Introduction to Sports Biomechanics: Analysing Human Movement ...

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BOX 6.2 LOCATION OF MAIN JOINT SAGITTAL AXES OF ROTATION AND JOINT CENTRES OF ROTATION (see also Table 5.1) Joint Sagittal axis Joint centre Shoulder About 10% of the distance between the most lateral point on the lateral border of the acromion process and the elbow joint axis, below the acromion process (Figure 6.5). Elbow Along line joining the medial and lateral epicondyles of the humerus (Figure 6.6(b)). Wrist Along line joining styloid processes on radius and ulna (Figure 6.6(a)). Hip Approximately along line joining the most proximal palpable point on the greater trochanter on the femur to the equivalent point on the contralateral femur (perhaps 1% of the distance from this point to the knee axis of rotation, superior to the greater trochanter). See Figure 6.5. Knee Along line joining medial and lateral condyles on femur (Figure 6.6(c)). Ankle Along line joining most palpable point of tibial malleolus and most lateral point on fibular malleolus (Figure 6.6(d)). Initially, when the broken ends of the bone are brought into contact, they are surrounded by a mass of blood. This is partly absorbed and partly converted, first into fibrous tissue then into bone. The mass around the fractured ends is called the callus. This forms a thickening, for a period of months, which will gradually be smoothed away, unless the ends of the bone have not been correctly aligned. In that case, the callus will persist and form an area where large mechanical stresses may occur, rendering the region susceptible to further fracture. THE JOINTS OF THE BODY THE ANATOMY OF HUMAN MOVEMENT At the centre of the head of the humerus (cannot be palpated). Midway along that line. Midway along that line. At the centre of the head of the femur (cannot be palpated). Midway along that line. Midway along that line. Joints, also known as articulations, occur between the bones or cartilage of the skeleton. They allow free movement of the various parts of the body or more restricted 237
INTRODUCTION TO SPORTS BIOMECHANICS 238 movements, for example during growth or childbirth. Other tissues that may be present in the joints of the body are dense, fibrous connective tissue, which includes ligaments, and synovial membrane. The nature and biomechanical functions of these and other structures associated with joints will not be considered here. Joint classification Overall, joints are classified according to the movement they allow. In fibrous joints, the edges of the bone are joined by thin layers of the fibrous periosteum, as in the suture joints of the skull, where movement is undesirable. With age these joints disappear as the bones fuse. These are immovable joints. Ligamentous joints occur between two bones. The bones can be close together, as in the interosseus talofibular ligament, which allows only a little movement, or further apart, as in the broad and flexible interosseus membrane of fibrous tissue between the ulna and radius, which permits free movement. These are not true joints and are classed as slightly movable. Cartilaginous joints either consist of hyaline cartilage, as in the joint between the sternum and first rib, or fibrocartilage, as in the intervertebral discs. Cartilaginous joints are classed as slightly movable. The third classification of joint has a joint cavity surrounded by a sleeve of fibrous tissue, the ligamentous joint capsule, which unites the bones. Friction between the bones is minimised by smooth hyaline cartilage. Although cartilage has been traditionally regarded as a shock absorber, this role is now considered unlikely. The functions of the cartilage in such joints are mainly to help to reduce stresses between the contacting surfaces, by widely distributing the joint loads, and to allow movement with minimal friction. The inner surface of the capsule is lined with the delicate synovial membrane, the cells of which exude the synovial fluid that lubricates the joint. This fluid converts potentially compressive solid stresses into equally distributed hydrostatic ones, and nourishes the bloodless hyaline cartilage. These freely moveable or synovial joints (Figure 6.7) are the most important in human movement. The changing relationship of the bones to each other during movement creates spaces filled by synovial folds and fringes attached to the synovial membrane. When filled with fat cells these are called fat pads. In certain synovial joints, such as the sternoclavicular and distal radioulnar joints, fibrocartilaginous discs occur that wholly or partially divide the joint. Synovial joints can be classified as follows, based mainly on how many degrees of rotational freedom the joint allows (Figure 6.7). Plane joints (also known as gliding or irregular joints) are joints in which only slight gliding movements occur. These joints have an irregular shape. Examples are the intercarpal joints of the hand (Figure 6.7(a)), the intertarsal joints of the foot, the acromioclavicular joint and the heads and tubercles of the ribs. The joints are classed in the literature both as non-axial, because they glide more or less on a plane surface, and multiaxial. The latter term is presumably used because the surfaces are not plane but have a large radius of curvature and, therefore, an effective centre of rotation
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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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INDEX 288 muscle length-tension rel
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INDEX 290 three-dimensional 146-7,
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INDEX 292 validity 220 vantage poin
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