Why? The Science of Athletics

HUMAN MECHANISM 99 volume during and after work. This increase is accounted for by the greater volume of blood which is brought to the muscle to enable it to do its work. Experiments carried o~t with animals show that the weight of the muscles may be as much as 20% greater as long as eight hours after violent exercise, and in this connection - the greater weight is due to lymph accumulation which probably increases the sarcoplasm content. In order that muscles may move our limbs, they must, of course, be attached to the bone. At each end of the muscle all the fibres of the tendons unite to form the main tendons of that muscle, the "origin" of which is· the fixed point of its attachment to the bone, its "inser– tion" being at the point where it joins the bone, or part, which it moves. 'Later on, when we are discussing leverage, we shall see how the circumstance of the tendons being long or short affects our activity. The blood-vessels, as we have seen, run in all directions through the muscle-substance, while the nerves, which are more excitable than the muscles, make contact through their nerve-endings. When the muscles respond to the orders conveyed to them through the nerve channels there is activity, which must be followed by a process of recovery, on account of the creation of fatigue. Fatigue is still a matter of primary interest to all physiologists and will be dealt with more fully in a later chapter ; meanwhile, the importance of our circulatory system is well exemplified by the fact that any circumstance which cuts off, or di~inishes, the blood supply to the muscles creates fatigue far more quickly than when the circumstances of activity are normal. . The muscles must be kept well supplied by blood to brmg them their food-stuffs, otherwise they will lack energy, although, in point of fact, they contain large reserve stores of their own. The blood-stream must also go on functioning to carry away the waste products of fatigue, but the . most important consideration of all