Why? The Science of Athletics

HUMAN MECHANISM 97 calls upon it but does not adjust its action to our orders. A voluntary muscle is made up of thousands of muscle– fibres, thin jelly-like threads, the largest not more than about a tenth of a millimetre in thickness and forty millimetres in length. These fibres are packed closely in bundles, and just how numerous they are can be understood from the circumstance that the biceps muscle of a man's arm, alone, contains 6oo,ooo of them. Each fibre, again, is composed of many fibrils, which probably supply that all-important contractile power, as yet so little understood by scientists. The fibrils are immersed in liquid sarco– plasm and surrounded by a membrane-sarcolemma. In the midst of these bundles of fibres are almost innumerable blood- vessels for the supply of Fm. 1 3 fuel and oxygen. There is another characteristic ofvoluntary muscles which is still providing a problem, and that is the purpose of the cross-striations which occur at regular intervals and are usually more vivid in the muscles which we are able to move most quickly. . The greater redness of some muscle fibres is due to a greater accumulation of red pigment. These red fibres develop as the result of greater work. That is why the muscles of a well-trained athlete are more red than those of a person leading a sedentary life, just as the meat ofwild game is more red than that of domesticated animals. Fig. 13 shows the biceps muscle of an athlete's right arm, together with its tendon, nerve, vein and artery. The tendon, or sinew, in which the muscle terminates supplies the method of attachment to the bone ; the artery brings food and oxygen to the muscle; while the G