Oxygen debt is the oxygen that needs to be replaced or paid back to the various systems in the body, such as the lungs, hemoglobin and myoglobin (found in the muscles of the body) and body fluids. This repayment of oxygen would catabolize the lactic acid formed in the muscles back to carbon dioxide and water.


When the energy required by the body exceeds the oxygen supply available to the body, the muscles get their oxygen from the breakdown of the ATP (Adenosine Triphosphate) in the body. When this is also consumed, then additional ATP is produced by glycolisis without the use of oxygen (as it normally happens when ATP is produced in the body) and this process is called anaerobic glycolisis. This in turn, converts the pyruvic acid into lactic acid, which is then transported to the liver where it is broken into its two basic components, glucose and glycogen. Hence, the muscles get their energy supply when needed.


When a person goes through this process, he/she normally becomes short of breath, since all of the oxygen is consumed by the muscle cells as a result of the strenuous exercise involved, and the rest of the body feels the need to supply more oxygen faster. This is when the person starts gasping for breath, which will be fast and shallow.


Oxygen Requirement for Highly Strenuous Exercises


There is a maximum possible level of oxygen consumption during exercise and this is known as maximal oxygen uptake and athletes develop it to about twice the capacity of a normal non-athletic person. This permits the athletes to perform astounding feats with less effort than a non-athlete would be able to. The maximum oxygen uptake is achieved through specially focused training that gradually builds it up to the maximum possible levels. The athlete can never afford to let this level fall, and hence would require continuous training to maintain the required maximum level once it has been achieved.


The Oxygen Debt


As soon as the demanding type of exercise has ceased, the body reverses the processes in order to refill the oxygen that it has been depleted from different parts of the body. The following four major tasks are involved in the reversal process:


  1. ATP is restocked.

  2. Lactic acid is catabolized and removed (this is felt as acute pain in the muscles similar to a burning sensation).

  3. Refilling the store houses of oxygen in the myoglobin (a compound similar to hemoglobin that is found in the muscles).

  4. Glycogen is restored.


There are two major parts of oxygen debt:


  1. A fast component where the oxygen is reversed quickly through synthesis, which restores phosphagen in the muscles in the form of ATP, and PC – this component is known as Alactacid oxygen debt. This process is concurrent with the replenishment of oxygen levels in the muscle myoglobin.

  2. A slow component where the oxygen replenishment is used to remove the lactic acid accumulated in the blood and muscles – this component is known as Lactacid oxygen debt.


The oxygen debt would be in excess of the normal pre-exercise quantity of oxygen available in the body. Normally, the excess oxygen would be replenished in about 30 to 60 seconds after the exercise has ceased when the exercises are mild. However, the time of replenishment can take more than 24 hours when the exercises are extremely strenuous and there is lactate build up in the blood.


The last phase, i.e. the replenishment of glycogen in the liver depends upon how strenuous the exercises were and how much the oxygen debt in the body is. The period of replenishment varies a lot, from 2 hours to a number of days. It is worthwhile to mention that the replenishment is usually very fast in the initial hours after the exercises cease. Once a comfortable level has been achieved, the replenishment slows down and may span over a few days. This process can be helped and accelerated with the help of a high-carbohydrate diet.