VO₂max

VO₂max, or maximal oxygen uptake, is the highest rate at which the body can take up and use oxygen during intense exercise involving large muscle groups. It reflects the integrated ability of the cardiorespiratory system to deliver oxygen and of active tissues, particularly skeletal muscle, to extract and use it for aerobic metabolism. VO₂max is widely used as a measure of cardiorespiratory fitness and aerobic exercise capacity .^1,2

Physiologically, oxygen uptake can be described by the Fick principle as the product of cardiac output and the difference in oxygen content between arterial and venous blood. VO₂max therefore depends on both the maximum amount of oxygen-rich blood that can be delivered to working tissues and the tissues' ability to extract and use that oxygen. In healthy people, maximal cardiac output is an especially important determinant of differences in VO₂max .^1,2

VO₂max is usually measured during a progressively harder treadmill or cycling test while expired gases are analyzed. Oxygen uptake rises as exercise intensity increases until a maximal value is reached. Results can be reported as an absolute rate, typically liters of oxygen per minute, or relative to body mass, commonly milliliters per kilogram per minute. Testing protocols and methods of processing breath-by-breath measurements can influence the reported value .^2,3

VO₂max is related to the term VO₂peak, which refers to the highest oxygen uptake observed during a particular exercise test. A clear plateau in oxygen uptake is not always observed, so the absence of a plateau does not necessarily mean that VO₂max was not reached. A subsequent verification bout can be used to strengthen evidence that maximal oxygen uptake has been attained .^2,3