Why? The Science of Athletics

HUMAN MECHANISM SI consideration of the effect of different types of physical effort upon the blood stream. We know that but little carbon dioxide enters our lungs with the air we breathe, whereas the air we expel contains about 5% of C0 2 • If a man holds his breath this poison collects in the lungs, is carried by the blood to the brain, which issues an S 0 S to the respiratory centres and he is forced to go on breathing. But if, as when a man limbers-up for a race by practising some deep-breathing exercises without moving his limbs, deep breathing is used to get rid of a large proportion of C0 2 , then the breath can be held for a much longer period. More will be said about this later on when we come to consider tidal breathing and the elimination of C0 2 • Meanwhile, even the presence of hremoglobin in the blood does not prevent an athlete in action from requiring the circulation of a considerable amount of blood to carry the oxygen to supply his needs, but the action of the muscles themselves helps the heart to bear the load that is placed upon it in this way. This is where we come to the effects of different types of effort. In a partly static performance, such as weight lifting, which calls for a violent effort in which the body remains stationary and rjgid, there is a certain amount of stagnation in the veins and fatigue ensues swiftly, because the action of the athlete does not tend to accelerate the blood-flow back to the heart. Not quite so much hindrance in the return of blood to the heart is found in the case of rowing. Here the movements, although powerful, are comparatively slow, and do in fact impose a somewhat excessive strain upon the heart-muscle itself, which tends to become over– developed. This may seem curious, in view of the fact ~hat the greatest oxygen consumptioi_J. ever recorded was In the case of an oarsman, but the undue strain is placed upon the heart by the circumstance of the bodily move– ments not being rapid enough to aid the circulation. F