Introduction to Sports Biomechanics: Analysing Human Movement ...

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THE ANATOMY OF HUMAN MOVEMENT Figure 6.9 Structural classification of muscles. Collinear muscles: (a) longitudinal; (b) quadrate rhomboidal; (c) quadrate rectangular; (d) fan-shaped; (e) fusiform. Pennate muscles: (f) unipennate; (g) bipennate; (h) multipennate. Pennate, or penniform, muscles (Figures 6.9(f) to (h)), have shorter fascicles than collinear muscles; the fascicles are angled away from an elongated tendon. This arrangement allows more fibres to be recruited, which provides a stronger, more powerful muscle at the expense of range of movement and speed of the limb moved. They account for 75% of the body’s muscles, mostly in the large muscle groups, including the powerful muscles of the lower extremity. This classification is further divided into the following groups: Unipennate muscles lie to one side of the tendon, extending diagonally as a series of short, parallel fascicles, as in Figure 6.9(f); the tibialis posterior muscle of the ankle is an example. Bipennate muscles (Figure 6.9(g)) have a long central tendon, with fascicles in diagonal pairs on either side. This group includes the rectus femoris muscle of the thigh and the flexor hallucis longus, which flexes the big toe (hallux). Multipennate muscles converge to several tendons, giving a herringbone effect (Figure 6.9(h)), for example the deltoid (deltoideus in Latin). 245
INTRODUCTION TO SPORTS BIOMECHANICS 246 Types of muscle contraction The term ‘muscle contraction’ refers to the development of tension within the muscle. The term is a little confusing, as contraction means becoming smaller in much English usage. Some sport and exercise scientists would prefer the term ‘action’ to be used instead, but as this has yet to be widely adopted, I will use muscle contraction, of which there are three main types: In isometric, or static, contraction, the muscle develops tension with no change in overall muscle length, as when holding a dumbbell stationary in a biceps curl. In concentric contraction, the muscle shortens as tension is developed, as when a dumbbell is raised in a biceps curl. In eccentric contraction, the muscle develops tension while it lengthens, as in the lowering movement in a biceps curl. Both concentric and eccentric contractions can, theoretically, be at constant tension (isotonic) or constant speed (isokinetic). However, most contractions normally involve neither constant tension nor constant speed. Group action of muscles When a fibre or muscle develops tension both ends tend to move; whether these movements actually occur depends on the resistance to movement and on the activity of other muscles. Furthermore, when a muscle develops tension, it tends to perform all of its possible actions at all joints it crosses. Because of these axioms, muscles act together rather than individually to bring about the movements of the human body, with each muscle playing a specific role – this is one important feature of coordinated movement. In such group actions, muscles are classified according to their role, as follows. Please note that the muscle group terminology used here is that normally used in sports biomechanics; however, many anatomists now prefer different names for these muscle group roles. The muscles that directly bring about a movement by contracting concentrically are known as the agonists, which means ‘movers’. This group is sometimes divided into prime movers, which always contract to cause the movement, and assistant movers, which only contract against resistance or at high speed. However, electromyography (see below) does not usually support such a simple distinction. If we accept such a distinction, then brachialis and biceps brachii would be prime movers for elbow flexion while brachioradialis would be generally considered to be an assistant mover. This distinction is closely related to the idea of spurt and shunt muscles touched on later in this section. Antagonists are muscles that cause the opposite movement from that of specified agonists. Their normal role in group action is to relax when the agonists contract,
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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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