Why? The Science of Athletics

HUMAN MECHANISM 75 the heart accommodation is halved under maximum strain. After violent effort the heart-rate decreases gradually to normal, and although the two nerves which govern the heart do not cause it to beat, their action has yet much to do with the deceleration process, because they influence its rate and affect its strength. The vagus nerve, which is- an involuntary nerve and has its starting point in a nerve centre situated in the underside of the brain, is concerned with slowing down the action of the heart, whereas the "sympathetic" nerve-fibres, . which have their origin in the upper part of the spinal cord, cause the heart-beat to become stronger and more rapid when they are stimulated. As soon as the athlete begins limbering-up, preparatory to competition, the exercise he is taking automatically removes the vagus effect by means of the nervous system, so that his heart begins to beat more rapidly ; and almost at once, and equally automatically, the sympathetic nerve becomes active and the heart-rate rises still higher. Before leaving these specific considerations of various questions in relation to the human heart, let us take two final points, which are of vital interest to all athletes and those who are called upon to take charge of them. Let us agree, to begin with, that the length of time a man can go on and the severity of the effort he can make are contingent upon the amount of oxygen-debt he can incur ; but the extent to which a man can take oxygen into his lungs depends, inter alia, upon the rate at which his heart can drive the blood around his body. Increase in this pressure imposes an immense amount of work upon the heart, and even well-trained athletes cannot take in more than approximately 4 litres of oxygen per minute. Could they take in more they would obtain far greater relief under strain, exhaustion would not follow so quickly upon athletic fatigue, and a man capable of ru:ming a mile in what is ·approximately the world's mile record time of 4 mins. 7 secs. would be capable of