T 3D KINEMATICS OF THE SINGLE LEG FLAT AND DECLINE SQUAT · Bachelor of Applied Science (Human...

THE 3D KINEMATICS OF THE SINGLE LEG

FLAT AND DECLINE SQUAT

Stephen Timms

Bachelor of Applied Science (Human Movements Studies)

Professor Keith Davids, Dr Anthony Shield, Dr Marc Portus

Submitted in fulfilment of the requirements for the degree of

Masters of Science (Research)

School of Human Movements

Faculty of Health

Queensland University of Technology

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

Keywords

Kinematics, biomechanics, single leg squat, physiotherapy screening protocols,

lumbopelvic stability, intrinsic injury risk, malalignment, hip strength, ankle

dorsiflexion

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

Abstract

Background: Pre-participation screening is commonly used to measure and assess

potential intrinsic injury risk. The single leg squat is one such clinical screening

measure used to assess lumbopelvic stability and associated intrinsic injury risk.

With the addition of a decline board, the single leg decline squat (SLDS) has been

shown to reduce ankle dorsiflexion restrictions and allowed greater sagittal plane

movement of the hip and knee. On this basis, the SLDS has been employed in the

Cricket Australia physiotherapy screening protocols as a measure of lumbopelvic

control in the place of the more traditional single leg flat squat (SLFS). Previous

research has failed to demonstrate which squatting technique allows for a more

comprehensive assessment of lumbopelvic stability. Tenuous links are drawn

between kinematics and hip strength measures within the literature for the SLS.

Formal evaluation of subjective screening methods has also been suggested within

the literature.

Purpose: This study had several focal points namely 1) to compare the kinematic

differences between the two single leg squatting conditions, primarily the five key

kinematic variables fundamental to subjectively assess lumbopelvic stability; 2)

determine the effect of ankle dorsiflexion range of motion has on squat kinematics in

the two squat techniques; 3) examine the association between key kinematics and

subjective physiotherapists’ assessment; and finally 4) explore the association

between key kinematics and hip strength.

Methods: Nineteen (n=19) subjects performed five SLDS and five SLFS on each leg

while being filmed by an 8 camera motion analysis system. Four hip strength

measures (internal/external rotation and abd/adduction) and ankle dorsiflexion range

of motion were measured using a hand held dynamometer and a goniometer

respectively on 16 of these subjects. The same 16 participants were subjectively

assessed by an experienced physiotherapist for lumbopelvic stability. Paired samples

t-tests were performed on the five predetermined kinematic variables to assess the

differences between squat conditions. A Bonferroni correction for multiple

comparisons was used which adjusted the significance value to p = 0.005 for the

paired t-tests. Linear regressions were used to assess the relationship between

kinematics, ankle range of motion and hip strength measures. Bivariate correlations

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

between hip strength measures and kinematics and pelvic obliquity were employed to

investigate any possible relationships.

Results: 1) Significant kinematic differences between squats were observed in

dominant (D) and non-dominant (ND) end of range hip external rotation (ND p =

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

stability using the SLS. The association between kinematics and the subjective

measures of lumbopelvic stability also remain tenuous between and within SLS

screening protocols. More functional measures of hip strength are needed to further

investigate these relationships.

Conclusion: The type of SLS (flat or decline) should be taken into account when

screening for lumbopelvic stability. Changes to lower limb kinematics, especially

around the hip and pelvis, were observed with the introduction of a decline board

despite no difference in frontal plane knee movements. Differences in passive ankle

dorsiflexion range of motion yielded variations in knee and ankle kinematics during

a self-selected single leg squatting task. Clinical implications of removing posterior

ankle restraints and using the knee as a guide to illustrate changes at the hip may

result in inaccurate screening of lumbopelvic stability. The relationship between

sagittal plane lower limb kinematics and hip strength may illustrate that self-selected

squat depth may presumably be a useful predictor of the lumbopelvic stability.

Further research in this area is required.

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

Table of Contents

Keywords .................................................................................................................................................i

Abstract .................................................................................................................................................. ii

Table of Contents .................................................................................................................................... v

List of Figures ...................................................................................................................................... vii

List of Tables ...................................................................................................................................... viii

List of Abbreviations ..............................................................................................................................ix

Statement of Original Authorship ........................................................................................................... x

Acknowledgments ..................................................................................................................................xi

CHAPTER 1: INTRODUCTION ....................................................................................................... 1

1.1 Background .................................................................................................................................. 1

1.2 Purposes ....................................................................................................................................... 4

1.3 Hypotheses ................................................................................................................................... 5

1.4 Thesis Outline .............................................................................................................................. 5

CHAPTER 2: LITERATURE REVIEW ........................................................................................... 7

2.1 Methodology ................................................................................................................................ 7

2.2 Sport and Exercise Related Injury................................................................................................ 7

2.3 Intrinsic Injury Risks of the Lower Limb .................................................................................... 9 2.3.1 Strength Deficiencies ........................................................................................................ 9 2.3.1.1 Strength Deficiencies and General Injury Incidence ...................................................... 10 2.3.1.2 Regionally Specific Injuries and Associated Strength Deficits ...................................... 12 2.3.2 Lower Limb Alignment - The ‘Medial Collapse’ ........................................................... 17 2.3.2.1 Clinical Implications of Medial Collapse ....................................................................... 19 2.3.3 Hip Strength, Lower Limb Malalignment and Force Attenuation .................................. 22 2.3.3.1 Running .......................................................................................................................... 22 2.3.3.2 Landing ........................................................................................................................... 23 2.3.3.3 Cricket Fast Bowling ...................................................................................................... 25 2.3.4 Ankle Dorsiflexion Range of Motion ............................................................................. 26

2.4 Exercise and Sport Related Epidemiology ................................................................................. 30 2.4.1 Cricket Epidemiology ..................................................................................................... 31

2.5 Screening Protocols Used To Assess Risk ................................................................................. 35

2.6 Functional Testing to Assess Intrinsic Risk: .............................................................................. 38 2.6.1 Trendelenburg Assessment ............................................................................................. 38 2.6.2 The Squat ........................................................................................................................ 39 2.6.3 The Single Leg Squat ...................................................................................................... 40 2.6.4 Single Leg Flat Squat Vs Single Leg Decline Squat. ..................................................... 46

2.7 Summary and Implications ........................................................................................................ 53

CHAPTER 3: RESEARCH DESIGN ............................................................................................... 55

3.1 Participants ................................................................................................................................. 55

3.2 Research Design......................................................................................................................... 55 3.2.1 Anthropometry ................................................................................................................ 55 3.2.2 Single Leg Squatting Protocol ........................................................................................ 55 3.2.3 Single Leg Squatting 3-Dimensional Motion Capture .................................................... 57

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

3.2.4 Anatomical Modelling .................................................................................................... 58 3.2.4.1 Kinematic Modelling and Data Output ........................................................................... 58 3.2.4.2 Data Filtering .................................................................................................................. 60 3.2.5 Strength Testing Protocol ............................................................................................... 60 3.2.6 Ankle Dorsiflexion Range of Motion ............................................................................. 63

3.3 Analysis ..................................................................................................................................... 64 3.3.1 Data Analysis.................................................................................................................. 64 3.3.2 Statistical Analysis ......................................................................................................... 65 3.3.2.1 Comparing SLDS and SLFS kinematics ........................................................................ 65 3.3.2.2 Ankle Dorsiflexion Range of Motion and Kinematics ................................................... 66 3.3.2.3 Subjective Lumbopelvic Screening and Kinematic Comparison.................................... 66 3.3.2.4 Strength Measures Vs Kinematics .................................................................................. 67

3.4 Ethics and Limitations ............................................................................................................... 68

CHAPTER 4: RESULTS ................................................................................................................... 70

4.1 Subjects ...................................................................................................................................... 70

4.2 Kinematics of the SLFS and SLDS ........................................................................................... 70 4.2.1 End of Range Angles ...................................................................................................... 70 4.2.2 Mean Angles ................................................................................................................... 71 4.2.3 Additional Kinematic Observations ............................................................................... 72

4.3 Ankle Dorsiflexion Range of Motion ........................................................................................ 75

4.4 Qualitative and Quantitative Assessment of Pelvic Obliquity and Hip Rotation ....................... 77

4.5 Strength Measures ..................................................................................................................... 81

CHAPTER 5: DISCUSSION ............................................................................................................. 84

5.1 3D Kinematics of the Single Leg Flat and Decline Squats ........................................................ 84 5.1.1 Pelvic Obliquity .............................................................................................................. 85 5.1.2 Weight Bearing Hip Rotation and Adduction ................................................................. 85 5.1.3 Lateral Flexion of the Lumbar Spine Relative to the Pelvis ........................................... 87 5.1.4 Frontal Plane Movement of the Knee ............................................................................. 87 5.1.5 Additional Kinematic Observations ............................................................................... 88

5.2 Ankle Dorsiflexion .................................................................................................................... 90

5.3 Kinematic and Subjective Clinical Assessment ......................................................................... 93

5.4 Kinematics and Strength Analysis ............................................................................................. 95

CHAPTER 6: CONCLUSIONS ........................................................................................................ 99

6.1 Direct Response To Study Hypotheses ...................................................................................... 99

6.2 Concluding Statements ............................................................................................................ 101

BIBLIOGRAPHY ............................................................................................................................. 105

CHAPTER 7: APPENDICES .......................................................................................................... 117

7.1 Appendix A: UWA Model outputs .......................................................................................... 117

7.2 Supplementary Results ............................................................................................................ 118

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

List of Figures

Figure 1 Illustration of the decline squat in the sagittal (left) and frontal (right) plane......................... 56

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

used to store the Joint Coordinate Systems (JCS) ................................................................ 57

Figure 3 Coronal and sagittal screenshots of a SLFS in VICON Nexus ............................................... 58

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

[177] ..................................................................................................................................... 59

Figure 5 A) Illustration of the hip coordination system (XYZ), femoral coordinate system

(xyz), and the Joint Coordinate System (JCS) for the right hip [1]. 5 B) Graphical

representation of knee flexion in the sagittal plane. ............................................................. 60

Figure 6 Example of the abduction strength test conducted in lying supine during the study.

The dynamometer is held against the lateral malleolus and subjects are asked to

build up force against the dynamometer. ............................................................................. 61

Figure 7 Example of the internal rotation strength test. ........................................................................ 62

Figure 8 Example of the knee to wall test. The angle of the tibia relative to the vertical is

represented by “” and was reported as ankle dorsiflexion. The distance (mm) the

hallux was away from the wall is represented by “d”. ......................................................... 63

Figure 9 Sagittal plane representations of the SLDS and SLFS conditions at EOR (A and B

respectively) and a direct comparison of the squatting conditions (C) Frontal plane

representations of the SLDS and SLFS conditions at EOR (D and E respectively)

and a direct comparison of the squatting conditions (F). ...................................................... 74

Figure 10 A graphical representation of the ND ankle and knee kinematics with respect to the

clinical measure of ankle dorsiflexion. ................................................................................. 76

Figure 11 Kinematic scatter plot of the dominant hip rotation and frontal plane knee as

categorised by subjective physiotherapy rating. ................................................................... 79

Figure 12 Comparison of the hip external rotation kinematics for the SLFS and SLDS when

plotted against normalised hip external rotation strength. The shape “” represents

the SLFS ND hip rotation (º) whilst the shape “” represents the SLDS ND hip

rotation angles. ..................................................................................................................... 82

Figure 13 The pelvic obliquity kinematics for both squatting protocols compared with hip

abduction strength. The symbol “” represents the SLFS ND pelvic obliquity

angles (º) whilst the symbol “o” represents SLDS ND pelvic obliquity angles (º) .............. 83

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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

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accurate screening protocols allowing for appropriate musculoskeletal interventions

[18]. Appropriate interventions assist the management of any predispositions to

injury, which in turn may influence the incidence of lower limb musculoskeletal

injury in cricket.

1.2 PURPOSES

This study had numerous goals. The first was to compare the kinematic

differences between the flat and decline squatting conditions, primarily the five key

kinematic variables fundamental to subjectively assess lumbopelvic stability. These

variables were; 1) pelvic obliquity; 2) hip abduction/ adduction angles of the weight

bearing (WB) hip; 3) hip internal/external rotation angles of the WB hip; 4) the

degree of lateral flexion of lumbar spine relative to pelvis and 5) frontal plane

excursion of the knee on the weight bearing limb.

The second aspect was centred on the basis for the employment of a decline

board for the single leg squat. Determining the effect of ankle dorsiflexion range of

motion has on squat kinematics is vitally important in determining the future role that

that decline board has in screening for lumbopelvic stability with the single leg squat.

The third aspect was to examine the association between squat kinematics and

the associated subject clinical assessment. Understanding the terms of agreement

between qualitative and quantitative measurements of movement is an essential

element in validating such tests.

The fourth and final facet was to assess what relationship, if any, the

aforementioned key kinematic variables had with measures of hip strength. An

understanding of the relationship between kinematics and strength may provide

insight into pathomechanics patterns highlighted by functional screening tools such

as the single leg squat.

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


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

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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

T 3D KINEMATICS OF THE SINGLE LEG FLAT AND DECLINE SQUAT · Bachelor of Applied Science (Human...

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