Treatment & Procedure
VO2max test (cardiopulmonary exercise testing)
Biohacking
In cardiopulmonary exercise testing, you run or cycle to exhaustion while a breathing mask analyses every breath. The result is your maximal oxygen uptake, VO2max, a number that in large studies predicts mortality as strongly as smoking or diabetes. Sports medicine clinics, performance testing labs and longevity practices are therefore increasingly offering the test to healthy people as well. The predictive value of the measurement is well supported; whether measuring alone makes anyone fitter is a different question.
In short
The higher your cardiorespiratory fitness, the lower your mortality, with no apparent upper limit: among 750,302 US veterans, the least fit had a roughly fourfold higher risk of death than the extremely fit, and in 122,007 exercise tests at a US clinic it was fivefold. These large cohorts, however, estimated fitness from treadmill performance; with actual gas exchange measurement, a cohort of 4,137 healthy adults followed for an average of 24 years shows the same pattern. Since 2016, the American Heart Association has recommended assessing fitness like a vital sign. Smartwatches estimate VO2max reasonably well for groups, but with large errors for the individual. In a randomized trial, adding a fitness test to a preventive health check did not make participants fitter after one year. As a test on request without symptoms, cardiopulmonary exercise testing is usually self-pay in Germany.
What it is and what it promises
Cardiopulmonary exercise testing (CPET, in German “Spiroergometrie”) combines an exercise test on a treadmill or cycle ergometer with gas exchange analysis. The load increases in stages, and a mask measures breath by breath how much oxygen you take up and how much carbon dioxide you exhale; ECG and blood pressure are recorded alongside. The highest oxygen uptake reached, relative to body weight in millilitres per kilogram per minute, is VO2max, often called VO2peak in studies. One MET, the unit used in many cohort studies, corresponds to 3.5 ml/kg/min.
The promise is compelling: a single, objectively measured number that sums up how well heart, lungs, blood and muscles work together, and that says more about life expectancy than many lab values. The test also provides thresholds that can be used to set training zones, and a baseline against which progress can be read. How to train VO2max is covered on the page Zone 2 & VO2max training; this page is about the measurement. Related markers are grip strength and heart rate variability.
What is well supported
That low fitness goes hand in hand with higher mortality is among the most robust findings in preventive medicine. A meta-analysis of 33 cohort studies with 102,980 healthy people found a relative risk of death of 0.87 and a relative risk of cardiovascular events of 0.85 for each additional MET of exercise capacity (Kodama 2009). Among 750,302 US veterans aged 30 to 95, the association held for men and women, all racial groups studied and into the ninth decade of life; no increased risk was found with extremely high fitness (Kokkinos 2022).
It is also established that measurement by gas exchange analysis shows the same picture as estimation: in the Ball State cohort of 4,137 healthy adults who had undergone cardiopulmonary exercise testing, low compared with high fitness was associated with a 73 percent higher risk of death (Imboden 2018). Cardiopulmonary exercise testing is the reference method against which watches and formulas are measured.
From this, the American Heart Association concluded in 2016 that cardiorespiratory fitness should be assessed as a clinical vital sign. It may be a stronger predictor than smoking, high blood pressure, high cholesterol or type 2 diabetes, and, added to the classic risk factors, it improves risk classification (Ross 2016).
What the studies show
Mandsager 2018 – 122,007 exercise tests
Retrospective cohort at a US academic medical centre: 122,007 patients referred for a treadmill exercise test between 1991 and 2014, followed for a median of 8.4 years, 13,637 deaths. Compared with low fitness, elite fitness was associated with an adjusted hazard ratio of 0.20 (95 % CI 0.16 to 0.24). Below-average compared with above-average fitness, at 1.41, weighed as heavily as smoking (1.41) and more heavily than diabetes (1.40) or coronary artery disease (1.29). Fitness was not measured by gas exchange but as estimated METs from treadmill performance.
Kokkinos 2022 – 750,302 veterans
The largest analysis to date: 750,302 US veterans aged 30 to 95, including 45,232 women and 26,989 people in their eighties, followed for a median of 10.2 years, 174,807 deaths. The lowest risk was at about 14 METs, with a hazard ratio of 0.24 in men and 0.23 in women. The least fit had a roughly fourfold higher risk than the extremely fit (hazard ratio 4.09; 95 % CI 3.90 to 4.20). Here too, fitness was derived from the treadmill performance achieved.
Imboden 2018 – directly measured
The Ball State cohort closes the gap to actual cardiopulmonary exercise testing: 4,137 healthy adults who had signed up for the test themselves, mean age 42.8 years, followed for an average of 24.2 years, 727 deaths. Low compared with high measured fitness was associated with a hazard ratio of 1.73 for all-cause mortality (95 % CI 1.20 to 3.50), 2.27 for cardiovascular death and 2.07 for cancer death. For each additional MET, the rates were 11.6, 16.1 and 14.0 percent lower.
Molina-Garcia 2022 – watches versus the lab
Meta-analysis of 14 validation studies on wearables that estimate VO2max. Devices that rely on resting data overestimated by an average of 2.17 ml/kg/min, with limits of agreement from minus 13.07 to plus 17.41. Devices that use exercise data were almost right on average (minus 0.09), but with limits from minus 9.92 to plus 9.74 ml/kg/min. The authors’ conclusion: useful for population data, but the error for the individual is large.
Lambe 2026 – Apple Watch Series 10
40 healthy adults underwent treadmill cardiopulmonary exercise testing and then let the watch generate its own estimate. The watch underestimated by an average of 6.25 ml/kg/min, with limits of agreement from minus 18.23 to plus 5.73; the mean absolute percentage error was 13.2 percent. It placed only 14 percent of participants in the correct fitness percentile of the US reference database FRIEND, and a further 34 percent were one band off.
Høj 2018 – does the test make you fitter?
Randomized trial in Denmark: 2,201 middle-aged adults received a preventive health check with or without a fitness test. After one year, fitness in the test group was not higher; the difference was minus 0.7 ml/kg/min (95 % CI minus 2.0 to plus 0.6). Limitations: fitness was measured with a submaximal cycle test, not by cardiopulmonary exercise testing, and only 901 participants attended the follow-up.
Where the data stop
The most impressive figures come from cohorts that did not measure fitness but estimated it from treadmill performance, mostly in people referred for an exercise test for medical reasons. Measured by gas exchange analysis, the association has been confirmed in considerably smaller groups, with thousands rather than hundreds of thousands of participants, but in the same direction.
These are observational data. Fit people also differ in many other ways, and these studies do not show that an increased VO2max lowers risk to the same extent; what intervention studies say about this is covered on the page Zone 2 & VO2max training. A study testing whether cardiopulmonary exercise testing prevents disease or deaths in healthy people does not exist in the sources reviewed; the only randomized trial on fitness testing in a health check found no gain in fitness after one year.
For the watch on your wrist: useful for following a trend over months or comparing groups, but no substitute for the measurement when your own number is supposed to support a decision.
Status, approval and legal
Cardiopulmonary exercise testing is an established medical examination, not a product with its own approval. When there is a medical reason, such as unexplained shortness of breath or known heart or lung disease, it is ordered by a physician. As a fitness or longevity check without symptoms, it is not one of the early detection examinations covered by statutory health insurance in Germany and is billed privately under the German scale of fees for physicians (GOÄ). Whether your own health insurer contributes something through additional benefits is something you can find out from them.
In the GOÄ, the spiroergometric examination is number 606 with 379 points. That comes to 22.09 euros at the single rate and 50.81 euros at the usual 2.3-fold rate, for this one service alone. Consultation, physical examination and further measurements are billed separately, so the total bill is higher.
Since 2016, the American Heart Association has recommended assessing cardiorespiratory fitness in practice like a vital sign (Ross 2016). The VO2max reading on a watch is the manufacturer’s estimate, not a medical measurement.
Safety
A test to exhaustion is strenuous but well studied. In a clinic analysis of 5,060 cardiopulmonary exercise tests in patients with serious heart disease, including heart failure, hypertrophic cardiomyopathy, pulmonary hypertension and aortic stenosis, there were 8 serious adverse events, 0.16 percent, mostly sustained ventricular tachycardia; nobody died (Skalski 2012). For healthy adults, the sources reviewed here provide no separate complication rate. There is no radiation.
The examination takes place under medical supervision with ECG and blood pressure monitoring. Anyone who is acutely ill or knows chest pain, palpitations or shortness of breath during exertion should mention this beforehand. The more common risk lies in interpretation: a single number, especially from a watch, is a snapshot and not a diagnosis.
BK-Score Supported, with caveats
| Human evidence | 7 | |
|---|---|---|
| Mechanism | 7 | |
| Safety data | 7 | |
| Hype gap | 5 | |
| Track record of use | 9 |
Evidence 7, because the predictive value is established in very large cohorts (Kodama 2009 with 33 studies and 102,980 healthy people, Kokkinos 2022 with 750,302 veterans), but with VO2max measured directly by gas exchange only in smaller cohorts such as Ball State with 4,137 adults, and because the only randomized trial on fitness testing in a health check found no gain in fitness after one year (Høj 2018). Mechanism 7, because it is physiologically clear what is being measured – oxygen uptake integrates heart, lungs and muscles – but only partly why the value is so closely linked to mortality. Safety 7, because even in high-risk patients serious adverse events occurred in 0.16 percent of 5,060 tests, none fatal, while separate figures for healthy people are missing from the sources reviewed. Hype 5, because the core of the promise holds, but it is overstated that measuring itself achieves something and that the watch on the wrist delivers the same, although in individual cases it is off by an average of 13 percent. Track record 9, because cardiopulmonary exercise testing has been routine in cardiology, pulmonology and sports medicine for decades. Direction positive.
The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless. “Track record of use 9” means used long and widely – that is not proof of efficacy.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)
Frequently asked questions about the VO2max test
How meaningful is VO2max for life expectancy?
As a predictor, very. In a meta-analysis of 33 cohorts, the relative risk of death fell to 0.87 for each additional MET of exercise capacity, and among 750,302 US veterans the least fit had a roughly fourfold higher risk than the extremely fit. These are observational data: they predict risk but do not prove cause.
Is my smartwatch’s VO2max accurate enough?
Useful for trends and group comparisons, only rough for the individual value. In a meta-analysis of 14 studies, even the better, exercise-based estimates were off by up to about 10 ml/kg/min in individual cases. In a study of 40 adults, the Apple Watch Series 10 underestimated by an average of 6.25 ml/kg/min.
What is the difference from a standard exercise ECG?
The exercise ECG estimates fitness from the performance achieved; cardiopulmonary exercise testing measures oxygen uptake directly from the breathing air. The largest cohorts on mortality are based on the estimate; directly measured VO2max shows the same association in smaller cohorts.
What does cardiopulmonary exercise testing cost, and does health insurance pay?
When there is a medical reason, it is ordered by a physician. As a fitness or longevity check without symptoms, it is usually self-pay. Under the GOÄ, number 606 alone comes to 50.81 euros at the usual 2.3-fold rate; consultation, examination and further measurements are added.
Is the test dangerous?
It is strenuous but well studied. Even in people with serious heart disease, serious adverse events occurred in 0.16 percent of 5,060 tests, none of them fatal. The test takes place under medical supervision with ECG; symptoms during exertion should be raised beforehand.
Does measuring make me fitter?
Not on its own. In a randomized trial with 2,201 adults, fitness one year after a health check with a fitness test was no higher than without one. The value of the number depends on what happens afterwards, that is, on training.
Related
- Related topicZone 2 & VO2max training
- Related topicCoronary calcium score (CAC scan)
- Related topicMuscle as an Organ (Grip Strength & Myokines)
- Related topicDEXA scan (body composition and bone density)
- Related topicHeart rate variability (HRV)
- Related topicOxygen multistep therapy (after von Ardenne)
Sources
- Mandsager K et al., JAMA Netw Open 2018 – cohort, 122,007 exercise tests, fitness and mortality (PMID 30646252)
- Kodama S et al., JAMA 2009 – meta-analysis, 33 cohorts, fitness as a predictor of mortality and cardiovascular events (PMID 19454641)
- Kokkinos P et al., J Am Coll Cardiol 2022 – cohort, 750,302 US veterans, fitness and mortality across age, race and sex (PMID 35926933)
- Imboden MT et al., J Am Coll Cardiol 2018 – Ball State cohort, fitness measured by cardiopulmonary exercise testing and mortality (PMID 30384883)
- Ross R et al., Circulation 2016 – American Heart Association scientific statement, fitness as a clinical vital sign (PMID 27881567)
- Molina-Garcia P et al., Sports Med 2022 – meta-analysis, 14 validation studies, VO2max estimation by wearables (PMID 35072942)
- Lambe R et al., Mayo Clin Proc Digit Health 2026 – validation study, Apple Watch Series 10 VO2max against gas exchange measurement (PMID 42094313)
- Skalski J et al., Circulation 2012 – 5,060 cardiopulmonary exercise tests in high-risk patients, safety (PMID 23091065)
- Høj K et al., Eur J Public Health 2018 – randomized trial, fitness testing in preventive health checks (PMID 29016823)
- German scale of fees for physicians (GOÄ), § 5 and fee schedule no. 606 – spiroergometric examination
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-10-15.