Why? The Science of Athletics

104 WHY?-THE SCIENCE OF ATHLETICS · Function of Oxygen in tuming Lactic Acid back into Glycogen Had we no means of removing this poisonous substance from our muscles our activities would very quickly cease, but, as we have seen, the blood-stream carries something else besides food-stuffs to the fibres of the muscles. That something else is oxygen, and it is the function of oxygen to remove the lactic acid from our muscles after it has been liberated by the contraction of the muscle. If the supply of oxygen is inadequ-ate the lactic content of the muscle will become too great to allow it to function. In order that a fatigued muscle may resume its functions the lactic acid must, by the aid of oxygen, be reconverted into glycogen, and this is what happens. In the contraction of the muscle glycogen is turned into lactic acid plus energy ; then follows the recovery process, during which the lactic acid is turned back into glycogen minus energy; and then the reconverted glycogen, plus oxygen, produces carbonic acid and water plus energy. The period required for recovery is contingent upon the quantity of blood-sugar available, the temperature obtaining, and, of course, the degree of severity of the exercise which has induced the presence of lactic acid in the muscle substance. We have a good deal more to learn yet about our muscles, for instance the efficiency of a muscle can be measured by the ratio of its mechanical work to the energy of the food-stuffs with which it is supplied, and this efficiency may be as high as 25% in favourable conditions. We will not treat of the strength of muscles and the tasks they can perform until we come to discuss the subject of leverage. It should, however, be pointed out · to the athlete that his safety margin is indeed a small one, since it is because the athlete all too often remembers only the wonderful feats of strength he has seen performed, forgets, or has never known, the comparatively fragile nature of the composition of his own make-up, and so imposes upon his mechanism those undue strains which