Introduction to Sports Biomechanics: Analysing Human Movement ...

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THE ANATOMY OF HUMAN MOVEMENT Figure 6.17 Two-dimensional muscle force components: (a) brachialis acting on forearm and humerus; (b) angle of pull; (c) stabilising and turning components of muscle force; (d) to (f) effect of angle of pull on force components. The magnitude and direction of the muscle force vector (F) have been kept constant through figures (a) to (f). anterior to the ankle on the dorsal surface of the foot and would be a dorsiflexor. An anatomical pulley may also provide a greater angle of pull, thus increasing the turning component of the muscle force. The patella achieves this effect for quadriceps femoris, improving the effectiveness of this muscle as an extensor of the knee joint. 257
INTRODUCTION TO SPORTS BIOMECHANICS ELECTROMYOGRAPHY – WHAT MUSCLES DO This and the next two sections are intended to provide you with an appreciation of the applications of electromyography to the study of muscle activity in sports movements. This includes the equipment and methods used and the processing of electromyographic data. We will also touch on the important relationship between muscle tension and the recorded signal, known as the electromyogram (abbreviation EMG, which is also, somewhat loosely, used as an abbreviation for electromyography). Electromyography is the technique for recording changes in the electrical potential of a muscle when it is caused to contract by a motor nerve impulse. The neural stimulation of the muscle fibre at the motor end-plate results in a reduction of the electrical potential of the cell and a spread of the action potential through the muscle fibre. The motor action potential (MAP), or muscle fibre action potential, is the name given to the waveform resulting from this depolarisation wave. This propagates in both directions along each muscle fibre from the motor end-plate before being followed by a repolarisation wave. The summation in space and time of motor action potentials from the fibres of a given motor unit is termed a motor unit action potential (MUAP, Figure 6.18). A sequence of MUAPs, resulting from repeated neural stimulation, is referred to as a motor unit action potential train (MUAPT). The physiological EMG signal is the sum, over space and time, of the MUAPT from the various motor units (Figure 6.18). Figure 6.18 Schematic representation of the generation of the EMG signal. 258 Electromyography is the only method of objectively assessing when a muscle is active. It has been used to establish the roles that muscles fulfil both individually and in group actions. The EMG provides information on the timing, or sequencing, of the activity of various muscles in sports movements. By studying the sequencing of muscle activation, the sports biomechanist can focus on several factors that relate to skill, such as any overlap of agonist and antagonist activity and the onset of antagonist activity at the end of a movement. It also allows the sports biomechanist to study changes in muscular activity during skill acquisition and as a result of training. Electromyography can also be used to validate assumptions about muscle activity that are made when
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Introduction to Sports Biomechanics
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First edition published 1997 This e
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Contents List of figures x List of
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Study tasks 216 Glossary of importa
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FIGURES 1.26 Underarm throw - femal
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FIGURES 5.9 Typical path of a swimm
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Tables 2.1 Examples of slowest sati
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Preface Why have I changed the cove
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Introduction MISSING TEXT The first
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INTRODUCTION principal movements in
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INTRODUCTION TO SPORTS BIOMECHANICS
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Figure 2.2 ‘Principles’ approac
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Figure 2.13 Identifying critical fe
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Page 229 and 230: INTRODUCTION TO SPORTS BIOMECHANICS
Page 265 and 266: Figure 6.8 Main skeletal muscles: (
Page 279: INTRODUCTION TO SPORTS BIOMECHANICS
Page 305 and 306: INDEX 282 balls air flow past 173 b
Page 307 and 308: INDEX 284 energy 219 kinetic 219 mi
Page 309 and 310: INDEX 286 isokinetic contraction 24
Page 311 and 312: INDEX 288 muscle length-tension rel
Page 313 and 314: INDEX 290 three-dimensional 146-7,
Page 315: INDEX 292 validity 220 vantage poin
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