Why? The Science of Athletics

86 WHY?-THE SCIENCE OF ATHLETICS upon the severity and the duration of that effort, governed by the oxygen income of the particular individual under– taking such effort, and the size of the oxygen debt it is possible for him to secure. The sprinter, obviously, has little or no income and so must create a big oxygen debt, which he will liquidate in the process . of rest– recovery. It is this consideration of income and credit which determines the limitation of the sprint-distance at a furlong, or, possibly, 300 yards. The distance runner, on the other hand, breathes regularly as he runs, and therefore lives- partly on his income and draws on his allowable oxygen credit only as his fatigue increases. The first, and easiest, way to make use of available oxygen is to take exercise of such an easy nature that oxygen-income and oxygen-consumption will balance one another, that is to say, the individual will work just hard enough to use up the oxygen passing through the lungs during the period of exercise. The second method, which is the one mainly employed by distance runners, is to live partly on income and partly on credit. The third method is that of the sprinter who runs right into debt, because the severity of his effort cannot possibly be met out of his income. Both the middle-distance runner, who borrows moderately, and the sprinter, who overdraws his credit, have to pay off the oxygen debt after exercise by rest and recuperation. Field events men fall into a different category. Their efforts may be as violent as those of the sprinter and they can have no oxygen income during the performance of jumping, pole vaulting, throwing or shot putting, but each effort is very brief and the time that elapses before it is one's turn to try again should be ample for any trained man to pay off the oxygen debt his brief effort has caused him to incur. Nature makes no difficulty about allowing the athlete an overdraft which is sufficient for his needs, and Nature is, moreover, an admirable bank-manager in that she provides a means of paying off one's overdraft. What