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Assessing the Accuracy of Fitness Smartwatch Data for Cardiovascular and Physical Activity Monitoring: A Validation Study in Digital Health
Published on: February 21, 2025
Accuracy of VO2 max Estimates From Apple Watch Series 10
Rory Lambe1,2, Moritz Schumann3, Lauren Donnelly1
1School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland.
Mayo Clinic Proceedings. Digital Health
|May 7, 2026
Summary
The Apple Watch Series 10 underestimates maximal oxygen uptake (VO2 max) compared to indirect calorimetry. While not accurate for individual assessment, it may be useful for population studies.
Area of Science:
- Cardiovascular Physiology
- Exercise Science
- Wearable Technology Validation
Background:
- Maximal oxygen uptake (VO2 max) is a key indicator of cardiorespiratory fitness.
- Wearable devices offer convenient methods for health monitoring, but their accuracy needs validation.
- Assessing VO2 max with consumer wearables like the Apple Watch is of growing interest.
Purpose of the Study:
- To evaluate the accuracy of VO2 max estimates from the Apple Watch Series 10.
- To compare Apple Watch VO2 max estimates against criterion measures obtained via indirect calorimetry.
- To determine the validity of the Apple Watch for assessing cardiorespiratory fitness.
Main Methods:
- Participants underwent a maximal exercise treadmill test using indirect calorimetry (modified Åstrand protocol).
- VO2 max estimates were simultaneously generated using the Apple Watch Series 10.
- Agreement was analyzed using Bland-Altman analysis, mean absolute error, and mean absolute percentage error.
Main Results:
- Apple Watch Series 10 significantly underestimated VO2 max compared to indirect calorimetry (mean difference: -6.25 mL/kg/min).
- Wide limits of agreement (-18.23 to 5.73) indicate substantial individual variability.
- Mean absolute error was 6.79 mL/kg/min (13.2% error), with correct fitness percentile classification for only 14% of participants.
Conclusions:
- Apple Watch VO2 max estimates demonstrate poor agreement at the individual level.
- The device may have utility for population-level cardiorespiratory fitness assessment in research.
- Further longitudinal studies are required to assess measurement reliability and potential use as an alternative to traditional methods.
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