Prolonged, moderate-intensity exercise that uses up oxygen at or below the level in which your cardio-respiratory (heart-lung) system can replenish oxygen in the working muscles. "Aerobic", meaning with oxygen, is the only type of exercise which burns body fat to meet its energy demands. Bodybuilders engage in aerobic exercise to develop additional cardio-respiratory fitness, as well as to eliminate excess body fat to achieve peak muscularity. Common aerobic activities are running, swimming, cycling, dancing, and walking.