Why? The Science of Athletics

HUMAN MECHANISM that violent athletic exercise brings into action muscle– fibres which otherwise would lie virtually dormant, and tiny blood channels-the capillaries-which otherwise might remain closed and in reserve. But the supply of blood, and therefore oxygen, to all these fibres must be increased, as will be readily understood from the state– ment that a sprinter running 100 yards in fast time requires about 30 times as much oxygen as he would need in normal activity. But while the blood is passing through the capillaries, the organs and tissues of the body are taking in oxygen and nutrition, so that a slow– moving, regular blood-stream is best suited to the inter– change of materials. On the other hand, the heart is bound to pump blood faster right out to the capillaries of a man indulging in violent action, because the total calibre of the arterial system increases as the capillaries are reached. The blood-flow in the aorta-the great artery-is about go ft. per minute when it leaves the heart, but in the capillaries is no more than 2 in. per minute. Further, when the capillaries rejoin to form the lesser veins the blood-stream is accelerated, because arterial capacity is decreased, and in fact blood returns to the heart via the upper and lower vena cava at half the speed at which it left. The importance of proper training now becomes more apparent than ever, on account of the way in which the intermittent blood-flow in the arteries is controlled to provide the regular stream of the capillaries. Training does, and must, tend to make the walls of the arteries more elastic, because the smaller vessels and capillaries · offer considerable resistance to the blood-flow. Where– fore each heart-beat makes demands upon the elasticity of the walls of the larger arteries, the heart-beats being repeated with just enough rapidity to make the outflow of blood into the capillaries continuous, through the arterial system being distended to the point where the elasticity of the arterial walls will force through the capillaries, between each heart-beat and · the next, an