Oxygen consumption is the amount of oxygen taken up and utilized by the body. The oxygen taken into the body at the level of the lungs is ultimately used for the production of ATP in the mitochondria of our cells. Because most of the energy in the body is produced aerobically, VO2 can be used to determine how much energy a subject is expending. VO2 can be reported in absolute terms (L/min) or relative to body mass (ml/kg*min). Oxygen consumption is dependent on the ability of the heart to pump out blood, the ability of the tissues to extract oxygen from the blood, the ability to ventilate and the ability of the alveoli to extract oxygen from the air