EPOC or Excess Post-Exercise Oxygen Consumption is the amount of oxygen a body takes in above the normal oxygen needs following exercise. It is often seen as an oxygen debt, built up during intense exercise which could not be sustained by the aerobic system alone. However there are other mechanisms that increase EPOC as well.

EPOC is a reaction of the body after exercise to restore it to its previous state before exercise. During exercise energy stores are depleted, body temperature rises, the blood needs to be supplied with new oxygen and heart and breathing rate have to return to normal levels. All these processes, need energy and oxygen, which causes the elevated oxygen consumption.

Since these processes increase energy expenditure, they are said to aid in weight loss and decreases in body fat. One of the reasons high intensity interval training is effective in reducing body fat, despite relatively low caloric expenditure, is the recovery period afterwards. High intensity exercise requires a longer recovery time than lower intensity exercise of equal energy cost.

In other words, although high intensity interval training is hard work, it will increase energy expenditure through EPOC. This causes weight loss after training during rest periods. Despite that the focus of EPOC research has been on cardiovascular training, strength training will also increase EPOC, because it places higher demands on muscle metabolism and damages muscle fibers which need recovery afterwards.