Oxygen debt is a physiological phenomenon which occurs when someone has consumed oxygen at a rate faster than it can be replaced, leading to a deficit in oxygen which causes increased respiration as the body attempts to replace the used oxygen. Classically, oxygen debt occurs when people exercise, which is why people breathe heavily after exercising. By training, athletes can increase their physical endurance, thereby reducing the rate at which oxygen debt sets in, allowing them to work harder and longer than people who are not in good physical condition.
A number of factors contribute to the development of oxygen debt. For muscles to work well, they must be oxygenated. Oxygen is also used in the production of ATP, a substance which is critical to muscle function. When the body's supply of oxygen begins to get depleted, it switches to anerobic respiration to power the muscles, causing a buildup of lactic acid as a byproduct. Lactic acid can lead to cramps, and the only way to break it down is to oxidize it. These factors combine to encourage the body to supply more oxygen through means like dilating the blood vessels, increasing the heart rate, and increasing respiration.
Eventually, people will become fatigued to the point that they cannot exercise any longer until the debt has been addressed by resting and breathing deeply. Deep breathing allows the body to reoxygenate the blood, make more ATP, and break down the lactic acid. After a set rest period, it will be possible to engage in physical activity again, although people may find that they will fatigue more quickly with a second round of exercise unless they have recovered completely.
People may refer to the increased respiration which occurs after heavy exercise as “oxygen debt” or “oxygen debit.” Others prefer “recovery oxygen” or “excess postexercise oxygen consumption.” Oxygen is not the only thing which the body may need to replenish after strenuous exercise; people may require electrolytes to restore the balance of electrolytes in the body, along with nutritional support which will help their bodies make necessary neurotransmitters.
When breathing after exercise, it is important to take deep, long breaths to get oxygen deep into the lungs, although it may be tempting to breathe quickly as the body feels starved for oxygen. Slow, deep breaths will bring more oxygen into the lungs, repaying the debt and allowing the heart rate to slow while the blood vessels contract down to normal size and the needed oxygen circulates through the body.