Introduction to Sports Biomechanics: Analysing Human Movement ...

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form muscle. The epimysium separates the muscle from its neighbours and facilitates frictionless movement. The contractile cells are concentrated in the soft, fleshy central part of the muscle, called the belly. Towards the ends of the muscle the contractile cells finish but the perimysium and epimysium continue to the bony attachment as a cord-like tendon or flat aponeurosis, in which the fibres are plaited to distribute the muscle force equally over the attachment area. If the belly continues almost to the bone, then individual sheaths of connective tissue attach to the bone over a larger area. The strength and thickness of the muscle sheath varies with location. Superficial muscles, particularly near the distal end of a limb have a thick sheath with additional protective fascia. The sheaths form a tough structural framework for the semi-fluid muscle tissue. They return to their original length even if stretched by 40% of their resting length. Groups of muscles are compartmentalised from others by intermuscular septa, usually attached to the bone and to the deep fascia that surrounds the muscles. Muscle activation Naming muscles THE ANATOMY OF HUMAN MOVEMENT Each muscle fibre is innervated by cranial or spinal nerves and is under voluntary control. The terminal branch of the nerve fibre ends at the neuromuscular junction or motor end-plate, which touches the muscle fibre and transmits the nerve impulse to the sarcoplasm. Each muscle is entered from the central nervous system by nerves that contain both motor and sensory fibres, the former of which are known as motor neurons. As each motor neuron enters the muscle, it branches into terminals, each of which forms a motor end-plate with a single muscle fibre. The term motor unit is used to refer to a motor neuron and all the muscle fibres that it innervates, and these can be spread over a wide area of the muscle. The motor unit can be considered the fundamental functional unit of neuromuscular control. Each nerve impulse causes all the muscle fibres of the motor unit to contract fully and almost simultaneously. The number of fibres per motor unit is sometimes called the innervation ratio. This ratio can be less than 10 for muscles requiring very fine control and greater than 1000 for the weight-bearing muscles of the lower extremity. Muscle activation is regulated through motor unit recruitment and the motor unit stimulation rate (or rate-coding). The former is an orderly sequence based on the size of the motor neuron. The smaller motor neurons are recruited first; these are typically slow twitch with a low maximum tension and a long contraction time. If more motor units can be recruited, then this mechanism dominates; smaller muscles have fewer motor units and depend more on increasing their stimulation rate. As noted in the introduction to this chapter, in the scientific literature muscles are nearly always known by their Latin names. The full name is musculus, which is often 243
INTRODUCTION TO SPORTS BIOMECHANICS 244 omitted or abbreviated to m or M., followed by adjectives or genitives of nouns. The name may refer to role, location, size or shape of the muscle. An example of a muscle named after its location is the latissimus dorsi – the broadest (latissimus) muscle of the back. The flexor digitorum profundus is named after its role – the deep (profundus) flexor of the fingers. The trapezius muscle – the English name is identical to the Latin one for this, but for only a few other, muscles – is named after its trapezoidal shape. Some English names have become accepted, such as the anterior deltoid; obvious English translations of the Latin names, for example the deep flexor of the fingers (see above) are – somewhat sadly in my view – not commonly encountered in most scientific literature. Muscles are often described by their role, such as the flexors of the knee and the abductors of the humerus. Most muscles have more than one role in movement; multijoint muscles have roles at more than one joint. Structural classification of muscles The internal structure or arrangement of the muscle fascicles is related to both the force of contraction and the range of movement and, therefore, serves as a logical way of classifying muscles. There are two basic types each of which is further subdivided. Collinear muscles (Figures 6.9(a) to (e)) have muscle fascicles that are more or less parallel. A collinear muscle is capable of shortening by about one-third to one-half of its belly’s length. Such muscles have a large range of movement, which is limited by the fraction of the muscle length that is tendinous. These muscles are very common in the extremities and are further divided as follows. Longitudinal muscles consist of long, strap-like fascicles parallel to the long axis, as shown schematically in Figure 6.9(a); examples are the rectus abdominis muscle of the abdominal wall and the sartorius, the longest muscle in the human body, which crosses the hip and knee joints across the front of the thigh. Quadrate muscles are four-sided, usually flat, with parallel fascicles, as in Figures 6.9(b) and (c). They may have a rhomboid shape as in the schematic representation of the rhomboideus major – a muscle of the scapula – in Figure 6.9(b), or rectangular, as, for example, the pronator quadratus, located on the anterior aspect of the forearm near the wrist and shown schematically in Figure 6.9(c). Fan-shaped muscles (Figure 6.9(d)) are relatively flat with almost parallel fascicles that converge towards the insertion point. A good example is the pectoralis major muscle on the upper anterior surface of the trunk. Fusiform muscles are usually rounded, tapering at either end (Figure 6.9(e)), and include the elbow flexors: brachialis, brachioradialis and biceps brachii. The location of the last of these is certainly familiar to most, if not all, sport and exercise science students. The brachialis lies directly underneath the biceps brachii, is a single joint muscle and is the main elbow flexor.
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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: Figure 6.8 Main skeletal muscles: (
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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