oxygen debt

Physiological state produced by vigorous exercise, in which the lungs cannot supply all the oxygen that the muscles need. In other words, the lungs and bloodstream, pumped by the heart, cannot supply sufficient oxygen for aerobic respiration in the muscles. In such a situation the muscles can continue to break down glucose to liberate energy for a short time using anaerobic respiration. This partial breakdown produces lactic acid, which results in a sensation of fatigue when it reaches certain levels in the muscles and the blood. This explains why it is possible to run faster in a sprint than over longer distances. During the sprint, the muscles can respire anaerobically. Once the vigorous muscle movements cease, the body breaks down the accumulated lactic acid on top of the ‘normal’ breakdown of glucose in aerobic respiration, using up extra oxygen to do so. Panting after exercise is an automatic mechanism to ‘pay off’ the oxygen debt.