Validity of Apple Watch 6 and Polar A370 for monitoring energy expenditure while resting or performing light to vigorous physical activity.

Objectives: The purpose of this study was to assess the validity of energy expenditure measurements taken by the Apple Watch 6 and Polar A370 during resting, light- to vigorous-intensity running on the treadmill and ground, and post-exercise of each speed.
Design: Randomized cross-over trial.
Methods: This study included 11 male adults (22.5 ± 1.8 years old). Participants were asked to wear the Apple Watch 6 and the Polar A370 simultaneously to measure energy expenditure under various intensities of physical activities on the treadmill and ground, which were then compared with results from a gas metabolism analysis system.
Results: Monitoring energy expenditure for both treadmill and ground, the Apple Watch 6 (range: 13.40-50.34 %) had a higher mean absolute percent error than the Polar A370 (range: 12.74-27.70 %) in resting and running state, while the mean absolute percent error of the Apple Watch 6 (range: 9.71-32.81 %) is smaller than that of the Polar A370 (15.79-43.51 %) in post-exercise. The Apple Watch 6 tends to overestimate energy expenditure, with a mean percent error ranging from -6.61 % to 53.24 %, while the Polar A370 tends to underestimate energy expenditure, with a mean percent error ranging from -3.51 % to 11.33 %. No estimated energy expenditure of both devices fell in the equivalence testing zone.
Conclusions: For young adult males, the Apple Watch 6 and Polar A370 provide similar levels of accuracy in monitoring energy expenditure during treadmill and ground running exercise. However, both devices are still inadequate in this regard.
Competing Interests: Declaration of interest statement The authors declare no conflict of interest.
(Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)