Assessing Accuracy Of Smartwatch-based Estimation Of Maximum Oxygen Consumption Using Different Watches

PURPOSE: Maximal oxygen consumption (VO2max) is a predictor of overall health and a key measure of cardiovascular fitness and aerobic capacity. As wearable technology advances, smartwatches are increasingly used to track cardiovascular health metrics. However, the validity of these estimations by smartwatches remains an area of limited research. This study aims to evaluate the validity and reliability of maximal oxygen consumption estimates from two leading smartwatches. METHODS: 15 participants (11 M, 4F), aged 19-29 (23.8 ± 3.2) years, were recruited and met inclusion criteria for the study. VO2max for all participants was determined in a controlled laboratory environment using a metabolic gas analyzer. Subjects completed a graded exercise test on a treadmill until reaching subjective exhaustion. This value was then compared with the estimated VO2max values from two smartwatch devices (Watch A, Watch B), calculated while wearing the watches for at least 3 consecutive days and measured directly after an outdoor run. The watches were synced between runs and returned after the study period. Baseline descriptive data calculations were performed. Reliability was measured using Intraclass Correlation Coefficient (ICC). Bland-Altman analyses were utilized to explore VO2max values. RESULTS: Measured VO2max in the lab setting was significantly lower than the predicted VO2max (mL·min-1·kg-1) from Watch A (mean 45.28 ± 6.51 vs. mean 48.68 ± 7.03) (p = .041) and Watch B (mean 47.69 ± 8.64 vs. mean 52.83 ± 5.83) (p = .041) with a medium effect size. ICC average measures (2,2) for Watch A (0.836, p = .003) and for Watch B (0.856, p = .001) suggested good reliability for VO2max estimates for both watches and the lab setting measurements. Bland-Altman analyses confirmed overestimation and consistent agreement. CONCLUSION: Both smartwatches tended to overestimate VO2max compared to lab measurements but exhibited good reliability across trials. Either device may be acceptable for recreational users to track VO2max outside of a laboratory setting. However, healthcare professionals should be aware of estimation limitations when prescribing intensity for cardiorespiratory fitness.