THESIS

NEUROMUSCULAR ADAPTATIONS

OF THE ANKLE WITH STABILITY TRAINING

Colin D. Meakin

B.H.K.

This thesis is presented for the degree of Masters of Science of

The University of Western Australia

September 2002

Department of H u m a n Movement and Exercise Science

Faculty of Science

ii

ABSTRACT

Stability training on a wobble board has a long history of use in physiotherapy

clinics as a method of rehabilitation from lower limb injuries. Injury prevention of the

lower limbs in sport represents a relatively n e w application of this form of exercise.

The purpose of this thesis was to investigate the effects of wobble board 1i_riing on the

activation pattern and reflex response in the muscles crossing the left ankle joint during

a novel stable and unstable task. Fourteen moderately trained, healthy university

students were recruited and assigned to a control group or a training group. The

experimental tasks involved applying various levels of plantar torque to a stable

(1 D O F ) and unstable (3 D O F ) footplate on a specially constructed ankle perturbation

rig. Nine potentiometers measured the three-dimensional position of the footplate and a

force transducer under the ball of the foot measured the applied torque. W h e n the force

and position parameters of the desired task were met, a dorsiflexing perturbation was

given to induce a stretch reflex. Electromyographic ( E M G ) data were recorded from

five superficial muscles crossing the ankle joint to determine muscle activation patterns

and stretch reflex profiles before and after a stability training intervention. Pre and post

testing sessions for each subject were separated by a period of three weeks. During this

period, the training group participated in a total of 10 training sessions lasting 20

minutes each and the control group was asked to maintain their normal daily activities.

The results showed that an increase in the level of E M G was recorded from peroneus

longus following wobble board training. The increase in activation of this muscle m a y

represent an increase in the strength of the contribution from peroneus longus. Wobble

board training also resulted in an increase in agonist-antagonist co-contraction of the

ankle joint during weak levels of plantar torque. In addition, a reduction in amplitude

and increase in the onset latency of the stretch reflex was recorded in four superficial

muscles of the ankle joint during post training. Presynaptic inhibition represents the

most likely neural mechanism for the observed reduction in the stretch reflex amplitude.

It appears that a brief period of wobble board training has the ability to increase the

activation of the peroneal muscles and improve ankle joint stability by increasing

agonist-antagonist co-contraction and decreasing the stretch reflex amplitude in the

superficial muscles of the ankle joint. These neuromuscular adaptations have the

potential to stabilize the ankle joint and offer dynamic protection prior to and during

heel contact, helping to prevent inversion sprains.

iii

ACKNOWLEDGEMENTS

I would like to take this opportunity to thank several people who have given m e

both personal and academic support throughout the completion of this thesis.

First, I would like to thank Dr. Richard Lockwood for helping m e take this giant

step across the world. You and your family's energy have truly made this Australian

experience complete.

To Dr. David Lloyd, for all the skills and insight that you offer as a researcher.

To Rachel Skoss for your guidance. Without your help this thesis would have

taken an entirely different path.

To Dr. Thor Besier, for your friendship and remarkable ability to have the

answer to eveiything.

Special thanks to all the staff and postgraduate students of the Department of

H u m a n Movement and Exercise Science for helping to create an exciting and friendly

learning environment.

To Gaye and Fraser, Tim and Judy and m y family for their support and

understanding, enabling m e to challenged myself and completed a degree on the other

side of the world.

And last but not least, to m y roommates Jonas, Daina and Siri for so many great

memories and for helping to create a happy, stable home environment M a y # 9

Vincent Street live on forever (or until I come back to W A so I'll have a place to crash).

TABLE OF CONTENTS

iv

CHAPTER 1- THE PROBLEM 1

INTRODUCTION 1

STATEMENT OF THE PROBLEM 2

HYPOTHESES 3

ACRONYMS AND DEFINITIONS OF TERMS 3

DELIMITATIONS 5

LIMITATIONS 5

THESIS OVERVIEW 5

CHAPTER 2- REVIEW OF LITERATURE 6

INTRODUCTION 6

ANKLE INJURY AND SPORTS 6

ANATOMY AND BIOMECHANICS OF THE ANKLE JOINT COMPLEX 7

Biomechanics 7

Ankle Joint Stability 8

ETIOLOGY OF INJURY TO THE LATERAL LIGAMENT COMPLEX 10

PATHOLOGICAL ANATOMY OF LATERAL ANKLE SPRAINS 10

WOBBLE BOARD TRAINING AS A METHOD OF INJURY PREVENTION 11

STABILITY OF A SYSTEM 12

Joint Stability 12

Postural Stability. 12

WOBBLE BOARD TRAINING CHALLENGES SYSTEM STABILITY 13

Postural Stability Challenge 13

Ankle Joint Stability Challenge 14

THE PROPRIOCEPTIVE SYSTEM 15

Role of Proprioceptors 75

Proprioceptors and Muscle Coordination for a Specific Task 16

PROPRIOCEPTORS AND THE STRETCH REFLEX RESPONSE 18

CO-CONTRACTION AND REFLEX STABILIZATION 19

Adaptability of the Stretch Reflex. 20

The Co-contraction Response 20

ACUTE ADAPTATIONS TO THE STRETCH REFLEX DURING CO-CONTRACTION 21

CHRONIC NEURAL ADAPTATIONS TO MUSCLE RECRUITMENT AND REFLEXES 23

V

Principles of Training 24

Chronic Adaptations to Muscle Recruitment 24

Chronic Adaptations to the Stretch Reflex 25

CHAPTER 3- METHODS AND PROCEDURES 28

EXPERIMENTAL APPROACH 28

SUBJECTS 28

EXPERIMENTAL DESIGN 29

EXPERIMENTAL APPARATUS 31

DATA COLLECTION 33

Rig Force and Position Data 33

Electromyography 34

Data Collection and Trigger 34

DATA ANALYSIS 35

Muscle Activation Profiles 35

Stretch Reflex Profiles 38

STATISTICAL ANALYSIS 39

CHAPTER 4- ADAPTATIONS OF THE CO-CONTRACTION RESPONSE

WITH STABILITY TTL_NING 41

RESULTS 41

Net Muscle Activation 41

Individual Muscle Activation Profiles 42

Co-contraction 44

DISCUSSION 46

Individual Muscle Activation Profiles 46

Co-contraction 49

Implications for the Prevention of Lateral Ankle Sprains 51

CHAPTER 5- ADAPTATIONS OF THE SHORT LATENCY REFLEX WITH

STABHITY TRAINING 53

RESULTS 53

Net Ml Reflex Amplitude 53

Ml Reflex Amplitude Profiles for Individual Muscles 55

Net Ml Reflex Onset Time. 57

Ml Reflex Onset Time Profiles for Individual Muscles 59

vi

DISCUSSION 61

Ml Reflex Amplitude Profiles for Individual Muscles 61

Ml Reflex Onset Time Profiles for Individual Muscles 64

Implications for the Prevention of Lateral Ankle Sprains 65

CHAPTER 6- SUMMARY, CONCLUSIONS AND RECOMMENDATIONS..... 67

SUMMARY 67

CONCLUSIONS 69

RECOMMENDATIONS FOR FUTURE RESEARCH 70

REFERENCES 72

APPENDICES 76

APPENDIX A- Consent Form 76

APPENDIX B- Subject hrformation Sheet 77

APPENDIX C- Selection Criteria 79

APPENDLXD- Testing and Training Timetable 81

APPENDIX E- Stabmty Training Regime 82

APPENDLXF- Evaluation of Performance (Group 1) 83

APPENDIX G- Evaluation of Performance (Group 2) 84

APPENDIX H- Activation Front Panel 85

APPENDLXI- Activation Block Diagram 86

APPENDIX J- Reflex Front Panel 88

APPENDLXK- Reflex Block Diagram 89

vii

LIST OF FIGURES

FIGURE 2.1 Antero-lateral view of the ankle joint complex illustrating sub

joints and biomechanical actions 7

FIGURE 2.2 a) Lateral and b) Medial views of the ankle joint complex

illustrating the surrounding ligaments 8

FIGURE 2.3 Superficial muscles that cross the ankle 9

FIGURE 2.4 An individual balancing on a wobble board 13

FIGURE 2.5 EMG and Kinematic data from the flexors and extensors of the forearm

during a pointing movement (heavy dashed line) and a reversal

movement (thin solid line) 17

FIGURE 2.6 The neural circuit of a stretch reflex 18

FIGURE 2.7 EMG from soleus after stretch illustrating the short latency (Ml),

medium latency (M2) and long latency (M3) responses. 18

FIGURE 2.8 Amplitude of the stretch reflex in the soleus muscle during various

levels of co-contraction and plantar flexion 22

FIGURE 3.1 The experimental environment. 30

FIGURE 3.2 The ankle perturbation rig. 32

FIGURE 3.3 The target-matching display. 32

FIGURE 3.4 Processing of raw muscle activation EMG. 35

FIGURE 3.5 A polar plot graph illustrating the muscle activation profile, pre and post

training during a 3 DOF 40% plantarflexion task on the ankle

perturbation rig. 36

FIGURE 3.6 Processing of Raw Reflex EMG 38

FIGURE 4.1 Net activation of all 5 muscles averaged over all 8 tasks 41

FIGURE 4.2 Muscle activation polar plots 43

FIGURE 4.3 Net activation of all 5 muscles in each task. 44

FIGURE 4.4 Co-contraction ratios for flexor and extensor muscles in each task 44

FIGURE 4.5 Co-contraction index of all 5 muscles in each task 45

FIGURE 4.6 EMG from vastus lateralis during a maximum contraction, cross-

sectional area of quadriceps femoris and the MVCforce during

isokinetic training and detraining 48

FIGURE 5.1 Ml reflex amplitude for each muscle averaged over all 8 tasks. 53

FIGURE 5.2 Ml Reflex amplitude for each task averaged over all 4 muscles 54

FIGURE 5.3 Average Ml reflex amplitude in each task for the 4 superficial muscles of

the ankle. 56

viii

FIGURE 5.4 Ml reflex onset time for each muscle averaged over all 8 tasks 57

FIGURE 5.5 Ml reflex onset time for each task averaged over all 4 muscles 58

FIGURE 5.6 Average Ml reflex onset time in each task for the 4 superficial muscles

of the ankle. 60

ix

LIST OF TABLES

TABLE 4.1 Percent change in the net activation of the 5 superficial muscles of the

ankle for trained and control subjects 41

TABLE 5.1 Percent change in the amplitude of the Ml reflex response in 4

superficial muscles of the ankle for trained and control subjects 54

TABLE 5.2 Percent change in the Ml reflex amplitude between 1 and 3 DOF tasks

at equivalent levels of plantar torque for trained and control subjects..... 55

TABLE 5.3 Percent change in the onset time for the Ml reflex response in 4

superficial muscles of the ankle for trained and control subjects 58

CHAPTER 1- THE PROBLEM

1

Introduction

The lower extremity, consisting of the hip, knee and ankle, is the most

frequently injured part of the body in sports such as football. Hip and knee injuries can

be diverse in nature. However in the ankle, the vast majority (85%) of injuries are

sprains localized to the lateral ligament complex, which makes it the most commonly

injured structure of the body in athletic sport (Garrick and Requa, 1988). Physiotherapy

clinics around the world have long recognized the rehabilitative potential of wobble

board training. However, injury prevention of the lower limbs in sport represents a

relatively new application of this form of exercise, and will be the focus of this thesis.

Recently, stability training (wobble board training) programs have been reported to be

among the most effective methods to prevent ankle sprain injuries in sport (Thacker et

al., 1999). For example, a 2 0 % decrease in the incidence of ankle sprains was seen in

soccer players after 30 days of training on wobble boards (Tropp et al., 1985). A n

improvement in ankle joint stability is thought to represent the neuromuscular

mechanism underlying this reduction in the number of ankle injuries after training.

However, the exact nature of the neuromuscular adaptations that result from stability

training has yet to be elucidated.

Stability is defined as "the ability of a system to resist perturbation and return to

equilibrium." Ligaments and joint articular surfaces play a large role in maintaining

ankle joint stability. Muscles also have a significant contribution to the level of

dynamic stability of the loaded and unloaded ankle owing to their anatomical moment

arms (McCullough and Burge, 1980). At present, a lack of understanding surrounds the

adaptations that take place in the ankle musculature after stability training. Most studies

hypothesize that stability training on a wobble board increases proprioception (Bemier

and Perrin, 1998), improves contraction strategies (Konradsen et al., 1997) and

optimizes the reflex response of the ankle joint muscles (Trimble and Koceja, 1994;

Sheth et al., 1997). The paucity of Uterature in this area is most likely due to the

methodological difficulties involved in evaluating training adaptations of the ankle joint

muscles.

Passive (viscoelastic), intrinsic (contractile) and reflex components contribute to

the level of muscular stability imparted to a joint. These reflex and intrinsic contractile

2

components of muscular joint stability indicate that the stretch reflex and level of

muscular contraction have the potential to alter the stability of a joint For example, if

mechanically opposing muscles surrounding a joint contract simultaneously (co-

contraction), the joint experiences a net increase in stiffness and overall stability (Crone

and Nielsen, 1994). In addition, the stretch reflex has been shown to generate large

forces in a contracting muscle, after a moderate degree of stretch is applied (Toft et al.,

1991). If a stretch reflex occurs in a co-contracting muscle, it m a y have the potential to

destabilize the underlying joint.

It is thought that a brief period of wobble board U_ning involving balancing

exercises will result in a change in the neuromuscular contribution to ankle joint

stability. T w o major neuromuscular factors that contribute to ankle joint stability are

the co-contraction response and the stretch reflex of the superficial muscles of the ankle.

It has been suggested that wobble board training could result in an increase in the co-

contraction strategy around the ankle prior to heel contact reducing the potential for a

lateral ankle sprain (Konradsen et al., 1997). In addition, a large stretch reflex could

occur prior to heel contact if the heel's path towards the ground is deviated by a root or

uneven surface. This stretch reflex has the potential to destabilize a co-contracting

joint, causing a decrease in overall ankle joint stiffness prior to heel contact. This, in

turn, would result in an increased risk of injury (Llewellyn et al., 1990). However, it is

thought that the increased level of co-contraction involved in wobble board training

could result in a decrease in this monosynaptic stretch reflex (Nielsen et al., 1993;

Trimble and Koceja, 1994) and by doing so, reduce it's potential to destabilize a co-

contracting joint (Llewellyn et al., 1990).

Statement of the Problem

The neuromuscular mechanisms underlying the reduction in ankle sprains after

stability training are unknown. It has been hypothesized that a slight increase in the co-

contraction level around the ankle prior to heel contact would increase joint stiffness,

delaying the time from ankle perturbation to ligament injury. The primary aim of this

study was to determine if a stability training program could increase the co-contraction

ratio of the muscles surrounding the ankle joint, when the subject performs a novel

ankle joint task. A n ankle perturbation rig was chosen as the ideal environment to

analyze changes in the co-contraction ratio of the ankle joint. This rig offered the

ability to directly challenge all the ankle joint muscles in a highly repeatable 3 D O F task

3

and to remove all visual and vestibular influences that would be present in less

experimentally controlled tasks such as locomotion.

It has been concluded in the literature that the stretch reflex response is too slow

to provide any protection to the ankle joint during an ankle sprain. However, the stretch

reflex may have the potential to destabilize a co-contracting joint and as a result the

amplitude of the stretch reflex is usually reduced in weak to moderately co-contracting

muscles. The second aim of this study was to determine if stability training could result

in a habitual reduction in the amplitude of the stretch reflex response in the ankle

musculature.

Hypotheses

The following hypotheses were developed and tested.

1. Wobbleboard training results in an increase in the co-contraction ratio of the ankle

musculature during both a novel stable and unstable task.

2. Wobbleboard training results in an increase in the net activation of the ankle

musculature during both a novel stable and unstable task.

3. Wobbleboard training results in a decrease in the amplitude of the monosynaptic

stretch reflex in the ankle musculature during both a novel stable and unstable task.

4. Wobbleboard training results in a delay in the onset time of the stretch reflex in the

ankle musculature during both a novel stable and unstable task.

Acronyms and Definitions of Terms

acute adaptations- Short term changes in the motor system due to a single

bout of physical activity.

afferent- Feedback from sensory receptors.

co-contraction- Simultaneous contraction of mechanically opposing

muscles.

C O P - Center of pressure.

chronic adaptations- Long term, cumulative changes in the motor system due to

multiple bouts of physical activity.

D O F - Degrees of freedom.

H-reflex-

impedance -

monosynaptic-

muscle stiffness-

percent MVPF-

presynaptic inhibition

proprioception-

recurrent inhibition-

re fie x-

Renshaw cell-

stability-

stretch reflex-

stretch reflex path way -

The H-reflex is a clinical tool used to assess the excitability

of the motomeuron pool. Since the H-reflex and the stretch

reflex share the same monosynaptic pathway, it is c o m m o n

practice in the Uterature to directly relate the results of H-

reflex testing to the excitability of stretch reflex.

The automatic capability of a system to resist an applied

load.

One synapse.

A combination of passive (viscoelastic), mtrinsic

(contractile) and reflex components of a contracting muscle.

Percentage of the maximum voluntary plantar flexion

torque recorded in the 3 D O F task on the rig.

Inhibition of the action potentials transmitted in an axon

before it synapses with a target cell.

A specialized variation of the sensory modality of touch that

encompasses the sensation of movement and joint position.

A local feedback circuit of a motomeuron that can modify

the stretch reflex loop through Renshaw cells.

A stereotyped motor response of an organism to a sensory

stimulus.

A n interneuron involved in a local feedback circuit with a

motomeuron. The Renshaw cell receives input from

supraspinal sources.

The ability of a system to resist perturbation and return to

equilibrium.

Multiple bursts of E M G in a stretched muscle before

voluntary contraction begins.

A monosynaptic feedback loop that involves a la afferent

neuron that extends from a muscle spindle, to the spinal

cord where it contacts a motomeuron and returns to the

homonymous muscle.

5

Delimitations

• Participants were either male or female age 19-30.

• Subjects were to be moderately active individuals with no history of heavy aerobic,

anaerobic or strength train ing in the year prior to testing.

• Subjects were to have no previous history of stability training.

• The knee was secured to ensure that the muscle activation strategies of the lower

limb to complete the tasks were uniform between all trials.

• Both experimental and control subjects were instructed how to do the experimental

tasks on the rig and were required to complete ten training sessions in the 1 and 3

D O F tasks, both pre and post tiuining.

• All training was conducted at the Department of H u m a n Movement and Exercise

Science at U W A .

Limitations

• Different muscular strategies employed by individual subjects to do the

experimental tasks will decrease the power of intra-subject comparisons.

• Different muscular strategies employed by different subjects to do the experimental

tasks will decrease the power of inter-subject comparisons.

Thesis Overview

This thesis is divided into 6 chapters. Chapter 2 reviews the related literature in the

areas of biomechanics and neuromuscular physiology of the ankle joint complex. Chapter

3 presents the methods used to collect the experimental data for this thesis including the

experimental design, the experimental apparatus, data collection and data analysis.

Chapter 4 describes the muscle activation profiles of the five superficial muscles crossing

the ankle joint when subjects performed various stable and unstable ankle tasks and

Chapter 5 describes the monosynaptic stretch reflex amplitude and onset time for the same

muscles in the same stable and unstable tasks. Both pre and post testing data for the

trained and control groups are presented and discussed in each of these chapters and the

implications for the prevention of lateral ankle sprains are assessed. The final chapter

summarizes the major findings from this thesis and suggests future directions for research

investigating the chronic neuromuscular adaptations induced by specific ti_ning regimes

and the prevention of lower limb injuries.

6

CHAPTER 2- REVIEW OF LITERATURE

Introduction

Stability training has long been recognized in physiotherapy clinics around the

world for its positive role in ankle rehabilitation after injury. In addition to this

rehabilitative role, recent Uterature has revealed that stability training is an effective

method to prevent ankle sprain injuries in healthy individuals during sporting activities

(Thacker et al., 1999). Despite the accumulating evidence to support this fact, no studies

have been able to identify the neuromuscular mechanisms underlying the decreased

incidence of ankle sprains in sport after stability training. In fact, only Sheth and

colleagues (1997) have attempted to tackle the problem and dealt with adaptations in the

onset time of the reflex response in the various muscles of the ankle. The lack of Uterature

regarding the neuromuscular mechanisms of injury prevention after stability training of the

ankle is most likely due to the methodological difficulties involved in evaluating training

adaptations to this joint The present study will focus on neuromuscular adaptations in the

muscles crossing the ankle joint to stabilize the ankle joint after stability training, using a

specially constructed ankle perturbation rig. Obtaining experimentally determined data

about h o w stability training effects the activation pattern and reflex response in the ankle

muscles will provide the necessary, fundamental evidence to validate the prescription of

stability training as a method of injury prevention.

This review of the literature will focus on research that is relevant to understanding

the biomechanics of ankle sprain injuries and the potential of stability training as a method

of injury prevention. The neuromuscular challenge provided by stability training to the

ankle joint will be explored and the possible training adaptations that result will be

examined. Inferences will be made about h o w these training adaptations to the ankle

musculature might improve ankle joint stability.

Ankle Injury and Sports

The lower extremity, consisting of the hip, knee and ankle, is the most commonly

injured area of the body in athletes (Garrick and Requa, 1988). Hip and knee injuries can

be diverse in nature. However in the ankle, the vast majority (85%) of injuries are

sprains localized to the lateral ligament complex (Balduini and Tetzlatf, 1982). This

makes the lateral ligament complex of the ankle the most commonly injured structure of

the body in athletic sport. In fact, injuries of the lateral ankle complex account for up to

4 5 % of all injuries in sports (Garrick, 1982).

Despite these figures, ankle injuries attract only a fraction of the attention given

in the medical Uterature to knee or shoulder problems. This is most likely because ankle

Ugament injuries lack the permanently disabling quaUties that come with injury to the

knee and shoulder, as weU as the associated costs of surgical intervention.

Anatomy and Biomechanics of the Ankle Joint Complex

Biomechanics

The talocrural (tibiotalar, fibulotalar and tibiofibular) joints and the subtalar

(talocalcaneal) joint makes up the three degree of freedom (DOF) Ugamentous stmcture

known as the ankle joint complex. Dorsi and plantar- flexion refer to rotation of the

ankle in the sagittal plane. Inversion and eversion refer to rotation of the ankle in the

frontal plane and adduction and abduction refer to rotation of the ankle in the transverse

plane. Movements of the ankle are most commonly triplanar, such as pronation, which

is a combination of plantarflexion, inversion and adduction (TJonatelli, 1996).

abduction

A - tibiotalar joint B - tibiofibular joint C - fibulotalar joint D - talocalcaneal joint

plantarflexion

Figure 2.1 Antero-lateral view of the ankle joint complex illustrating sub

joints and biomechanical actions (modified from Primal Pictures, 2000).

8

Ankle Joint Stability

Static joint stabUity is defined as the abUity of a system to resist perturbation and

return to equilibrium (Enoka, 1994). During the loading phase of gait (weight-bearing),

ligaments, joint articular surfaces and muscles aU play a role in ankle joint stability

(McCuUough and Burge, 1980; DonatelU, 1996). However, in the unloaded position the

articular surface does not contribute to joint stabiUty, leaving the Ugaments and muscles

to maintain the integrity of the ankle joint.

The three lateral collateral Ugaments shown in Figure 2.2a resist any inversion

moment about the ankle joint complex. Due to it's orientation, the calcaneofibular

Ugament is the most important inversion stabilizer, foUowed by the anterior talofibular

Ugament and then the posterior talofibular Ugament (McConkey, 1987). The deltoid

Ugament shown in Figure 2.2b resists any eversion moment about the ankle joint

complex. The primary stabilizer for adduction involves the anterior talofibular Ugament

and the deltoid Ugament where as, abduction is stabilized by the calcaneofibular

Ugament (DonatelU, 1996). The posterior talofibular Ugament is the primary stabilizer

during plantar flexion (DonatelU, 1996).

a) Lateral View b) Medial View

Figure 2 _ a) Lateral and b) Medial views of the ankle joint complex

illustrating the surrounding ligaments (Pictures, 2000)

Muscles also have a significant contribution to the level of dynamic stabiUty of

the loaded and unloaded ankle owing to their anatomical moment arms (McCuUough

and Burge, 1980). Only the actions of the superficial ankle joint muscles iUustrated in

Figure 2.3 wiU be discussed in this study as no analysis of the deeper muscles was

attempted due to technical difficulties in recording E M G activity from these muscles.

Peroneus longus inserts on the latero-dorsal aspect of the 1st cuneiform bone and the

base of the 1st metatarsal. The line of action of this muscle aUows it to evert the foot

and resist inversion of the ankle joint (Neptune et al., 1999). TibiaUs anterior inserts on

the medio-dorsal aspect of the 1st cuneiform bone and the base of the 1st metatarsal. The

line of action of this muscle aUows it to invert the foot and resist eversion of the ankle

joint (DonatelU, 1996). TibiaUs anterior is also a prime dorsiflexor and can help resist

sudden plantarflexion of the ankle joint. The triceps surae muscle group, including

medial gastrocnemius, lateral gastrocnemius and soleus aU insert on the calcaneous

bone via the achiUes tendon. This muscle group, in combination with peroneus longus

acts to plantarflex the foot and resist any dorsiflexing moments of the ankle joint

complex (DonatelU, 1996).

Peroneus Longus Tibialis Anterior Gastrocnemius Soleus

Figure 2 3 Superficial muscles that cross the ankle (Draves, 1986).

10

Etiology of Injury to the Lateral Ligament Complex

The term "ankle inversion" used to classify lateral ankle sprains can be

misleading as it is often taken as the description of the events leading to the injury. The

actual biomechanical motion that results in a lateral ankle sprain involves supination, a

combination of ankle plantar flexion, and adduction of the foot (Shephard, 1987).

Ankle sprains most commonly occurs at the moment the foot makes contact with

the ground such as when landing from a jump or at the termination of the swing phase

in running and walking. At foot strike in both of these situations, the ankle joint is in an

active state of plantarflexion, wtdle the foot is adducted (McConkey, 1987). This

position effectively decreases the bony contribution to stabiUty and ankle joint support

is mainly provided by muscular and ligamentous structures. In addition, plantarflexion

causes the lateral malleolus to maintain a more distal orientation in reference to the

medial malleolus, causing a slight inversion (McConkey, 1987). This staggered

positioning of the malleoli means that the medial malleolus has a greater potential to act

as a fulcrum for an inversion sprain (McConkey, 1987).

The general mechanism of the lateral ankle sprain during foot strike situations

involves improper foot and heel positioning prior to weight bearing. This causes an

inversion lever arm to result through the subtalar axis (Tropp et al., 1985). W h e n

weight is applied to this joint configuration, a varus (mverting) thrust occurs driving the

foot into inversion and helping cause a lateral ankle sprain (Tropp et al., 1985).

Environmental factors that can predispose the heel to improper positioning

include irregular surfaces such as a rutted footbah field or another player's foot, as weU

as poorly fitting shoes with a broken heel-cup support. Anatomical considerations

include a tight triceps surae complex, weak peroneal muscles, hyper mobUe subtalar and

midtarsal joints and impaired ankle proprioception (Garrick, 1977; Shephard, 1987).

Pathological Anatomy of Lateral Ankle Sprains

During a lateral ankle sprain, the strength of the peroneal muscles is overcome

and the anterior talofibular Ugament is the first to rupture due to its relative weakness

and compromising orientation in plantarflexion (McConkey, 1987). A s the forces

associated with the injurious event increase, tearing of the anterior and lateral capsule

occurs. The next Ugament susceptible to damage is the calcaneofibular Ugament,

foUowed by the posterior talofibular Ugament (McConkey, 1987). The stages of injury

have been shown to always begin with rupture to the anterior talofibular Ugament and

the degree of capsular and Ugament injury depends on the length of the inverting lever

arm and the amount force that is appUed to it (Shephard, 1987).

Wobble Board Training as a Method of Injury Prevention

Ankle sprains are the most common injury in the sporting world (Shephard,

1987). Sprains to the lateral Ugament complex alone have resulted in more game time

lost by athletes than any other single sporting injury. The prevention of ankle sprains is

a major industry within the sporting world. Recently, Thacker and colleagues (1999)

reviewed the most effective methods for the prevention of ankle sprain injuries in sport.

The methods evaluated included external prophylactic supports (ankle taping and

orthotic braces), stabiUty training programs involving wobble board exercises, and

athlete education (Thacker et al., 1999). The success of stabiUty toining programs as a

method of ankle sprain prevention is of particular interest to this study.

For example, Tropp and colleagues (1985) conducted an epidemiological study

that evaluated the incidence of ankle sprain injuries in soccer players after a ten-week

wobble board training regime. The study involved a pre test/post test randomized

groups design involving 65 experimental and 171 control subjects. During the six-

month evaluation period ankle sprains were recorded in 2 5 % of the control group and in

only 5 % of the ankle disc trained group. This study provided evidence that suggested

wobble board training has the potential to reduce the incidence of lateral ankle sprains

in sport. However, the author gave no explanation of the mechanisms underlying this

reduction.

To date, the neuromuscular adaptations that result from wobble board training

have been hypothesized to include an increase in proprioception and overall stabiUty of

the ankle joint (Laskowski, 1997 October), and an improvement in the abitity of ankle

muscles to react to a perturbation (Sheth et al., 1997). However, Uttle to no

experimental evidence has been provided to support these speculations.

Neuromuscular adaptations leading to an improvement in joint stabiUty represent the

most probable explanation for the reduction in the number of ankle sprains observed

by Tropp and colleagues (1985) after wobble board training. The next section of this

Uterature review will explore the definition of stabiUty and the neuromuscular

mechanisms that m a y contribute to ankle joint stabiUty.

12

Stability of a System

IiquiUbrium is the unique state of a system that occurs when aU the forces acting

on the system sum to zero (Enoka, 1994). StabiUty is the abitity of a system to maintain

equiUbrium. It wiU be shown h o w both joint stabiUty and postural stabiUty are

challenged when attempting to balance on a wobble board, and h o w this challenge may

result in neuromuscular adaptations to the ankle joint muscles. First, however, both

joint stabiUty and postural stabiUty wiU be defined and discussed.

Joint Stability

StabiUty of any joint in the human body is influenced by joint stiffness and the theory of

musculoskeletal system impedance. Impedance is defined as "the automatic capabiUty

of a system to resist an appUed load before voluntary intervention takes place." (Winters

et al., 1988) The stiffness of a joint is determined by the passive (viscoelastic),

intrinsic (contractile), and reflex components of it's surrounding muscles. Evidence for

this separation comes from the fact that significant increases in joint stiffness have been

shown to accompany a hyperactive stretch reflex (Sinkjaer and Magnussen, 1994) as

w e U as the fact that increases in intrinsic stiffness by co-activation of antagonistic

muscles have been shown to increase joint stiffness (Winters et al., 1988). In this

manner, the level of contraction of antagonistic muscles and the stretch reflex have the

ability to alter ankle joint stabiUty and directly affect the ability of the joint to resist

perturbation.

Postural Stability

A human body in quiet, upright stance can be modeUed as an inverted segmental

pendulum whose centre of mass is free to sway in a variety of directions (Morasso and

Schieppati, 1999). A s the body sways, somatosensory, visual, and vestibular

information from sensory receptors detect variations in body position (centre of mass)

and help eUcit muscular responses from postural muscles to maintain postural stabiUty

(Dietz, 1992). EquiUbrium of the inverted segmental pendulum is disturbed when the

line of action of the centre of mass faUs outside the base of support. (The base of

support is defined as the area under, and between the feet,) A return to stabiUty after the

centre of gravity is disturbed reUes on the ground reaction force generated by an

involuntary muscular response (postural activity). The success of this postural activity

to returning stabiUty to the body is determined by two factors; the degree to which the

13

line of action for the centre of mass is displaced and whether it breaks the boundaries

defined by the base of support and whether the dynamics of the muscular response can

provide a sufficient ground reaction force to return the system to equiUbrium (Enoka,

1994).

Wobble Board Training Challenges System Stability

In order to investigate the neuromuscular adaptations of the ankle joint that

result after wobble board training, an understanding of how wobble board training

challenges the ankle joint complex is essential. As seen in Figure 2.4, wobble board

training provides a unique challenge to the neuromuscular system, which can be divided

into two tasks. One is to maintain postural stabiUty on a decreased base of support, and

the other is to maintain position control of the wobble board deck using the ankle

musculature. Each of these tasks may cause an increase in co-contraction of the ankle

musculature and a decrease in the magnitude and apparent strength of the stretch reflex

in an attempt to stabilize the ankle joint complex (LleweUyn et al., 1990). Both of these

neuromuscular mechanisms wiU now be examined.

Figure 2.4 A n individual balancing on a wobble board.

Postural Stability Challenge

The use of co-contraction as a stabilization strategy, when a joint is subject to an

unstable load, has been reported by several authors (Akazawa et al., 1983; Hogan, 1984;

LleweUyn et al., 1990; D e Serres and Milner, 1991; Crone and Nielsen, 1994; Voigt et

al., 1998). If the centre of mass of the body is equated to an unstable load around the

ankle joint, paraUels can be drawn between balancing on a wobble board and the tasks

reported in this. O f these, only LleweUyn and coUeagues have assessed contraction

14

patterns of the ankle musculature when postural stabiUty is chaUenged by a decrease in

the base of support. They noted that the "normal reciprocal activation pattern of tibialis

anterior and S O L muscles in treadmill walking was replaced by a partem dorninated by

co-contraction whUe beam walking'' (LleweUyn et al., 1990). This change in muscle

strategy was suggested to be a result of the increased instability inherent in beam

walking due to the decreased base of support, especially in the medio-lateral plane

(Llewellyn et al., 1990). Although this co-contraction observation was made during

walking, it can be assumed that the task of balancing on a wobble board also requires a

significant increase in agonist-antagonist co-contraction due to the decreased base of

support offered by the wobble board.

Ankle Joint Stability Challenge

It has been noted that one of the conditions favouring co-contraction involves

the precise control of limb position under load (Smith, 1981; Colebatch and McCloskey,

1987; D e Serres and Milner, 1991; Doemges and Rack, 1992; Buchanan and Lloyd,

1995). Maintaining a horizontal deck position on the wobble board is a fairly precise

position control task and the ankle joint is under load from the weight of the body

during this task. It is expected that the position control task to maintain the wobble

board deck in a horizontal plane will increase the level of co-contraction in the ankle

joint. Therefore, the overall intrinsic contribution to ankle joint stabiUty while standing

on a wobble board results from a combination of co-contraction to maintain postural

stabiUty whUe standing on a decreased base of support and co-contraction to maintain

horizontal position control of the wobble board deck.

It has been suggested that the ankle musculature are required to co-contract

when the position control task of maintaining the wobble board deck in a horizontal

plane is introduced (Doemges and Rack, 1992; Buchanan and Lloyd, 1995). W h e n the

centre of mass is displaced during this position control task, a deck tilt perturbation is

given to the ankle which can result in anywhere from 1-7 degrees of stretch to the

muscles of the ankle. With various degrees of muscular stretch, an involuntary stretch

reflex involving contraction of the stretched muscle is elicited to return the deck (and

the ankle) back to the desired horizontal position. Thus afferent sensory information

may play an important role in maintaining balance on a wobble board, the contribution

of which wiU be discussed in the next section.

15

T h e Proprioceptive System

Sensory information is used to determine the muscular coordination strategy for

a particular task and stimulate segmental reflexes (Lephart, 1997; Lephart et al., 1998).

In this manner, the proprioceptive system plays an important role in determining the

level of ankle joint stabiUty by regulating the intrinsic and reflex components of

musculoskeletal impedance.

Role of Proprioceptors

The perception and execution of musculoskeletal movement is regulated by the

C N S and depends on the contribution of afferent sensory input from 3 main subsystems:

the somatosensory system, the visual system and the vestibular system (Lephart, 1997).

The somatosensory system detects both sensory stimuli elicited by the environment and

sensory stimuli from internaUy generated movements (Lephart et al., 1998). This

section is particularly concerned with how the body uses somatosensory information to

determine an appropriate muscular response for a particular task and stimulate

segmental reflexes.

Sensory receptors distributed throughout the body generate afferent sensory

information, which is relayed to the central nervous system (CNS) by action potentials.

These receptors are referred to as mechanoreceptors and provide feedback about the

body's o w n geometry and ifs surrounding environment (Lephart, 1997).

Mechanoreceptors are classified into proprioceptors and exteroceptors. Proprioceptors

consist of muscle spindles, cutaneous (skin) receptors, tendon organs, and joint

receptors and provide feedback generated by the body itself, regardless of whether this

movement is internaUy or externaUy generated (Lephart et al., 1998). Exteroceptors on

the other hand provide feedback generated by external stimuli and include cutaneous

receptors, visual, auditory and vestibular inputs (Enoka, 1994).

Afferent information from proprioceptors plays many roles in all owing the body

to interact with its surroundings and is essential for several levels of motor control

including segmental spinal reflexes, brainstem reflexes, long loop reflexes and

voluntary movements (Lephart, 1997). Proprioceptor generated feedback plays an

important role in defining the geometry of the human multijoint system in space. This

sense is termed proprioception and includes both position and movement sense (Enoka,

1994). Proprioception information is used in a feed forward manner as a frame of

reference for the generation of an appropriate motor command for the completion of a

16

specific task. In addition, proprioceptor feedback aUows the cerebeUum to compare the

actual limb position to the desired limb position, and plan a corrective motor response

(RothweU, 1994). Joint displacement is another way to stimulate proprioceptors and

results in a rapid reflex response to the perturbation in homonymous, synergistic and

opposing muscles (RothweU, 1994).

Proprioceptors and Muscle Coordination for a Specific Task

The C N S can utilize several different contraction strategies to accomplish a

specific goal directed movement. Proprioceptors and the parameters of the desired task

determine the selection of the correct contraction strategy (GottUeb, 2000). For

example, Figure 2.5 (bottom) shows the E M G activity for the biceps and triceps during

two different types of movements. Both movements begin with the arm in a 140-degree

position and have the subject flex quickly in the horizontal plane towards a target at 100

degrees. The duration of movement was 300ms. The heavy dashed line illustrates a

fast flexion in which the subject was to stop and point at a target. The thin, solid line

shows a reversal movement in which flexion to the same target was immediately

foUowed by a rapid extension of the forearm to the starting point. Figure 2.5 (top)

represents the acceleration and angle data for each movement In the interval bounded

by the two dotted vertical lines, the joint torque and kinematic data is the same, but the

flexor and extensor muscle E M G patterns are significantly different from one another.

Significant co-contraction of the two muscles is evident in this interval during the

pointing movement, whereas, reciprocal activation is evident in the reversal movement.

Reciprocal coordination results in the generation of torque about a joint and

involves contraction of the agonist and inhibition of the antagonist. The main purpose

of this contraction strategy is to maximize the efficiency of movement (GottUeb, 2000).

The goal of the fast reversal movement in Figure 2.5 was to move to a target and return

to the starting point as fast as possible. These parameters made reciprocal activation the

desired muscle coordination strategy for the completion of the task (GottUeb, 2000).

Co-contraction results in an increase in the stiffness of a joint and involves the

simultaneous contraction of agonist and antagonist muscles. The main purpose of this

contraction strategy is to improve the stabiUty of a joint; however, the net efficiency of

the intended movement suffers however. The goal of the fast flexion movement was to

point at the target as quickly and precisely as possible. These parameters made co-

contraction the desired muscle coordination strategy for the completion of the task

(GottUeb, 2000).

17

Figure 2.5 E M G and Kinematic data from the flexors and extensors of the

forearm during a pointing movement (heavy dashed line) and a reversal

movement (thin solid line) (modified from Gottlieb, 2000).

The body is able to utilize many other types of contraction strategies to

accomplish a goal directed movement such as activation of 2 joint muscles and

synergistic muscles (Prilutsky, 2000). The situation wiU be general ized however, so

that for a specific goal directed movement, the body is constantly attempting to find the

best combination of efficiency and stabiUty to complete the desired task. This means

the body constantly regulates the level of co-contraction and reciprocal coonlination to

complete a task depending on the parameters of the movement (GottUeb, 2000).

The next question that arises is whether or not the decision for the contribution

of each of these contraction strategies to a particular movement is reflexive or

voluntary? But what do reflex and voluntary mean? A recent article by Prochazka et al.

(2000) states that most movements of daily life are neither purely reflexive, nor purely

voluntary but fall somewhere along a continuum between these two extremes. During

repetitive movements, the body's abiUty to detect and rank cutaneous proprioceptive

inputs is reduced. For example in routine locomotion static fusimotor drive reduces the

responsiveness of spindles. However, fusimotor drive is increased in novel or difficult

voluntary motor tasks. It has been hypothesized that this modulation in fusimotor drive

as movements shift back and forth along the reflex-voluntary continuum provides

evidence of the biphasic nature of the motor control system (Prochazka et al., 2000).

From this evidence, it can be seen h o w the proprioceptive system plays an important

role in regulating the contraction strategy of muscles surrounding a joint However, the

input from the proprioceptive system is determined by the parameters of the given

18

movement Therefore for a given goal directed movement, muscle length, force, joint

angle and torque as weU as more ambiguous factors such as stabiUty, fatigue and

comfort aU help to determine the pattern and degree to which muscles are reflexively or

voluntarily activated (GottUeb, 2000).

Proprioceptors and the Stretch Reflex Response

Reflexes are a stereotyped motor response of an organism to a sensory stimulus.

The neural circuitry underlying a simple reflex is iUustrated in Figure 2.6 and involves a

sensory receptor, its afferent innervation and a short latency connection with a group of

motor units. The main function of the stretch reflex is to provide the body a quick,

efficient muscular response to a perturbation (Enoka, 1994). Figure 2.7 iUustrates a

typical stretch reflex in tibialis anterior. Stretch of the muscle was appUed at the zero

second mark and a dramatic increase in E M G was recorded prior to the onset of

voluntary contraction

Motor neuron

Sensory Neuron

Renshaw CeU

Stretch

Figure 2.6 The neural circuit of a stretch reflex (modified from RothweU, 1994).

Time (ms)

Figure 2.7 E M G from soleus after stretch illustrating the short latency (Ml),

medium latency (M2) and long latency (M3) responses.

19

(220ms). The stretch reflex usually consists of at least two components. The short

latency (Ml in Figure 2.7) response is thought to involve a monosynaptic neural

pathway that is hardwired to the spinal cord. The medium latency (M2 in Figure 2.7)

response is thought to have a more complex origin and may involve higher brain centers

such as the motor cortex (Thihnann et al., 1991). A third stretch reflex component (M3

in Figure 2.7) is occasionally observed. The morphology of the various components of

the stretch reflex may vary, but in general, the onset time for the M l response is 30ms,

the M 2 response begins at about 60ms and the M 3 response starts at 100ms (Enoka,

1994).

The main sensory receptor involved in the stretch reflex is the muscle spindle.

Muscle spindles Ue in between muscle fibers and transmit information on the rate of

change of muscle length back to the C N S (Enoka, 1994). The equatorial region of a

muscle spindle contains the ceU's nuclei, which are arranged in either a cluster or a

chain formation (RothweU, 1994). This central region is devoid of contractile fibers, as

opposed to the poles, which have many contractile elements. Large Group la afferents

spiral around the equatorial region of aU muscle spindles and the smaller Group II

afferents mainly connect to the nuclear chain fibers. W h e n a muscle is stretched, group

la afferents are deformed (Lephart, 1997). This deformation causes an action potential

to be transmitted to several ascending pathways as weU as to the spinal cord, where la

fibers synapse on a motor neuron. The signal is then sent back to the homonymous

muscle and results in a muscular contraction. Beta and G a m m a motor neurons contact

the myofilament-rich polar regions of aU muscle spindles. This aUows muscle spindles

to adjust their sensitivity by contracting and stretching their equatorial region (Lephart,

1997).

Co-contraction and Reflex Stabilization

StabiUty training on a wobble board can be divided into two main tasks;

maintaining control of the center of mass on a decreased base of support and

maintaining position control of the wobble board deck during perturbations. It has been

suggested that these two tasks eUcit a co-contraction response from the ankle, and

repetitively stimulate the stretch reflex under a state of muscular co-contraction. The

following section wiU look at the adaptabiUty of the stretch reflex, the co-contraction

response, and the modulation of the stretch reflex that occurs during varying levels of

co-contraction.

20

Adaptability of the Stretch Reflex

The stretch reflex is a short latency contractile response of a muscle due to an

unexpected stretch. Figure 2.6 shows the neural circuit that is responsible for the

generation of this muscular response. A n important feature to note is the involvement

of the Renshaw CeU in this circuit The addition of this ceU into the neural pathway

aUows a variety of inputs to modify the morphology of the stretch reflex response. The

Renshaw CeU can be activated by supraspinal input cutaneous and joint receptors and

by a coUateral branch of the alpha motor neuron axon (RothweU, 1994). For example,

the circuit involving the Renshaw ceU and the coUateral axon of the motomeuron is

called recurrent inhibition. Activation of recurrent inhibition is distributed to many

other motor neurons and results in a decrease in the excitabiUty of those motor neurons

(Enoka, 1994).

The Renshaw ceU only represents part of the highly complex, adaptive nature of

the stretch reflex. Unexpected stretch of a muscle can trigger input from many

receptors including tendon organs and Group II afferents (Lephart, 1997). This barrage

of afferent information can significantly modify the morphology of the stretch reflex

response through what is known as presynaptic inhibition (Nielsen and Kagamihara,

1993). If an interneuron synapses on the afferent la axon close to where it contacts the

motor neuron, afferent input through this interneuron has the potential to inhibit the

action potential in the la axon before it is transmitted to the motor neuron (Nielsen and

Kagamihara, 1993).

The Co-contraction Response

During certain voluntary tasks or environmental situations, the C N S utilizes

antagonistic co-contraction to stabilize a joint Co-contraction can occur during a

motor task when limb position must be precisely controUed, with (Colebatch and

McCloskey, 1987; Doemges and Rack, 1992; Buchanan and Lloyd, 1995) and without

load (Smith, 1981). Co-contraction can also occur when it is important to prevent

external mechanical perturbations, such as when the stabiUty of a joint is challenged due

to an unstable load (Akazawa et al., 1983; Hogan, 1984; LleweUyn et al., 1990; D e

Serres and Milner, 1991)

Three levels of the C N S are thought to control the co-contraction response of

antagonistic muscles. First segmental spinal reflex co-contraction can be induced by

varus - valgus perturbations to the knee and are thought to be a result of stimulation to

21

Ugament and/or capsular proprioceptors (Kim et al., 1995; Buchanan et al., 1996).

Second, involuntary (unconscious) co-contraction occurs to stabilize the joint during

cUffkult motor tasks such as beam walking (LleweUyn et al., 1990), during the learning

phase of a novel task (Smith, 1981), or to support an unstable load (De Serres and

Milner, 1991). The cerebeUum is thought to control this unconscious (x>-contraction

pattern by increasing and decreasing the firing of Purkinje cells in the posterior part of

the anterior lobe (Humphrey and Reed, 1983; RothweU, 1994). Tasks i^uiring

reciprocal muscle activation are associated with an increase in Purkinje ceU firing,

where as co-contraction of antagonistic muscles is associated with a 7 0 % decrease in

Purkinje ceU firing. Third, the co-contraction response is also under voluntary control

such as when an individual consciously resists an imposed joint movement by

contracting mechanically opposing muscles and stiffening that joint.

Acute Adaptations to the Stretch Reflex during Co-contraction

Net joint stiffness is a summation of passive (viscoelastic), mtrinsic (contractile)

and stretch reflex components of contracting muscles . Co-contraction stabilizes a joint

by increasing the intrinsic muscular stiffness of mechanically opposing muscles. In

addition, Toft et al. (1991) has shown that the stimulation of a stretch reflex in a

contracting muscle has the potential to significantly alter the contraction strength of that

individual muscle. Together, these findings suggest that if a large stretch reflex occurs

in a muscle that is co-contracted with it's antagonistic muscle, the joint these co-

contracting muscles are stabilizing wiU become destabilized (LleweUyn et al., 1990).

Therefore, the body must have some mechanism to decrease the ampUtude of the stretch

reflex during co-contraction in order to protect a co-contracting joint from

destabilization.

The reduction in the ampUtude of the stretch reflex during tight to moderate co-

contraction has been documented by several authors. For example, LleweUyn et al.

(1990) noted an increase in tibiaUs anterior and soleus co-contraction and a

corresponding decrease in the soleus H-reflex during beam walking versus tteadmiU

walking. Nielsen et al. (1994) ensured that the E M G level in the soleus muscle was the

same during co-contraction and isolated plantarflexion. It was observed that the stretch

reflex was decreased during weak co-contraction compared to isolated plantarflexion in

the soleus muscle at matched background E M G levels. The mechanisms behind the

observed suppression in the stretch reflex during co-amtraction are beUeved to include

presynaptic inhibition (Nielsen and Kagamihara, 1993; Trimble and Koceja, 1994;

22

Lloyd, 2001), inhibition via Renshaw cells (Carter et al., 1993), or a combination of

both. Due to the overwhelming support in the Uterature, presynaptic inhibition wiU be

adopted by this author as the mechanism to explain the reduction in the stretch reflex

ampUtude during co-contraction of antagonistic muscles.

Interneurons mediating presynaptic inhibition have been shown to be controlled

by several descending inhibitory pathways as weU as by flexor la and lib afferents in

man (Baldissera et al., 1981; Hultborn et al., 1987). From this evidence it has been

suggested that both central and peripheral pathways are involved in the regulation of

presynaptic inhibition of la sensory afferents (Nielsen and Kagamihara, 1993).

However, during voluntary movement suppression of the H reflex was found to occur

during both the preparatory phase and the contraction phase of movement (Nielsen and

Kagamihara, 1993). Since no peripheral feedback could have occurred prior to

movement, the changes observed in the H-reflex during this time by Nielsen and

Kagamihara (1993) could only have been caused by central control of the intemeurons

involved in the presynaptic inhibition. Therefore, the contribution from a central

pathway is the most likely source of presynaptic inhibition seen during voluntary

movements such as co-contraction of antagonistic muscles in man and may suggest that

a specific co-contraction motor command exists (LleweUyn et al., 1990; Nielsen and

Kagarnihara, 1993; Trimble andKoceja, 1994).

03

02 Reflex

Amplitude (milli-volts) 0.1

0.0 I i I ' » ; i i

0 5 10 15 20 25 30 35

Background Soleus E M G

Figure 2.8 Amplitude of the stretch reflex in the soleus muscle during various

levels of co-contraction and plantar flexion (modified from Nielsen,

1994).

Plantar flexion Co-contraction

I ?

T T I ? <> 6 o f 1 I

I - 0

-?"f _ Rest

23

It is important to note the nonUnear fashion in which reflexes contribute to the

overati stiffness of a joint Figure 2.8 shows the observations made by Nielsen et al.

(1994), that the stretch reflex response of the soleus muscle in some subjects was

smaller during weak co-contraction than isolated plantarflexion at matched background

E M G levels. However, during high co-contraction levels, the stretch reflex in the soleus

muscle was found to be higher than that observed during isolated plantar flexion at

matched background E M G levels. (It must be kept in mind whUe this graph is analyzed

that the absolute magnitude of the reflex ampUtude is not of concern here. The reader

should focus on the increase or decrease in reflex amplitude of the ̂ -contracting soleus

muscle when compared to an equivalent plantar flexion task.) Considering that the

mechanical effect of the stretch reflex is larger during weak contractions (Toft et al.,

1991) and that a single stretch reflex in a muscle that is co-contracted with it's

antagonistic muscle can destabilize that co-contracted joint (LleweUyn et al., 1990) a

decrease in the stretch reflex during low co-contraction levels could be seen as

beneficial to joint stabiUty. In fact LleweUyn et al. (1990) suggested the balance of a

subject could be threatened if a large reflex discharge of an individual ankle muscle

occurred whUe co-contraction of the ankle joint was being used to stabilize die body on

a decreased base of support (beam walking) It can be assumed that during strong co-

contraction, the intrinsic muscle stiffness contribution to joint stabiUty is high and a

sudden reflex discharge has less potential to destabilize die joint than at low co-

contraction levels. It is therefore less imperative for the body to suppress the

monosynaptic stretch reflex to maintain joint stabiUty in a state of strong co-contraction.

Chronic Neural Adaptations to Muscle Recruitment and Reflexes

It has been suggested in this thesis that wobble board training employs 2 tasks;

to maintain the center of mass inside a reduced base of support and to maintain position

control of the wobble board deck. The reviewed Uterature has shown that the body

increases the co-contraction response of the ankle musculature in an attempt to stabilize

the ankle joint during these two tasks (Smith, 1981; LleweUyn et al., 1990). In addition,

recent evidence has suggested that the body actively decreases the ampUtude of the

stretch reflex during co-contraction to ensure the stabiUty of a co-contracting joint

(LleweUyn et al., 1990; Nielsen et al., 1993; Nielsen and Kagamihara, 1993).

From this line of evidence, the question arises as to whether the neuromuscular

mechanisms underlying the reduction in ankle sprain injuries after wobble board

training involves an increase in agonist-antagonist co-contraction and decrease in the

24

stretch reflex ampUtude of the ankle musculature. In order to further explore this

possibiUty, an analysis of the abitity of agonist-antagonist co-contraction and the stretch

reflex ampUtude to adapt to environmental stress wiU be undertaken.

Principles of Training

W h e n the neuromuscular system is chall enged through a training regime,

adaptations result. The adaptations that occur directly relate to two important principles

of training, the overload principle and the specificity principle (Enoka, 1994). The

overload principle suggests that there is a threshold (percent maximum for force

production) that must be exceeded before an adaptive response wiU occur. The

specificity principle suggests that the training adaptations that result are specific to the

system that is overloaded.

Chronic Adaptations to Muscle Recruitment

The co-contraction response involves simultaneous activation of antagonistic

muscles and results in an increase in the stiffness of a joint. This muscle recruitment

strategy is used when a task requires precision or during a novel exploratory task, when

the stabiUty of a joint is challenged and when a movement is strong and rapid. The co-

contraction response can be seen as inhibitory to the generation of torque around a joint

because it decreases the efficiency of the muscle contribution to uniplanar, isotonic

movements (Enoka, 1997). However, co-contraction is beneficial to joint stabiUty due

to the increase in joint stiffness it provides (Smith, 1981). For a specific movement the

body must determine whether efficiency or stabiUty is the most important aspect for the

completion of a specific task and regulate the co-contraction response accordingly. Is it

possible then, to adapt the co-contraction response through a specific training program

to optimize the co-contraction strategy for task involving either torque generation or

joint stabiUty?

Carolan and CafarelU (1992) conducted a novel study providing convincing

evidence that strength training improves torque generation by altering the co-contraction

strategy of mechanicaUy opposing muscles. After only 1 week of isometric resistance

training, an increase in the strength of the knee extensors was associated with a 20 %

reduction in hamstring co-contraction (Carolan and CafarelU, 1992).

N o Uterature could be located that evaluated adaptations in the co-contraction

response after stabiUty training. The large void that exists in relation to this topic was

25

very surprising. However, unpublished observations suggest that wobble board training

results in a 2 0 % increase in the co-contraction ratio to stabilize the knee during cutting

manoeuvres (Besier et al., 1999). It has been hypothesized that stabiUty training on a

wobble board challenges the co-contraction response of the ankle musculature through

both deck position control and postural control tasks. A s suggested by the specificity

principle, adaptations of the neuromuscular system are specific to the part of the body

that is overloaded. This author suggests that stabiUty training on a wobble board wiU

result in an increase in the co-contraction ratio of the ankle musculature when a subject

performs a novel ankle task.

Chronic Adaptations to the Stretch Reflex

The stretch reflex is a short latency contractile response of a muscle due to an

unexpected stretch. Depending on the level of contraction, the stretch reflex has the

abitity to generate mechanicaUy significant amounts of torque in the muscles

surrounding a joint (Toft et al., 1991). It has even been suggested that a large stretch

reflex has the abiUty to destabilize a joint stabilized by low levels of co-contraction

(LleweUyn et al., 1990). Therefore, an increase in the stretch reflex excitabiUty could

aid the generation of torque about a joint and a decrease in the stretch reflex excitabiUty

could improve joint stabiUty. Adaptations in the stretch reflex response after stabiUty

training have been sparsely reported in contrast to the wealth of Uterature available on

changes to the excitabiUty of stretch reflexes after strength training.

Most of the studies that analyzed the adaptations of the stretch reflex to strength

training have used potentiation ratios, and H-reflexes to compare pre and post training

motomeuron and reflex excitabiUty. The general consensus in the Uterature is that

strength training results in an increase in the reflex potentiation ratio and therefore, an

increase in stretch reflex excitabiUty (Sale et al., 1983; Sale, 1988; Enoka, 1997).

Potentiation ratios express the E M G response to supramaximal nerve stimulation at rest

as a fraction of the response during voluntary contraction (Sale, 1988). This method has

the potential to indicate the fraction of the motomeuron pool participating in an E M G

response.

Several mechanisms have been impUcated as the source of this reflex

potentiation including changes in the pattern of motor unit recruitment. A n increase in

the number of activated motor units would aUow a larger number of motorneurons to

participate in the reflex response. A n increase in the discharge rate of motor units has

been observed in strength trained individuals and would aUow a higher degree of

26

contraction to occur for a specific reflex response. In addition, an alteration in motor

unit discharge pattern such as increased synchronization could result in reflex

potentiation and has been implicated as the source of the muscular specific changes that

result in an increase in strength (Sale et al., 1983; Sale, 1988; Enoka, 1997).

O f particular interest to this study, though, is the possibitity that the increase in

reflex potentiation seen in weight training is the result of chronic adaptations to afferent

fibers, interneurons, and motoneurons. Adaptations in afferent fibers or interneurons

would result in a stronger excitation of motorneurons. Adaptations in motomeurons

could make them easier to excite. Both hypotheses have been tested at rest pre and post

strength training through H-reflexes and shown no changes in either condition (Sale et

al., 1983; Sale, 1988; Enoka, 1997). From these findings, it has been concluded that

changes in motomeuron excitabiUty result in the observed changes in the stretch and H-

reflex amplitude with strength training.

Only 4 studies were found that analyzed chronic adaptations in the stretch reflex

response of the ankle musculature after various types of stabiUty training involving a

decrease in the base of support such as wobble board training or dancing (Nielsen et al.,

1993; Trimble and Koceja, 1994; Mynark and Koceja, 1997; Voigt et al., 1998). Each

of the 4 studies used the H-reflex technique to evaluate the stretch reflex, and found a

significant decrease in the H-reflex response between stabiUty trained individuals and

controls. It should be emphasized again here, that the H-reflex tests the excitabiUty of

the motomeuron pool from the la monosynaptic pathway, whereas the muscle stretch

reflex tests the whole la monosynaptic pathway including spindle sensitivity (LleweUyn

et al., 1990; Nielsen and Kagamihara, 1992). For example, Trimble and Koceja (1994)

found that after seven blocks of balancing trials, subjects were able to reduce the gain of

their standing H-reflexes by 26.2%. N o studies could be located that analyzed the

stretch reflex response after stability training.

A s suggested by the specificity principle, adaptations from training relate

directly to h o w the training regime challenges the neuromuscular system. Evidence has

been provided in this section that indicates resistance (strength) training results in an

increase in the stretch reflex ampUtude in a co-contracting joint (Sale et al., 1983; Sale,

1988; Enoka, 1997) and stabiUty training has the potential to decrease the stretch reflex

amplitude in a co-contracting joint (Nielsen et al., 1993; Trimble and Koceja, 1994;

Mynark and Koceja, 1997; Voigt et al., 1998). Ibis author has hypothesized that

balancing on a wobble board increases the agonist-antagonist co-contraction of the

ankle musculature which results in a decrease in the stretch reflex in these co-

27

contracting ankle muscles. It can further be hypothesized that an elongated period of

stabiUty training on a wobble board wiU result in a long term adaptation in the stretch

reflex ampUtude of the ankle muscles.

28

CHAPTER 3- METHODS AND PROCEDURES

Experimental Approach

A n ankle perturbation rig and associated data coUection software were used in

this thesis (Skoss et al., 1999) to evaluate the training adaptations of the ankle

musculature. Position control of the footplate in a stable (1 D O F ) and unstable (3 D O F )

condition were the experimental tasks employed on the ankle perturbation rig. These

conditions were chosen because of the different levels of co-contraction they induced in

the muscles surrounding the ankle during pUot studies. The experimental tasks were

performed under different levels of plantarflexion torque. Dorsiflexing perturbations

were appUed to the baU of the foot via a pneumatic R A M in the various 1 and 3 D O F

conditions when the position and force parameters for that task were met.

E M G was measured from five major muscles crossing the left ankle joint to

evaluate the adaptations in the morphology of the stretch reflex response and the

changes in muscle activation patterns used to perform the 1 and 3 D O F tasks post

stabiUty training. To aid processing and analysis of aU E M G data the author designed

two L A B V I E W programs (See Appendix H-K for L A B V I E W diagrams).

Subject's abiUty to maintain a wobble board as flat as possible, without touching

the edges to the floor was used to determine an index of improvement (See Appendix F

and G for Evaluation of Performance).

Subjects

Eight experimental and eight control subjects (9 male and 7 female) with no

prior history of lower limb injury volunteered for this investigation. The sixteen

recruited subjects were divided randomly into a control group and an experimental

group with no regard to gender. Sufficient power was expected from this subject pool

based on prior Uterature by Sheth and coUeagues (1997) in which they randomly

divided 10 m e n and 10 w o m e n into a control group and an experimental group. High

skin impedance caused one control and one experimental subject to be discarded,

leaving 8 males and 6 females. Subjects were aU moderately trained, healthy University

students between the ages of 20 and 30. Only moderately trained individuals were

chosen because this population represents the largest potential for training adaptations.

Subjects were taken through a training protocol and informed consent was obtained

prior to data coUection along with an evaluation of their history of physical activity (See

Appendix A and C for Consent Form and Selection Criteria).

Experimental Design

Each subject was tested twice in the neuromuscular lab on an ankle perturbation

rig in the various 1 and 3 D O F tasks. Pre and post testing sessions for aU subjects were

separated by a period of three weeks (See Appendix D for Timetable). During this

period, the experimental group participated in a total of 10 training sessions lasting 20

minutes each and the control group was asked to maintain their normal datiy activities.

Training sessions commenced on the Monday, Wednesday and Friday of each week and

the experimenter supervised each session to ensure that the training subjects compUed

1 0 0 % with the stabiUty training regime. The total duration, timing of training sessions

and length of each session corresponded to suggestions made in the current Uterature

(Enoka, 1997; Rozzi et al., 1999) and were chosen to maximize the potential neural

adaptations that could take place in a minimal amount of time. Control subjects were

asked to maintain their usual level of datiy activity and to avoid any stabiUty training

exercises for the duration of the testing and training timetable outlined in Appendix D.

During the training regime, subjects were required to touch the edge of the

wobble board to the ground in a controUed fashion 20 times in several different 1 and 2

foot balancing positions of various degrees of difficulty (See Appendix E for complete

StabiUty Training Regime). The training regime combined aspects of several wobble

board training regimes reported in the Uterature including controUed side to side and

front to back movements (Wester et al., 1996), a progressive reduction in stability and

increased difficulty during individual training sessions (Cerulti et al., 2001) as weU as

perturbations to induce reflex responses in the ankle muscles (Fitzgerald et al., 2000). It

was thought that these exercises would maximize the level of co-contraction

experienced by the ankle joint and induce a reflex response while the ankle muscles

were in a state of co-contraction.

The day prior to pre testing, aU subjects completed a 30-minute training session

in an attempt to familiarize the subjects with the testing procedures and reduce any

training effects that might result from repeated trials and testing sessions on the ankle

perturbation rig. B y the end of the training session, aU subjects were able to perform the

most difficult 3 D O F task in five seconds or less.

Prior to testing the subjects left foot was cast into a special mould. During

testing subjects lay prone on the ankle perturbation rig and their left foot was mounted

30

Figure 3J1 The experimental environment

to the rig. Figure 3.1 illustrates the experimental environment that was used for each

testing session. The eight experimental tasks involved plantar torque at 0%, 15%, 2 5 %

and 4 0 % of each subject's maximum plantar torque force in a 1 and 3 D O F condition.

The maximum plantar torque values in the 1 and 3 D O F amdrtions used for each testing

session were recorded at the beginning of both the pre-testing and post-testing sessions

for each subject In addition to these force control tasks, subjects were required to

maintain three d_D__donal position control of their foot W h e n both the force and

position control requirements were met for a given task the experimenter triggered a

ckxsiflexmg perturbation. Five perturbations were gh en in each of the eight

experimental tasks and each trial was separated by a 30-secood interval to reduce the

effects of fatigue. Subjects were instructed not to react to the pertuibation and to relax

immediately after it cwcurred.

It has been hypothesized that a slight increase in the co-contraction level around

the ankle prior to heel contact would increase joint stiffness at the time of heel contact,

irKxeasing the time from ankle pertmbation to Ugament injury (Konradsen et aL, 1997).

A stable (1 D O F ) and unstable (3 D O F ) task were chosen because of the dramatic

increase in muscular co-contraction that has been noted in the Uterature when a joint is

subject to an unstable toad (De Serres and MUner, 1991). It was decided that an

analysis of any adaptations in the co-contraction response of die ankle joint from

31

stabiUty training would include both the stable (1 D O F ) and unstable (3 D O F )

conditions on the ankle perturbation rig.

It has been hypothesized that a stretch reflex has the potential to destabilize a co-

contracting joint (LleweUyn et al., 1990), causing die joint to be more prone to injury.

The plantar torque values of 0%, 15%, 2 5 % and 4 0 % were chosen because of the

observations by Nielsen and Sinkjaer (1994) that a decrease in the stretch reflex

response of soleus occurred during weak co-contraction, but no suppression occurred

during high co-contraction levels. It has been hypothesized that during strong co-

contraction, the intrinsic muscle stiffness contribution to joint stabiUty is high and a

sudden reflex discharge has less potential to destabilize a joint than at low co-

contraction levels (LleweUyn et al., 1990). It was decided that the 1 5 % and 2 5 % tasks

presented die greatest potential to see any adaptations in the morphology of the stretch

reflex due to stabiUty training.

Experimental Apparatus

A n ankle perturbation rig and a visual target matching display were used to

achieve the desired force and position control tasks of the ankle.

Figure 3.2 illustrates the ankle perturbation rig used in this study. Three

mechanical arms, incorporating nine potentiometers (three potentiometers per arm) were

attached to a footplate and returned position data of the footplate in the horizontal,

vertical and lateral planes of motion. A Kistler force transducer under the ball of the

foot returned force data in the X, Y and Z directions. In addition, the footplate was

mounted to a pneumatic R A M , which was propeUed by compressed air. A switch was

attached to the R A M and could be triggered by the experimenter at any time. The entire

rig was rigidly mounted to a bed, which allowed the subject to Ue prone whUe their left

foot was secured to the rig.

Figure 3 _ The ankle perturbation rig.

The target matching display shown in Figure 3.3 was designed in LAB VIEW

and run on a P C computer, with the monitor placed in front of the subject The force

displayed by the target-matching program was calculated using the X, Y and Z forces

appUed to the footplate. The target-matching program was able to record the peak force

exerted by the subject on the force plate. After the subjects maximum force in a

condition was entered, the bar at the bottom of the screen indicated the percent of

maximum torque that was subsequently applied to the footplate. The target-niatehing

program represented the position of the footplate in space as a yeUow triangle and the

target was a red triangle. Plantarflexion and dorsiflexion moved the yeUow triangle up

and down respectfully, abduction and adduction moved the triangle right and left and

inversion and eversion rotated the triangle clockwise and counterclockwise.

Figure 3 3 The target-matching display.

33

M a n y factors ensured that the ankle perturbation rig could detiver a repeatable set of

stimulus and induce similar biomechanical motion in the ankle joint during post testing

and pre testing sessions. Prior to perturbation, the target matehing display and casting

of the foot into the rig resulted in the subject repeatedly placing his foot and heel in the

identical position. This allowed the length of the muscles to be the same prior to

perturbation. The force transducer under the baU of the foot atiowed the subject to

apply an identical percent of maximum voluntary contraction (in the 3 D O F condition)

to the footplate. This resulted in a similar level of muscular contraction in each of the 5

superficial muscles of the ankle prior to perturbation during both pre and post testing

sessions and facilitated the comparison of these values. During the perturbation, sintilar

motion of the ankle joint during both pre and post testing was ensured by a strap that

secured the subject's leg to the table just above the knee and by the casting of the foot

onto the footplate of the rig. In addition, R A M movement was identical in every

perturbation and was very strong, covering a total distance of 30 millimetres in 0.67

m/sec, reducing the likelihood that musculoskeletal impedance would affect ankle joint

motion. The R A M displacement was then held for 1.2 seconds before being returned to

its original position. These precautions ensured that the ankle joint biomechanics and

the contraction strategy of the 5 superficial muscles of the ankle prior to and during the

perturbation were identical. In addition, it has been noted in a previous study using the

same ankle perturbation rig that: "The kinematics of the dorsi-flexion perturbation was

highly repeatable between and within ID and 3 D conditions and between and within

torque levels. There was no variation between reflex responses in the 3 D condition

when the perturbation was appUed mid line of the foot and 1 0 m m medial and lateral of

the mid line. The kinematics of inversion/eversion and adduction/abduction of the

ankle were highly repeatable and similar in the first 15ms of perturbation, thus the

monosynaptic response at about 30-40 m s would not have been modulated (Skoss,

2002)."

Data Collection

Rig Force and Position Data

Force data was collected in the X, Y and Z directions by a Kistler force plate

that was mounted under the baU of the foot. Position data of the footplate in the

horizontal, vertical and lateral directions was coUected by nine potentiometers

incorporated into three movable arms (three potentiometers per arm).

34

Electromyography

Electromyography ( E M G ) data was digitaUy sampled at 2000 H z from a five-

channel E M G rack. Grass P5 series preamps (Grass-Telefactor, Rl, U S A ) were used

and data was high pass filtered at 30 H z and low pass filtered at 1000 H z with a 50 H z

notch and stored for later analysis. Bipolar surface electrodes were placed on medial

and lateral gastrocnemius. Branched surface electrodes were placed on soleus, tibialis

anterior and peroneus longus in the hopes that this spatial arrangement would minimize

the amount of crosstalk in these muscles (Koh and Grabiner, 1993). Surface electrode

placements and preparation were in accordance with Delagi et al. (1982). The skin was

shaven and exfoliated using course plastic scrubbers and then cleaned with alcohol prior

to electrode placement. The electrode positions were marked with indeUble ink so that

the electrode placements could be repeated to improve pre/post-test vatidity.

Due to the small size and potential cross talk from surrounding muscles, the use

of fine wire intramuscular electrodes to measure E M G from soleus, tibialis anterior and

peroneus longus was considered. Ethical complications associated with this procedure

ruled out the use of fine wire electrodes however and surface electrodes were used

instead. A branched electrode set up (15cm inter-electrode distance) was chosen over

the standard single differential method for these muscles due to the significant decrease

in cross talk that has been shown to accompany the use of branched surface electrodes

(Koh and Grabiner, 1993).

Data Collection and Trigger

A three-second epoch of E M G data was coUected by W A V E V t E W on a P C

computer synchronously with the force and position data from the ankle perturbation

rig. The experimenter triggered the data coUection for a desired task after the subject

stabilized their ankle in the correct position and applied the correct amount of force. At

an arbitrary moment during the beginning of the three-second coUection epoch, the

experimenter triggered the pneumatic R A M . Movement of the R A M began 610ms after

the trigger was pressed. The R A M traveUed at a speed of 0.67 m/sec and covered a

total distance of 30 millimetres, which resulted in a ramp perturbation that lasted for 20

miUiseconds. The R A M displacement was held for 1.2 seconds before being returned to

its original position.

35

Data Analysis

Data analysis was spUt into two parts. First the activation strategies used to

stabilize the ankle joint whtie performing the position and torque tasks were examined

during a 500ms epoch prior to perturbation. Second, the morphology of the

monosynaptic stretch reflex response in each muscle from the perturbation was

assessed. The author designed two L A B V I E W programs to aid data analysis in either

case.

Muscle Activation Profiles

R a w E M G was high pass filtered using a second order recursive Butterworth

filter (cut off frequency of 30 H Z ) to remove movement artifact then fuU wave rectified

and filtered using a low pass Butterworth filter (cut off frequency of 10 Hz). The

processing of R a w E M G with a high and low pass filter was similar to the technique

used in previous perturbation studies involving the evaluation of E M G activation of

individual muscles surrounding a joint (Buchanan et al., 1996). Figure 3.4 illustrates

the muscle activation profile obtained foUowing fuU wave rectification and filtering.

The muscle activation profiles for each muscle during the 500 m s epoch prior to R A M

movement were then normalized to the peak filtered E M G obtained during a maximum

plantar-flexion in the 3 D O F condition (Potvin et al., 1996) . To obtain the level of

activation for each muscle in a specific task, the 500 m s activation profiles were

averaged over 5 trials and the average of this 500 m s epoch was calculated to return a

single value (See Appendix H and I for L A B V I E W Activation Front Panel and Block

Diagrams).

Figure 3.4 Processing of raw muscle activation E M G .

The average muscle activation of each muscle across aU 5 trials was then

calculated for the 0%, 15%, 2 5 % and 4 0 % tasks in both the 1 and 3 D O F conditions.

Mean activation for aU muscles in each task were calculated during pre and post testing

for both the experimental and control groups.

36

Polar plots were constructed to help iUustrate the activation patterns for each of

the 5 muscles surrounding the ankle during pre and post testing between the control and

experimental groups across all 1 and 3 D O F tasks. A similar approach has been used in

previous studies in order to report EMG/force data from individual muscles (Buchanan

and Lloyd, 1997) and from muscles surrounding the knee (Besier et al., 1999). Figure

3.5 nlustrates the muscle activation polar plot corresponding to the 3 D O F 4 0 % task.

The muscles have been arranged evenly around the plot to best approximate their

Figure 3.5 A polar plot graph illustrating the muscle activation profile, pre and

post training during a 3 D O F 4 0 % plantarflexion task on the ankle

perturbation rig.

magnitude and contribution to stabiUty of the left ankle. Each concentric pentagon

displays the magnitude of the muscle activation, with maximum activation towards the

outside of the pentagon and zero activation at the center. Because aU muscle activation

data was normalized to the peak muscle activity during a maximum 3 D O F

plantarflexion task, aU values were less than 1.0.

Each node on the polar plot does not represent the anatomical insertion point for

a particular muscle of the ankle joint In addition, the muscles of the ankle joint are not

connected in the fashion that is suggested by the polar plots. Therefore, care must be

taken when interpreting polar plot graphs. For example, medial gastrocnemius, lateral

gastrocnemius and soleus aU have a common insertion into the AchiUes tendon, and

therefore should aU be placed at the same node of the polar plot However, to ensure

that the magnitude of activation for each muscle can be determined from the graph, the

muscle insertions have been placed an equal distance apart around the outside of the

graph.

Co-contraction ratios (CCR) were calculated for each subject using the mean

activation of aU flexor and extensor muscles about the ankle during the 0%, 15%, 2 5 %

37

and 4 0 % tasks in the 1 and 3 D O F conditions. Muscles classified as plantar flexors of

the ankle joint included medial gastrocnemius, lateral gastrocnemius, soleus and

peroneus longus (DonatelU, 1996). The only muscle that can be classified as a dorsi

flexor of the ankle joint is tibialis anterior (DonatelU, 1996).

The CCR of the ankle was determined as foUows:

IF extensor activation > flexor activation, IF extensor activation < flexor activation,

CCR = flexor activation CCR = extensor activation extensor activation flexor activation

The above formula for detennining the co-contraction ratio was an adaptation of

a method developed by Lloyd and Buchanan (2001) to quantify the magnitude of the

varus and valgus moments that resulted from the activation of muscles surrounding the

knee. In this method, eight muscles surrounding the knee were grouped as either H A M s

or Q U A D s and the average E M G activation level for each muscle in a group were

added. The co-contraction ratio was then calculated by dividing one group by the other.

In order to ensure the ratio was equal to or less than 1, the muscle group in the

denominator for the co-contraction ratio equation was always the one with the greatest

activation level. The co-contraction ratio described in the formula above parallels the

formula developed by Lloyd and Buchanan (2001). The only notable difference

between the two equations is that the five superficial muscles of the ankle were grouped

as flexors and extensors instead of eight knee muscles and that the total flexor and

extensor activation was the average of aU the muscles in that group, not the sum.

In order to take into account the degree of activation of the 5 muscles

surrounding the ankle, a co-contraction index ( C O ) was calculated for each

experimental task, both pre and post testing for the experimental and control groups.

The rational behind this was that a co-contraction ratio of 1.0 might indicate absolute

co-contraction but there may only be a weak level of muscular activation of aU the

muscles surrounding the ankle joint This formula aUows a quantification of the

magnitude of muscular co-contraction that is occurring around the ankle for a particular

task. The net activation represents the average activation of aU 5 ankle muscles during

each specific task.

38

C C I = C C R x Net Activation

Stretch Reflex Profiles

The short latency, M l , stretch reflex was the only reflex examined in this thesis

because it has been shown that this reflex response is particularly susceptible to training

adaptations (Nielsen et al., 1993; Trimble and Koceja, 1994; Mynark and Koceja, 1997;

Voigt et al., 1998). R a w E M G data was fuU wave rectified. N o raw reflex E M G data

was filtered in an attempt to preserve the clarity of any changes that might occur in the

M l reflex amplitude due to training. The reflex profile for each muscle was then time

locked to the onset of R A M movement (610ms after the trigger) and reported for a

200ms epoch. Figure 3.6 illustrates the typical reflex profile foUowing full wave

rectification and time locking. A U epoched reflex data was then normalized to the peak

filtered E M G (Butterworth low pass filter, 30 Hz) obtained during a maximum plantar­

flexion in the 3 D O F condition. To obtain the reflex ampUtude and onset for each

muscle in a specific task the ampUtude and onset values were recorded for each of the 5

trials and then averaged over aU 5 trials (See Appendix K for L A B V I E W Reflex Block

Diagrams).

|M2

me

Ml I

50 75 100 125 150 175 200 225

% maximal Ml EMG

Figure 3.6 Processing of R a w Reflex E M G .

Due to the large number of trials involved for aU subjects (640) the ampUtude of

the short latency stretch reflex was determined automaticaUy by L A B VIEW. The

program was designed to record the maximum E M G in a 30-miUisecond window, after

the onset of the M l reflex for each muscle in aU eight tasks. This 30-niilUsecond

window for M l reflex ampUtude detection was chosen because it atiowed the greatest

chance of recording the M l stretch reflex ampUtude (Ml reflex occurs at 30

milliseconds) and the least chance of recording part of the M 2 reflex ampUtude by

RAM Movement

39

mistake (M2 reflex occurs at 60-milUseconds). Due to the reproducibitity of the stretch

reflex and the accuracy of this method of measurement the reliabiUty of this procedure

was deemed to be acceptable after being compared to an interactive method of

ampUtude detection. The experimenter determined the onset time of the short latency

stretch reflex by using a method similar to the one used by Seth and coUeagues (1997).

The 'onset' cursor on the L A B V I E W front panel was moved to the initial point on the

stretch reflex E M G profile where the E M G signal was estimated to be 5 % of the

maximal M l stretch reflex E M G ampUtude (See Appendix J for L A B V I E W Reflex

Front Panel). All values were then written to a file and the process was repeated for

each subject. It should be noted here, that Seth and coUeagues (1997) reUed on a

computer to determine the 5 % maximal M l stretch reflex value that represented the

reflex onset time. The same procedure was accomplished by hand in die present study.

A study by Hodges and Bui (1996) supports the visual determination of the M l stretch

reflex onset time and concluded that "The visual determination of E M G onset was

found to be highly repeatable between days." (Hodges and Bui, 1996).

Reflex amplitudes and onsets for aU muscles were averaged for the 0%, 15%,

2 5 % and 4 0 % tasks in both the 1 and 3 D O F conditions. Mean reflex amplitudes and

onsets for all muscles in each task were calculated during pre and post testing for both

the experimental and control groups.

Statistical Analysis

A U statistics were run using Datadesk© statistical software package. A n

A N O V A with repeated measures was conducted in aU cases. W h e n significant

differences were evident between the desired factors an alpha level of p < 0.05 was

appUed and post hoc Scheffe tests were used to determine any significant difference.

A 2-way A N O V A (group x pre/post) was appUed to the muscle activation data

when the net activation levels were averaged over aU tasks. The same type of analysis

was also used for all reflex data when the reflex response (onset and ampUtude) from

each muscle was averaged over aU tasks. Post-hoc (group x pre/post) tests were then

performed to determine if any significant difference occurred between pre and post

testing in the trained group and between pre and post testing in the control group. These

post-hoc tests were also used to determine if any significant difference occurred

between pre-testing in the training group and pre-testing in the control group.

A 4-way A N O V A (group x D O F x torque x pre/post) was applied to aU muscle

activation and reflex data when the net activation, CCR, CCI, net amplitude and net

40

onset for each task was averaged over aU muscles. This type of analysis was also used

for aU reflex data when the reflex response (ampUtude and onset) from individual

muscles was averaged over aU subjects. Pooling of subjects in this manner for both the

muscle activation and reflex data was conducted in order to focus on the main effect

that might have taken place during pre and post testing for the training and control

groups. Post-hoc (group x D O F x torque x pre/post) tests were then applied to

determine if any significant clifferences occurred for each task between pre and post

testing in the trained group and between pre and post testing in the control group.

These post-hoc tests were also used to determine if any significant difference occurred

between pre-testing in the training group and pre-testing in the control group.

In some cases, a 2-way A N O V A (DOF x torque) was appUed to the dependent

variable instead of a 4-way A N O V A (group x D O F x torque x pre/post). This analysis

aUowed pooling of the data for each of the 8 tasks for the trained and control subjects

during both pre and post testing in order to focus on the main effect that resulted

between the 8 tasks. Post-hoc tests (DOF x torque) were then used to determine the

significant differences between the 8 individual plantar torque tasks and between the 1

D O F and 3 D O F conditions.

41

CHAPTER 4- ADAPTATIONS OF THE CO-CONTRACTION

RESPONSE WITH STABILITY TRAINING

Results

The muscle activation data was recorded in aU 1 and 3 D O F tasks 500 m s prior

to R A M movement during the same testing sessions that gave rise to the reflex data.

Net Muscle Activation

Figure 4.1 iUustrates the net muscle activation (i.e. average activation of aU 5

muscles in each task) averaged over aU tasks for the trained and control groups, pre and

post testing. A n increase in net activation was recorded foUowing training in the

experimental group, whtie a decrease in net activation was recorded post testing in the

control group. A 2-way A N O V A (group x pre/post) revealed that these changes in net

activation were significant (p < 0.05). Table 4.1 gives a summary of the percentage

change in the net activation of the 5 superficial muscles of the ankle averaged over aU 8

tasks in the trained and control groups, pre and post testing.

0.40 i

0.35

0 "

0-5

Net Muscle Activation 0JO

0.15

0.10

0.05

0.00

Pre Train Post Train Pre Control Post Control

Figure 4.1 Net activation of all 5 muscles averaged over all 8 tasks.

(* = significant difference to pre-test p < 0.05)

Table 4.1 Percent change in the net activation of the 5 superficial muscles of the

ankle for trained and control subjects.

S U B J E C T G R O U P Percent change in net activation (%)

A U Muscles

Train 19.01*

Control -15.06

42

Individual Muscle Activation Profiles

To aUow a better understanding of individual muscle contributions to the

activation pattern of the left ankle, polar plots were used. Figure 4.2 iUustrates the

average muscle activation polar plots from 7 trained and 7 control subjects in aU 1 and 3

D O F tasks. Data for pre and post testing sessions are displayed on the same graph.

Several trends were noted in the training and control groups between tasks and pre-post

testing sessions. A 4-way A N O V A (group x D O F x torque level x pre/post) was

applied to aU net activation and peroneal activation data and revealed a significant

difference in these two dependant variables (p < 0.05).

Increase in Net Activation with Increased Plantar Torque

As the level of plantar torque increased in the 1 and 3 D O F conditions so did the

level of net activation. In order to increase the power in this observation, trained and

controls subjects, both pre and post testing were pooled for analysis. Post-hoc tests

(DOF x torque) showed that this increase was significant between each task as the level

of plantar torque increased in the 1 and 3 D O F conditions (p < 0.05).

Increase in Net Activation during 3 DOF vs. 1 DOF tasks

A n increase in net activation is evident in both the trained and control groups

between the stable 1 D O F condition and unstable 3 D O F condition at equivalent levels

of plantar torque. Again, in order to increase the power in this observation trained and

control subjects, both pre and post testing were pooled for analysis. Post-hoc tests

(DOF x torque) revealed that this increase in net activation was highly significant

between aU 1 and 3 D O F conditions at equivalent levels of plantar torque (p < 0.01).

Increase in Net Activation Post Training

A n increase in net activation can be seen in each task during post testing for the

trained group. Post-hoc tests (group x D O F x torque x pre/post) showed that this

increase was significant for every 1 and 3 D O F task except the 0 % 3 D O F condition (p <

0.05). Post testing data for the control group reveals an opposite trend. A decrease in

net activation was recorded in each task during post testing. This decrease was only

significant for the 1 5 % 1 D O F task and the 0 % 3 D O F task (p < 0.05).

Increase in Peroneal Activation during 3 DOF tasks

A n increase in activation of peroneus longus is evident pre and post testing in

both the trained and control groups during aU unstable 3 D O F tasks when compared to

the stable 1 D O F task at an equivalent level of plantar torque. Post-hoc tests (group x

D O F x torque x pre/post) revealed that this increase in activation was highly significant

43

between every 1 and 3 D O F task in the training and control group, both pre and post

testing (p < 0.01). This indicates that peroneus longus provides stabiUty to the subtalar

joint and is a potentially critical muscle in preventing inversion ankle sprain injuries as

indicated by Neptune and coUeagues (1999).

Increase in Peroneal Activation Post Training

A n increase in peroneal activation during post testing is evident in the polar

plots for the trained group. Post-hoc tests (group x D O F x torque x pre/post) showed

that the increase in peroneal activation was significant for every case except the 0 %

1 D O F task in the trained group (p < 0.05).

TRAINED CONTROLS

mg pi mg P* mg pi

mg pi mg pi mg pi

mg pl mg pl mg pl

Figure 4.2 Muscle activation polar plots. Both pre and post testing a Pre Tr«m

data is shown on the same graph for each task. • Pos, Train

O Pre Control

Co-contraction

44

The level of co-contraction of the left ankle during each of the 8 tasks was

determined using a co-contraction index (CCI). The CCI was calculated as the product

of the net activation and the co-contraction ratio (CCR). Figure 4.3 mustrates the net

activation (i.e. average activation of aU 5 muscles) for each task in the trained and

control groups, pre and post testing. Figure 4.4 shows the C C R for the flexors and

extensors of the ankle for each task in both groups during pre and post testing.

0.70

0.60

0.50

Net Muscle Activation " °

0.30

0.20

0.10

0.00

0% 15% 25% 1DOF

40% 0% 15% 25% 3 DOF

40%

Figure 4 3 Net activation of all 5 muscles in each task.

(* = significant difference to pre-test, p < 0.05)

(t = significant difference to control group pre-test, p < 0.05)

CCR

1.20

1.00

0.80

0.60

0.40

0.20

0.00

0% 15% 25% 40% 0% 15% 25% 40% 1 DOF 3DOF

Figure 4.4 Co-contraction ratios for flexor and extensor muscles in each task.

(* = significant difference to pre-test, p < 0.01)

(f = significant difference to control group pre-test, p < 0.05)

45

The trends and statistical analysis conducted on the net activation data have been

discussed in a previous section of this chapter. Upon close evaluation of Figure 4.4, an

increase in the C C R during post testing is evident for the trained group in the 0 % and

1 5 % tasks (low torque) for both the 1 and 3 D O F conditions. To faciUtate further

analysis a 4-way A N O V A (group x D O F x torque x pre/post) showed that there was a

significant difference in the C C R data (p < 0.05). Post-hoc tests (group x D O F x torque

x pre/post) revealed that the increase in the C C R for the trained group was significant

for the 0 % and 1 5 % tasks in the 1 and 3 D O F conditions (p < 0.05). In addition, an

increase in the co-contraction ratio is evident between aU 1 and 3 D O F tasks at

equivalent levels of plantar torque and as the level of plantar torque increases in each

condition. A 2-way A N O V A (DOF x torque) was appUed to aU cases and showed no

significant difference in the CCR.

Upon analysis of Figure 4.5, an increase in the CCI during post testing in the

trained group and a decrease in the CCI for the control group can be seen in most tasks.

Again, a 4-way A N O V A (group x D O F x torque x pre/post) showed that this change

was significant (p < 0.05). Post-hoc tests (group x D O F x torque x pre/post) revealed a

significant increase in the CCI for the 0 % and 1 5 % tasks in both the 1 and 3 D O F

conditions for the trained group (p < 0.05). The same analysis did not reveal any

significant difference in the CCI for the control group.

Figure 4.5 Co-contraction index of all 5 muscles in each task.

(* = significant difference to pre-test, p < 0.05)

(f = significant difference to control group pre-test, p < 0.05)

46

In addition, an increase in the co-contraction index is evident between aU tasks.

Post hoc tests ( D O F x torque) revealed that the CCI was significantly clifferent between

aU 1 and 3 D O F tasks at equivalent levels of plantar torque and as the level of plantar

torque increased in each condition (p < 0.05).

Discussion

Individual Muscle Activation Profiles

Acute Adaptations

The increase in net activation that occurred as the level of plantar torque

increased for each task was an intuitively obvious outcome of this study. In order to

generate greater forces, an increase in muscle activation and associated E M G is

necessary. However, it is interesting to note the pattern of muscle activation that

emerged. Upon closer evaluation of the muscle polar plots, it is evident that die

increase in net E M G measured between the 0%, 15%, 2 5 % and 4 0 % tasks was used for

a combination of torque generation and joint stabiUty. Medial gastrocnemius, lateral

gastrocnemius and soleus are the major plantar flexors of the ankle joint Each of these

muscles experienced an increase in activation as the levels of plantar torque increased in

the trained and control groups. Peroneus longus is a major evertor of the ankle joint and

plays a role in plantar flexion (Kapit, 1993). A n increase in activation occurred in this

muscle in die training and control groups as the level of plantar torque increased in an

attempt to maintain joint stabiUty and generate plantar torque during each task. This

trend is most readily apparent in the 3 D O F condition. It is interesting to note the

activation patterns of tibiaUs anterior during increased plantar torque. TibiaUs anterior

had a major contribution to the net activation during the 0 % and 1 5 % plantar torque

levels, but increased plantar torque resulted in a decrease in E M G recorded from this

muscle in the trained and control groups. TibiaUs anterior is a major dorsiflexor of the

ankle joint so any contribution it made to the net activation during each plantarflexion

task can be attributed to it's role as a stabilizer of the ankle joint. In fact, Neptune and

coUeagues (1999) have shown that tibiaUs anterior provides ankle stabiUty by co-

contracting with the plantarflexors and peroneus longus.

The increase in net activation between the 1 and 3 D O F tasks in this experiment

supports the evidence to suggest that maintaining joint stabiUty in the face of an

unstable load requires a significant increase in the initial tonic activity of all muscles

(De Serres and Milner, 1991). This increase in muscle activation in an unstable

47

situation is most likely related to a change in the firing pattern of proprioceptors

surrounding the unstable joint. Data recorded from la afferents in cats suggests that

fusimotor drive is low during routine locomotor tasks, but is greatly enhanced in

exploratory, novel or difficult tasks such as beam walking (Prochazka, 1989). A direct

comparison between cats and subjects in this experiment is compticated by the different

unstable tasks that were used in either experiment. However, conclusions can be drawn

because enhanced la afferent firing was only observed in cats when the joint was subject

to periods of instabiUty on the beam, or when the task became difficult. It can be

assumed that the neural strategy to accompUsh the 3 D O F task in humans is similar to

that adopted by the cat during periods of instabiUty while beam walking. The increase

in activation of the muscles surrounding the ankle joint during all 3 D O F tasks in the

training and control group may be due to the increased fusimotor drive from la afferents

experienced by these muscles.

A n increase in the level of E M G recorded from peroneus longus was largely

responsible for the increased net activation during all unstable 3 D O F tasks. This

significant increase in peroneus longus both pre and post testing in the training and

control groups suggests that peroneus longus plays a large role in maintaining stabiUty

of the ankle joint complex. Fmdings from Neptune and coUeagues (1999) reinforce this

concept by revealing that peroneus longus activity has a large contribution to joint

stabiUty during certain cutting tasks. Research from their study also led them to

conclude that peroneus longus is a critical muscle for the stabilization of the subtalar

joint.

Chronic Adaptations

Strength training of a muscle causes neural adaptations and morphological

changes to occur and ultimately leads to an increase in the level of E M G recorded from

that muscle (Enoka, 1994). Figure 4.6 illustrates evidence to support a separation in

these two factors and shows the time course of changes in E M G compared to whole-

muscle cross-sectional area during 60 days of isokinetic training and 40 days of

detraining. The increase in E M G in this study was disproportionately larger than

the increase in the size of the muscle. This evidence supports the conclusion that it is

possible to increase M V C force without a morphological adaptation in the muscle. A n

increase in E M G , therefore, has the potential to indicate an increase in the strength of

the muscle. The large increase in E M G and M V C force observed in Figure 4.6 after the

first 20 days of training was most likely due to an adaptation in the nervous system

itself.

48

C .2 c.

150-

140 -

<"-* 110 4.

100-1

• MVC force A CSA o EMG

20 40 60 80

Time (days) 100

Figure 4.6 E M G from vastus lateralis during a maximum contraction, cross-

sectional area of quadriceps femoris and the M V C force during

isokinetic training and detraining (modified from Enoka 1994).

Balance training has been shown to result in an increase in the strength of the

muscles surrounding the ankle joint to an equivalent level as that experienced by

strength training (Wyrick, 1970). The increase in net E M G recorded in the training

group during post testing in the present study has the potential to corroborate these

findings and indicates that stabiUty training on a wobble board may improve the

strength of the muscles surrounding the ankle joint. Due to the brief nature of the

stabiUty training regime in this study (three weeks), the increase in net activation

recorded during post-testing in the trained group can be attributed to the neural

adaptation of the muscles surrounding the ankle joint

Changes in the synchronization of the motor unit pool is one of the most

frequently cited neuromuscular adaptations to strength training and is thought to

contribute to an increase in the rate of force development and improve the coordination

of multiple muscles to promote skiUed muscle synergies such as co-contraction

(Semmler, 2002). In addition, past Uterature has suggested that motor unit

synchronization is a source of increased E M G levels and associated muscular strength

(Milner-Brown et al., 1975). Motor units with a high degree of synchrony tend to

discharge action potentials at roughly the same time. The analysis of motor unit

synchroriization involves comparing the E M G from a single motor unit to a population

of motor units. Using this technique, Milner-Brown et al. (1975) have shown that the

amount of motor unit synchronization in a hand muscle increased after a six week

program of strength training. This increase in synchronization was thought to be the

49

result of an enhancement of the descending drive from the motor cortex and the

cerebeUum (Milner-Brown et al., 1975). Despite the convincing evidence provided by

Milner-Brown and coUeagues (1975), it has been shown that increased motor unit

synclffonization does not directly alter the magnitude of force output and associated

muscle strength (Yao et al., 2000). Instead it has been suggested that increased

synchronous motor unit activity at the initiation of a contraction would lead to a greater

rate of force development (Semmler, 2002).

O f significant interest to the present study is the evidence suggesting that an

increase in synchronization of the motor unit pool is responsible for the improved

coordination of multiple muscles to promote skiUed muscle synergies such as co-

contraction. It has been shown that motor unit synchronization exists between

functionally simtiar muscles, such as the left and right masseter muscles during jaw

clenching (Semmler, 2002). But this same motor unit syncliroriization does not exist

during co-contraction of antagonistic muscles of the upper limbs (Semmler, 2002).

From this evidence it was suggested that functionally linked muscles result from shared

synaptic drive and that even a relatively small contribution from branched common

inputs (after training) can be highly influential in deterrnining a pattern of co-

contraction or muscle synergy between common muscles (Semmler, 2002). It was

concluded that the functional significance of motor unit synchronization may Ue in the

selection and activation of common inputs between muscles (Semmler, 2002).

A n increase in the level of E M G recorded from peroneus longus was partly

responsible for the increased net activation in all tasks during post-testing in the training

group. The increase in E M G of this muscle may reflect the abitity of wobble board

training to improve the strength of peroneus longus and could be a result of adaptations

in the synchrony of the motor neuronal pool. However, several other explanations are

possible for the increased activation recorded form peroneus longus after wobble board

training. The increase in E M G could have been due to an increase in the neural drive to

peroneus longus, or an improvement in muscle co-ordination such as the increase in

agonist-antagonist co-contraction recorded to stabilize the joint.

Co-contraction

Acute Adaptations

A n increase in net activation was recorded when each 1 D O F task was compared

to the 3 D O F task with an equivalent torque percentage. This increase in net activation

was associated with an increase in the co-contraction ratio in the trained and control

50

groups for most of the pre and post testing tasks. LleweUyn et al. (1990) have shown

that beam walking involved greater co-contraction of tibiaUs anterior and soleus

muscles when compared to tread miU walking and attributed this change in contraction

strategy to the decrease in base of support inherent in beam walking. The 3 D O F

condition on the ankle perturbation rig offers a significant decrease in the base of

support when compared to the 1 D O F condition. Maintenance of ankle joint stabiUty

during aU 3 D O F tasks by co-contraction of tibialis anterior with the plantarflexors of

the ankle is evident from the increase in the co-contraction ratio that was recorded.

These findings suggest that peripheral feedback could be used to stimulate centraUy

controUed co-contraction strategies in a similar fashion as that described in previous

research (Humphrey and Reed, 1983; GottUeb, 2000).

Chronic Adaptations

Carolan and CafarelU (1992) have recorded adaptations in the co-contraction

response in the knee extensor muscles after strength training. I)uring isometric

contractions of the knee extensors, activity in biceps femoris can reach 2 2 % of

m a x i m u m values. After the knee extensors are trained for one-week, activation of

biceps femoris decreased by approximately 2 0 % . This decrease in co-contraction

significantly contributed to the increase in force measured from the extensors of the

knee. These findings support the evidence to suggest that co-contraction is a specific

neural strategy used by the C N S and that functional adaptation of this neural strategy is

possible after brief periods of training.

In order to compare the level of co-contraction experienced by the ankle joint

during pre and post testing in the same task, it is important to consider the net activation

and the co-contraction ratio for each task together. A n increase in net activation was

recorded during post testing in all 1 and 3 D O F tasks for the trained group. However,

an increase in the co-contraction ratio only occurred in the 0 % and 1 5 % tasks for each

condition. The resulting co-contraction index was significantly larger during post-

testing for the trained subjects in aU 0 % and 1 5 % tasks. These findings suggest that

three weeks of stabiUty training has the abitity to improve co-c»ntraction ratios at low

levels of muscle activation but has no effect on the co-contraction ratio during moderate

to high levels of muscle activation. The increase in the co-contraction index during low

levels of muscle activation can most probably be attributed to neural adaptations that

increased the activation of the muscles surrounding the ankle joint.

51

Implications for the Prevention of Lateral Ankle Sprains

Peroneal weakness is one of the four main causes of lateral ankle instabiUty

along with a reduction in proprioception, mechanical instabiUty and tibiofibular sprains

(Bosien et al., 1955; Johnson and Johnson, 1993). In addition, Neptune and coUeagues

(1999) have shown that peroneus longus activity starts before impact and rises more

abruptly during the side-shuffle. This evidence indicates that peroneus longus has a

large contribution to the stabiUty of the subtalar joint and provides a dynamic protective

mechanism prior to heel strike. The peroneus longus muscle can, therefore, be

implicated as a potentiaUy critical muscle for the prevention of lateral ankle sprain

injuries.

A n increase in the level of E M G was recorded from the peroneus longus muscle

during post testing in the trained group in 7 of the 8 tasks on the ankle perturbation rig.

A n improvement in the synchronization of the motor unit pool is one of the most

plausible explanations for this increase in E M G (Enoka, 1997). It is possible that the

increase in activation recorded from peroneus longus is correlated with an increase in

the strength of this muscle. However, due to methodological difficulties, any change in

the strength of individual muscles such as peroneus longus could not be determined.

From the evidence and supporting Uterature it can be hypothesized that an increase in

peroneal activation on the ankle perturbation rig could translate to an increase in

peroneal activation prior to heel contact and during weight bearing (Enoka, 1997;

Neptune et al., 1999). Considering that peroneus longus is a critical muscle for the

stabiUty of the subtalar joint, any increase in activation of this muscle may have the

potential to protect the joint against lateral ankle sprains (Neptune et al., 1999). This

suggests that a period of wobble board training has the abitity to prevent injuries of the

ankle joint complex by increasing the level of E M G activation and strength in the

peroneus longus muscle.

The impact at heel contact is compensated for by stiffening of the ankle joint by

co-contraction of the flexor and extensor muscle 150-180 m s prior to heel strike (Dietz,

1992). The timing of this activation depends on foot position and the expected ground

contact time. For most movements the E M G partem is pre-programmed and generated

on a spinal and/or a brain stem level. Fmdings from this study and others suggest that it

is possible to alter the co-contraction pattern of flexors and extensors of a particular

joint through training (Carolan and CafarelU, 1992; Besier et al., 1999)

A n increase in the co-contraction ratio of the flexor and extensor muscles of the

ankle was recorded during weak co-contraction in the training group during post-testing.

52

A n increase in the co-contraction ratio of the flexor (tibiaUs anterior) and extensor

(soleus, medial gastrocnemius, lateral gastrocnemius, peroneus longus) muscles is most

likely correlated with an increase in stabUity of the subtalar joint. It can be

hypothesized that an increase in the co-contraction ratio on the ankle perturbation rig

could translate to an increase in the co-contraction ratio prior to heel contact and during

weight bearing. A n y improvement in the co-contraction ratio in the sagittal plane

around the ankle before heel contact has the potential to increase overall ankle joint

stiffness and delay the time from ankle perturbation to Ugament injury (Konradsen et

al., 1997). This suggests that a period of wobble board training has the abiUty to

prevent injuries of the ankle joint complex by improving the co-contraction ratio of the

flexor and extensor muscle of the ankle.

53

CHAPTER 5- ADAPTATIONS OF THE SHORT LATENCY

REFLEX WITH STABILITY TRAINING

Results

A small M l reflex was recorded from tibiaUs anterior and was not reported, as

any reflex activity in this muscle after dorsiflexion was most likely due to cross talk.

Net Ml Reflex Amplitude

Figure 5.1 iUustrates the M l reflex ampUtude for each muscle averaged over aU

8 tasks. Data for 7 trained and 7 control subjects, both pre and post testing is presented.

W h e n ati 8 tasks were averaged, a 2-way A N O V A (group x pre/post) was

appUed to each muscle individuaUy and showed that the amplitude for the M l reflex in

3 of the 4 ankle muscles was significantly different (p < 0.05). Post hoc Scheffe tests

(group x pre/post) revealed that the ampUtude of the M l reflex during post testing in the

training group was significantly different than pre-testing values in lateral

gastrocnemius, soleus and peroneus longus (p < 0.05). N o significant difference was

noted during pre-testing between the training and control groups in this analysis.

Table 5.1 gives a summary of the percent change in ampUtude for the M l reflex

during post-testing in the trained and control groups. Note that in the trained group, a

decrease in the ampUtude of the M l reflex response occurred in each of the 4 muscles,

but this decrease was only significant for lateral gastrocnemius, soleus and peroneus

longus (p < 0.05).

M l Reflex 6 M

Amplitude 5oo (normalized to M V C to 3DOF

task) 3oo

Figure 5.1 M l reflex amplitude for each muscle averaged over all 8 tasks.

(* = significant difference to pre-test, p < 0.05)

54

Table 5.1 Percent change in the amplitude of the M l reflex response in 4

superficial muscles of the ankle for trained and control subjects.

S U B J E C T

GROUP

Train

Control

mg

-29.66

4.10

Change in amplitude (±%)

lg sol

-23.46*

-3.38

-25.96*

41.04*

Pl

-55.15*

1.47

* = significant difference to pre-test (p < 0.05)

Figure 5.2 iUustrates the M l reflex ampUtude for each task averaged over aU 4

muscles. A 4-way A N O V A (group x D O F x torque x pre/post) reveal no significant

difference (p < 0.05) and as a result interactions between pre and post testing data in the

trained and control groups could not be determined. However, for each 1 D O F task, the

ampUtude of the M l reflex appears to be less for the 3 D O F task at an equivalent level

of plantar torque. In order to increase the power in this observation, trained and control

subjects, both pre and post testing were pooled for analysis and a 2-way A N O V A (DOF

x torque) showed a significant difference in the ampUtude of the M l stretch reflex

between all 1 and 3 D O F tasks (p < 0.01). Post-hoc tests (DOF x torque) revealed that

this decrease was significant between aU 1 and 3 D O F tasks at equivalent levels of

plantar torque (p < 0.01). These tests also reveal a significant difference between the

0 % and 1 5 % tasks in the 1 and 3 D O F conditions (p < 0.01).

6.00

M l Reflex

5.00

4.00

3.00 Amplitude (normalized to average M V C of2 oo all muscles in 3

D O F task) 1.00

0.00

• Pre Train

• Post Train

D Pre Control

D Post Control

0% 15% 25% 1DOF

40% 0% 15% 25% 3DOF

40%

Figure 5_ M l Reflex amplitude for each task averaged over all 4 muscles.

55

Table 5.2 summarizes the percent change in the M l reflex ampUtude between

the 1 and 3 D O F tasks at equivalent plantar torque levels for the training and control

groups.

Table 5.2 Percent change in the Ml reflex amplitude between 1 and 3 DOF tasks

at equivalent levels of plantar torque for trained and control subjects.

PLANTAR

TORQUE

0%

15%

25%

40%

Train Pre

-25.05

-17.63

-19.22

-15.43

Change in amplitude (±%)

Train Post

-23.44

-22.97

-15.41

-32.27

Control Pre

-20.60

-16.73

-21.03

-13.85

Control Post

-7.10

-7.58

-2.59

-6.09

Ml Reflex Amplitude Profiles for Individual Muscles

Figure 5.3 iUustrates the M l reflex ampUtude in aU tasks for each of the 4

superficial muscles of the ankle. Both pre and post testing data for 7 trained and 7

control subjects is presented and standard deviations were high in aU cases. A 4-way

A N O V A (group x D O F x torque x pre/post) was applied to each muscle individually

and reveal no significant difference (p < 0.05) in any of the muscles. As a result

interactions between pre and post testing data in the trained and control groups could

not be detennined for any of the superficial muscles of the ankle. A 2-way A N O V A

(DOF x torque) was then applied in an attempt to pool subjects and increase the power

in the differences observed between tasks, but no significant difference was found with

this analysis in any of the 4 superficial muscles of the ankle (p < 0.05).

Each graph in Figure 5.3 iUustrates a similar trend in all 4 muscles towards a

reduction in M l reflex ampUtude in most 3 D O F tasks when compared to the 1 D O F

task at an equivalent plantar torque level. This trend is most readUy apparent in medial

gastrocnemius and lateral gastrocnemius muscles. Each graph in Figure 5.3 also

emphasizes the trend in aU 4 muscles towards an increase in M l reflex ampUtude as the

level of plantar torque increased from 0 % to 1 5 % in most 1 and 3 D O F conditions. This

trend is apparent in each of the 4 superficial muscles of the ankle.

56

9.00

•40

7.00

Ml Reflex "• Amplitude j ^

mg

• Pre Train

• Poet Tram

a Pre Control

D Past Control

0% 15% 25% 40% 0% 15% 25% 40%

1 DOF 3DOF

lg sol

Ml Reflex Amplitude

5J0 -j|

U t •- I

ZJ0 -1 1

roo -fl

•JM •-••

T

-1

A

~ [j - 1

1

n

-

.

-

Lt

T

T

~\1

•

- -

0% 15% 25% 40% 0% 15% 25% 40%

1 DOF 3DOF

0% 15% 25% 40% 0% 15% 25% 40%

1 DOF 3DOF

Pl

Ml Reflex Amplitude

0% 15% 25% 40% 0% 15% 25% 40%

1DOF 3DOF

Figure 53 Average M l reflex amplitude in each task for the 4 superficial muscles

of the ankle. Y values normalized to M V C in the 3 D O F task.

57

Net Ml Reflex Onset Time

Figure 5.4 iUustrates the M l reflex onset for each muscle averaged over aU 8

tasks. Data for 7 trained and 7 control subjects, both pre and post testing is presented.

W h e n aU 8 tasks were averaged, a 2-way A N O V A (group x pre/post) showed

that the onset time for the M l reflex in 3 of the 4 muscles was significantly different (p

< 0.05). Post hoc Scheffe tests (group x pre/post) showed that the onset time for the M l

reflex during post testing in the training group was significantly different than pre­

testing values in lateral gastrocnemius, soleus and peroneus longus (p < 0.05). This

analysis also revealed that the onset time for the M l reflex during pre-testing was

significantly different between the training and control groups in soleus and peroneus

longus (p < 0.05).

Table 5.3 gives a summary of the percent change in onset time for the M l reflex

in each of the 4 muscles during post-testing in the trained and control groups. Note that

in the trained group an increase in the onset time occurred in aU muscles, but this

increase was only significant for lateral gastrocnemius, soleus and peroneus longus (p <

0.05).

• Pre Train

• Post Train

• Pre Control

D Post Control

Figure 5.4 M l reflex onset time for each muscle averaged over all 8 tasks.

(* = significant difference to pre-test, p < 0.05)

(t = significant difference to control group pre-test, p < 0.05)

58

Table 53 Percent change in the onset time for the M l reflex response in 4

superficial muscles of the ankle for trained and control subjects.

S U B J E C T

GROUP

Train

Control

mg

7.01

1.66

Change in

lg

6.54*

-0.08

onset time (±%)

sol

7.41*

-1.47

Pl

11.44*

-1.57

* = significant difference to pre-test (p < 0.05)

Figure 5.5 iUustrates the M l reflex onset time for each task averaged over aU 4

muscles. A 4-way A N O V A (group x D O F x torque x pre/post) was appUed and

showed that the difference was significant (p < 0.01). Post-hoc tests (group x D O F x

torque x pre/post) revealed that the increase in the M l reflex onset time for the trained

group was highly significant (p < 0.01) for aU but the 4 0 % 3DOF task (significant to p

< 0.05). N o trend was evident between any 1 and 3 D O F tasks at equivalent levels of

plantar torque or as the level of plantar torque increased in a particular condition.

39.00

37.00

35.00

33.00 M l Reflex Onset (ms) 3100

29.00

0% 15% 25% 40% 1DOF

0% 15% 25% 40% 3 DOF

Figure 5.5 M l reflex onset time for each task averaged over all 4 muscles.

(+ = significant difference to pre-test, p < 0.01)

(* = significant difference to pre-test, p < 0.05)

(f = significant difference to control group pre-test, p < 0.05)

59

Ml Reflex Onset Time Profiles for Individual Muscles

Figure 5.6 iUustrates the M l reflex onset time in aU tasks for each of the 4

superficial muscles of the ankle. Both pre and post testing data for 7 trained and 7

control subjects are presented. A 4-way A N O V A (group x D O F x torque x pre/post)

was appUed to each muscle individuaUy and reveal a significant difference in soleus and

peroneus longus (p < 0.05). A s a result, interactions between the trained and control

groups both pre and post testing could not be determined for medial gastrocnemius or

lateral gastrocnemius.

Post-hoc tests (group x D O F x torque x pre/post) for soleus revealed that the

delay in reflex onset time during post-testing for the trained group was significant in 5

of the 8 tasks (p < 0.05). In addition these tests showed that pre-testing data for the

trained and control groups were significantly different in aU but the 4 0 %

1 D O F task (p< 0.05).

Post-hoc tests (group x D O F x torque x pre/post) for peroneus longus revealed

that the delay in reflex onset time during post-testing for the trained group was

significant in 7 of the 8 tasks (p < 0.05). In addition these tests showed that pre-testing

data for the trained and control groups were significantly different in all but the 0 % 1

D O F task (p < 0.05).

Each graph in Figure 5.6 iUustrates a similar trend in the onset time of the M l

reflex response in all 4 muscles during pre-testing for the trained group in each task.

This trend is towards a delay in M l reflex onset time across most tasks in aU 4 muscles

during post-testing for the trained group. N o trend is evident between 1 and 3 D O F

tasks at equivalent levels of plantar torque or as the level of plantar torque increased in a

particular condition.

60

mg

Ml Reflex Onset (ms) J7_0 -

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urn -

25.00

T

T

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ph

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i,

.-

-

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-H

a Pre Tram

D Post Trail

D Pre Control

a Post Contt m

0% 15% 25% 40% 0% 15% 25% 40%

1 DOF 3DOF

lg sol

41-0

3S.00

Ml Reflex »*> Onset (ms)

0% 15% 25% 40% 0% 15% 25% 40%

1DOF 3DOF

0% 15% 25% 40% 0% 15% 25% 40%

1DOF 3DOF

47.00

45.00

41-0

Ml Reflex MM Onset (ms) Wjl0

35.00

33.00

31.00

29.00

27.00

25-0

Pi

*

11

*

*

t t t

T |

W | mm | _^JiJJ_+_|l

* *

t t t

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0% 15% 25% 40% 0% 15% 25% 40%

1 DOF 3DOF

Figure 5.6 Average M l reflex onset time in each task for the 4 superficial muscles

of the ankle.

(* = significant difference to pre-test, p < 0.05)

(f = significant difference to control group pre-test, p < 0.05)

61

Discussion

Ml Reflex Amplitude Profiles for Individual Muscles

Acute Adaptations

Nielsen et al. (1994) have observed that after a dorsiflexing perturbation to the

foot, the M l stretch reflex response from soleus was smaUer during weak to moderate

co-contraction than isolated plantarflexion at matched background soleus E M G levels.

However, during high co-contraction levels, the stretch reflex in soleus was found to be

higher than that observed during isolated plantar flexion at matched background soleus

E M G levels. It has been shown in a previous chapter that plantarflexion tasks for the 3

D O F condition in the present study involve a larger degree of co-contraction from

tibiaUs anterior and the plantarflexors of the ankle when compared to the equivalent 1

D O F task. If the 1 and 3 D O F tasks in this experiment are equated to the co-contraction

and plantarflexion tasks in the experiment conducted by Nielsen, then simi lar find ings

could be expected. The data presented in this study confirm the findings that at low

levels of co-contraction (3DOF condition), the M l reflex amplitude in soleus is

decreased when compared to the equivalent 1 D O F condition. Moderate to high levels

of co-contraction (3 D O F condition) also revealed a decrease in the M l reflex amplitude

in aU muscles when compared to the equivalent 1 D O F condition, which could be

interpreted as being contrary to the findings of Nielsen.

Several explanations could account for this discrepancy. First, the conflict in

results could be due to a difference in the definition of "highly co-contracting muscle"

between the two studies. However, "highly co-contracting" in the present study is

defined as 4 0 % of maximum plantarflexion torque, where as a sinular level of 5 0 % of

maximum plantarflexion torque was used in the Nielsen study. Second, the rationale to

equate the 3 D O F tasks with the co-contraction tasks in the Nielsen study may be

unfounded. Indeed, no attempt was made in the present study to ensure that the

background soleus E M G levels in the 1 and 3 D O F conditions were equivalent for a

specific task.

Data presented in this study also expands the effects of co-contraction on the M l

reflex amplitude to include aU the superficial muscles of the ankle joint which supports

results reported by Trimble and Koceja (1994), but refutes those of Nielsen. CentraUy

controUed pre-synaptic inhibition of the la afferent is a possible candidate to explain the

reduction in M l reflex ampUtude seen during co-contraction (3 D O F condition) in each

of these muscles. Evidence for this can be taken from Nielsen and Kagamihara (1993)

who found that during voluntary movement, suppression of the H reflex occurred during

62

both the preparatory phase and the contraction phase of movement. Since no peripheral

feedback could have occurred prior to movement, the changes observed in the H-reflex

during this time could only have been caused by central control of the interneurons

involved in the presynaptic inhibition (Nielsen and Kagarnihara, 1993). In addition,

Llewellyn et al. (1990) suggested that a large reflex discharge of the ankle musculature

during co-contraction in an unstable position had the potential to endanger the balance

of a subject. Considering the large mechanical effect of the stretch reflex (Toft et al.,

1991), a decrease in the M l reflex amplitude during co-contraction could be seen as

beneficial to joint stabUity. The increase in pre synaptic inhibition was found to be

sufficient in reducing the amplitude of the M l reflex in weak, moderate and highly co-

contracting muscles. There was no sign of the inabUity of presynaptic inhibition to

depress the reflex amplitude in highly co-contracting muscles reported by Nielsen.

A s the level of tonic activity increased in both the 1 and 3 D O F tasks, so did the

amplitude of the stretch reflex in each of the 4 superficial muscles of the ankle. A large

initial increase in reflex amplitude is apparent in most muscles, followed by a gradual

plateau effect for the 2 5 % and 4 0 % tasks. Surprisingly, a slight decrease in the reflex

ampUtude was also noted in several muscles between the 2 5 % and 4 0 % tasks. Evidence

for these trends is most apparent when the M l reflex amplitude for each task was

averaged over all 4 muscles (Figure 5.2). This observation was consistent with several

authors w h o have also noted the presence of the "reflex gain" phenomenon in the ankle

musculature (Marsden et al., 1976; Kearney and Chan, 1982). Kearney reported that the

area under both the M l and M 2 reflex response in tibialis anterior increased with

increasing tonic activity but no plateau effect was noted. A direct comparison between

this situation and the present experiment is complicated by the fact that minimal to no

reflex response was recorded from tibiaUs anterior. However, the Uterature and data

from this thesis both suggest that the excitabiUty (or amplitude) of the stretch reflex

increases with increasing muscular contraction force.

Data from the control group showed that the test, re-test results for the ampUtude

of the stretch reflex on the ankle perturbation rig were very sinular. However, large

standard deviations were recorded across aU tasks in every sampled muscle for both the

training and control groups. These findings suggest that the reflex ampUtude in a

particular muscle for a single subject doing a certain task was remarkably consistent but

reflex ampUtudes from subject to subject varied greatly. T w o possible procedural

complications, including poor electrode placement and high impedance could

explanation this inter-subject variability. Checks were done prior to every testing

63

session to ensure that the impedance from each muscle did not exceeded five kOhms

and guidelines for electrode preparation and placement were rigorously followed. The

likelihood that these two variables influenced the results for the reflex ampUtudes

recorded is negtigible. The most probable explanation for the recorded inter-subject

variability in M l stretch reflex amplitude is the difference in muscle fiber type that can

exist between individuals in the same muscle.

History of muscular training and genetic factors both play a role in determining

the fiber type in a particular muscle of an individual. It is weU known in

musculoskeletal physiology that Type S motorneurons supply Type I (SO) muscle fibers

and Type F motorneurons supply Type lib (FG) muscle fibers (Alway et al., 1989;

Hather et al., 1991; Enoka, 1994). The smaUer diameter Type S motorneurons are more

easily excited by an action potential in la afferents than the larger diameter Type F

motorneurons. A large percentage of type lib (FG) muscle fibers in a particular muscle

would result in a motomeuronal pool with a higher threshold for recruitment and a

subsequent reduction in reflex amplitude. Considering the evidence presented by Enoka

(1994) that suggests physical training has the abitity to alter fiber type of a particular

muscle from type H a to type flb, it is possible that the training history of the lower limbs

and genetics were diverse in the subject pool for this study. It must be noted here that

every attempt was made during the subject selection process to ensure homogeneity in

the training backgrounds of all subjects. However a more rigorous selection process

including muscle biopsies has the potential to reduce the variabiUty in the M l reflex

response. It is most likely that a combination of genetic variability in fiber type and

training history of the lower limb were jointly responsible for the differences in M l

stretch reflex ampUtude seen between subjects in a specific muscle.

Chronic Adaptations

After several weeks of knee extension exercises, an increase in the proportion of

Type Ha muscle fibers and a decrease in the proportion of Type lib muscle fibers was

noted in vastus lateraUs (Hather et al., 1991). This evidence supports the beUef that

exercises involving strength training has the abitity to change Type lib (FG) muscle

fibers into Type H a (FOG) muscle fibers (Hather et al., 1991; Enoka, 1994). Similarly,

endurance training may be able to change Type I (SO) fibers into Type H a (FOG) fibers.

A change in the percent fiber type in a particular muscle from Type H a (FOG) muscle

fibers towards Type lib (FG) results in a lower excitabiUty of the motomeuronal pool in

that muscle (Enoka, 1994). This is mainly due to the larger diameter of the Type F

64

motomeuron supplying the Type D b muscle fiber. Therefore, it is possible that the

reduction in amplitude of the M l stretch reflex in each muscle across most tasks during

post-testing for the trained group resulted from a change towards the Type D b (FG)

muscle fiber in each muscle.

Due to the brief nature of the wobble board training regime in this study, it is

more likely that the change in M l stretch reflex amplitude was due to an adaptation in

the nervous system, rather than a change in the muscle itself. A n alternate explanation

is that the reduction in reflex amplitude post training was caused by a reduction in the

transmission of action potentials across the la afferent synapse. A n adaptation in

centraUy controlled presynaptic inhibition represents the most likely mechanism to

result in the long term modulation of neural transmission in the la afferent (Nielsen and

Kagamihara, 1993; Trimble and Koceja, 1994; Lloyd, 2001). A n example can be taken

from baUet dancers w h o must co-contract the antagonistic muscles of their ankles in

order to maintain balance during classic baUet postures. Several authors have noted a

large increase in presynaptic inhibition during co-contraction (Nielsen and Kagamihara,

1993; Nielsen et al., 1994). As a result, Nielsen et al. (1993) have been able to show a

significant reduction in the soleus H-reflex in ballet dancers compared to weU trained

athletes. It can be concluded that daily co-contraction induced by standing on a wobble

board (decreased base of support), with a short-term increase of presynaptic inhibition

results in long term reduction of la afferent synaptic transmission and a reduction in the

M l stretch reflex response (Trimble and Koceja, 1994; Lloyd, 2001).

Ml Reflex Onset Time Profiles for Individual Muscles

Acute Adaptations

N o short term changes in the onset time of the M l stretch reflex were noted

between equivalent 1 and 3 D O F tasks or as the level of plantar torque increased in a

specific condition. This suggests that clifferent neural strategies (i.e. reciprocal

activation and co-contraction) and changes in the level of tonic activity in a muscle have

no effect on the onset time of the stretch reflex.

Chronic Adaptations

The onset times for the M l stretch reflex in peroneus longus (36 ms), and each

of the triceps surae group (30-33ms) prior to stabUity training corresponds to those

reported in the Uterature (Kearney and Chan, 1982; Sheth et al., 1997). However, a

delay in the onset time of approximately three-five m s was noted in each muscle for

65

most tasks during post testing in the training group. Only Sheth and coUeagues (1997)

have attempted to determine adaptations in the onset times of different muscles of the

ankle after stabiUty trairiing. They recorded the reflex response of tibiaUs anterior,

tibialis posterior, peroneus longus and flexor digitorum longus to a sudden inversion

moment about the ankle induced by the release of a trap door. The results show that 8

weeks of wobble board training caused a delay in the response of the anterior and

posterior tibialis muscles of the ankle. These muscles act to create an inversion moment

around the foot N o delay in the onset time of the principal evertor, peroneus longus,

was reported. They argued that a delay in the onset time of the inverters of the foot

would allow a pure eversion moment to be created around the ankle by peroneus longus

in the event of an inversion ankle sprain. The physiological mechanism for this delay in

reflex onset time will be discussed in the following section.

In the present study, however, a delay in the onset time of peroneus longus was

noted and minimal to no reflex response was recorded from tibiaUs anterior. The delay

in the onset time of both these muscles would counter act each other and they would

presumably contract simultaneously. This would offer no eversion moment to protect

against an inversion ankle sprain. N o explanation could be given for the delay in the

M l stretch reflex response in each of the 4 superficial muscles of the ankle joint after

stability training.

Implications for the Prevention of Lateral Ankle Sprains

Co-contraction of the flexor and extensor muscles of the ankle joint prior to heel

strike improves the stability of the ankle joint complex. The stretch reflex has been

shown to generate large forces in a contracting muscle, after a moderate degree of

stretch is applied (Toft et al., 1991). Therefore, if a stretch reflex occurs in a co-

contracting muscle of the ankle joint prior to heel strike, it has the potential to

destabUize the ankle joint complex (LleweUyn et al., 1990).

A decrease in the amplitude of the stretch reflex was recorded in each of the 4

superficial muscles of the ankle joint during post-testing in the training group. Chronic

presynaptic inhibition of the la afferents induced by training under a state of co-

contraction represents the most likely neural mechanism for this reduction in M l stretch

reflex amptitude. It can be hypothesized that a decrease in the stretch reflex would

reduce its potential to destabilize a co-contracting joint and result in an improvement in

ankle joint stabiUty prior to heel strike. This suggests that a period of wobble board

66

haining has the abiUty to prevent injuries of the ankle joint complex by reducing die

amplitude of the M l stretch reflex in each of the superficial muscles of the ankle joint.

It has been shown in a separate study that wobble board training has the

potential to delay the onset time of tibiaUs anterior and posterior muscles but not in

peroneus longus (Sheth et al., 1997). It was argued that the delay in onset time of the

evertor muscles of the ankle joint would help to establish a muscle contraction pattern

favorable for the correction of excessive ankle inversion. However a large body of

literature suggests that the peroneal muscle cannot react fast enough to protect the ankle

from injury in the case of a sudden inversion sprain (Konradsen et al., 1997). Since no

change the peroneal reflex response was reported by Sheth, and a three miUisecond

delay was reported in this study, there is no evidence to suggest that wobble board

training protects against lateral ankle sprains by improving peroneal muscle reflex onset

time. In fact, it has been suggested that the fastest activation rate of a muscle m a y be

physiologically limited and impossible to improve upon.

It is interesting to note that the reaction time for the peroneus longus muscle

during a forced inversion, reported by most articles, has been detennined in an

experimental setting. It is possible that in the out of laboratory setting, a time delay can

occur during the forced inversion that would result in a lateral ankle sprain. For

example, if an uneven surface slows the inversion motion, or if a shoe slides on the

gravel before weight is appUed to the ankle joint, sufficient time m a y elapse for

muscular protection to be estabUshed. If this is the case, then any change in the

muscular contraction onset times that favored the correction of excessive ankle

inversion could protect against a lateral ankle sprain. It is interesting to note that a

delay in the onset time of the evertor muscles and normal invertor muscles of the ankle

joint were reported by Sheth and coUeagues (1997) after ankle disk trairung and

represents just such an improvement. A similar pattern of delayed evertor and normal

invertor reflex onset times was not evident in the present study however.

67

CHAPTER 6- SUMMARY, CONCLUSIONS AND

RECOMMENDATIONS

Summary

Wobble board training is an effective method to prevent ankle sprains in healthy

individuals during sporting activities (Tropp et al., 1985). A n improvement in ankle

joint stabiUty is thought to represent the neuromuscular mechanism underlying this

reduction in the number of ankle injuries after stabiUty training, however, the exact

nature of this mechanism is still to be elucidated (Thacker et al., 1999). The paucity of

Uterature in this area is most likely due to the methodological difficulties involved with

evaluating the training adaptations of the muscles crossing the ankle joint. However,

the controUed experimental environment employed by the present thesis has allowed

reliable data to be coUected both pre and post framing and raised several possible

neuromuscular adaptations that could explain the mechanism by which wobble board

training acts to prevent ankle sprains in healthy individuals.

Muscles have a significant contribution to the level of dynamic stability of the

loaded and unloaded ankle owing to their anatomical moment arms (McCuUough and

Burge, 1980). —trinsic (contractile properties) and reflex components help contribute to

the level of stabiUty these muscles impart to the ankle joint. Therefore, the stretch

reflex and level of muscular contraction have a significant potential to alter joint

stability.

The purpose of this thesis was to evaluate the neuromuscular adaptations in five

superficial muscles that cross the ankle joint after stability training. A specially

constructed ankle perturbation rig (Skoss et al., 1999) was used to provide

experimentaUy controUed 1 and 3 D O F tasks that chaUenged the stabiUty of the ankle

joint.

The foUowing hypotheses were tested in this thesis:

1. Wobbleboard Iraining results in an increase in the co-contraction ratio of the ankle

musculature during a novel stable and unstable task.

2. Wobbleboard training results in an increase in the net activation of the ankle

musculature during a novel stable and unstable task.

68

3. Wobbleboard framing results in a decrease in the ampUtude of the monosynaptic

stretch reflex in the ankle musculature during a novel stable and unstable task.

4. Wobbleboard framing results in a delay in the onset time of the stretch reflex in the

ankle musculature during a novel stable and unstable task.

Sixteen moderately trained, healthy University students were recruited and

divided into a control group and an experimental group. A U subjects were tested twice

and performed a series of force and position control tasks with the left ankle in a 1 and 3

D O F condition on an ankle perturbation rig. Pre and Post testing sessions were

separated by a period of three weeks and during this time the experimental group was

involved in 10,20 minute training sessions on a wobble board. During data analysis one

subject from either group was discarded due to high impedance levels.

E M G from 5 major muscles crossing the ankle joint were coUected at 2000 H z

using bipolar and branched surface electrodes. Data analysis was spUt into two parts.

First the activation strategies used to stabilize the ankle joint while performing the

position and torque tasks were examined 500ms prior to perturbation. Second, the

morphology of the monosynaptic stretch reflex response in each muscle from the

dorsiflexing perturbation was assessed. Only activation strategy data was normalized to

the maximum E M G recorded in the 3 D O F condition. The author designed two

L A B V I E W programs to aid analysis of the muscle activation and stretch reflex data.

The unstable 3 D O F tasks resulted in a higher co-contraction ratio of the flexor

and extensor muscles of the left ankle than the stable 1 D O F tasks at equivalent plantar

torque levels. These findings suggest that peripheral feedback is used to stimulate

cenfraUy controlled co-contraction strategies to stabilize a joint In addition, a decrease

in the monosynaptic stretch reflex was seen in aU 3 D O F tasks when compared to the

equivalent 1 D O F task. The suppression in reflex amplitude is most likely due to an

increase in pre-synaptic inhibition associated with the increase in co-contraction caused

by the 3 D O F tasks.

After three weeks of stability training, an increase in the activation of peroneus

longus was recorded. This change was most likely due to the increase demand for

peroneus longus to help stabilize the ankle joint during the wobble board training

sessions. The increase in activation of peroneus longus could offer dynamic protection

to the ankle joint during an inversion sprain and may represent an increase in the neural

drive to this muscle.

69

A n increase in the co-contraction ratio of the flexor and extensor muscles of the

ankle joint at low contraction levels was also noted after stability framing. This change

was most probably due to the increase in co-contraction of the ankle joint required to

complete the deck control and stabiUty tasks involved in the wobble board training

regime. These findings suggest that it is possible to alter the centrally controlled co-

contraction pattern of the flexors and extensors of a particular joint through training.

A n y improvement in the co-contraction ratio around the ankle before heel contact would

increase joint stiffness during heel contact and increase the time from ankle perturbation

to ligament injury (Konradsen et al., 1997).

In addition, a reduction in amplitude and increase in the onset latency of the

stretch reflex was recorded in four superficial muscles of the ankle joint during post

training. This change was most likely due to the perturbations that were used to induce

reflex responses whUe the ankle was under a state of co-contraction during the wobble

board training regime. Chronic presynaptic inhibition of the la afferents induced by

training under a state of co-contraction represents the most likely neural mechanism for

this reduction in M l stretch reflex amplitude (Nielsen et al., 1993; Trimble and Koceja,

1994; Mynark and Koceja, 1997; Voigt et al., 1998). A decrease in the stretch reflex

would reduce its potential to destabilize a co-contracting joint and result in an

improvement in ankle joint stability prior to heel strike.

The neuromuscular adaptations observed in this study after wobble board

training have the potential to stabilize the ankle joint and offer dynamic protection prior

to and during heel contact helping to prevent inversion sprains.

Conclusions

O n the basis of the findings of the present study, it can be concluded that:

1. A joint subject to load on a decreased base of support will experience an increase in

the co-contraction ratio of the flexors and extensors crossing that joint.

2. A joint subject to load on a decreased base of support will experience a reduction in

the monosynaptic stretch reflex in the muscles crossing that joint.

3. Wobble board training results in an increase in the activation of the peroneus longus

muscle.

70

4. Wobble board training results in an increase in the co-contraction ratio of the

superficial flexor and extensor muscles crossing the ankle joint.

5. Wobble board training results in a decrease in the net activation of the superficial

muscles crossing the ankle joint.

6. Wobble board training results in a decrease in the amplitude of the Ml stretch reflex

in the superficial muscles crossing the ankle joint.

7. Wobble board training results in an increase in the onset latency of the Ml stretch

reflex in the superficial muscles crossing the ankle joint.

Recommendations for Future Research

The findings of the present investigation suggest that further research into the

neuromuscular adaptations of muscles after stabiUty training would be beneficial.

Obtaining conclusive data about h o w these training regimes affect the activation pattern

and reflex response in the muscles surrounding a joint wiU provide the necessary,

fundamental experimental evidence to vatidate the prescription of stabiUty training as a

method of injury prevention.

1. The maximum EMG used to normalize aU muscle activation data to was not a true

maximum of each muscle, but the maximum level of activation a subject could

attain in the 3 D O F task on the ankle perturbation rig. Normalization procedures in

the fiiture should involve the maximum E M G possible from each muscle out of the

experimental task. A larger subject pool would also increase the power.

2. Further investigation of activation patterns is warranted to determine if stability

training can improve the reciprocal activation of mechanically opposing muscles

around a joint in addition to its abUity to increase the co-contraction ratio of a joint.

For example, it has already been shown that strength training involving pure

flexion-extension motions can reduce knee joint co-contraction, making movements

more efficient (Carolan and CafarelU, 1992).

71

3. Further investigation into the effects of the vestibular system on the reflex response

of the muscles surrounding the ankle should be undertaken. The ankle perturbation

rig aUows a simple transition between the prone and standing positions.

4. The effects of stability fraining on the neuromuscular properties of other joints

including the knee and shoulder should be evaluated. Special perturbation rigs must

first be constructed and designed to provide an experimentally controlled

environment for the testing of these joints. Obtaining conclusive data about h o w

stabUity fraining regimes affect other joints is essential to vatidate the prescription of

these forms of training as a method of injury prevention for these joints.

5. A plethora of devices designed to challenge the stability of a joint are now available

on the retail market. These devises could enhance the framing potential of a short

term fraining regime and should be evaluated (i.e. the C O R E board from Reebok).

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72

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30(5): 447-55. Fitzgerald, G.K., Axe, M.J., et al. (2000). "The efficacy of perturbation fraining in

nonoperative anterior cruciate ligament rehabiUtation programs for physical active individuals." Phvs Ther 80(2): 128-40.

Garrick, J.G. (1977). "The frequency of injury, mechanism of injury, and epidemiology of ankle sprains." A m J Sports M e d 5(6): 241-2.

Garrick, J.G. (1982). "Epidemiologic perspective." Clin Sports M e d 1(1): 13-8. Garrick, J.G. and Requa, R.K. (1988). "The epidemiology of foot and ankle injuries in

sports." Clin Snorts M e d 7(1): 29-36. GottUeb, G.L. (2000). "Miniinizing stress is not enough [comment]." Motor Control

4(1): 64-7; discussion 97-116. Hather, B.M., Tesch, P.A., et al. (1991). "Influence of eccentric actions on skeletal

muscle adaptations to resistance fraining." Acta Physiol Scand 143(2): 177-85. Hodges, P.W. and Bui, B.H. (1996). "A comparison of computer-based methods for the

deterxnination of onset of muscle contraction using electromyography." Elecfroencephalogr Clin Neurophysiol 101(6): 511-9.

Hogan, N. (1984). "Adaptive control of mechanical impedance by coactivation of antagonist muscles." IEEE transactions on automatic control 29(8): 681-90.

Hultborn, H., Meunier, S., et al. (1987). "Assessing changes in presynaptic inhibition of I a fibres: a study in man and the cat." J Physiol 389: 729-56.

Humphrey, D.R. and Reed, D.J. (1983). "Separate cortical systems for control of joint movement and joint stiffness: reciprocal activation and coactivation of antagonist muscles." Adv Neurol 39:347-72.

Johnson, M.B. and Johnson, C.L. (1993). "Electromyographic response of peroneal muscles in surgical and nonsurgical injured ankles during sudden inversion." J Orthop Sports Phvs Ther 18(3): 497-501.

Kapit W . (1993). The Anatomy Colouring Book. N e w York, Harper Collins. Kearney, R.E. and Chan, C.W. (1982). "Contrasts between the reflex responses to

tibiaUs anterior and triceps surae to sudden ankle rotation in normal human subjects." Elecfroencephalogr Clin Neurophysiol 54(3): 301-10.

Kim, A.W., Rosen, A.M., et al. (1995). "Selective muscle activation following electrical stimulation of the coUateral Ugaments of the human knee joint." Arch Phvs M e d Rehabil 76(8): 750-7.

Koh, T.J. and Grabiner, M.D. (1993). "Evaluation of methods to minimize cross talk in surface electromyography." J Biomech 26(Suppl 1): 151-7.

Konradsen, L., Voigt M., et al. (1997). "Ankle inversion injuries. The role of the dynamic defense mechanism." A m J Sports M e d 25(1): 54-8.

Laskowski, E. (1997 October). "Refining RehabiUtation With Proprioception Training: Expediting Return to Play." The Physician and Sportsmedicine 25(10):

Lephart, S.M., Pincivero, D.M., et al. (1998). "Proprioception of the ankle and knee." Sports M e d 25(3): 149-55.

Lephart, S.M., Pincivero, D. M., Giraldo, J. L., Fu, F. H. (1997). "The role of proprioception in the management and rehabilitation of athletic injuries." American Journal of Sports Medicine 25(1):

LleweUyn, M., Yang, J.F., et al. (1990). "Human H-reflexes are smaller in difficult beam walking than in normal freadmtil walking." Exp Brain Res 83(1): 22-8.

Lloyd, D.G. (2001). "Rationale for training programs to reduce anterior cruciate Ugament injuries in AusfraUan football." J Orthop Sports Phvs Ther 31(11): 645-54; discussion 61.

74

Lloyd, D.G. and Buchanan, T.S. (2001). "Strategies of muscular support of varus and valgus isometric loads at the human knee." J Biomech 34(10): 1257-67.

Marsden, CD., Merton, P.A., et al. (1976). "Stretch reflex and servo action in a variety of human muscles." J Physiol 259(2): 531-60.

McConkey, J.P. (1987). "Ankle Sprains, Consequences and Mimics." Medicine and Sport Science 23: 39-55.

McCullough, CJ. and Burge, P.D. (1980). "Rotatory stability of the load-bearing ankle. A n experimental study." J Bone Joint Surg fBr] 62-B(4): 460-4.

Milner-Brown, H.S., Stein, R.B., et al. (1975). "Synchronization of human motor units: possible roles of exercise and supraspinal reflexes." Elecfroencephalogr Clin Neurophysiol 38(3): 245-54.

Morasso, P.G. and Schieppati, M . (1999). "Can muscle stiffness alone stabilize upright standing?" J Neurophysiol 82(3): 1622-6.

Mynark, R.G. and Koceja, D.M. (1997). "Comparison of soleus H-reflex gain from prone to standing in dancers and controls." Elecfroencephalogr Clin Neurophysiol 105(2): 135^10.

Neptune, R.R., Wright, I.C., et al. (1999). "Muscle coordination and function during cutting movements." M e d Sci Sports and Exerc 31(2): 294-302.

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75

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Skoss, R.L., Lloyd, D.G, et al. (1999). "Differential muscular responses to foot perturbations of varying degrees of freedom." In: Fifth IOC Congres on Sport Sciences. Sydney, Australia.

Smith, A.M. (1981). "The coactivation of antagonist muscles." Can J Physiol Pharmacol 59(7): 733-47.

Thacker, S.B., Stroup, D.F., et al. (1999). "The prevention of ankle sprains in sports. A systematic review of the Uterature." A m J Sports M e d 27(6): 753-60.

TMlmann, A.F., Schwarz, M., et al. (1991). "Different mechanisms underlie the long-latency stretch reflex response of active human muscle at different joints." J Physiol (Lond) 444: 631-43.

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Voigt M., Chelti, F., et al. (1998). "Changes in the excitabiUty of soleus muscle short latency stretch reflexes during human hopping after 4 weeks of hopping training." Eur J Appl Physiol 78(6): 522-32.

Wester, J.U., Jespersen, S.M., et al. (1996). "Wobble board training after partial sprains of the lateral Ugaments of the ankle: a prospective randomized study." J Orthop Sports Phvs Ther 23(5): 332-6.

Winters, J., Stark, L., et al. (1988). "An analysis of the sources of musculoskeletal system impedance." J Biomech 21(12): 1011-25.

Wyrick, W . (1970). "Effects of strength training and balance practice on final performances of three balance tasks." Percept Mot Skills 30(3): 951-6.

Yao, W., Fuglevand, R.J., et al. (2000). "Motor-unit synchronization increases E M G ampUtude and decreases force steadiness of simulated contractions." J Neurophysiol 83(1): 441-52.

APPENDICES-

76

APPENDIX A- Consent Form

THE UNIVERSITY OF WESTERN AUSTRALIA

Colin Meakin M S c Candidate

Department of Human Movement & Exercise Science Parkway Entrance No. 3 Nedlands, Western Australia 6907 Telephone: +61 8 9380 7355 Facsimile: +61 8 9380 1039 Email: cmeakin(@cvllene.uwa.edu.au

NEUROMUSCULAR ADAPTATIONS OF THE ANKLE WITH STABILITY TRAINING

-Consent Form-

_(subject name), have read the information sheet provided in this handout and understand the procedures involved in the study I a m about to take part in. Any questions I have about this experiment have been answered to m y satisfaction. I agree to participate in this study, with the knowledge that I a m free to withdraw at any time without prejudice.

I agree that research data gathered from this study may be pubUshed provided my name or other identifying information is not used.

Participant: Date: Investigator: Date:

*The Human Research Ethics Committee at the University of Western Australia requires that all participants are informed mat, if they have any complaint regarding the manner in which a research project is conducted, it may be given to the researcher or, alternatively, to the Secretary, Human Research Ethics Committee, Registrar's Office, University of Western Australia, Nedlands, W A 6907 (telephone number 9380-3703). All study participants will be provided with a copy of the Information Sheet and Consent Form for their personal record's.

77

APPENDIX B- Subject Information Sheet

THE UNIVERSITY OF £fnnM<S?"

_. _ . MSc Candidate

WESTERN AUSTRALIA Department of Human Movement & Exercise Science Parkway Entrance No. 3 Nedlands, Western Australia 6907 Telephone: +618 9380 7355 Facsimile: +61 8 9380 1039 Email: cme-kin@cyllene.uwa.edu.au

NEURAL ADAPTATIONS OF THE ANKLE WITH STABTLITY TRAINING

-Subject Information Sheet-

BACKGROUND Sprains to the lateral Ugament complex of the ankle account for up to 4 5 % of aU injuries in sport and have resulted in more g a m e time lost by athletes than any other sporting injury. StabiUty training programs are among the most effective methods to prevent sport induced ankle sprains. However, the neuromuscular mechanism underlying this decrease in the incidence of ankle sprains after stabUity training is unknown.

Current Uterature in the area suggests that a period of wobble board training, involving balancing exercises results in an improvement in ankle joint movement and position sense as weU as adaptations in the co-contraction strategy and stretch reflex of the ankle musculature.

ATM OF THIS STUDY The 2 aims of this study are to determine if a stabiUty training program can increase the co-contraction response of the ankle joint and decrease the ampUtude of the stretch reflex in the muscles surrounding the ankle. A n increase in the co-contraction strategy of the ankle joint could improve ankle joint stabiUty during static and dynamic situations. A decrease in the ampUtude of the stretch reflex in the ankle musculature has the potential to reduce the abiUty of the stretch reflex to destabilize a co-contracting joint.

GENERAL PROCEDURES A s a subject, you witt be asked to give informed consent and may discontinue with the testing at any time. Y o u wiU be evaluated on a postural control rig and on an ankle perturbation rig both pre and post training. For the ankle perturbation rig your foot wiU be cast into a rigid orthotic and surface electrodes wiU be appUed to measure the level of muscle activity in your ankle. Y o u wiU be asked to Ue in prone (stomach down) and plantarflex your left foot (away from your shin). The ankle perturbation rig wiU then dorsiflex your left foot (towards your shin) using a pneumatic R A M seen in the picture below. The total displacement wiU be 3 cm, and result in a stretch to the muscles of the ankle.

78

APPENDIX B- (continued)

DETAILED PROCEDURES

Sample-S experimental and 8 control subjects are to be randomly selected from a group of moderately trained individuals.

Training-The experimental group is to be involved in 10, 20 minute training sessions over a period of 3 weeks using wobble board exercises detaUed in page 3 of this handout.

Familiarization of the Ankle Perturbation- Prior to pre and post testing on the ankle perturbation rig, subjects wiU be instructed h o w to do the tasks. Subjects wiU then be given training trials in the 1 and 3 D O F tasks.

Ankle Perturbation Rig- The co-contraction response and the stretch reflex ampUtude of the superficial muscles of the left ankle wiU be measured in both the control and experimental groups pre and post training. Subjects wiU be asked to plantar-flex their left foot and generate various levels of torque in a 1 and 3 D O F task. The torque level, and foot position required wiU be visible on a computer screen. W h e n the desired position and force parameters are met, the experimenter wUl trigger a dorsiflexing perturbation.

BENEFITS As a subject, after foUowing the wobble board training regime you wiU experience an improvement in balance and a reduced risk of injury to your lower leg during sports. This study will provide concrete experimental evidence of the neuromuscular mechanisms underlying the decrease in lower limb injuries after wobble board training. This information wiU be used to validate the abiUty of stabiUty training regimes to prevent lower limb injuries.

RISKS Minimal to no risk of injury is involved with the wobble board training regime and the stabiUty index rig if the guidelines set out by the experimenter on page 3 are foUowed. The ankle perturbation rig has been designed to take into account the end range of motion of your ankle joint and can only apply forces and movements that have no potential to damage your Ugaments. The shaving and cleaning of the skin around the ankle could cause a slight burning sensation. In addition, surface E M G electrodes may cause irritation to your skin. It should be noted here that if you, as the subject, have a substantial amount of leg hair, noticeable patches wiU be left around the ankle and take up to 3 weeks to grow back.

SUBJECT RIGHTS Participation in this research is voluntary and you are free to withdraw from the study at any time and for any reason, without prejudice in any way. If̂ in the unlikely event you become iU or injured as a result of participating in this study you wiU be provided with treatment and/or reimbursement for associated medical expenses. This does not preclude any rights that you might have under West AustraUan law.

For further iriformation on the above study please feel free to contact the foUowing individuals.

Colin Meakin 9380-7355 Dr David Lloyd 9380-3919 Dr Richard Lockwood 9380-2366

Thank-you for participating in this study.

79

APPENDIX C- Selection Criteria mm Igl THE UNIVERSITY OF

Sgg WESTERN AUSTRALIA

History of Physical Activity

The following survey attempts to determine the type and level of physical activity you have participated in over your entire lifespan, and over the past two months.

1. During your life time, have you ever trained for a competitive sport at the state, national, or international level?

•Yes •No •If yes, what type of sport did you train for?. .

2. During the two months have you trained for a competitive sport at the state, national or international level?

• Yes • No • If yes, what type of sport did you train for? .

3. During your life time, what are the major leisure activities that you have participated in? What was the average times per week that you engaged in each activity?

Y/N Times per Week Badminton Dancing Field Hockey Footy Soccer (jymnastics Hiking (hilly terrain) Martial Arts NetbaU Rugby Skateboarding Surfing TaiChi Tennis VolleybaU Wmcburfing

• During your lifetime, have you ever partaken in any sort of activities that you think might involve stability training of the ankle? Describe.

Y/N Times per W e e k Aerobic fitness class Cycling outdoors (light) Cycling outdoors (sweaty) Jogging (light) Jogging (sweaty) Skating (blade/ice) Golf Stak-climbing (continuous) Stretching exercises Snowboarding Swimming Walking Weight training(upper body) Weight training(lowerbody) Other

80

APPENDIX C- (continued)

• During your Hfetime, have you ever sustained an injury to your knee or your ankle? Describe.

4. During the two months prior to the initial testing period, what are the major leisure activities that you have participated in? O n average, how many times per week do you engage in each activity?

Badminton Dancing Field Hockey Footy Soccer Gymnastics Hiking (hilly terrain) Martial Arts Netball Rugby Skateboarding Surfing TaiChi Tennis VoUeybaU Windsurfing

Y/N Times per W e e k Y/N Times per W e e k Aerobic fitness class Cycling outdoors (light) Cycling outdoors (sweaty) Jogging (light) Jogging (sweaty) Skating (blade/ice) Golf Stair-climbing (continuous) Stretehing exercises Snowboarding Swiriirriing Walking Weight __ning(upper body) Weight training(lower body) Other

• IXiring the last two months, have you partaken in any sort of activities that might involve stability training of the ankle?

During the last two months, have you been taking any medications?

5. IXiring the last two months, what activities are involved with your normal daily working schedual.

Yes/No Balancing Walking (light objects) Walking (with object ~ 1 Okgs) Walking (with object < 20kgs) Movirig/p_hing objects >30kgs Using heavy tools Climbing stairs Other _

H o w much sleep did you get last night?

• D o you feel well rested today?

81

A V D V v m v r_ nr «<.*:._ ̂ -.A T---:..;-_ T:-~.,.*»L.IA

THE UNIVERSITY OF WESTERN AUSTRALIA

TESTING AND TRAINING TIMETABLE -for the study-

Neuromnscular Adaptations of the Ankle with Stability Training

MONTH JULY

AUGUST

SEPT

DAY Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

Sunday

DATE

28 29 30 31 1

2 3 4 5 6 7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

30 31

1 2 3

TRAINING

GROUP 1

FAMILIARISE

PRE-TESTING

TRAINING 1

TRAINING 2

TRAINING 3

TRAINING 4

TRAINING 5

TRAINING 6

TRAINING 7

TRAINING 8

TRAINING 9

TRAINING 10

POST-TEST

GROUP 2

FAMILIARISE

PRE-TESTING

TRAINING 1

TRAINING 2

TRAINING 3

TRAINING 4

TRAINING 5

TRAINING 6

TRAINING 7

TRAINING 8

TRAINING 9

TRAINING 10

POST-TEST

CONTROL

GROUP 1

PRE-TEST

POST-TEST

GROUP 2

PRE-TEST

POST-TEST

*—_. _. —ill-_#—__ _— l o i i u g a u u -lAuiiug • iiutiauic

82

A P P E N D I X E- Stabiuty Training Regime ISP J"HE U N I ™ I T Y OF wJEgj) WESTERN AUSTRALIA

STABILITY TRAINING R E G I M E

Timing- The stabiUty timning regime involves a total of 10,20 minute sessions of wobble board training. Training days will take place every Monday, Wednesday and Friday over a period of 3 weeks and will be conducted in the Neuromuscular Performance lab (Room 135) at the Department of Human Movement and exercise science at U W A .

WARM-UP EXERCISES 1. Stand with both feet centered on the wobble board. Complete 2 clockwise circles

followed by two counterclockwise circles. Repeat 10 times.

T R A I N I N G EXERCISES-one foot 2. Stand in a "forward lunge" position with one foot on the wobble board, slowly and

lightly tap die toe edge followed by the heel edge of the board on the ground. Repeat 20 times on each foot.

3. Stand in a "toe supported forward lunge" position with one foot on the wobble board. Align your nose, knee and toe on the wobble board. Slowly and lightly tap the toe edge followed by the heel edge of the board on the ground. Repeat 20 times on each foot.

4. While balancing with one foot on the wobble board, Ughtly tap the toe edge followed by the heel edge of the board on the ground. Repeat 20 times on each foot.

5. Stand in a "side lunge" position with one foot on the wobble board, slowly and lightly tap the left side followed by the right side of the board on the ground. Repeat 20 times on each foot.

6. Stand in a "toe supported side lunge" position with one foot on the wobble board. Align your nose, knee and toe on the wobble board. Slowly and lightly tap the left side followed by the right side of the board on the ground. Repeat 20 times on each foot.

7. While balancing with one foot, lightly tap the left side edge followed by the right side edge of the wobble board on the ground. Repeat 20 times on each foot.

T R A I N I N G EXERCISES-two feet 8. Place one foot in front of the other, heel to toe, along the center of the wobble board.

Lightly tap the heel edge followed by the toe edge of the board on the ground. Continue for 2 minutes, throw and catch a basketball during the last minute..

EVALUATION OF PERFORMANCE-two feet 9. Balance on the wobble board for as long as possible while maintaining a horizontal

deck position, without touching the edges to the ground. Continue for 2 minutes, throw and catch a basketball during the last minute.

83

A P P E N D I X F- Evaluation of Performance (Group 1) I | T H E UNIVERSITY O F

|8|| WESTERN AUSTRALIA

EVALUATION OF PERFORMANCE ON A WOBBLE BOARD

-for the study-

Neuromuscular Adaptations of the Ankle with Stability Training

GROUP 1

MONTH AUGUST

DAY Tuesday Wed Thursday Friday

Saturday

Sunday

Monday

Tuesday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tuesday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tuesday

Wed Thursday

Friday

DATE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

GROUP 1 Pre-test

Training 1

Training 2

Training 3

Training 4

Training 5

Training 6

Training 7

Training 8

Training 9

Training 10

Subject 1

8

12

10

16

15

15

18

20

20

19 Post-test

Subject 2

5

7

7

10

5

8

8

12

10

8

Subject 3

10

15

16

20

21

25

24

22

25

28

Subject 4

12

14

10

16

15

20

22

26

24

23

(*time reported in seconds)

Note: Each subject was instructed to balance on a wobble board for as long as possible while mamtaining a horizontal deck position, without touching the edges to the ground and to continue the exercise for 2 minutes. The experimenter lay on lus/her side and used a stopwatch to count the time between successive taps of the edge of the wobble board on the ground.

84

A P P E N D I X G- Evaluation of Performance (Group 2) R l T H E UNIVERSITY O F

juR WESTERN AUSTRALIA

EVALUATION OF PERFORMANCE ON A WOBBLE BOARD

-for the study-

Neuromuscular Adaptations of the Ankle with Stability Training

GROUP2

MONTH AUGUST

DAY Wed Thursday Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

Sunday

Monday

Tueday

Wed Thursday

Friday

Saturday

DATE

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

GROUP 2

Pre-test

Training 1

Training 2

Training 3

Training 4

Training 5

Training 6

Training 7

Training 8

Training 9

TraininglO

Post-test

Subject 5

15

18

22

25

28

26

29

33

30

35

Subject 6

5

7

6

9

8

8

7

9

10

10

Subject 7

12

15

18

28

35

40

48

45

48

50

Subject 8

10

9

14

18

15

16

19

16

21

19

(*time reported in seconds)

Note: Each subject was instructed to balance on a wobble board for as long as possible while maintaining a horizontal deck position, without touching the edges to the ground and to continue the exercise for 2 minutes. The experimenter lay on his/her side and used a stopwatch to count the time between successive taps of the edge of the wobble board on the ground.

85

APPENDIX H- Activation Front Panel

Input He prefix (nrjak)

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A P P E N D I X I- Activation Block Diagram

86

IIMI £§)»] Sta BBsi O H

^ ^ ^. 4- ^ _B _B IMS _B _H USH HE3 ___) t_E_ BS3

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87

APPENDIX I- (continued)

I

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88

APPENDIX J- Reflex Front Panel

Input Fie Prefix: Subject Into* fAse)

DiipSnrn'reRrSubiect Initials

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89

APPENDIX K- Reflex Block Diagram

APPENDIX K- (continued)

90

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