Why? The Science of Athletics

I "' WHY?-THE SCIENCE OF ATHLETICS amount of blood equal to the amount leaving the heart at each beat. If the walls of the arteries were to become entirely inelastic, the flow of blood in the capillaries would be intermittent, because the heart would pump as much blood as left it into the capillaries and the flow would cease when the heart-beat finished. That is why it is so dangerous for old athletes, whose arteries are becoming hardened, to take part in veterans' races. The functiem which brings into play the elasticity of the larger arteries is called "peripheral resistance" ; the estimate -of the force which drives the blood through the tissues and organs of the body is commonly termed "blood-pressure". This all-important blood-pressure de– pends upon (a) the amount of blood forced into the aorta by the heart-beat per minute, and (b) the amount of peri– pheral resistance. The blood-output varies according to the heart-beats per minute and the strength of each beat, and (b) the greater the peripheral resistance the higher will be the blood-pressure. But the human system, as will appear later, has means of its own for increasing or decreasing the number of heart-beats per minute, of adjusting the force of the beats and the peripheral resist– ance to the needs of any particular part or organ of the body at any given time, so that a blood-pressure suitable to the . needs of the particular circumstances obtaining may be produced. Thus, when a person is reclining the normal heart– beat is about 6o, but when that persons stands up, the rate rises, normally, to 75, and in the intermediate sitting position is about 72. A short, sharp sprint will raise the rate of heart-beat per minute by as much as· 25%, and so, ag~in, we see the need for training, to enable the heart tQ support the strain. · It should be remembered that a hot bath and pleasur– able excitement both stimulate the action of the heart. That is one of the reasons why a man limbers-up before a competition to get his body warm, and why a man