Why? The Science of Athletics

I 10 WHY?-THE SCIENCE OF ATHLETICS Not a great deal need be said here The Heart about the heart, since what has been written already regarding the blood system has covered most of the necessary ground. In some respects the heart approximates more closely to the structure of the voluntary muscles and yet must be considered as being mainly an involuntary muscle, sinc8 its action is certainly not subject to our own will. Its function is purely and simply that of pumping blood round the body, and -it uses up oxygen and fuel, just as does any other muscle. - · The heart rate, as we saw in an earlier chapter, rises rapidly in response to exercise. As we shall see in. more detail later on, it is influenced also by excitement and emotion, and is carried on, in circumstances of excitement, owing to the presence in the blood of a substance called adrenalin, which is produced by the suprarenal glands that lie deeply embedded in the body close to the kidneys.