VO2 max measures the maximum rate at which the body can consume oxygen during intense exercise. The abbreviation combines volume, O2 for oxygen, and “max,” so the measure is commonly used as an indicator of cardiorespiratory fitness and endurance capacity.
A laboratory test usually involves running on a treadmill or pedalling a cycle ergometer while exercise intensity rises progressively. The participant breathes through equipment that measures ventilation and the oxygen and carbon dioxide content of inhaled and exhaled air. The result may be reported as litres per minute or, more commonly for comparisons between people, millilitres per kilogram of body mass per minute.
VO2 max reflects the whole oxygen-transport system: the lungs take in oxygen, the heart pumps oxygenated blood, blood vessels deliver it, and muscle mitochondria use it to make energy. Training can improve the measure, while age, genetics, altitude, body size, and health also influence it.
A related term, VO2 peak, means the highest oxygen-consumption value reached in a test, even when a formal maximum plateau is not demonstrated. Elite endurance athletes can record values above 90 mL/kg/min, while many untrained adults score much lower.