


Sig. (2-tailed) .780 .345

SLDS ND EOR Ankle

Dorsiflexion Angle

Pearson Correlation -.081 .262

Sig. (2-tailed) .766 .327

SLFS Dom Knee EOR

Flexion Angle


Sig. (2-tailed) .433 .340

SLFS Dom EOR Ankle

Dorsiflexion Angle


Sig. (2-tailed) .006* .404

SLDS Dom Knee EOR

Flexion Angle

Pearson Correlation .320 -.010

Sig. (2-tailed) .227 .970

SLDS Dom EOR Ankle

Dorsiflexion Angle

Pearson Correlation .575 -.229

Sig. (2-tailed) .020* .393

Results of the linear regression using the goniometer data showed

commonalties with previous bivariate results. Significant linear relationships were

observed between clinical measures of ankle dorsiflexion SLFS D Ankle (p = 0.006;

R2 = .429), SLFS ND Knee (p = 0.015; R

2 = .352) and SLFS ND Ankle (p = 0.027;

R2 = .305) kinematics. Only the dominant ankle (p = 0.020; R

2 = .331) was found to

76


have a relationship with the decline squat. For a complete table of results, refer to

Table 16 on page 120.

Figure 10 A graphical representation of the ND ankle and knee kinematics with respect to the clinical

measure of ankle dorsiflexion.

When the bivariate and linear regression results are pooled, it indicates there

was a coupling of increased measured range of ankle dorsiflexion and kinematic

measures of ankle dorsiflexion. Moreover, increased dorsiflexion range on the non-

dominant leg translated into greater squat depth, as characterised by increased knee

flexion in the SLFS but not for the SLDS.


4.4 QUALITATIVE AND QUANTITATIVE ASSESSMENT OF PELVIC

OBLIQUITY AND HIP ROTATION

Each subject was assessed by an experienced physiotherapist as having either

normal or excessive pelvic/lumbar spine motion as well as hip rotation. A one-way

ANOVA was employed to investigate any significant differences between those

deemed to have normal lumbopelvic motion and those without. This analysis was

employed for both conditions and for both the dominant and non-dominant limbs. No

significant differences were observed in any of the conditions at the deepest point of

the squat (EOR) for the SLDS (Table 7). Descriptive statistics indicated only the

non-dominant leg in the SLDS showed potential to exhibit difference in the means

(normal 25.3°; excessive 32.7°) however this difference remained non-significant.

Despite the non-significance of the results, the descriptive statistics indicated that

those who were assessed as having normal lumbopelvic movement by the

physiotherapist on the non-dominant side maintained a more level pelvis at the EOR

point of the SLDS in comparison to the excessive movers for the non-dominant leg

only. As mentioned, no other appreciable differences were observed however, the

normal motion groups kinematic data generally indicated the presence of a more

level pelvis than those who were adjudicated as having excessive movement.

Table 7 The average pelvic obliquity and relative lateral flexion measurements as categorised by

qualitative physiotherapy assessment (“Normal” vs. “Excessive” movement) for the SLDS.

Single Leg Decline Squat Condition at EOR

Normal Excessive Comparison

(Normal v Excessive)

N Mean SD n Mean SD F p Cohen’s d Cohen’s d Effect Size

Rating

D Pelvic Obliquity

9

28.2° 8°

7

28.9° 11.7° .022 .884 -0.077 0 or near zero

D Lateral Flexion 4.1° 2.8° 4.5° 4.9° .043 .838 -0.111 0 or near zero

D Hip Adduction 6.3° 2.4 7.2° 5° .022 .645 -0.257 SMALL -ve

D Hip External Rotation 5.6° 5.1 11.5° 6.5° 4.067 .063 -1.098 LARGE -ve

D FP Knee Excursion -1° 5.8 2.5° 6.1° 1.319 .270 -0.631 MODERATE -ve

ND Pelvic Obliquity

6

25.3° 8.5°

10

32.7° 6.7° 3.700 .075 -1.070 LARGE -ve

ND Lateral Flexion 2.9° 3.1° 3.8° 3.7° .274 .609 -0.275 SMALL -ve

ND Hip Adduction 4.3° 3.3° 6.4° 3.8 1.257 .281 -0.619 MODERATE -ve

ND Hip External Rotation 10.1° 5.2° 12.8° 8.3° .509 .487 -0.393 SMALL -ve

ND FP Knee Excursion 1.1° 6.9° -1.1° 6.1° .395 .540 0.368 SMALL +ve

78


The lack of significant results observed in the SLDS analysis was not

reciprocated in the SLFS analysis (Table 8). Analysis comparing the external hip

rotation and frontal plane movement of the knee for the dominant limb in the SLFS

yielded significant differences between those who were assessed as normal and those

that weren’t. Those subjects who were assessed as having normal pelvic obliquity

tended to be, on average, less externally rotated at hip by roughly 6°. This more

neutral hip in the normal pelvic obliquity group was accompanied by a knee position

in adduction (valgus) as opposed to abduction (varus). The difference in frontal plane

movement of the knee was roughly 7°. It was interesting to observe that these

changes in frontal plane movement of the knee were not mirrored in the analysis of

the non-dominant leg.

Table 8 The average pelvic obliquity and relative lateral flexion measurements as categorised by

qualitative physiotherapy assessment (“normal” and “excessive” movers) for the SLFS

Single Leg Flat Squat Condition at EOR

Normal Excessive Comparison

(Normal v Excessive)

N Mean SD N Mean SD F p Cohen’s

d Cohen’s d Effect

Size Rating

D Pelvic Obliquity

6

29.6° 7.8°

10

30.9° 7.2° .109 .747 -0.187 0 or near zero

D Lateral Flexion 4.7° 2.7° 3.3° 2.7° 1.039 .325 0.554 MODERATE +ve

D Hip Adduction 9° 4.9° 12.5° 3.7° 2.069 .172 -0.898 LARGE -ve

D Hip External Rotation 2° 5.4° 8.3° 5.4° 5.003 .042* -1.247 LARGE -ve

D FP Knee Excursion 5.3° 6.1° -1.5° 6.1° 6.279 .025* 1.192 LARGE +ve

ND Pelvic Obliquity

4

32° 7.2°

12

30.1° 7.7° .188 .671 0.267 SMALL +ve

ND Lateral Flexion 2.1° 1.9° 3.2° 3.6° .366 .555 -0.355 SMALL -ve

ND Hip Adduction 9.9° 2.1° 9.1° 4.9° .088 .771 0.192 0 or near zero

ND Hip External Rotation 7.7° 5.3° 9.8° 9.2° .173 .173 -0.264 SMALL –ve

ND FP Knee Excursion .9° 7.7° -1.1° 6.5° .252 .624 0.313 SMALL +ve

*significant to the .05 level

Further analysis into the normal and excessive mover subgroups was

undertaken. The same method used to compare qualitative assessments with

kinematic data was employed to compare qualitative assessments with strength

differences as observed in Table 9

No conclusive results were found in the analysis investigating the relationships

between strength and subjective assessments of the physiotherapist. These results


were in line with kinematic analysis previously outlined and may indicate that

strength measures alone appear not to have a relationship with the subjective

judgements of the physiotherapist.

Figure 11 Kinematic scatter plot of the dominant hip rotation and frontal plane knee as categorised by

subjective physiotherapy rating.

A bivariate analysis was employed to investigate the presence of any

relationships between the subjective measures of movement from the physiotherapist

and the objective kinematic and strength data. Given that excessive femoral rotation

may happen at different stages of the decent or ascent and not necessarily at the

deepest point of the squat (EOR), the mean angle and range (minimal knee flexion –

maximal knee flexion) kinematic data was also used to comprehensively investigate

any potential relationships.

80


Table 9 Mean strength measurements as categorised by qualitative physiotherapy assessment for each

squat condition.

Physiotherapist’s Subjective Rating

Squat

Weight

Bearing

Limb

Strength

Measure

Normal Pelvic Motion Excessive Pelvic Motion

n

Strength Variable

n

Strength Variable

IR ER AD AB IR:E

R

ADd:

ABd Factor IR ER AD AB

IR:E

R

ADd:

ABd Factor

SLDS

D (N)

9 182 213 213 228 .861 .941 -.163

7 193 241 240 230 .906 1.044 .285

(Norm) .221 .261 .261 .280 .861 .941 -.180 .239 .265 .298 .285 .906 1.043 .211

ND (N)

6 173 193 212 229 .897 .945 -.086

10 171 215 225 217 .827 1.037 .092

(Norm) .217 .242 .264 .287 .823 .946 .017 .208 .260 .272 .263 .915 1.037 -.097

SLFS

D (N)

6 195 213 226 231 .908 .993 .178

10 182 212 225 228 .864 .982 -.053

(Norm) .233 .261 .271 .277 .908 .993 -.067 .227 .264 .280 .285 .864 .981 .026

ND (N)

4 172 200 247 222 .880 1.118 .206

12 172 209 211 221 .844 .964 -.035

(Norm) .204 .236 .291 .262 .909 1.118 -.261 .214 .259 .262 .275 .871 .965 .015

A number of moderate and large significant relationships were observed in this

analysis as observed in the correlation matrix in Table 12. The EOR analysis yielded

a significant (r = -.524; p = .037) relationship between the quantified and subjective

measures of rotation in the SLDS on the dominant leg. This indicated that the more

abducted (varus) the knee was at the EOR point, the greater the tendency for the

physiotherapist to assess the subject as having more internal rotation of the hip.

Further results were observed in the range kinematic data (EOR – start of

range) which yielded two significant relationships. Firstly, a moderate significant

correlation (r = 0.523; p = 0.038) was observed between hip abduction/adduction

kinematics and the physiotherapy assessment. This indicates that a subject with a

greater range of frontal plane hip movement between the start of the squat and the

end of the squat had a significant chance of being assessed as having excessive

internal rotation. Consequently, if a subject started in a neutral hip position and

finished in a more adducted position then this would yield a positive range value then

someone who remained neutral. It is therefore understandable that greater adduction

angles are coupled with a greater incidence of internal rotation angles as these events

are not mutually exclusive.


4.5 STRENGTH MEASURES

The findings for the non-dominant leg illustrate that there was a moderate

positive correlation between hip external rotation strength and the external rotation

kinematics for both raw data in Newtons (r = 0.458; p = 0.049) and when normalised

for body weight (r = 0.469; p = 0.043) for the SLFS. These results were not coupled

for the SLDS, although these relationships approached significance (Newtons p =

0.066; Norm p = 0.075). This illustrates that as a subject’s hip external strength

increased, the kinematic data tended to show a reduction in hip external rotation at

the EOR position. Only one other significant result was generated for the ND leg.

Normalised hip abduction strength had a moderate positive correlation with the level

of pelvic obliquity in the SLDS (r = 0.498; p = 0.030) but not for the SLFS. This

result indicated that as the level of hip abduction strength increased relative to body

weight, the more level the pelvis tended to be at the deepest part of knee flexion.

No other kinematic variables formed noteworthy relationships with the

remaining strength variables.

82


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.

Results from the dominant leg yielded no significant relationships between

kinematics and raw strength data (in Newtons) or when data was normalised for body

weight (Norm) as observed in Table 11, Table 12,

Table 13 and Table 14. However, a few non-significant trends emerged. As

raw external rotation strength increased in subjects, a trend towards greater knee

abduction angles were observed in the SLDS at the EOR point for the dominant leg,

but not the SLFS. Pelvic obliquity in the SLDS on the dominant leg tended to show

relationships with external rotation (r = 0.445; p = 0.056), adduction (r = 0.407; p =

0.084) and abduction strength (r = 0.394; p = 0.096) when normalised for body

weight as well as the hip strength factor (r = 0.408; p = 0.083). These pelvic


obliquity/strength trends were not exhibited in the non-dominant limb for the SLDS

or either limb for the SLFS.

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)

The correlation matrices illustrating the relationships between hip strength

measures and EOR kinematics are outlined in Table 11, Table 12,

Table 13 and Table 14 in Appendix B.

84

84 Chapter 5: Discussion

Chapter 5: Discussion

This study was undertaken at the Queensland University of Technology in

conjunction with the Cricket Australia Centre of Excellence Sport Science Sport

Medicine Unit. The objectives of this study were:

1. To compare the kinematic differences between the two single leg squatting

conditions, primarily the five key kinematic variables (relative lateral lumbar

flexion, pelvic obliquity, hip rotation and frontal plane movement of the hip and

knee) 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.

5.1 3D KINEMATICS OF THE SINGLE LEG FLAT AND DECLINE

SQUATS

The SLS replicates an athletic position commonly assumed in sport which

requires the control of the trunk and pelvis on the weight bearing femur in all three

planes of movement [25, 27, 36]. The ability of an athlete to control these multi-

plane movements may play a pivotal role in avoiding abnormal patterns of loading

[91]. These patterns include excessive femoral internal rotation, femoral adduction,

knee valgus, tibial internal rotation and foot pronation of the weight-bearing limb

with resultant excursion of the contralateral non-weight bearing ilium and excessive

lateral flexion of the trunk [25, 27, 36, 37, 40].

Chapter 5: Discussion 85

5.1.1 PELVIC OBLIQUITY

The variable pelvic obliquity in the present study was derived from a global

measure of the pelvis within the laboratory space. As such, comparisons can be made

between the way a physiotherapist would assess pelvic obliquity and the kinematics.

Analysis of the kinematic data indicates a depression of the contralateral non-weight

bearing Ilium of roughly 30° in both squat conditions when the knee was maximally

flexed. Statistical results indicate that there were no significant differences in the

pelvis in the y-axis (“obliquity”) in either the mean angle and EOR angle. A lack of

significant differences between the pelvic obliquity kinematics illustrates the pelvis

remains similar between squatting conditions. This is in contrast to the original

hypothesis which suggested that the introduction of a decline board would alter

pelvic kinematics. Clinically, the results from the kinematic data signify that either

SLS protocol could be used interchangeably in a screening context to report obliquity

of the pelvis.

The Trendelenburg test is a simple clinical test of pelvic obliquity [151] which

can examine the integrity of hip abductor musculature, evaluate hip abduction

strength [149], assist in the identification of abnormal gait patterns [152] and as also

diagnose for gluteus medius tears [153]. Hip abduction weakness is indicative of the

pelvis on the non-weight bearing side lowering in single leg stance due to the

inability of the hip abductors to support the weight of the body [154]. The same

principles surrounding pelvic obliquity and hip abduction strength apply to the single

leg squat [149]. Resultantly, pelvic obliquity kinematics during the single leg squat

may presumably have some relationship with hip muscle function which is discussed

in greater detail in Section 5. 4: Kinematics and Strength Analysis.

5.1.2 WEIGHT BEARING HIP ROTATION AND ADDUCTION

As hypothesised, significantly lower levels of hip external rotation were

observed in the SLFS compared to the SLDS in the mean angles and at the EOR

(except the dominant p = 0.006). These findings indicate that during the SLDS,

subjects maintained higher levels of external rotation during the descent, stopped at a

more externally rotated position and ascended in a more externally rotated hip

86


position. The difference in hip rotation was in addition to significantly greater levels

of hip adduction in the SLFS (10.1° ± 5.5°) compared to the SLDS (6.2° ± 3.5°) for

the EOR position and mean angle for the non-dominant leg. The dominant mean

adduction angle failed to remain significant (p = 0.022).

There were a few differences in the dominant and non-dominant limbs in

specific elements of the kinematic variables in this study. The disparity between

limbs is presumably due to the differences in muscle activation patterns and joint

coordination [168, 189]. The differences may also be explained in part by the

prolonged exposure of asymmetrical actions synonymous with cricket, such as

bowling. Prolonged exposure to bowling has been demonstrated to unevenly

condition the muscles of the lower back [72, 73] and presumably alter movement

patterns and coordination of the lower limb. Discrepancies in muscle conditioning

and coordination may partially explain some of the results observed in the present

study.

Yamazaki and colleagues [161] recently completed a study comparing the

differences in 3D kinematics of single leg squatting between ACL injured patients

and healthy controls. Sixty three (32 male, 31 female) ACL injured patients

performed half squats the day before ACL reconstruction and were compared to and

26 healthy control subjects with no knee injuries. When comparing the injured and

uninjured legs within subjects, the injured leg of the male subjects demonstrated less

external knee and hip rotation, less knee flexion and more knee varus than that of the

uninjured leg of the male subjects [161]. The kinematics observed in the injured legs

draw parallels between the disparity between the SLDS and SLFS. Subjects

performing the SLFS also produced less external rotation and less knee flexion. As

mentioned however, frontal plane knee movement remained the same between

conditions. As none of the subjects in the present study had a history of knee

problems, it is presumably the frontal plane movements of the knee which

discriminates between the injured and non-injured [25, 32, 83, 170]


The altered kinematics of hip external rotation and adduction have relevance to

the unpublished work of Farhart and colleagues who prospectively assessed the

SLDS as a predictor of lumbar spine and lower limb injury in fast bowlers in cricket.

Their results indicated that bowlers with low hip adduction angles at the

commencement of the rear leg (right leg for right-handed bowlers) SLDS had

reduced injury risk, whilst bowlers with greater hip external rotation during the front

leg SLDS were at increased injury risk. As mentioned previously, the reviewers’

criticised the use of the decline board as it may have changed the normal kinematics

of the squat, and therefore, may not be comparable to functional sport movement

conducted on flat ground. Given that hip adduction and external rotation have shown

to be altered during the SLDS compared to the SLFS in this study, the reviewers’

concerns may be justified.

5.1.3 LATERAL FLEXION OF THE LUMBAR SPINE RELATIVE TO THE PELVIS

No statistical differences were observed between SLS conditions with lumbar

lateral flexion relative to pelvis. This non-finding is most likely due to the small level

of movement that is possible around anatomical region in addition to limited

sensitivity of the VICON motion analysis system to detect such small changes [177].

Lumbopelvic instability isn’t simply the movement around the lumbar spine [37] and

to not demonstrate significant findings in this area is not disheartening. When

assessing lumbopelvic stability every effort should be made to induce a more

challenging position to the subject. A more challenging position may be produced by

requesting subjects to squat as deep as possible rather than a self-selected depth.

Greater physical demands during the squat presumably allow for the better

discrimination of lumbar movement and ultimately any pathomechanics associated

with lumbopelvic instability. This principle surrounding squat depth and difficulty

presumably holds true for both single leg squat protocols.

5.1.4 FRONTAL PLANE MOVEMENT OF THE KNEE

The employment of the decline board and its resultant alleviation of calf

tension [38, 39], has found to alter the sagittal plane kinematics of the lower limb

joints during the SLS [42, 44]. Several studies have investigated the frontal plane

88


kinematics of the knee during single leg squat [25, 166, 167, 170, 172], step down

[54, 90] and landing [85, 88, 89, 97, 98, 102, 103] activities indicating a link between

particular patterns of movement and injury. However, the results from this study are

the first to illustrate significant differences in hip kinematics between squats in the y-

and z- axis, but not the y-axis for knee kinematics.

Kinematic and statistical results from the frontal plane movement of the knee

suggest that there is no difference between SLS conditions. Subjects in both SLS

exhibited knee varus measurements of less than 2° at EOR and maintained an almost

neutral knee angle throughout the squat (< 1°). However, the frontal plane and

transverse planes of movement of the hip were found to be significantly different.

This finding should be considered as one of the major aspects of the study as it has

clinical implications for the assessment of lumbopelvic stability using the SLS.

Crossley and colleagues [165] employed the single leg squat to assess performance

of 32 asymptomatic participants during the single leg task.

5.1.5 ADDITIONAL KINEMATIC OBSERVATIONS

Further analysis was employed to illustrate the kinematic differences between

the conditions outside the key screening variables. These results indicated that

subjects maintained greater flexion angles for the thorax, weight bearing hip, knee

and ankle in the SLDS indicating subjects stayed in a deeper squat for longer (see

Figure 9Error! Reference source not found.). Knee and ankle data supported

previous 2D [41, 44] and 3D [43] analyses comparing the SLDS and SLFS. Greater

mean flexion angles at the WB hip were coupled with increased femoral adduction

and decreased external rotation angles in the SLFS as previously outlined. These

were also coupled with greater axial rotation of the pelvis away from the WB limb in

the SLDS. When these kinematic differences are pooled with those previously

discussed, it illustrates that the introduction of the decline board directly affects not

only the ankle and knee joints but also the kinematics about the hip joint in all three

planes.


The non-weight bearing (NWB) hip flexion and hip adduction angles were

larger in the SLFS. This coupling may be a result of the hip being closer to the

ground during the SLFS consequently drawing the NWB hip towards the midline of

the body as to not allow ground contact with the contralateral foot. Constraints of the

calf and ankle during the SLFS may also cause greater levels of instability, which

may manifest itself in the use of the NWB hip as a counter balance to any lateral

flexion of the trunk.

The disparity between the mean angle and the EOR analyses were minimal but

there were two noteworthy variations in the EOR analysis. The first variation is the

lack of any significant difference in the weight bearing hip flexion angle between the

two squatting conditions. This may indicate that whilst subjects remained more

flexed during the entire squat task, the EOR hip flexion angles were not significantly

different between squat conditions. This result was surprising given that it was

originally hypothesized that this was one area that subjects could manufacture depth

during the SLFS in the absence of greater knee and ankle flexion. The second

variation was the internal rotation of the tibia relative to the femur being significantly

smaller in the SLFS. This is most likely due to the limitations imposed by the

anatomical structures of the ankle in particular the talocrural joint which limits

rotation of the tibia when fully dorsiflexed.

Finally, there were differences in dominant and non-dominant limb kinematics

particularly with hip rotation and relative lateral flexion of the lumbar spine. In each

case, the subject’s non-dominant leg equated to the plant or ‘front’ leg associated

with the bowling action which is required to withstand repeated vertical ground

reaction forces of up to seven times body weight [111]. External rotation was

consistently larger in the non-dominant or front leg when compared to the dominant

or back leg. The disparity between limbs is presumably due to the preference and

dominance of one limb over the other but may also be explained in part by the

prolonged exposure of asymmetrical actions synonymous with cricket, such as

bowling. Prolonged exposure to asymmetrical tasks may unevenly condition the

muscles, movement patterns and coordination of the lower limb, which may in turn

partially explain the observed differences in the current study.

90


A tendency for subjects to move towards external rotation in the front leg may

be due to an increased tightness in the muscles controlling eccentric hip internal

rotation during the bowling action over a long period [164]. The loss in hip internal

rotation range may also reflect early clinical signs of hip joint pathology [190] as a

consequence of prolonged exposure to repeated high impact forces [111] of front

foot contact during fast bowling. Limited hip internal rotation may increase the range

of motion and stress that the lumbar spine has to undergo [191] during fast bowling.

This may also partially explain the differences in relative lateral flexion of the

lumbar spine observed between the dominant and non-dominant limbs. Limited hip

internal rotation may also decrease the ability of the lower limb to effectively

dissipate ground reaction forces associated with running. An adequate range of hip

internal rotation in conjunction with knee flexion and midfoot pronation are required

during the early part of stance during running to achieve adequate shock absorption

[192]. A measure of hip rotation flexibility on each subject may provide insight into

whether the preferences are due to having limitations in internal rotation or excessive

external rotation of the hip.

5.2 ANKLE DORSIFLEXION

The premise of the SLDS as a screening and rehabilitation modality

presumably is to reduce the constraints of the talocrural joint by commencing the

squat in position of greater plantar flexion. The initial position of increased plantar

flexion has been shown to increase ankle, knee and hip flexion during the squat [38,

39, 43, 44]. Comparable results were observed in this study with participants with

greater recorded measures of ankle dorsiflexion having greater corresponding flexion

of the knee and ankle as illustrated in Section 5.3 and 5.4. As a result, larger sagittal

plane movement of the lower limb joints yields greater net movement throughout the

squat resulting in a deeper squat. It is this position of greater squat depth that

presumably then promotes the differences in selected hip kinematics in the other

planes.


Greater clinical measures of ankle dorsiflexion were associated with SLFS

kinematics of the dominant ankle, non-dominant knee and non-dominant ankle. Only

the dominant ankle was found to have a relationship with the decline squat.

Restricted 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]. 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 [104, 117, 123].

Ankle injuries are common in a number of populations from athletes [17, 65,

66, 120], dancers [122], soldiers [121], general active population [24] and even

children [117]. Despite the frequency of such injuries, little is known about

prevention, particularly in children [117]. Tabrizi and colleagues [117] demonstrated

that reduced ankle dorsiflexion predisposes children to such fractures and sprains.

These investigators hypothesized that a twisting fall produces a torsional and

dorsiflexion moment on the foot [117]. Gradual absorption of energy by controlled

dorsiflexion through a flexible gastrocnemius-soleus complex may prevent injury,

whereas sudden loading in the presence of a tight calf muscle may result in a sprain

or fracture [117].

Limitations in ankle dorsiflexion have been shown in this study to correlate

with a decrease in self-selected depth of squat possibly eluding to less than optimal

shock absorption qualities of the lower limb. Ankle dorsiflexion range, as measured

by the dorsiflexion lunge test, was found to be an independent, although not

significant, predictor of lower extremity injury risk in AFL football [65, 66]. With

respect to cricket, Dennis and colleagues [17] investigated the reliability of a field-

based musculoskeletal screening protocol for fast bowlers to measure potential risk

factors for injury. Bowlers with an ankle dorsiflexion lunge of 12.1–14.0 cm on the

leg contralateral to the bowling arm being at a significantly increased risk than

92


bowlers with a lunge of >14 cm [17]. Bowlers with a lunge of ≤ 12 cm were also at

an increased risk, but not significantly so [17].

Dennis and colleagues [17] hypothesised that a lack of ankle dorsiflexion on

the front foot impact leg could relate to injuries in fast bowlers in a number of ways.

Tight calf musculature with a lack of ankle dorsiflexion may contribute to higher

ground reaction forces at front foot impact as there is less displacement available to

attenuate the impact [17]. Resultant force increases coupled with the compromised

function of the calf muscle could increase load up the kinetic chain on to the knee

and patellar tendon, hip and even lumbar spine [48, 108, 120, 125]. It may also be

possible that greater ankle dorsiflexion ROM may contribute to an improved force

attenuating alignment of the tibia and femur when the ankle joint is fully flexed,

which has been speculated to cause changes in optimal pelvis and lumbar spine

alignment in weight bearing [91].

The relationship between ankle dorsiflexion and landing biomechanics has

been investigated by Fong and colleagues [104]. The findings demonstrated

significant correlation between ankle dorsiflexion and knee flexion displacement in

addition to vertical and posterior ground reaction forces [104]. It was 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 [104]. Decrements to force attenuation as a

result of ankle dorsiflexion range limitations may additionally be a risk for the

development of patellar tendinopathy in elite volleyballers [120], metatarsal stress

fractures in soldiers [121, 128] due to its contribution to lower limb shock absorption

as previously mentioned.

The available evidence pertaining to reduced ankle dorsiflexion and injury

suggests that constraints associated with ankle dorsiflexion appear to influence lower

limb pathologies, particularly overuse. It may be that ankle dorsiflexion ROM itself

is not an independent risk factor, but rather injury incidence is the product of reduced

ankle dorsiflexion [17, 104, 117, 120] and other the compensatory biomechanics


[129]. As such, ankle dorsiflexion may simply be one of a number of variables that

interrelate to contribute to injury.

The argument that a deeper squat alters kinematics of the squat was in part both

supported and rejected by the results of this study. As previously mentioned, the

results observed in this study highlighted differences in hip rotation and adduction

between the deeper SLDS squat and the shallower SLFS as characterised by sagittal

plane movement of the lower limb joints. However, numerous other kinematics

remained unchanged, the most noteworthy being the frontal plane movement of the

knee. The likelihood is that a greater squat depth is needed before significant

modifications are observed in the squat technique and kinematics. A more plausible

scenario to observe changes in kinematics may involve subjects to approach a

maximal squat depth rather than a self-selected depth similar to that employed in this

study.

5.3 KINEMATIC AND SUBJECTIVE CLINICAL ASSESSMENT

Clinical tests are often used to assess function, though few have been validated

despite being described in the literature [149]. Whist the aim of this study was not to

validate the SLS as a screening protocol; it was interesting to note that there was

some support for the subjective assessment of the clinician. The emergence of

relationships between kinematics and the subjective assessment of lumbopelvic

stability, particularly the SLFS, demonstrates that there is some level of agreement

between the objective and subjective measures but remains tenuous for the most part.

Analysis comparing the external hip rotation and frontal plane movement of

the knee for the dominant limb in the SLFS yielded significant differences between

those who were assessed as normal and those that were not. Those subjects who were

assessed as having normal pelvic obliquity tended to be, on average, less externally

rotated at hip by roughly 6°. This more neutral hip in the normal pelvic obliquity

group was accompanied by a knee position in adduction (valgus) as opposed to

abduction (varus). The difference in frontal plane movement of the knee was roughly

94


7°. It was interesting to observe that these changes in frontal plane movement of the

knee were not mirrored in the analysis of the non-dominant leg.

The discrepancy between the dominant and dominant legs may be partially

explained by two studies that employed the single leg squat. McCurdy and observed

no significant differences between dominant and non-dominant leg strength Langford

[173] during a 1RM SLS for apparently healthy young men and women. Whilst

Madhaven and colleagues [168] demonstrated that muscle synergy around the knee

changes as the accuracy of the task improves during a resisted SLS. When pooled,

these studies may indicate that the differences between the dominant and non-

dominant legs in the present study are not a result of differences in net force

production, but rather the activation and coordination of muscles around the knee.

No significant differences between the “normal” and “excessive” movers were

observed in any of the conditions at the deepest point of the squat (EOR) for the

SLDS. Descriptive statistics indicated only on the non-dominant leg in the SLDS

showed a difference (7.4°) in the average pelvic obliquity EOR point between

“normal” and “excessive” movers (normal 25.3°; excessive 32.7°). This non

significant disparity indicated that those who were assessed as having normal

lumbopelvic movement by the physiotherapist on the non-dominant side generally

maintained a more level pelvis at the EOR point of the SLDS when compared to the

excessive movers for the non-dominant leg only.

Those participants who were adjudicated as having ‘normal’ pelvic movement,

generally presented with more of a level pelvis than those who were adjudicated as

having excessive movement who tended to have a more obliquely orientated pelvis.

A plausible explanation for these results is discussed in Section 5.4 Kinematics and

Strength Analysis.

Frontal plane movement of the knee is often used clinically as a reference for

the degree of hip internal rotation and adduction [165]. Results from this study


indicate that smaller hip adduction angles and larger hip external rotation were

observed in the SLDS despite no difference in the frontal plane movement of the

knee between squatting conditions. Differences at the hip but not at the knee during

differing SLS protocols may have further clinical implications to the Cricket

Australia physiotherapy screening data which also uses frontal plane knee positions

to infer hip and pelvic movement. Three years of physiotherapy screening data has

illustrated that those who have performed better on the SLDS have been more likely

to become injured. This may be attributable to using the knee as guide to

lumbopelvic movement despite the inability of frontal plane movement of the knee to

accurately reflect movement at the hip. Acknowledgement of these findings should

be considered when attempting to use screening data between the differing SLS

conditions interchangeably.

5.4 KINEMATICS AND STRENGTH ANALYSIS

The results from the present study demonstrated moderate positive correlations

with the pelvic obliquity kinematics, illustrating a tendency for the pelvis to remain

increasingly level with greater abduction strength. However, the relationship between

strength and pelvis kinematics was observed in the SLDS condition but not the SLFS

condition. The presence of a strength kinematic correlation in only one condition

presumably was a consequence of the altered alignment of the hip between the two

conditions as previously discussed in the 3D kinematics of the single leg flat and

decline squat (Section 5.1). In particular, hip abduction was shown to be significantly

less (more neutral) in the SLDS which seemingly promoted greater muscle activation

and subsequent control of pelvis kinematics. Previous research has indicated that 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 capable in balancing a number of biomechanical forces in the body [29].

Limited information exists on the relationship between hip abduction

movement and gluteus medius strength [149]. Hip abduction angles have been shown

to be affected by hip abduction strength in runners [101, 193]. A study by Snyder and

colleagues [101] illustrated that strength training of the hip abductors and external

96


rotators favourably altered the lower extremity biomechanics and joint loading in

running. Moreover, those with reduced levels of hip strength have been shown to

demonstrate pathological patterns of movement [166] leading to increased incidence

of lower limb injuries [31, 32, 51, 52].

The relationship between pelvic obliquity and abduction strength remains

inconclusive [47, 194]. DiMattia and colleagues [149] found a weak positive

correlation between hip-abduction strength and hip-abduction angle during both the

Trendelenburg and SLFS tests. The usefulness of these tests for assessing hip

abduction strength in a healthy physically active population has been considered

limited [149]. However, the significant relationships observed between hip abduction

strength and pelvic obliquity refutes the conclusion that the SLS has limited

application for assessing hip abduction strength. It appears that the altered hip

kinematics in the SLDS may provide a superior environment compared to the SLFS

for the hip abductors to influence lower limb alignment. An enhanced relationship

between hip abduction strength and kinematics presumably has obvious clinical

implications for the assessment of hip abduction strength.

External rotation strength was shown to reduce movements into internal

rotation during both single leg squatting manoeuvres, particularly for the non-

dominant leg. Movement into hip internal rotation have been postulated by others to

be a consequence of weakness in the muscles controlling eccentric hip internal

rotation [25, 26]. Willson and colleagues [25] have suggested that participants with

greater hip external rotation strength may be better suited to resist internal rotation

moments during the SLS.

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. Due to the tendency of the hip to go

through a relatively large range of flexion during the squat, the altering of hip

musculature moments is an important concept to incorporate into the seemingly

unconvincing link between strength measures and kinematics. Through the


development of a three-dimensional computer model of the hip muscles, Delp and

colleagues [95] demonstrated that a trend toward internal rotation with hip flexion

was apparent in a large majority of the hip muscle compartments, suggesting that

internal rotation is exacerbated by hip flexion [95]. A tendency to internally rotate at

the hip during the SLS has been supported by Ageberg and colleagues [167]. The

exacerbation of internal rotation during hip flexion further augments the findings of

this study regarding the relationship between external rotation strength measures and

rotational hip kinematics.

Whilst no significant relationships were observed, trends emerged between hip

abduction strength and knee valgus for both squatting conditions. The emergence of

a relationship between hip abduction strength and frontal plane movement of the

knee has supported previous research. Evidence suggests that increased knee valgus

might also be associated with reduced hip abduction and external rotation strength

[90]. Hollman and colleagues [90] explored the relationships among frontal plane hip

and knee angles such as knee valgus, hip muscle strength, and EMG recruitment in

women during a step-down. Strong significant correlations between knee valgus and

hip adduction angles were observed. Gluteus maximus recruitment was moderately

and negatively correlated 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 and greater knee valgus angles during

the step down task [90].

Zeller and colleagues [36] used three dimensional (3D) motion analysis system

to investigate the kinematic differences between males and females during the SLS.

Women had approximately 4° more hip adduction the men when performing an SLS

and the authors postulated that increased knee values in women during SLS might

occur because of decreased neuromuscular control in the hip muscles [36]. The link

between decrements in neuromuscular control and knee altered kinematics may also

provide insight into why the strength measures had a greater relationship with the

non-dominant kinematics that those of the dominant leg.

98


The influence of hip abduction strength on knee valgus kinematics may further

be 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 [195]. The multiple

functions of gluteus medius is congruent with the theory of Gottashalk and

colleagues [49] who have postulated that the gluteus medius functions primarily as a

hip stabiliser and pelvic rotator during gait, rather than a hip abductor.

A possible limitation of this facet of the current study was the strength testing

protocols employed in this study encouraged ‘pure’ single plane movements.

Assessing strength in a singular plane whilst essentially static may have inadvertently

reduced the capacity of the strength results to correlate with the multiplanar dynamic

movements of the squat. Hip strength does occur as an isolated entity but rather

concomitantly with the activation of other muscles acting about the hip joint [195].

Calls for dynamic measures of gluteus medius have been made, as it has been

suggested that static measures are inappropriate for predicting the biomechanics of

functional tasks [47].

Chapter 6: Conclusions 99

Chapter 6: Conclusions

6.1 DIRECT RESPONSE TO STUDY HYPOTHESES

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.

Differences in the kinematics between the single leg flat and decline squats are clear.

The employment of the decline board promotes greater squat depth by removing any

potential constraints of the ankle which supported the previous literature [41, 43, 44].

At the end of self-selected depth, hip external rotation and hip adduction kinematics

were shown to be larger in the SLDS compared to the SLFS. The differentiation

between hip external rotation kinematics remained during the mean angle analysis

whilst hip adduction kinematics only differed on the non-dominant limb. Pelvic

obliquity, relative lateral flexion of the trunk failed to demonstrate significant

differences between the squatting conditions thereby refuting the original hypothesis.

2. Reduced ankle dorsiflexion range of motion will have a linear relationship with

kinematics of the knee and ankle for the SLFS but not the SLDS

Greater ankle dorsiflexion range of motion as measured using a knee to wall test

demonstrated positive significant correlations with flexion of the knee and ankle on

the non-dominant limb for the SLFS but not the SLDS in line with the original

hypothesis. Dominant limb results were less clear with correlations being observed

in both the SLFS and SLDS for ankle kinematics. Ankle dorsiflexion when measured

with a goniometer returned similar results to the knee to wall. A linear relationship

with the D SLFS ankle, ND SLFS knee, ND SLFS ankle D SLDS ankle was

observed. These results indicate distal limitations affect proximal sagittal plane

kinematics of the lower limb at least for the ND leg. Further work is needed to

examine the kinematic differences at the hip as a result of ankle dorsiflexion

limitations and the effectiveness of the SLDS is on modifying kinematics.

100

100 Chapter 6: Conclusions

3. Kinematics for pelvic obliquity, hip rotation and relative lumbar flexion will

correlate with the subjective clinical assessment of the same movements.

Strength measures had tenuous associations with the subjective assessments of

lumbopelvic stability with no significant relationships being observed. The null

hypothesis could consequently not be rejected. Investigating functional screening

protocols that subjectively correspond with the objective movement and/or strength

being assessed is vital for the future development of pre-participation screens.

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.

For the non-dominant leg, external rotation strength and abduction strength were

found to be significantly correlated with hip rotation kinematics and pelvic obliquity

respectively for the SLFS only. No significant relationships were observed in the

dominant leg for either squat condition, although a few non-significant trends

emerged for the SLDS. As previously mentioned, the investigation of a functional

screening metric that concomitantly measures leg strength in numerous planes of

motion is warranted.


6.2 CONCLUDING STATEMENTS

To maximise athletic function, stability through the pelvis and hips, proximal

lower limb, spine and abdominal structures is required [27]. The importance of

proximal stabilisation for lower extremity injury prevention [26] particularly the

knee [31, 32, 34, 51, 79] has been well documented in the literature. It appears that

adequate lumbopelvic-femur strength 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]. Support for the previous

statement has been demonstrated in the relationships between hip strength measures

and kinematics within previous literature and within selected results of this study.

Pre-participation screening tests are used to assess function [17, 23, 149]. The

SLS is one such clinical screening measure used to assess lumbopelvic stability. The

SLDS has been employed in the Cricket Australia physiotherapy screening protocols

as a measure of lumbopelvic stability in the place of the more traditional SLFS. The

premise for this choice is to remove potential dorsiflexion restrictions allowing

greater squat depth and conceivably greater demands upon the lumbopelvic

musculature. Previous research has been unable to demonstrate clear differences

between the flat and decline squat conditions relating to the pelvis and weight-

bearing hip, particularly in the frontal and transverse planes. This study obtained a

deeper understanding of the differences between the two conditions around the

weight-bearing hip.

When the results from the key kinematic variables are pooled they clearly

illustrate the differences between the two squatting conditions. Kinematics of the

lumbopelvic region as characterised by pelvic obliquity and lateral flexion of the

lumbar spine relative to the pelvis were not significantly different between SLS

protocols. Significantly smaller levels of hip adduction and larger external rotation

angles were observed in the SLDS for both the dominant and non-dominant leg. Hip

adduction and rotation angle differences between squatting conditions were

asynchronous with differences in frontal plane movements of the knee. The

similarities and differences in the kinematics may have detrimental clinical

102

102 Chapter 6: Conclusions

implications for the assessment of the hip joint, and by extension lumbopelvic

stability by extrapolating frontal plane movement of the knee. The current study

illustrated that whilst the knee, pelvic and lumbar kinematics may remain similar

between conditions, significant differences at the hip can concomitantly occur.

Consequently, the interpretation of the SLS performance in any physiotherapy

protocol is dependent on the type of squat.

There were a few differences in the dominant and non-dominant limbs in some

of the kinematic variables in this study. The disparity between limbs is presumably

due to the preference and dominance of one limb over the other but may also be

explained in part by the prolonged exposure of asymmetrical actions synonymous

with cricket, such as bowling. Prolonged exposure to asymmetrical tasks may

unevenly condition the muscles, movement patterns and coordination of the lower

limb, which may in turn partially explain the observed differences in the current

study.

Additional kinematic results indicated that the decline squat allowed for

maintaining a greater squat depth as characterised by greater mean flexion angles in

the torso, WB hip and knee. It is worth noting however that the significant

differences centred around 5° of actual movement. It is unclear if these significant

kinematic differences translate into noticeable variation at the clinical level. The

differences in kinematics presumably have implications for athletes who perform

activities on a decline slope such as downhill runners and skiers as mechanisms of

force attenuation may be altered.

Further focal points of this study centred on highlighting the interrelationships

between strength, range of motion, subjective measures of lumbopelvic stability and

3D kinematics of the lower limbs during the single leg squat. Firstly, tenuous

associations between hip strength and lower limb alignment were observed.

However, there was a relationship between squat depth and measured hip strength.

Such a relationship may illustrate that simply the depth of a self selected squat may

be an indicator of squat depth in the absence of posterior ankle restraints. Differences


in ankle dorsiflexion range of motion yielded variations in knee and ankle kinematics

further highlighting the potential to alter lower limb kinematics. 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.

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Appendix A 117

Chapter 7: Appendices

7.1 APPENDIX A: UWA MODEL OUTPUTS

Table 10 UWA model outputs and practical meanings

C3D Name

Sign Output Convention Notes

ThoraxAngle X + Forward flexion

- Backward extension

ThoraxAngle Y + R Lateral Flexion

- L Lateral Flexion

ThoraxAngle Z + Rotation to the L

- Rotation to the R

PelvisAngle X + Forward flexion Anterior pelvic tilt

- Backward extension Posterior pelvic tilt

PelvisAngle Y + R lateral flexion Right hip lower

- L lateral flexion Left hip lower

PelvisAngle Z + Rotation to L Left hip back

- Rotation to R Right hip back

PeltoThorAngle X + Forward flexion

- Backward extension

PeltoThorAngle Y + R lateral flexion Bend to right

- L lateral flexion Bend to left

PeltoThorAngle Z + Rotation to L Turned to left

- Rotation to R Turned to right

LumRigAngle X + Flexion Flexion extension angle of Lumrig in the global coordinate

system - Extension

LumRigAngle Y + R Lateral Flexion Lateral Flexion angle of the lumbar rig in the global

coordinate system - L Lateral Flexion

LumRigAngle Z + L Axial Rotation Axial rotation angle of the lumbar rig in the global

coordinate system - R Axial Rotation

PelLumAngle X + Flexion Relative flexion extension angle between pelvis and lumbar

rig - Extension

PelLumAngle Y + R Lateral Flexion Relative lateral flexion angle between the pelvis and lumbar

rig - L Lateral Flexion

PelLum Angle Z + Pelvis rotated to the Right

Relative axial rotation angle between the pelvis and thorax - Pelvis rotated to the Left

HipAngle X + Flexion Thigh flexion

- Extension Thigh extension

HipAngle Y + Adduction Adduction of the thigh towards midline of body

- Abduction Abduction of thigh away from midline of body

HipAngle Z + Internal Rotation Internal rotation of thigh

- External Rotation External rotation of thigh

KneeAngle X + Flexion Knee flexion

- Extension Knee hyperextension

KneeAngle Y + Adduction Knee in varus position

- Abduction Knee in valgus position

KneeAngle Z + Internal Rotation Internal tibial rotation compared to femur

- External Rotation External tibial rotation compared to femur

118

118 Supplementary Results

7.2 SUPPLEMENTARY RESULTS

Table 11 Non-dominant leg strength (in Newtons) and EOR kinematic correlation matrix

ND IR

Strength

(N)

ND ER Strength

(N)

ND AD Strength

(N)

ND AB Strength

(N) ND IR:ER

ND

ADd:ABd

ND Hip Strength

Factor (N)

SLFS ND Pelvic

Obliquity

Pearson Correlation -.112 -.059 .110 .346 -.053 -.063 .166

Sig. (2-tailed) .647 .810 .652 .146 .831 .797 .498

SLFS ND Relative Lateral

Flexion

Pearson Correlation .221 .124 .125 .180 -.012 .066 .184

Sig. (2-tailed) .411 .648 .646 .504 .965 .807 .494

SLFS ND Hip

Adduction

Pearson Correlation .394 .091 -.222 -.076 .263 -.216 -.074

Sig. (2-tailed) .095 .712 .360 .757 .276 .374 .764

SLFS ND Hip

Rotation

Pearson Correlation .110 .458* .221 .311 -.379 -.009 .439

Sig. (2-tailed) .655 .049 .363 .195 .109 .972 .060

SLFS ND Knee

Valgus/Varus

Pearson Correlation .079 .282 .083 .088 -.241 -.014 .205

Sig. (2-tailed) .747 .242 .734 .720 .320 .955 .399

SLDS ND Pelvic

Obliquity

Pearson Correlation -.037 -.073 -.005 .362 .044 -.211 .122

Sig. (2-tailed) .881 .766 .983 .128 .857 .387 .618

SLDS ND

Relative Lateral Flexion

Pearson Correlation .340 -.009 .180 .150 .231 .130 .126

Sig. (2-tailed) .197 .972 .504 .579 .389 .632 .643

SLDS ND Knee

Valgus/Varus

Pearson Correlation .227 .034 -.234 -.315 .211 -.075 -.211

Sig. (2-tailed) .349 .891 .334 .189 .387 .759 .387

SLDS ND Hip

Rotation


Sig. (2-tailed) .941 .066 .473 .364 .064 .980 .120

SLDS ND Knee

Valgus/Varus

Pearson Correlation .070 .268 -.032 -.023 -.229 -.047 .106

Sig. (2-tailed) .775 .268 .898 .927 .347 .849 .665

Table 12 Non-dominant leg strength (normalised to body weight) and EOR kinematic correlation matrix

ND IR

Strength

(Norm)

ND ER

Strength

(Norm)

ND AD

Strength

(Norm)

ND AB

Strength

(Norm)

Norm IE:ER

Ratio

(Norm)

Norm AD:AB

Ratio

(Norm)

ND Hip Strength

Factor

(Norm)

SLFS ND Pelvic

Obliquity


Sig. (2-tailed) .854 .901 .606 .145 .283 .801 .566

SLFS ND Relative

Lateral Flexion

Pearson Correlation .149 .081 .066 .128 .175 .069 .150

Sig. (2-tailed) .581 .766 .808 .636 .516 .801 .578

SLFS ND Hip

Adduction

Pearson Correlation .450 .178 -.093 .070 .378 -.222 .209

Sig. (2-tailed) .053 .467 .705 .776 .111 .362 .391

SLFS ND Hip

Rotation

Pearson Correlation .128 .469* .248 .303 .125 -.012 .412

Sig. (2-tailed) .601 .043 .305 .208 .611 .960 .080

SLFS ND Knee

Valgus/Varus

Pearson Correlation .208 .408 .218 .255 .063 -.018 .384

Sig. (2-tailed) .393 .083 .371 .293 .797 .943 .104

SLDS ND Pelvic

Obliquity

Pearson Correlation .121 .042 .101 .498* -.342 -.211 .270

Sig. (2-tailed) .623 .865 .682 .030 .152 .386 .263

SLDS ND Relative

Lateral Flexion


Sig. (2-tailed) .309 .830 .616 .679 .570 .630 .628

SLDS ND Knee

Valgus/Varus

Pearson Correlation .154 -.009 -.235 -.342 .314 -.078 -.152

Sig. (2-tailed) .530 .970 .332 .151 .190 .750 .534

SLDS ND Hip

Rotation


Sig. (2-tailed) .937 .075 .450 .433 .850 .993 .214

SLDS ND Knee

Valgus/Varus


Sig. (2-tailed) .427 .102 .638 .526 .982 .830 .203

Supplementary Results 119

Table 13 Dominant leg strength (in Newtons) and EOR kinematic correlation matrix

D IR

Strength

(N)

D ER

Strength

(N)

D AD

Strength

(N)

D AB

Strength

(N) D IR:ER

D

ADd:ABd

D Hip Strength

Factor (N)

SLFS D Pelvic

Obliquity

Pearson Correlation .185 .238 .178 -.084 .053 .266 .190

Sig. (2-tailed) .448 .326 .466 .734 .831 .272 .436

SLFS D Relative

Lateral Flexion


Sig. (2-tailed) .142 .891 .853 .818 .064 .917 .588

SLFS D Hip Adduction

Pearson Correlation .035 -.309 .064 .080 .249 -.005 -.040

Sig. (2-tailed) .888 .198 .793 .744 .304 .984 .870

SLFS D Hip

Rotation


Sig. (2-tailed) .917 .789 .238 .252 .961 .652 .371

SLFS D Knee

Valgus/Varus


Sig. (2-tailed) .432 .748 .347 .564 .550 .471 .360

SLDS D Pelvic Obliquity


Sig. (2-tailed) .983 .125 .119 .210 .330 .608 .146

SLDS D Relative

Lateral Flexion


Sig. (2-tailed) .115 .532 .823 .749 .230 .994 .378

SLDS D Knee

Valgus/Varus

Pearson Correlation -.081 -.450 -.332 -.074 .211 -.279 -.324

Sig. (2-tailed) .742 .053 .166 .763 .386 .248 .175

SLDS D Hip

Rotation


Sig. (2-tailed) .899 .855 .969 .445 .961 .723 .906

SLDS D Knee Valgus/Varus


Sig. (2-tailed) .465 .813 .392 .762 .343 .377 .548

Table 14 Dominant leg strength (normalised to body weight) and EOR kinematic correlation matrix

D IR

Strength (Norm)

D ER

Strength (Norm)

D AD

Strength (Norm)

D AB

Strength (Norm)

D IR:ER (Norm)

D AD:AB (Norm)

D Hip

Strength

Factor (Norm)

SLFS D Pelvic Obliquity

Pearson Correlation .128 .180 .119 -.079 .046 .268 .109

Sig. (2-tailed) .601 .461 .627 .748 .851 .267 .658

SLFS D Relative Lateral Flexion

Pearson Correlation .290 -.146 -.057 -.105 .470 .029 -.018

Sig. (2-tailed) .276 .589 .834 .698 .066 .915 .948

SLFS D Hip Adduction

Pearson Correlation .135 -.112 .167 .230 .245 -.003 .126

Sig. (2-tailed) .581 .648 .494 .343 .312 .990 .607

SLFS D Hip Rotation


Sig. (2-tailed) .362 .225 .064 .055 .965 .651 .074

SLFS D Knee Valgus/Varus


Sig. (2-tailed) .156 .251 .132 .196 .544 .467 .102

SLDS D Pelvic

Obliquity


Sig. (2-tailed) .650 .056 .084 .096 .324 .599 .083

SLDS D Relative Lateral Flexion

Pearson Correlation .334 .053 -.038 -.067 .316 .002 .082

Sig. (2-tailed) .206 .845 .888 .804 .234 .993 .764


Pearson Correlation -.074 -.376 -.258 -.045 .208 -.282 -.230

Sig. (2-tailed) .763 .113 .286 .855 .393 .242 .343

SLDS D Hip Rotation


Sig. (2-tailed) .631 .575 .497 .193 .964 .721 .372



Sig. (2-tailed) .209 .592 .186 .349 .341 .372 .218

120

120 Supplementary Results

Table 15 Results from independent t-tests comparing the strength measures of normal and excessive movers in

both squat conditions.

Squat

Condition Strength Variable

Dominant Limb Comparison Non-Dominant Limb Comparison

(Normal vs. Excessive) (Normal vs. Excessive)

T p Effect Size T p Effect Size

Decline

IR (N) -0.681 0.507 .180 0.100 0.922 .027

ER (N) -0.112 0.912 .030 -0.965 0.351 .250

AD (N) -1.479 0.161 .368 -0.582 0.570 .154

AB (N) -0.134 0.896 .036 0.812 0.431 .212

IR:ER (N) -0.595 0.561 .157 0.839 0.416 .219

ADd:ABd (N) -1.432 0.174 .357 -0.874 0.397 .227

Hip Strength Factor (N) -0.848 0.411 .221 -0.306 0.764 .082

IR (Norm) -0.899 0.384 .234 0.513 0.616 .136

ER (Norm) -0.204 0.841 .054 -0.716 0.485 .188

AD (Norm) 0.343 0.145 .091 -0.344 0.736 .193

AB (Norm) 0.602 0.767 .159 1.418 0.178 .354

IR:ER (Norm) -.602 0.557 .205 -1.253 0.231 .318

ADd:ABd (Norm) -1.399 0.183 .350 -0.869 0.399 .226

Hip Strength Factor (Norm) -0.928 0.369 .240 0.240 0.814 .064

Flat

IR (N) 0.790 0.443 .207 -0.012 0.991 .003

ER (N) 0.306 0.764 .082 -0.347 0.734 .092

AD (N) 0.179 0.955 .048 1.586 0.135 .390

AB (N) 0.156 0.878 .417 0.053 0.958 .014

IR:ER 0.577 0.573 .152 0.602 0.711 .159

ADd:ABd 0.143 0.888 .038 0.135 0.199 .036

Hip Strength Factor (N) 0.419 0.681 .111 0.371 0.716 .188

IR (Norm) 0.310 0.761 .083 0.561 0.583 .148

ER (Norm) -0.144 0.888 .039 -0.816 0.428 .213

AD (Norm) -0.352 0.730 .094 1.102 0.289 .283

AB (Norm) -0.434 0.671 .115 -0.684 0.505 .180

IR:ER 0.584 0.568 .227 0.437 0.669 .116

ADd:ABd 0.154 0.880 .138 1.356 0.197 .341

Hip Strength Factor (Norm) -0.210 0.837 .056 -0.527 0.606 .140

Table 16 Linear regression modelling comparing the clinical measure of ankle dorsiflexion and sagittal plane

kinematics of the knee and ankle for both SLS conditions.

* Denotes statistical significance (p = 0.05)

Condition Leg Joint P R2

Single Leg Flat Squat

Dominant Knee 0.433 0.044

Ankle 0.006* 0.429

Non-Dominant Knee 0.015* 0.352

Ankle 0.027* 0.305

Single Leg Decline Squat

Dominant Knee 0.227 0.103

Ankle 0.020* 0.331

Non-Dominant Knee 0.345 0.064

Ankle 0.327 0.069

t 3d kinematics of the single leg flat and...

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