Oxygen consumption must be increased in order to replace the debt caused by exercise and vigorous activity. Under normal conditions, myoglobin, a pigment in the blood, serves as a small storehouse for oxygen. Pyruvate is used to create energy in the body, and glycogen is stored up and ready for a situation that will require a burst of energy, such as exercise. When these stores of oxygen are used up, the body processes must temporarily switch gears and take a new plan of action. When myoglobin is depleted, the muscles begin to work without oxygen. This process is commonly referred to as anaerobic. Because the supply of oxygen is now limited, components such as ATP, or adenosine triphosphate help to convert pyruvate into lactic acid. Lactic acid can then be converted into glucose or glycogen for use by the body as energy, or released into carbon dioxide and water as the body is moving strenuously. Once the body's vigorous activity has slowed down or ceased, depleted storage of ATP, myoglobin and glycogen will need to be replenished. The amount of time that replenishment takes depends upon how strenuous the activity was, and how much oxygen will be necessary for complete restoration. It will take anywhere from two hours up to several days for components such as the storage of glycogen to be recovered.

The amount of oxygen debt created exertion can be greatly lessened based on a number of factors. Maximum oxygen uptake is another phrase for aerobic capacity, and it's determined by things such as age, sex and weight. Females, people who are obese or overweight, and those who are older tend to have a smaller aerobic capacity, thus they may become 'out of breath' more quickly than others when exerting themselves. Changes in diet and proper muscle or weight training can decrease the amount of oxygen debt created during a workout. When this is accomplished, people experience less exhaustion while working out, weight training or even taking that walk to the mailbox!