Essay on Oxygen Debt and the Beneficial Effects of Exercise

During muscular exercise, blood vessels in the muscles dilate and blood flow is increased in order to increase the available oxygen supply, to allow the muscles required to function properly. Up to a point, the available oxygen is sufficient to meet the energy needs of the body. However, when muscular exertion is very great, oxygen cannot be supplied to muscle fibres fast enough, and the aerobic breakdown of pyruvic acid cannot produce all the ATP required for further muscle contraction. During such periods, additional ATP is generated by anaerobic respiration by glycolysis. In the process, most of the pyruvic acid produced is converted to lactic acid. This can only be done for a short time as the acid produced is toxic to the body, very quickly the muscles will begin to cramp and exercise cannot continue. Ultimately, once adequate oxygen is available, lactic acid must be catabolised completely into carbon dioxide and water. After exercise has stopped, extra oxygen is required to metabolise lactic acid; to replenish ATP, phosphocreatine, and glycogen; and to pay back any oxygen that has been borrowed from haemoglobin, myoglobin, air in the lungs, and body fluids.
The additional oxygen that must be taken into the body after vigorous exercise to restore all systems to their normal states is called oxygen debt

The need for oxygen to replenish ATP and remove lactic acid is referred to as the "Oxygen Debit" or "Excess Post-exercise Oxygen Consumption" (EPOC) - the total oxygen consumed after exercise in excess of a pre-exercise baseline level.
In low intensity, primarily aerobic exercise, about one half of the total EPOC takes place within 30 seconds of stopping the exercise and complete recovery can be achieved within several minutes (oxygen uptake returns to the pre-exercise level).
Recovery from more strenuous exercise, which is often accompanied by increase in blood lactate and body temperature, may require 24 hours or more before