What Is VO2 Max, and Why Does It Matter?

VO2 max, or maximal oxygen uptake, is the highest rate at which a person’s body can take in, transport and use oxygen during intense exercise. It is usually expressed in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min), and one metabolic equivalent (MET) corresponds to 3.5 mL/kg/min.^[1] Because it combines the work of the lungs, heart, blood and muscles, it is widely treated as the standard laboratory measure of cardiorespiratory fitness.^[2]

So what is VO2 max, and why does it matter? Large studies link a higher value with lower risk of death from all causes, and the American Heart Association (AHA) has argued that fitness deserves a place in routine clinical assessment.^[3] The relationship is an association, however, and a single number cannot describe health or athletic ability on its own.

History

The concept dates to the early 1920s. The British physiologist Archibald V. Hill, who shared the 1922 Nobel Prize in Physiology or Medicine for work on muscle, and his colleague Hartley Lupton studied runners in Manchester and published their findings on oxygen supply and use during exercise in 1923.^[4][5] Hill described maximal oxygen consumption as the point “beyond which no effort can drive it,” and he proposed that fatigue arises when the heart cannot deliver enough blood to meet the muscles’ demand for oxygen.^[5]

Later researchers have questioned how complete that model is. A 2012 editorial in the British Journal of Sports Medicine noted that the best athletes do not always have the highest VO2 max values and that brain-based regulation of pacing and effort may also limit performance.^[5]

Physiology

The oxygen pathway

VO2 max reflects a chain of steps that carries oxygen from the air to working muscle. The lungs pass oxygen into the blood, hemoglobin in red blood cells carries it, the heart pumps it, and muscle cells extract it to make energy. The AHA describes the measure as the integrated ability to deliver oxygen from the atmosphere to skeletal muscle.^[2] In equation form, oxygen uptake equals cardiac output multiplied by the difference between the oxygen content of arterial and venous blood.^[1]

What limits it

For healthy people exercising with the whole body at sea level, a 2000 review by David Bassett and Edward Howley concluded that the cardiorespiratory system is the main limit, with about 70 to 85 percent of the limitation linked to the maximal cardiac output. The authors cited maximal cardiac output of roughly 25 liters per minute in untrained people and about 40 liters per minute in highly trained athletes.^[1] Muscle itself can use far more oxygen than the whole body delivers: in one-legged exercise studies, a small muscle mass reached two to three times the whole-body uptake when it was well supplied with blood.^[1]

The same review reported that blood doping raised VO2 max by 4 to 9 percent, while beta-blocker drugs that reduce heart output lowered it by 5 to 15 percent. These interventions show how strongly blood volume and cardiac output shape the result.^[1]

Measurement

Laboratory testing

The reference method is a cardiopulmonary exercise test. A person runs or cycles while the workload increases in stages, and a mask or mouthpiece records the oxygen and carbon dioxide in each breath. The AHA calls direct gas analysis the “gold standard” for assessing fitness, but notes that it needs specialist equipment, trained staff and an exhaustive effort from the participant.^[2]

Deciding that a person has truly reached the maximum is not simple. Oxygen uptake is expected to level off as effort rises, yet Bassett and Howley noted that about half of subjects show no such plateau. Laboratories therefore also apply secondary criteria, such as a respiratory exchange ratio of at least 1.15 or blood lactate near 8 to 9 millimoles per liter.^[1] When a plateau is absent, the result is often called VO2 peak. Treadmill testing also gives higher values than cycling, by about 21 percent in one registry of heart patients.^[6]

Field tests and wearables

Cheaper options estimate the value indirectly. For young people, the AHA describes the 20-meter shuttle run as the most widely used test worldwide and advises reporting laps completed rather than values converted by formulas, which vary. Questionnaires are the least accurate method but can be acceptable for population studies.^[2] Consumer devices also report estimates. In a 2025 study in PLoS ONE, 30 participants wore an Apple Watch and then took a maximal treadmill test. The watch underestimated VO2 max by 6.07 mL/kg/min on average, with a mean absolute percentage error of 13.3 percent.^[7]

Typical values

Values vary with age, sex, genetics and training. One compilation lists about 45 mL/kg/min for untrained men and 38 for untrained women.^[8] Endurance athletes score far higher. The same compilation lists Norwegian cyclist Oskar Svendsen at 97.5 mL/kg/min, measured in 2012 at age 18, as the highest reported male value, and distance runner Joan Benoit at 78.6 for women, although it cautions that not all such scores are verified.^[8][9] Cycling Weekly reported that no one had publicly beaten Svendsen’s figure, and that an unverified 101.1 had been posted online by another athlete.^[9]

Fitness declines with age. In a registry of 15,045 tests on patients with heart disease, peak oxygen uptake fell by an average of 7 percent per decade, and men’s values averaged 23 percent higher than women’s.^[6] These figures describe patients, so they may differ in healthy populations. Because values are scaled to body weight, body composition also affects comparisons between people.

Why it matters for health

Mortality and disease risk

The AHA’s 2016 scientific statement reported that low cardiorespiratory fitness is associated with higher risk of cardiovascular disease, cancer death and death from any cause. It added that fitness may predict mortality more strongly than smoking, high blood pressure, high cholesterol or type 2 diabetes, and that adding it to traditional risk factors improves risk classification.^[3] The AHA’s 2020 statement on youth called low fitness a strong, independent predictor of cardiovascular disease and mortality in adults.^[10]

A 2009 meta-analysis in JAMA by Satoru Kodama and colleagues pooled 33 studies with about 103,000 participants. It found that a higher maximal aerobic capacity of 1 MET was linked to a 13 percent lower risk of death from all causes and a 15 percent lower risk of coronary heart disease or cardiovascular events.^[11]

In 2018, Cleveland Clinic researchers published a study in JAMA Network Open of 122,007 patients who took treadmill tests between 1991 and 2014. During a median follow-up of 8.4 years, “elite” performers, the top 2.5 percent for age and sex, had an 80 percent lower risk of death than the lowest group. The authors found that each step down in fitness raised risk by an amount comparable to or greater than that of coronary artery disease, smoking or diabetes, and that benefits continued at the highest levels.^[12][13]

Limits of the evidence

These are observational findings. People who are fitter may differ in diet, wealth, existing illness and other habits, and the Cleveland Clinic cohort consisted of patients referred for testing, so results may not generalize to everyone. The studies show that low fitness marks higher risk; they do not establish that raising an individual’s number will lower that person’s risk by a set amount.

Changing VO2 max

Training

Aerobic training can raise VO2 max, mainly by increasing the heart’s output and the blood’s capacity to carry oxygen.^[1] A 2019 meta-analysis of 53 trials in the Journal of Science and Medicine in Sport found that high-intensity interval training improved VO2 max in adults. Short, low-volume sessions were effective and time-efficient, while longer intervals and larger volumes produced bigger gains and outperformed moderate continuous training.^[14] For general activity targets, the American College of Sports Medicine’s 2011 position stand recommends at least 150 minutes of moderate-intensity exercise per week, typically about 30 minutes on five days. See also this explainer on how much exercise adults need.^[15]

Genetics and individual response

People respond very differently to the same program. In the HERITAGE Family Study, researchers found a maximal heritability of 47 percent for VO2 max gains. Across 742 sedentary adults in a 20-week program, the average gain was about 384 milliliters of oxygen per minute, but individual results ranged from no change to more than 1,000 milliliters per minute.^[16] A later genome-wide analysis of 473 participants identified a panel of 21 genetic variants that explained 49 percent of the variance in training response. People with 9 or fewer favorable variants gained 221 mL/min on average, versus 604 mL/min for those with 19 or more.^[17] The authors called for larger replication studies, so such panels are research tools rather than clinical tests.

Related concepts

VO2 max is often discussed alongside aerobic capacity and the anaerobic threshold, the effort level above which energy supply relies increasingly on non-oxygen pathways. A full entry is available under maximal oxygen uptake. This article is general information, not medical advice; people with heart conditions should consult a health professional before hard exercise.

FAQs

What does VO2 max stand for? It stands for maximal oxygen uptake, the highest rate at which the body can use oxygen during intense exercise, usually given in mL/kg/min.

How is VO2 max measured? The gold standard is a cardiopulmonary exercise test that analyzes exhaled gases while workload rises. Field tests and smartwatches give estimates with larger errors.

What is a good VO2 max? One compilation lists about 45 mL/kg/min for untrained men and 38 for untrained women, with endurance athletes far higher. Values fall with age, so comparisons should use age- and sex-matched norms.

Why does VO2 max matter for health? Studies including a 2009 meta-analysis found that each 1-MET higher capacity was linked to 13 percent lower all-cause mortality, though the findings are associations.

Can VO2 max be improved? Yes, mainly through aerobic and interval training, but genetics strongly influence how much a person gains, with a maximal heritability of 47 percent in the HERITAGE study.