Why? The Science of Athletics

HUMAN MECHANISM IOI upon one's energies ·at short notice·. What the athlete and his trainer must therefore aim at is the building up of both supplies and reserves of sugar. Now, glycogen is the fuel that is burnt, or used up,. during active exercise. It has to be replaced by the sugar which the blood– stream brings to the fibres of the muscles, because it is at least probable that glycogen is the only fuel that they can burn. In these circumstances one may almost, I suppose, call glycogen ''blood-sugar", and the blood gets the sugar which is required, either to replace wastage, or to supply energy, from the liver where it is stored, or from the intestinal tract which absorbs it from food during the process of digestion. Having read the foregoing the athlete may well wonder why his diet should not be made up almost exclusively of sugar. There are, however, many other useful things that he should eat, but the thing to remember is that all of them must be turned into sugar by the digestive system before the muscles can make use of them. Let us look a little more carefully at what takes place when the muscles are called upon to make a strenuous effort. In the first place the . suprarenal glands which control the sympathetic nervous system are stimulated, and adrenalin is released into the blood-stream, with two results, in that it raises the blood-pressure and it raises also the sugar content of the blood. Sugar is present in the blood in the form of glucose (dextrose) but is not stored in the body as such. The reserve supply is in the form of glycogen, which occurs not only in the liver but also in the muscles. The action of the suprarenal gland is that it changes the glycogen back into glucose, and glucose is the force that provides energy, by combining with oxygen which is carried in the blood. It will be seen therefore that an athlete needs a well– filled reservoir of glycogen when a prolonged effort 1s