The maximum rate at which your body can take in and use oxygen during intense exercise is called your VO2 max.
VO2 max stands for maximal oxygen consumption or maximal oxygen uptake. It measures the highest rate at which the body can consume oxygen during strenuous exercise, reflecting the combined performance of the lungs, heart, blood vessels and working muscles. It is widely used as an indicator of cardiorespiratory fitness and endurance capacity.
Scientists usually measure VO2 max with a graded exercise test on a treadmill or cycle ergometer. The workload increases progressively while equipment records breathing and the oxygen and carbon dioxide content of inhaled and exhaled air. Results may be reported in litres per minute or relative to body mass, commonly as millilitres per kilogram per minute.
A related term, VO2 peak, means the highest oxygen-consumption value reached during a test, even if a clear maximum plateau is not demonstrated. The two terms are often used loosely in popular fitness writing, but VO2 max is the stricter concept. British physiologist Archibald Hill helped establish the scientific foundations of maximal oxygen uptake research in the 1920s.