How accurate is the VO2 max on your watch?

Wearable VO2 max accuracy varies: an independent test of 28 adults found a 13.3% average error on Apple Watch, and a 13-study review found mixed results.

By Hydra Editorial

A watch’s VO2 max estimate can sit close to the laboratory value or well away from it. In an independent test of 28 adults, Apple Watch estimates had a mean absolute percentage error of 13.3% against laboratory testing. A 2025 review of 13 studies, mostly on Garmin watches, found smaller errors in most studies that reported them.

How does a watch estimate VO2 max?

VO2 max is the highest rate at which the body can use oxygen during hard exercise. The reference method is a treadmill test with gas analysis. A watch instead estimates it from submaximal data, mainly how heart rate responds to pace during a run or walk.

In Lambe et al., PLOS ONE 2025, 28 adults (mean age 32, most with high cardiorespiratory fitness) wore an Apple Watch Series 9 or Ultra 2 for 5 to 10 days and then completed a laboratory test. The watch underestimated VO2 max by a mean of 6.07 mL/kg/min (95% CI 3.77 to 8.38). The limits of agreement ran from minus 6.11 to 18.26 mL/kg/min, so individual errors were wide.

How much does the error vary between devices and people?

A 2025 systematic review in Frontiers in Sports and Active Living covered 13 studies of consumer wearables, most using Garmin watches with chest-strap heart rate sensors. Seven studies judged the estimates valid or acceptable against laboratory testing. Among studies reporting mean absolute percentage error, one was under 5%, four were 5 to 10%, and one, an Apple Watch Series 7 study, was 15.78%.

In one Garmin Forerunner 245 study, a second non-fatiguing run cut the error from 5.58% to 1.06%. Four studies cautioned that accuracy may differ in highly trained runners.

The review notes relatively small samples, no testing of the latest watch models, and accuracy over months or years as a gap. Why VO2 max matters at all is covered in our post on VO2 max, ageing and what is modifiable. The question here is measurement.

The bottom line

  • In 28 adults, Apple Watch VO2 max had a mean absolute percentage error of 13.3% and read 6.07 mL/kg/min low on average.
  • In a 13-study review, 7 studies judged wearable estimates valid or acceptable, and five studies reported a percentage error under 10%.
  • Accuracy varies by device, protocol and fitness level, and long-term accuracy has not been studied much.

Frequently asked questions

Is the Apple Watch VO2 max accurate?
In one independent laboratory comparison of 28 adults, Apple Watch estimates were on average 13.3% away from measured VO2 max and read 6.07 mL/kg/min low. The authors concluded the estimates need further refinement before clinical use. The sample was mostly highly fit.
Can a smartwatch replace a lab VO2 max test?
A 2025 review found that 7 of 13 studies judged wearable estimates valid or acceptable against laboratory testing, mainly in untrained adults, recreational athletes and team-sport players. Usefulness in elite endurance athletes was questionable. All the studies reviewed measured VO2 max in a laboratory treadmill test.

Sources

  1. Lambe R, O'Grady B, Baldwin M, Doherty C, 2025. Investigating the accuracy of Apple Watch VO2 max measurements: A validation study. PLOS ONE, article e0323741.
  2. Železnik Mežan L, 2025. Accuracy of wearables for determining the maximal oxygen uptake and lactate threshold: a qualitative systematic review. Frontiers in Sports and Active Living, volume 7, article 1707991.
Hydra Editorial

Hydra's editorial team. We write from primary research and cite every study we rely on, with its year and journal. We quantify claims wherever the evidence allows and state plainly where it does not: where a finding rests on a small or single trial, we say so in the text rather than in a footnote.