V̇O2 max (alsomaximal oxygen consumption,maximal oxygen uptake ormaximal aerobic capacity) is the maximum rate ofoxygen consumption attainable during physical exertion.[1][2] The name is derived from three abbreviations: "V̇" forvolume (the dot over the V indicates "per unit of time" inNewton's notation), "O2" foroxygen, and "max" for maximum and usually normalized per kilogram of body mass. A similar measure isV̇O2 peak (peak oxygen consumption), which is the highest rate attained during a session of submaximal physical exercise. It is equal to, or less than, the V̇O2 max. Confusion between these quantities in older and popular fitness literature is common.[3] The capacity of the lung to exchange oxygen and carbon dioxide is constrained by the rate ofblood oxygen transport to active tissue.
The measurement of V̇O2 max in the laboratory provides a quantitative value of endurance fitness for comparison of individual training effects and between people inendurance training. Maximal oxygen consumption reflectscardiorespiratory fitness andendurance capacity in exercise performance. Elite athletes, such ascompetitive distance runners,racing cyclists or Olympiccross-country skiers, can achieve V̇O2 max values exceeding 90 mL/(kg·min), while some endurance animals, such asAlaskan huskies, have V̇O2 max values exceeding 200 mL/(kg·min).
Inphysical training, especially in its academic literature, V̇O2 max is often used as a reference level to quantify exertion levels, such as 65% V̇O2 max as a threshold for sustainable exercise, which is generally regarded as more rigorous thanheart rate, but is more elaborate to measure.
V̇O2 max is expressed either as an absolute rate in (for example) litres of oxygen per minute (L/min) or as a relative rate in (for example) millilitres of oxygen per kilogram of the bodymass per minute (e.g., mL/(kg·min)). The latter expression is often used to compare the performance of endurance sports athletes. However, V̇O2 max generally does not vary linearly with body mass, either among individuals within a species or among species, so comparisons of the performance capacities of individuals or species that differ in body size must be done with appropriate statistical procedures, such asanalysis of covariance.[2]
Accurately measuring V̇O2 max involves a physical effort sufficient in duration and intensity to fully tax the aerobic energy system. In general clinical and athletic testing, this usually involves a graded exercise test in which exercise intensity is progressively increased while measuring:
V̇O2 max is measured during acardiopulmonary exercise test (CPX test). The test is done on atreadmill orcycle ergometer. In untrained subjects, V̇O2 max is 10% to 20% lower when using a cycle ergometer compared with a treadmill.[4] However, trained cyclists' results on the cycle ergometer are equal to or even higher than those obtained on the treadmill.[5][6][7]
The classic V̇O2 max, in the sense of Hill and Lupton (1923), is reached when oxygen consumption remains at a steady state ("plateau") despite an increase in workload. The occurrence of a plateau is not guaranteed and may vary by person and sampling interval, leading to modified protocols with varied results.[3]
V̇O2 may also be calculated by theFick equation:, when these values are obtained during exertion at a maximal effort. HereQ is thecardiac output of the heart,CaO2 is the arterial oxygen content, andCvO2 is the venous oxygen content. (CaO2 –CvO2) is also known as thearteriovenous oxygen difference.
The Fick equation may be used to measure V̇O2 in critically ill patients, but its usefulness is low even in non-exerted cases.[8] Using a breath-based VO2 to estimate cardiac output, on the other hand, seems to be reliable enough.[9]
The necessity for a subject to exert maximum effort in order to accurately measure V̇O2 max can be dangerous in those with compromised respiratory or cardiovascular systems; thus,sub-maximal tests forestimating V̇O2 max have been developed.
An estimate of V̇O2 max is based on maximum and resting heart rates. In the Uthet al. (2004) formulation, it is given by:[10]
This equation uses the ratio of maximum heart rate (HRmax) to resting heart rate (HRrest) to predict V̇O2 max. The researchers cautioned that the conversion rule was based on measurements on well-trained men aged 21 to 51 only, and may not be reliable when applied to other sub-groups. They also advised that the formula is most reliable when based on actual measurement of maximum heart rate, rather than an age-related estimate.
The Uth constant factor of 15.3 is given for well-trained men.[10] Later studies have revised the constant factor for different populations. According to Voutilainenet al. 2020, the constant factor should be 14 in around 40-year-old normal weight never-smoking men with no cardiovascular diseases, bronchial asthma, or cancer.[11]Every 10 years of age reduces the coefficient by one, as well as does the change in body weight from normal weight to obese or the change from never-smoker to smoker. Consequently, V̇O2 max of 60-year-old obese smoking men should be estimated by multiplying the HRmax to HRrest ratio by 10.
Kenneth H. Cooper conducted a study for theUnited States Air Force in the late 1960s. One of the results of this was theCooper test in which the distance covered running in 12 minutes is measured.[12] Based on the measured distance, an estimate of V̇O2 max [in mL/(kg·min)] can be calculated by inverting the linear regression equation, giving us:
whered12 is the distance (in metres) covered in 12 minutes.
An alternative equation is:
whered′12 is distance (in miles) covered in 12 minutes.
There are several other reliable tests and V̇O2 max calculators to estimate V̇O2 max, most notably themulti-stage fitness test (orbeep test).[13]
Estimation of V̇O2 max from a timed one-mile track walk (as fast as possible) in decimal minutes (t, e.g.: 20:35 would be specified as 20.58), sex, age in years, body weight in pounds (BW, lbs), and 60-second heart rate in beats-per-minute (HR, bpm) at the end of the mile.[14] The constantx is 6.3150 for males, 0 for females.
Correlation coefficientr for the generalized formula is 0.88.
Men have a V̇O2 max that is 26% higher (6.6 mL/(kg·min)) than women for treadmill and 37.9% higher (7.6 mL/(kg·min)) than women for cycle ergometer on average.[15] V̇O2 max is on average 22% higher (4.5 mL/(kg·min)) when measured using a treadmill compared with a cycle ergometer.[15]
| Percentile | Age group, in years | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Men | Women | |||||||||||||
| 20–29 | 30–39 | 40–49 | 50–59 | 60–69 | 70–79 | 80–89 | 20–29 | 30–39 | 40–49 | 50–59 | 60–69 | 70–79 | 80–89 | |
| Treadmill | ||||||||||||||
| 90 | 58.6 | 55.5 | 50.8 | 43.4 | 37.1 | 29.4 | 22.8 | 49.0 | 42.1 | 37.8 | 32.4 | 27.3 | 22.8 | 20.8 |
| 80 | 54.5 | 50.0 | 45.2 | 38.3 | 32.0 | 25.9 | 21.4 | 44.8 | 37.0 | 33.0 | 28.4 | 24.3 | 20.8 | 18.4 |
| 70 | 51.9 | 46.4 | 40.9 | 34.3 | 28.7 | 23.8 | 20.0 | 41.8 | 33.6 | 30.0 | 26.3 | 22.4 | 19.6 | 17.3 |
| 60 | 49.0 | 43.4 | 37.9 | 31.8 | 26.5 | 22.2 | 18.4 | 39.0 | 31.0 | 27.7 | 24.6 | 20.9 | 18.3 | 16.0 |
| 50 | 46.5 | 39.7 | 35.3 | 29.2 | 24.6 | 20.6 | 17.6 | 36.6 | 28.3 | 25.7 | 22.9 | 19.6 | 17.2 | 15.4 |
| 40 | 43.6 | 37.0 | 32.4 | 26.9 | 22.8 | 19.1 | 16.6 | 34.0 | 26.4 | 23.9 | 21.5 | 18.3 | 16.2 | 14.7 |
| 30 | 40.0 | 33.5 | 29.7 | 24.5 | 20.7 | 17.3 | 16.1 | 30.8 | 24.2 | 21.8 | 20.1 | 17.0 | 15.2 | 13.7 |
| 20 | 35.2 | 29.8 | 26.7 | 22.2 | 18.5 | 15.9 | 14.8 | 27.2 | 21.9 | 19.7 | 18.5 | 15.4 | 14.0 | 12.6 |
| 10 | 28.6 | 24.9 | 22.1 | 18.6 | 15.8 | 13.6 | 12.9 | 22.5 | 18.6 | 17.2 | 16.5 | 13.4 | 12.3 | 11.4 |
| Cycle ergometer | ||||||||||||||
| 90 | 62.2 | 50.5 | 41.9 | 37.1 | 31.4 | 26.2 | 18.7 | 46.0 | 32.0 | 27.3 | 22.4 | 20.3 | 18.0 | 18.1 |
| 80 | 57.0 | 39.0 | 35.1 | 31.6 | 27.0 | 22.6 | 17.3 | 40.9 | 27.0 | 23.5 | 20.4 | 18.5 | 16.8 | 14.3 |
| 70 | 52.8 | 35.5 | 31.4 | 28.4 | 24.5 | 20.6 | 16.2 | 37.5 | 24.5 | 21.8 | 18.9 | 17.4 | 15.9 | 12.9 |
| 60 | 48.3 | 31.6 | 29.0 | 26.3 | 23.3 | 19.4 | 14.6 | 34.3 | 22.9 | 20.3 | 17.8 | 16.4 | 15.0 | 11.3 |
| 50 | 44.0 | 30.2 | 27.4 | 24.5 | 21.7 | 18.3 | 13.2 | 31.6 | 21.6 | 18.8 | 16.9 | 15.7 | 14.5 | 10.9 |
| 40 | 40.8 | 27.9 | 25.4 | 23.1 | 20.7 | 17.1 | 12.2 | 28.9 | 19.9 | 17.9 | 16.1 | 15.0 | 13.6 | 10.1 |
| 30 | 37.4 | 25.7 | 23.8 | 22.0 | 19.1 | 16.0 | 11.1 | 25.6 | 18.6 | 16.6 | 15.2 | 14.2 | 12.9 | 9.4 |
| 20 | 34.5 | 22.6 | 21.9 | 20.2 | 17.5 | 14.7 | 9.7 | 21.9 | 17.0 | 15.4 | 14.3 | 13.4 | 12.0 | 8.7 |
| 10 | 28.8 | 19.1 | 19.8 | 17.2 | 14.7 | 11.0 | 8.4 | 18.8 | 15.0 | 13.7 | 13.0 | 12.2 | 10.7 | 7.8 |
The average untrained healthy male has a V̇O2 max of approximately 35–40 mL/(kg·min).[16][17] The average untrained healthy female has a V̇O2 max of approximately 27–31 mL/(kg·min).[16] These scores can improve with training and decrease with age, though the degree of trainability also varies widely.[18]
In sports where endurance is an important component in performance, such asroad cycling,rowing,cross-country skiing, swimming, andlong-distance running, world-class athletes typically have high V̇O2 max values. Elite male runners can consume up to 85 mL/(kg·min), and female elite runners can consume about 77 mL/(kg·min).[19]
Norwegian cyclistOskar Svendsen holds the record for the highest V̇O2 ever tested with 97.5 mL/(kg·min).[20][21]
V̇O2 max has been measured in other animal species. During loaded swimming, mice had a V̇O2 max of around 140 mL/(kg·min).[22]Thoroughbred horses had a V̇O2 max of around 193 mL/(kg·min) after 18 weeks of high-intensity training.[23]Alaskan huskies running in theIditarod Trail Sled Dog Race had V̇O2 max values as high as 240 mL/(kg·min).[24] Estimated V̇O2 max forpronghorn antelopes was as high as 300 mL/(kg·min).[25]
The factors affecting V̇O2 may be separated into supply and demand.[26] Supply is the transport of oxygen from the lungs to themitochondria (combiningpulmonary function,cardiac output,blood volume, and capillary density of the skeletal muscle) while demand is the rate at which the mitochondria can reduce oxygen in the process ofoxidative phosphorylation.[26] Of these, the supply factors may be more limiting.[26][27] However, it has also been argued that while trained subjects are probably supply limited, untrained subjects can indeed have a demand limitation.[28]
General characteristics that affect V̇O2 max include age,sex, fitness and training, and altitude. V̇O2 max can be a poor predictor of performance in runners due to variations inrunning economy andfatigue resistance during prolonged exercise. The body works as a system. If one of these factors is sub-par, then the whole system's normal capacity is reduced.[28]
The drugerythropoietin (EPO) can boost V̇O2 max by a significant amount in both humans and other mammals.[29] This makes EPO attractive to athletes inendurance sports, such as professional cycling. EPO has beenbanned since the 1990s as an illicitperformance-enhancing substance, but by 1998 it had become widespread in cycling and led to theFestina affair[30][31] as well as being mentioned ubiquitously in theUSADA 2012 report on theU.S. Postal Service Pro Cycling Team.[32]Greg LeMond has suggested establishing a baseline for riders' V̇O2 max (and other attributes) to detect abnormal performance increases.[33]
V̇O2 max/peak is widely used as an indicator of cardiorespiratory fitness (CRF) in select groups of athletes or, rarely, in people under assessment for disease risk. In 2016, theAmerican Heart Association (AHA) published a scientific statement recommending that CRF – quantifiable as V̇O2 max/peak – be regularly assessed and used as a clinical vital sign; ergometry (exercise wattage measurement) may be used if V̇O2 is unavailable.[34] This statement was based on evidence that lower fitness levels are associated with a higher risk of cardiovascular disease, all-cause mortality, and mortality rates.[34] In addition to risk assessment, the AHA recommendation cited the value for measuring fitness to validateexercise prescriptions,physical activity counseling, and improve both management and health of people being assessed.[34]
A 2023meta-analysis ofobservationalcohort studies showed an inverse and independent association between V̇O2 max and all-cause mortality risk.[35] Every onemetabolic equivalent increase in estimated cardiorespiratory fitness was associated with an 11% reduction in mortality.[35] The top third of V̇O2 max scores represented a 45% lower mortality in people compared with the lowest third.[35]
As of 2023, V̇O2 max is rarely employed in routine clinical practice to assess cardiorespiratory fitness or mortality due to its considerable demand for resources and costs.[36][37]
British physiologistArchibald Hill introduced the concepts of maximal oxygen uptake and oxygen debt in 1922.[38][27] Hill and German physicianOtto Meyerhof shared the 1922Nobel Prize in Physiology or Medicine for their independent work related to muscle energy metabolism.[39] Building on this work, scientists began measuring oxygen consumption during exercise. Key contributions were made by Henry Taylor at theUniversity of Minnesota, Scandinavian scientistsPer-Olof Åstrand andBengt Saltin in the 1950s and 60s, theHarvard Fatigue Laboratory, German universities, and the Copenhagen Muscle Research Centre.[40][41]