In more detail
VO₂ max is measured in a laboratory by analysing breathed gases during a graded treadmill or cycle test to exhaustion. Field estimates include the Cooper 12-minute run, (distance in metres − 504.9) / 44.73, and the heart-rate ratio method, 15.3 × maximum heart rate / resting heart rate. One MET equals 3.5 mL/kg/min. Untrained adults are often in the 30s and 40s, while elite endurance athletes reach 70 or more. It falls with age, rises with training and is partly inherited.
Why it matters
It is a strong predictor of endurance performance and is associated with long-term cardiovascular health. Smartwatch estimates can be several units off, so they are best used for trends. Heart-rate training zones are commonly set as a share of heart-rate reserve: (max − rest) × intensity + rest; maximum heart rate is roughly 220 − age, though individuals vary widely. Anyone with a heart condition should get medical clearance before maximal testing.
Example
Cooper test, 2,800 m in 12 min: (2,800 − 504.9) / 44.73 = 51.3 mL/kg/min
In METs: 51.3 / 3.5 = 14.7
Heart-rate ratio, max 190, rest 60: 15.3 × 190 / 60 = 48.5 mL/kg/min
70 % zone (Karvonen): (190 − 60) × 0.70 + 60 = 151 beats/min