In short
VO2 max is the maximum rate at which the body can take up and use oxygen during intense exercise, expressed in milliliters of oxygen per kilogram of body weight per minute, and is the standard measure of cardiorespiratory fitness.
VO2 max is determined by the combined capacity of the lungs to bring in oxygen, the heart to pump oxygenated blood, and the muscles to extract and use that oxygen (via mitochondrial density and capillary density). It is measured most accurately with a graded cardiopulmonary exercise test on a treadmill or bike while wearing a mask that analyzes inhaled and exhaled gases; it can also be estimated (with less accuracy) from submaximal tests, wearable-device algorithms, or step tests.
VO2 max is one of the most consistently studied predictors of all-cause mortality in the medical literature. A large cohort study published in JAMA Network Open in 2018 (Mandsager et al.) following over 120,000 patients undergoing exercise testing found that low cardiorespiratory fitness was associated with a higher mortality risk than traditional risk factors like smoking, diabetes, and cardiovascular disease, and that the benefit of higher fitness continued without a clear upper plateau, unlike some other risk factors.
VO2 max can be meaningfully improved through structured training, particularly a mix of zone 2 (moderate, sustainable-pace) endurance training and high-intensity interval training, and improvements are dose-responsive with training volume and intensity in human trials. It naturally declines with age even in trained individuals, though trained older adults typically maintain substantially higher VO2 max than sedentary peers decades younger.
Worth remembering
- Cardiorespiratory fitness measure: maximum oxygen uptake during peak exertion.
- One of the strongest studied predictors of all-cause mortality, per large cohort data.
- Trainable via zone 2 endurance work and high-intensity interval training.