%0 Journal Article
%@ 2561-1011
%I JMIR Publications
%V 2
%N 1
%P e6
%T Measuring Moderate-Intensity Exercise with the Apple Watch: Validation Study
%A Abt,Grant
%A Bray,James
%A Benson,Amanda Clare
%+ School of Life Sciences, The University of Hull, Cottingham Road, Kingston upon Hull, HU6 7RX, United Kingdom, 44 01482463397, g.abt@hull.ac.uk
%K smartwatch
%K wearables
%K technology
%K physical activity
%K cardiovascular health, Apple Watch
%D 2018
%7 28.02.2018
%9 Original Paper
%J JMIR Cardio
%G English
%X Background: Moderate fitness levels and habitual exercise have a protective effect for cardiovascular disease, stroke, type 2 diabetes, and all-cause mortality. The Apple Watch displays exercise completed at an intensity of a brisk walk or above using a green “exercise” ring. However, it is unknown if the exercise ring accurately represents an exercise intensity comparable to that defined as moderate-intensity. In order for health professionals to prescribe exercise intensity with confidence, consumer wearable devices need to be accurate and precise if they are to be used as part of a personalized medicine approach to disease management. Objective: The aim of this study was to examine the validity and reliability of the Apple Watch for measuring moderate-intensity exercise, as defined as 40-59% oxygen consumption reserve (VO2R). Methods: Twenty recreationally active participants completed resting oxygen consumption (VO2rest) and maximal oxygen consumption (VO2 max) tests prior to a series of 5-minute bouts of treadmill walking at increasing speed while wearing an Apple Watch on both wrists, and with oxygen consumption measured continuously. Five-minute exercise bouts were added until the Apple Watch advanced the green “exercise” ring by 5 minutes (defined as the treadmill inflection speed). Validity was examined using a one-sample t-test, with interdevice and intradevice reliability reported as the standardized typical error and intraclass correlation. Results: The mean %VO2R at the treadmill inflection speed was 30% (SD 7) for both Apple Watches. There was a large underestimation of moderate-intensity exercise (left hand: mean difference = -10% [95% CI -14 to -7], d=-1.4; right hand: mean difference = -10% [95% CI -13 to -7], d=-1.5) when compared to the criterion of 40% VO2R. Standardized typical errors for %VO2R at the treadmill inflection speed were small to moderate, with intraclass correlations higher within trials compared to between trials. Conclusions: The Apple Watch threshold for moderate-intensity exercise was lower than the criterion, which would lead to an overestimation of moderate-intensity exercise minutes completed throughout the day. 
%R 10.2196/cardio.8574
%U http://cardio.jmir.org/2018/1/e6/
%U https://doi.org/10.2196/cardio.8574