Velocometer: a telemetry-based device to measure ...

Velocometer: a telemetry-based device to measure intra-push changes in racing wheelchair velocity

Andrew D. Moss

A thesis submitted in partial fulfilment of the requirements of the Manchester Metropolitan University for the degree of Master of Science by Research

Department of Exercise and Sport Science Crewe+Alsager Faculty Manchester Metropolitan University August 2003

I certify that all material in this thesis that is not my own work has been identified and that no material is included for which a degree has previously been conferred upon me

Abstract Measurement of the intra-push changes that occur in racing wheelchair velocity is important because it assists in explaining how wheelchair athletes accelerate their wheelchairs. This information has direct application to training and coaching in wheelchair athletics. The purpose of this thesis is to present the design, functional characteristics and utility of a telemetry-based velocometer with the ability to measure intra-push changes in racing wheelchair velocity. Studies one to five describe the functional characteristics of the velocometer. Validity and system linearity: a linear relationship was found when velocity calculated from the velocometer was plotted against three test velocities. The average root mean square deviation (ARMSD) was used to compare velocity calculated from the velocometer with velocity calculated by manual digitising. The ARMSD calculated for each test speed from three trials was 0.06 ± 0.002, 0.27 ± 0.05 and 0.48 ± 0.16 m.s-1 at 1, 5 and 9 m.s-1 respectively. Dynamic response: the ARMSD calculated from the five acceleration and five deceleration trials was 0.29 ± 0.086 and 0.51 ± 0.115 m.s-1 respectively. Reliability: the ARMSD was used to compare the mean trial velocity calculated from velocometer and the speed of the wheelchair rear wheels spun using a DC servomotor. The mean and standard deviation of the differences were 0.079 ± 0.008 m.s-1, for the eight disc-wheel trials and -0.014 ± 0.019 m.s-1, for the eight spoke-wheel trials. Resistance: velocometer resistance calculated as a factor of the mechanical resistance of the wheelchair rear wheel spinning in air was 0.50 and 0.91 N, for the disc and spoke wheel trials respectively. Velocometer resistance calculated as a factor of the total mechanical resistance of the wheelchair/wheelchair-user system was 1.37 and 1.82 N, for the disc and spoke wheel trial respectively. The purpose of the sixth study was to use the velocometer in the analysis of the first six pushes of a sprint start in over-ground racing wheelchair propulsion. One experienced international male wheelchair athlete (age = 28 years; body mass = 60.6 kg; racing classification = T4) performed ten maximal over-ground sprint start trials, over approximately 10 m, in his own racing wheelchair fitted with a Velocometer. Each trial was filmed at 200 Hz using a “Pan and Tilt” system. Eight trials were manually digitised at 100 Hz. The raw co-ordinate data were smoothed using a quintic spline routine. The duration of each push cycle decreased from 0.82 ± 0.02 to 0.45 ± 0.01 s. Within each push the mean duration of the propulsive phase decreased from 0.62 ± 0.02 to 0.21 ± 0.01 s. The mean duration of the recovery phase increased from 0.20 ± 0.01 to 0.24 ± 0.02 s. The athlete contacted the rim progressively closer to top dead centre with each push. Similarly, the athlete released the rim progressively closer to bottom dead centre with each push. The data indicate that peak velocity occurs after release. This is due to the motion of the trunk. The main findings of this study support the observation that racing wheelchair propulsion is a complex form of locomotion and cannot be described accurately by using just the established definitions of a propulsive and a recovery phase. The velocometer provides an effective research tool for the measurement of intra-push changes in velocity, which can be used to further the body of knowledge with regard to racing wheelchair propulsion. ii

Acknowledgements My sincere thanks go to my supervisors, Dr Neil Fowler and Dr Vicky Tolfrey. They have been helpful, supportive, encouraging throughout the duration of this M.Sc. Neil, you have an amazing ability to explain clearly, and with some obvious excitement, the most complicated biomechanical concepts. Vicky, your guidance during my involvement with the British Wheelchair Racing Association (BWRA) sport science support project, gave me an invaluable grounding in applied work on which the foundations of this M.Sc thesis are based. I would also like to sincerely thank Tom McKee for his vast knowledge and expertise in the field of electronics, hard work and enthusiasm.

I would like to gratefully acknowledge Draft wheelchairs for allowing me the use of a state of the art racing wheelchair and Edward Grazier for trusting me with his carbon fibre wheels. As a cyclist I know how valuable these things are.

I am indebted to the individuals who gladly gave up their time for my studies. To Tanni Grey-Thompson and Chris Hallam, my thanks are for educating me in all things wheelchair racing. I wish all of you the best in your future racing.

I consider myself fortunate to have good friends. To Mark Johnson, Jason Martin and Ellen Dawson. I offer my sincere thanks for their friendship, support and advice over the last seven years.

Above all, I would really like to thank my mum for more things than I can possibly list here, but mainly her love and kindness. iii

Publications

The following parts of this thesis have been published or are under review for publication.

Publication

Moss, A. D., Fowler, N. E., Tolfrey, V. L. (2003). A telemetry-based velocometer to measure wheelchair velocity. Journal of Biomechanics, 36 (2), 253 – 257.

Under Review

Moss, A. D., Fowler, N. E., Tolfrey, V. L. An explanation of the intra-push velocity profile of over-ground racing wheelchair propulsion during the first six pushes of the sprint start.

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List of contents

Contents

Page

Title Page

i

Abstract

ii

Acknowledgements

iii

Publications

iv

List of contents

v

List of tables

ix

List of figures

x

Glossary of abbreviations

xii

Glossary of terms

xiv

1. Chapter 1

16

1.1. Introduction

16

1.1.1. Wheelchair sports and the Paralympic Games

16

1.1.2. British Paralympic success

16

1.1.3. Wheelchair sprinting: Technical background

17

1.1.4. A deterministic model for wheelchair sprinting

18

1.1.5. Summary

21

1.1.6. Aim

21

1.1.7. Objectives

22

1.1.8. Hypothesis

22

1.2. Literature review

23

v

1.2.1. Inclusion criteria

23

1.2.2. Wheelchair related research

24

1.2.3. Wheelchair racing: development of a sport

25

1.2.4. Ergonomics

26

1.2.4.1. Wheelchair-user interface: seat

28

1.2.4.2. Wheelchair-user interface: push-rim

29

1.2.4.3. Manual wheelchair propulsion daily use vs. sport

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1.2.5. Assessment of athletic wheelchair performance 1.2.5.1. Simulated wheelchair propulsion under realistic

31 32

Conditions 1.2.5.1.1. Wheelchair ergometers (WERGs)

34

1.2.5.1.2. Motor driven treadmills (MDTs)

36

1.2.5.1.3. Over-ground manual wheelchair propulsion

37

1.2.5.1.4. Protocols

56

1.2.5.1.5. Physiological assessment of the wheelchair

61

Athlete 1.2.5.1.6. Biomechanical assessment of the wheelchair 1.2.6. Summary

61 75

2. Chapter 2

77

2.1. A telemetry-based velocometer to measure wheelchair velocity

77

2.1.1. Design of the device

78

2.1.2. Sampling

81

2.1.3. Mounting

81

2.1.4. Calibration

81

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2.2. Study 1: validity and system linearity

83

2.2.1. Introduction

83

2.2.2. Method

84

2.2.3. Results

86

2.2.4. Discussion

88

2.3. Study 2: dynamic response

91

2.3.1. Introduction

91

2.3.2. Method

92

2.3.3. Results

94

2.3.4. Discussion

94

2.4. Study 3: reliability

96

2.4.1. Introduction

96

2.4.2. Method

97

2.4.3. Results

98

2.4.4. Discussion

100

2.5. Studies 4 and 5: resistance

102

2.5.1. Introduction

102

2.5.2. Method

103

2.5.3. Results

106

2.5.4. Discussion

108

3. Chapter 3

110

3.1. Study 6: an explanation of the intra-push velocity profile of over-ground racing wheelchair propulsion during the first six pushes of the sprint start

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110

3.1.1. Introduction

110

3.1.2. Method

111

3.1.2.1. Calibration

114

3.1.2.2. Pilot study

116

3.1.2.3. Data collection

119

3.1.2.4. Data analysis

121

3.1.2.5. Digitising error

123

3.1.3. Results

123

3.1.3.1. Coefficient of variation

131

3.1.3.2. Relative momentum analysis

131

3.1.4. Discussion

133

3.1.5. Conclusion

139

4. Chapter 4

141

4.1. General Discussion

141

4.1.1. Limitations

143

4.2. Conclusion

145

4.3. Future Recommendations

145

References

147

Appendices

174

viii

List of tables

Table

Title

Page

Table 1

Wheelchair coding for tables 2, 3 and 4

39

Table 2

Studies using a wheelchair ergometer to simulate

40

manual wheelchair propulsion Table 3

Studies using a motor driven treadmill to

51

simulate manual wheelchair propulsion Table 4

Studies

employing

over-ground

manual

54

Velocometer resistance calculated from rundown

107

wheelchair propulsion Table 5

trials Table 6

Actual and calculated pan and tilt calibration

114

values Table 7

Mean propulsive cycle data for the first six

124

pushes of the sprint start calculated from eight trials Table 8

Mean velocity data for the first six pushes of the

126

sprint start calculated from eight trials Table 9

Mean acceleration data for the first six pushes of the sprint start calculated from eight trials

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127

List of figures

Figure

Title

Page

Figure 1

A deterministic model for wheelchair sprinting

20

Figure 2

Optical encoder and transmitter assembly

79

Figure 3

Telemetry system block diagram

80

Figure 4

Calibration equation

82

Figure 5

Experimental set-up for studies 1, 2, 3 and 4

85

showing treadmill wheelchair mounting system (TWMS) Figure 6

Velocometer validity and system linearity

87

Figure 7

Wheelchair and velocometer wheel dimensions

90

Figure 8

Velocometer and manually digitised, 2D video

93

film data collected during (a) one acceleration trial and (b) one deceleration trial Figure 9

Agreement between the constant velocity of a

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wheel spinning in air and mean velocity calculated from the velocometer data, within a five percent error band, from (a) Ten disc wheel trials (b) Ten spoke wheel trials Figure 10

Study 5 experimental set-up showing camera and calibration pole placement in relation to the line of progression

x

105

Figure 11

Study 6 experimental set-up showing the pan and

113

tilt camera and calibration pole placement in relation to the line of progression Figure 12

Calibration procedure. Point denoted by cross is

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digitised as follows: 1) Top point at bottom of view, 2) Top point at top of view, 3) Bottom point at bottom of view, 4) Bottom point at top of view Figure 13

Upper extremity calibration frame

118

Figure 14

Wheelchair/wheelchair-user system model used

121

in the manual digitising of the 3D video film Figure 15

Intra-push

wheelchair

velocity

and

trunk,

129

shoulder and elbow angular displacement during the first six pushes of the sprint start Figure 16

Intra-push

wheelchair

velocity

and

trunk,

130

shoulder and elbow angular velocity during the first six pushes of the sprint start Figure 17

The relationship between relative, transfer and total momentum of the head and trunk during the first six pushes of the sprint start

xi

132

Glossary of abbreviations

Abbreviation

Clarification

ISMGF

International Stoke Mandeville Games Federation

NWAA

National Wheelchair Athletic Association

BPAA

British Paraplegics Athletics Association

IOC

International Olympic Committee

MDT

Motor Driven Treadmill

WERG

Wheelchair Ergometer

HAT

Head, Arms and Trunk

SCI

Spinal Cord Injury

CP

Cerebral Palsy

SB

Spina Bifida

AB

Able Bodied

BSEN

British Standard European Standards

ARMSD

Average root mean square deviation

TDC

Top Dead Centre

BDC

Bottom Dead Centre

WAnT

Wingate Anaerobic Test

P5

Highest mean power output from any five second period during (WAnT)

P30

Mean power output measured during 30 second (WAnT)

IOF

Index of Fatigue

Fiso

Isometric Strength

xii

HR

Heart Rate

VE

Ventilation rate

MTT

Montreal progressive Tack Test

Vc

Critical velocity test

Vch

Maximal velocity with lactate steady state test

RPE

Rating of Perceived Exertion

HLa

Blood lactate

V!O 2

Oxygen Uptake

V!O 2 Peak

Peak Oxygen Uptake

POaer

Maximal Aerobic Power Output

ME

Mechanical Efficiency

xiii

Glossary of terms

Term

Clarification

Quadriplegia.

Condition resulting from SCI at the level of the cervical vertebrae

Paraplegia

Condition resulting from SCI at the level of the thoracic vertebrae or below

Wheelchair /wheelchair Wheelchair and wheelchair user as one integrated unit user system Wheelchair/wheelchair- The point of integration between the wheelchair and the user interface

wheelchair user e.g. Seat cage, push-rim and gloves

Manual wheelchair

The act of locomotion in a push-rim wheelchair

propulsion Propulsive cycle

The movements that bring about locomotion from hand contact to subsequent hand contact at the start of the next propulsive cycle

“propulsive” or “push”

The period between the instant of hand contact to the

phase

instant of release while the hand is in contact with the push-rim

“non-propulsive” or

The period between the instant of release to the instant of

“recovery” phase

contact while the hand is not in contact with the push-rim

Total momentum

The combined contribution of all body segments to momentum of the system

Relative momentum

The contribution of a particular body segment to the total

xiv

momentum of the system Transfer momentum

The momentum that is transferred to a particular body segment from the proximal segment

xv

1.

Chapter 1

1.1.

Introduction

1.1.1. Wheelchair Sports and the Paralympic Games

Wheelchair sports were originally developed shortly after World War II by Sir Ludwig Guttman and colleagues as a rehabilitation tool, a means to provide exercise and recreation for young persons injured during the war. By 1952 the games had developed into the first international wheelchair sporting competition for the disabled. In the same year the International Stoke Mandeville Games Federation (ISMGF) was formed to develop and govern wheelchair sports. The ISMGF later established ties with the International Olympic Committee (IOC) and in 1960 the first international games for the disabled held in conjunction with the Olympic Games took place in Rome. During the 1964 Tokyo games the name “Paralympics” was coined. Subsequently, the Paralympic Games have been held every four years.

1.1.2. British Paralympic success

Of all the 18 Paralympic sports wheelchair racing is arguably the most high profile and, like mainstream athletics, sprint events take centre stage. Wheelchair sprinting (events from 100 to 800 m) is also where Britain achieves most of its success in international competition. British wheelchair athletes returned from the 1996 Paralympic Games in Atlanta, USA with nine medals. Two gold medals and new

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World records (Tanni Grey, 800m, time: 1.55.12 mins and David Holding, 100 m, time: 14.45 s), three silver medals (Tanni Grey, 100 m, 200 m and 400 m) and four bronze medals (Nicola Jarvis, 100 m and 200 m, Paul Williams, 100 m and David Holding 200 m). The success of British wheelchair athletes was shown to the world thanks to the extensive media coverage of the 2000 Olympic and Paralympic Games in Sydney, Australia. In the Paralympic Games British athletes finished second in the medal table, only surpassed by the host nation. Great Britain’s athletes officially became Britain’s most successful Paralympic Team ever. British wheelchair athletes returned with seven medals. Five gold medals (Tanni Grey – Thompson 100 m, 200 m, 400 m and 800 m and Deborah Brennan 200 m) and Two bronze medals (Deborah Brennan 200 m and David Holding 100 m). In addition Deborah Brennan set a new World record over 200 m with a time of 33.87 s.

1.1.3. Wheelchair sprinting: Technical background

The goal of the wheelchair sprinter is the same as that of the sprint runner, which is to cover the race distance in the shortest possible time. For the runner the race is made up of a number of strides. Each stride can be broken down further into two basic components, stride length and stride frequency. The same is true for the wheelchair athlete, the race consists of a number of propulsive cycles consisting of a push phase and a recovery phase. The push phase begins at the point of hand contact with the push-rim. During the push phase the propulsive impulse that brings about forward motion is imparted from the body to the push-rim. The recovery phase begins at the point at which the hand releases the push-rim. The movements that

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return the body to the point immediately before hand contact combine to make up the recovery phase. The push phase can be broken down into pushing length (the distance covered by the wheelchair with each push on the push-rim) and pushing frequency (the number of pushes per unit of time). Walsh (1986) states wheelchair velocity can only be increased through manipulation of one or both of these factors.

1.1.4. A deterministic model for wheelchair sprinting

The deterministic model for wheelchair sprinting (figure 1) identifies the key components that determine the success of a wheelchair sprint athlete. As stated previously the goal of the wheelchair sprinter is to cover the race distance in the shortest possible time, therefore, the goal of the wheelchair sprinter is the development of speed.

With the use of sophisticated laboratory based equipment sport scientists are able to measure many of the components shown in figure 1 during simulated racing wheelchair propulsion (RWP). Information relating to performance enhancement can then be collated and disseminated to coaches and athletes. Unfortunately RWP simulated in a laboratory environment is artificial compared to RWP in a competitive environment (Vanlandewijck et al. 2001). RWP data collected in this artificial environment provides a false description of RWP in a competitive environment and therefore may not be directly applicable to enhance the performance of wheelchair athletes. Scientists working to enhance the performance of wheelchair athletes must

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develop methods of collecting data during over-ground RWP in competition in order to gain an accurate picture of how wheelchair athletes propel their wheelchairs.

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Speed

Resistive Impulse

Propulsive Impulse

Contact Time

Wheel Velocity

Direct Propulsion Force

Contact Radius

Point of Contact

Indirect Propulsion Force

Total Muscle Force

Point of Release

Muscle Cross Sectional Area

Activation

Direction

Muscle Length

Point of Force Application

Seating Position

Wheelchair

Coefficient of Drag

Segmental Motion

Joint Angles

Segmental Lengths

Non-contact Time

Drag

Frontal Surface Area

Relative Momentum of Segments

Segmental Density

Athlete

Figure 1 A deterministic model for wheelchair sprinting

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Velocity

Pushrim Size

Mechanical Resistance

Friction

Rolling Resistance

1.1.5. Summary

The information above clearly identifies British wheelchair sprinting as being at the forefront of international disability sport. However, at present the ability of the sport scientist and coaches to further enhance the performances of these athletes is hampered by methodological constraints. To ensure the continued success of British wheelchair sprint athletes, equipment must be developed for the collection of data during over-ground wheelchair sprinting.

A velocometer that could measure racing wheelchair velocity, would provide a useful research tool in the study of propulsion technique. The device would allow the velocity profile of the wheelchair to be constructed. The velocity profile would provide information on the intra-push characteristics of propulsive cycle.

1.1.6. Aim

1. To design, produce and to test the utility of a velocometer to be used in the assessment of intra-push changes in wheelchair velocity during over-ground propulsion.

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1.1.7. Objectives

1. To assess the functional requirements of the velocometer in relation to best practice for the collection of data from wheelchair athletes.

2. To manufacture the velocometer in accordance with the functional requirements assessed in objective 1.

3. To test the velocometer in accordance with the functional requirements assessed in objective 1 by using the device to record the velocity profile of a racing wheelchair during a sprint trial.

1.1.8. Hypothesis

The velocometer provides an accurate and reliable method for quantifying intra-push changes in racing wheelchair velocity during over-ground propulsion.

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1.2.

Literature review

This literature review is intended to provide the reader with a summary of the findings of selected wheelchair related research. The literature under review covers the period from the mid 1970’s, when manual wheelchair propulsion first became the subject of scientific investigation, through to the present. In Sydney 2000 the world witnessed the most integrated and successful Paralympic Games to date. Wheelchair sport is now considered to be at the forefront of disability sport.

1.2.1. Inclusion criteria

The research reviewed in this section has been subjected to inclusion criteria. The criteria are intended to ensure only studies that do not suffer from the major limitations inherent in wheelchair related research are included. Preference has been given to studies in which data has been collected from athletes, using their own racing wheelchairs, during realistic simulated or actual over-ground manual wheelchair propulsion. Where appropriate, only studies which have utilised overground manual wheelchair propulsion or who have realistically simulated manual wheelchair propulsion using a motor driven treadmill are included. Studies using able-bodied subjects with little or no wheelchair experience have not been considered for inclusion. Studies in which daily use, basketball or “active” wheelchairs, interchanged between subjects, are also not included. Research findings related to lever operated or hand crank wheelchairs has been excluded on the basis that manual

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wheelchair propulsion is the most widely used method of locomotion for wheelchair users.

1.2.2. Wheelchair related research

Previously the global aim of many researchers conducting wheelchair related research has been to contribute to an improvement in the quality of life of lower limb disabled persons who rely on wheelchairs for everyday mobility. However, many researchers have used the growth and maturity of wheelchair sport as justification for scientific investigation (Steadward and Walsh 1986). Cooper (1990c) states that in recent years the progression of world records had slowed significantly, suggesting that a point had been reached in terms of equipment and training at which small differences become more significant. If continued improvements in wheelchair racing are to be made, greater knowledge of the interaction between an individual and their wheelchair will be required. To the sport scientist looking to enhance performance the wheelchair/wheelchair-user system poses a similar problem to that of any athlete whose interaction with a specific piece of equipment brings about a sporting performance. Cooper (1996) states manual wheelchair research can be divided into: design and testing; ergonomics and clinical assessment; physiology and nutrition; and biomechanics.

For a comprehensive collection of wheelchair related research papers the reader is directed to two published works edited by Woude et al. (1993) and Woude et al. (1999). These compilations of wheelchair related research papers, based on the

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proceedings of international workshops, show the variety and direction of wheelchair related research in 1991 and 1999.

1.2.3. Wheelchair racing: development of a sport

In possibly the first study specifically targeting wheelchair racing, Higgs (1983) characterised racing wheelchair construction in terms of success at the 1980 Olympic games for the disabled. He found that the wheelchairs of more successful athletes were characterised by lower seats, an increased seat angle to the horizontal, narrower frame and smaller push-rims. In relative comparison the chairs used by the successful sprinters had higher and more forward placed seats and a shorter chair length. No significant differences in rear wheel camber were found.

Hedrich et al. (1990) provides an excellent description of the developments in wheelchair racing between 1970 and 1990. Prior to the mid 1970s, wheelchair racing existed as an accelerated version of conventional wheelchair propulsion mechanics. The same wheelchairs used in everyday pursuits were used for sport (LaMere and Labanowich 1984a). Recent advancements in wheelchair technology and training have improved performance. However, the propulsion mechanics of wheelchair racing have been dramatically altered (Higgs 1986; LaMere and Labanowich 1984a, 1984b, Sanderson and Sommer 1985, Steadward and Walsh 1986). Contemporary wheelchair frames and wheels are built of aircraft quality alloys that are lighter and stronger than steel or aluminium. Sealed precision bearings are now used in order to

25

reduce mechanical friction and in order to reduce rolling resistance, bicycle racing wheels with narrow profiles and high pressure racing tyres are used.

To some degree the aerodynamic properties of the racer and the wheelchair have also been addressed. Similar to cycling many wheelchair racers wear skin tight, lightweight clothing to minimise aerodynamic drag. Athletes have chosen to reduce the number of rear wheel spokes, adopt radial rather than crossing spoke patterns and use flat rather than round spokes. These wheel modifications enhance the aerodynamic properties of the racing wheelchair. Many athletes have adopted a seating position with flexed upper trunk. Originally adopted because it assured upper torso stability while concurrently allowing more severely disabled racers to push as efficiently as their less disabled counterparts, athletes now believe that adopting this position improves their propulsive efficiency and reduces drag.

1.2.4. Ergonomics

Woude et al. (1989a) described ergonomics as the “optimisation of human work”. The ergonomic approach to the study of manual wheelchair propulsion seeks to optimise the wheelchair-user interface, the fit between the wheelchair user and the wheelchair itself. Cooper (1990c) states the seat cage and the push-rims are two of the most critical interfaces between the individual and his/her racing wheelchair. The seat cage provides support and stabilisation and determines body position with respect to the push-rims. The efficiency of the force transference is dependent upon the limb geometry with respect to the push-rim. The characteristics of the seat can be

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broken down into position (in relation to the rear wheel axel and therefore the pushrims, and height from the ground) and construction (upholstery). Seating can be further broken down in terms of the angle of the base from the horizontal and height of the backrest. Push-rims vary in the overall diameter, the diameter of the tubing used in there construction, the distance they are mounted from the surface of the rear wheels and the material covering the outer surface. These considerations have obvious implications for the design of performance wheelchairs. In the design of performance wheelchairs not only is the optimisation of the wheelchair-user interface, maximising the ability of the athlete, a prime consideration but also the performance characteristics of the wheelchair. Rolling resistance, internal friction and aerodynamic drag must all be considered.

For most wheelchair athletes seating is highly individual. In most modern racing wheelchairs the seat may be only a few pieces of strategically placed upholstery strapped to the frame of the wheelchair. Similarly, the sizes of the push-rims are also highly individual. Wheelchair athletes use push-rims that are of a smaller overall diameter than those typically seen on “daily use” or “active” wheelchairs. The reason is speed. Wheelchair athletes need to be able to accelerate their wheelchairs quickly to top speed and then continue to propel them at a high percentage of that top speed for the duration of the event. The size of the push-rim can be likened to the gearing on a bicycle. The smaller the gear, the faster the bicycle will travel at any given cadence.

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1.2.4.1.

Wheelchair-user interface: seat

The relationship between seat position and the biomechanics of manual wheelchair propulsion has received great attention (Hughes et al., 1992, Mâsse et al., 1992, Ruggles et al., 1994). Unfortunately a general lack of standardisation means that the results of these studies are difficult to compare and generalise to other groups. It is particularly difficult to infer useful information that can be applied to wheelchair sprint athletes. Walsh et al. (1986) investigated the effect of seat position on maximal linear velocity in wheelchair sprinting. The study utilised an adjustable wheelchair fixed to a WERG to assess the effects of nine different seating positions believed to cover the range of seating positions used by wheelchair athletes. The study found no significant differences between the maximal linear velocities measured for each of the nine seat positions. Meijs et al. (1989) investigated the effect of seat height on the physiological response and propulsion technique in wheelchair propulsion. Meijs et al. (1989) took into account the anthropometric dimensions of the nine male nonwheelchair users in order to obtain better standardisation across trials. The study found that seat height has a significant effect on physical load and propulsion technique. The paper states that the reason some authors (Brattgård et al., 1970, Brubaker et al., 1981, 1984) found no difference may have been due to the nonstandardisation of power output and seat height adjustment to individual’s anthropometrical dimensions. Meijs et al. (1989) concluded the range in which the wheelchair seat can be adjusted should cover an elbow angle of 100 to 120 °. The author also states that the results may underline the importance of adjusting wheelchair dimensions to the anthropometric characteristics of the user. These results are similar to a previous study conducted by Woude et al. (1989a). Woude et al.

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(1989a) indicated that, based on comparative physiological responses to propulsion, the optimum angle of elbow flexion, is between 100 and 120 °. To date no studies have successfully identified an optimal seating position for wheelchair sprint athletes.

1.2.4.2.

Wheelchair-user interface: push-rim

Gayle et al. (1990a) investigated the effect of two different sized push-rims (0.25 and 0.41 m overall diameter) on cardiorespiratory and perceptual responses to wheelchair propulsion. Fifteen male paraplegics (3 track athletes, 12 recreational athletes) performed three discontinuous laboratory based exercise tests and two 1600 m performance based track trials. A racing wheelchair (Stainless Medical Products Racer, San Diego, CA), modified for use with each subject, was used for the entire series of laboratory and track based trials. The results reported no significant differences in HR, V!O 2 , VE, HLa or RPE using different sized push-rims at 4 km.h-1. At 8 km.h-1 subjects demonstrated a 13 % lower steady state V!O 2 (p