Introduction to Sports Biomechanics: Analysing Human Movement ...

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Figure 6.14 Tension–time relationship. Muscle stiffness THE ANATOMY OF HUMAN MOVEMENT The mechanical stiffness of a muscle is the instantaneous rate of change of force with length – it is the slope of the muscle tension–length curve. Unstimulated muscles possess low stiffness (or high compliance). This rises with time during tension and is directly related to the degree of filament overlap and cross-bridge attachment. At high rates of change of force, such as occur in many sports, muscle is stiff, particularly in eccentric contractions for which stiffnesses over 200 times those for concentric contractions have been reported. Stiffness is often considered to be under reflex control with regulation through both the length component of the muscle spindle receptors and the force–feedback component of the Golgi tendon organs. The exact role of the various reflex components in stiffness regulation in fast human movements in sport remains to be fully established as do their effects in the stretch–shortening cycle (see below). It is clear, however, that the reflexes can almost double the stiffness of the muscles alone at some joints. Furthermore, muscle and reflex properties and the central nervous system interact in determining how stiffness affects the control of movement. 253
INTRODUCTION TO SPORTS BIOMECHANICS Figure 6.15 Force potentiation in the stretch–shortening cycle in vertical jumps; blue curves show knee joint angle and black ones the vertical component of the ground reaction force: (a) concentric (+) knee extension in squat jump; (b) eccentric (–) contraction followed immediately by concentric (+) contraction in counter-movement jump; (c) as (b) but with a 1 s pause between the eccentric and concentric phases. The angles and forces have been ‘normalised’ equally across the three jumps to fall within the ranges 0 to +1 and –1 to +1, respectively. 254
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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 265 and 266: Figure 6.8 Main skeletal muscles: (
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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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