I’m often asked: “Can I trust the VO₂max score from my GPS watch?” I don’t ever really have a good answer, other than that lab testing is ideal. Nevertheless, for recreational runners, seeing fitness increases can feel motivating, but for athletes chasing marginal gains, a misleading VO₂max estimate could be more frustrating than helpful.
A new study put the Garmin Forerunner 245 to the test against the gold standard laboratory treadmill ramp tests with respiratory gas analysis. The researchers recruited 35 endurance athletes, comprising 24 men and 11 women, with VO₂max ranging from moderately trained (VO₂max ~54 ml/kg/min) to highly trained (VO₂max ~67 ml/kg/min). Each athlete completed a lab-based VO₂max test and then performed two 15-minute outdoor runs on separate days at more than 70% of their maximum heart rate while wearing the Garmin, which generated its own VO₂max estimate.
Across the group, the watch underestimated VO₂max by ~4–5 ml/kg/min. The agreement with the lab was “moderate to good,” with error rates of around 7–8%. For moderately trained athletes (under ~60 ml/kg/min), the watch performed surprisingly well. Error dropped to just 2.8–4.1%, with decent consistency across runs. Essentially, if your fitness level is good but not elite, the watch’s estimate is fairly accurate. But the accuracy broke down for highly trained athletes. For those with a VO₂max above 60, Garmin underestimated by more than 6 ml/kg/min on average, with error rates of around 9–10%. Reliability was poor, and individual estimates varied widely. The second outdoor run improved accuracy slightly, suggesting the watch “learns” a bit after multiple sessions.
What this means for runners
If you’re a recreational or moderately trained runner, your Garmin’s VO₂max estimate is probably “good enough” to track fitness trends over time. But if you’re highly trained, expect it to undershoot your true VO₂max by a fair margin. Use it as a ballpark. For precise measurement—whether for training prescription, monitoring adaptations, or bragging rights—there’s still no substitute for a lab test with gas exchange.
 VO₂max values from the respiratory gas analysis during the ramp test protocol on the treadmill (ramp protocol) and VO₂max values estimated by the smartwatch after run 1 (smartwatch run 1) and run 2 (smartwatch run 2) in all athletes. |
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