VO₂max testing: how it's measured, and what the number means

You will see it written two ways:

• Absolute, in litres per minute (L/min). The total oxygen your body uses. Bigger people tend to have higher values.
• Relative, in millilitres per kilogram per minute (ml/kg/min). Absolute VO₂max divided by body mass. This is the number most people quote, and the one that lets you compare people of different sizes.

Clinics sometimes report fitness in METs instead. One MET is the oxygen you use sitting at rest, defined as 3.5 ml/kg/min. So a VO₂max of 35 ml/kg/min is 10 METs.²

Gas exchange

Air goes in with a known amount of oxygen. It comes out with less oxygen and more carbon dioxide. A metabolic analyzer measures how much air you breathe and the oxygen and carbon dioxide in it. The oxygen that went in but didn't come out is the oxygen your body used. Modern carts do this breath by breath, which is what made fast ramp tests possible.¹

The ramp protocol

After a warm-up, the load rises steadily: more watts on a bike, or more speed or incline on a treadmill. A classic study found the highest VO₂max values when the increments brought people to exhaustion in roughly 8 to 17 minutes, and recommended aiming for about 10.⁴ The same study found VO₂max was about 6% higher on the treadmill than on the bike, so always compare like with like.

A true max, or a peak?

The textbook sign of VO₂max is a plateau: work keeps rising but oxygen uptake doesn't. On a ramp test, many people never show a clear plateau. Labs have often fallen back on "secondary criteria" such as the respiratory exchange ratio, heart rate or blood lactate. Poole and Jones argue those cut-offs are often arbitrary and can give grossly inaccurate results, especially in people new to hard testing.¹

Their recommended fix is a verification bout: after a short rest, a constant effort at about 110% of the peak ramp work rate. If oxygen uptake doesn't climb higher, the ramp result was a true maximum.¹ Midgley and colleagues suggested treating values within measurement error, such as within 2%, as a match.⁵

If maximum isn't confirmed, the honest label is VO₂peak: the highest value you reached on the day.

The 12-minute run goes back to Kenneth Cooper's 1968 study comparing field and treadmill testing.⁸ Field tests don't give you thresholds.

For watches, the 2022 INTERLIVE meta-analysis of 14 studies concluded that exercise-based estimates work at the population level, but "the estimation error at the individual level is large".⁷ We cover the device studies in How accurate is your watch's VO₂max estimate?

• A 2009 meta-analysis of 33 studies and about 103,000 people found that each 1-MET higher level of fitness was associated with a 13% lower risk of death from any cause.⁹
• In 122,007 patients who took treadmill tests, the fittest group had an adjusted risk of death about one-fifth that of the least fit group (hazard ratio 0.20), with no upper limit of benefit observed.¹⁰
• The American Heart Association has argued that cardiorespiratory fitness should be assessed as a clinical vital sign.¹¹

Two cautions. These are associations from observational studies, not proof that raising your VO₂max will add years. And the large studies mostly estimated fitness from treadmill time or speed, not from measured gas exchange.^9,10

Two facts set the rhythm. First, training takes weeks to move VO₂max. A meta-analysis of interval-training studies lasting 6 to 13 weeks found an average gain of 0.51 L/min.¹² Second, repeat lab tests vary a little on their own. In one study, two lab tests on the same runners differed with a coefficient of variation of 4.0%.¹³ A change smaller than that may be noise.

In practice, that means testing at the start and end of a training block rather than every week. The training studies above ran for 6 to 13 weeks, which is a useful guide. Whatever you choose, keep conditions the same: same protocol, same machine, similar time of day, and similar rest and food beforehand.

A ramp test with gas analysis also gives your ventilatory thresholds. See Ventilatory thresholds VT1 and VT2, explained.

QuestionWhat is a good VO₂max?

It depends on your age, sex and how you were tested. Compare your result against age- and sex-specific tables built from measured tests, such as those from the FRIEND registry in the United States. In that registry, average peak oxygen uptake fell by about 13.5% per decade on treadmill tests, so the same number means more at 60 than at 30.¹⁴

QuestionIs VO₂peak the same as VO₂max?

Not quite. VO₂max is your true ceiling, confirmed by a plateau or a verification bout. VO₂peak is simply the highest value reached in a test. It can equal VO₂max, or sit below it if you stopped before reaching your limit. A good report labels which one you got.¹

QuestionHow long does a VO₂max test take?

The hard part is short. Lab protocols are usually set so the ramp lasts about 10 minutes, because ramps that are too short or too long can give a lower result.⁴ Add a warm-up, mask fitting and a cool-down, and the visit takes a good deal longer than the test itself.

QuestionCan my smartwatch measure VO₂max?

No. A watch estimates VO₂max from your heart rate, your pace and details such as age and weight. It does not measure the oxygen you use. Exercise-based watch estimates are close on average across groups, but a 2022 meta-analysis found the error for any one person can be large.⁷

QuestionIs a VO₂max test safe?

For most healthy people it is safe but very hard work. Talk to a doctor first if you have a heart, lung or other medical condition, or if you are unsure whether hard exercise is safe for you. Clinical tests for patients are supervised by trained staff.³

1. Poole DC, Jones AM. Measurement of the maximum oxygen uptake V̇O₂max: V̇O₂peak is no longer acceptable. J Appl Physiol. 2017;122(4):997–1002. PubMed 28153947
2. Jetté M, Sidney K, Blümchen G. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clin Cardiol. 1990;13(8):555–565. PubMed 2204507
3. American Thoracic Society, American College of Chest Physicians. ATS/ACCP statement on cardiopulmonary exercise testing. Am J Respir Crit Care Med. 2003;167(2):211–277. PubMed 12524257
4. Buchfuhrer MJ, Hansen JE, Robinson TE, et al. Optimizing the exercise protocol for cardiopulmonary assessment. J Appl Physiol. 1983;55(5):1558–1564. PubMed 6643191
5. Midgley AW, McNaughton LR, Polman R, Marchant D. Criteria for determination of maximal oxygen uptake: a brief critique and recommendations for future research. Sports Med. 2007;37(12):1019–1028. PubMed 18027991
6. Mayorga-Vega D, Bocanegra-Parrilla R, Ornelas M, Viciana J. Criterion-related validity of the distance- and time-based walk/run field tests for estimating cardiorespiratory fitness: a systematic review and meta-analysis. PLoS One. 2016;11(3):e0151671. PMC4795745
7. Molina-Garcia P, Notbohm HL, Schumann M, et al. Validity of estimating the maximal oxygen consumption by consumer wearables: a systematic review with meta-analysis and expert statement of the INTERLIVE network. Sports Med. 2022;52(7):1577–1597. PMC9213394
8. Cooper KH. A means of assessing maximal oxygen intake: correlation between field and treadmill testing. JAMA. 1968;203(3):201–204. PubMed 5694044
9. Kodama S, Saito K, Tanaka S, et al. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. 2009;301(19):2024–2035. PubMed 19454641
10. Mandsager K, Harb S, Cremer P, et al. Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Netw Open. 2018;1(6):e183605. PMC6324439
11. Ross R, Blair SN, Arena R, et al. Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign. A scientific statement from the American Heart Association. Circulation. 2016;134(24):e653–e699. PubMed 27881567
12. Bacon AP, Carter RE, Ogle EA, Joyner MJ. VO₂max trainability and high intensity interval training in humans: a meta-analysis. PLoS One. 2013;8(9):e73182. PMC3774727
13. Düking P, Van Hooren B, Sperlich B. Assessment of peak oxygen uptake with a smartwatch and its usefulness for training of runners. Int J Sports Med. 2022;43(7):642–647. PMC9286863
14. Kaminsky LA, Arena R, Myers J, et al. Updated reference standards for cardiorespiratory fitness measured with cardiopulmonary exercise testing: data from FRIEND. Mayo Clin Proc. 2022;97(2):285–293. PubMed 34809986