Oxygen debt

During muscular exercise, blood vessels dilate to allow increased blood flow to accommodate the body’s needs for increased oxygen. Up to a point, this process is sufficient. However, when exertion is exhaustive, oxygen cannot be supplied to muscle fibres fast enough.

Once adequate oxygen is available, lactic acid that has diffused from skeletal muscles (and transported to the liver for conversion to glucose), must be catabolised completely into carbon dioxide and water. After exercise is stopped, extra oxygen is required to perform this metabolism; replenishing ATP and paying back any oxygen that has been borrowed from haemoglobin, myoglobin, air in the lungs, and body fluids. This additional oxygen that must be taken into the body after vigorous exercise, in order to restore all systems is called oxygen debt.

Highly trained athletes can have maximal oxygen uptakes that are twice that of average people, owing to a combination of genetics and training. As a result they are capable of greater muscular activity without increasing their lactic acid production, and their oxygen debts are less.