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Measuring Moderate-Intensity Exercise with the Apple Watch: Validation Study

Abt, Grant; Bray, James; Benson, Amanda Clare


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Dr James Bray
Lecturer in Sport Nutrition & Physiology

Amanda Clare Benson


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 VO2rest and VO2max tests prior to a series of 5-min bouts of treadmill walking at increasing speed while wearing an Apple Watch on both wrists and with oxygen consumption measured continuously. Five-min exercise bouts were added until the Apple Watch advanced the green ‘exercise’ ring by 5 min (defined as the treadmill inflection speed). Validity was examined using a one-sample t-test, with inter- and intra-device reliability reported as the standardized typical error and intraclass correlation.
Results: The mean (SD) %VO2R at the treadmill inflection speed was 30 (7) % for both Apple Watches. There was a large underestimation of moderate-intensity exercise (left: mean difference -10% [95%CI: -14 to -7], d = -1.4; right: -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 over-estimation of moderate-intensity exercise minutes completed throughout the day.


Abt, G., Bray, J., & Benson, A. C. (2018). Measuring Moderate-Intensity Exercise with the Apple Watch: Validation Study. JMIR Cardio, 2(1), e6.

Journal Article Type Article
Acceptance Date Jan 3, 2018
Online Publication Date Feb 28, 2018
Publication Date Jan 1, 2018
Deposit Date Jan 3, 2018
Publicly Available Date Jan 10, 2024
Journal JMIR Cardio
Print ISSN 2561-1011
Electronic ISSN 2561-1011
Peer Reviewed Peer Reviewed
Volume 2
Issue 1
Pages e6
Keywords Smartwatch; Wearables; Technology; Physical activity; Cardiovascular health, Apple Watch
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Copyright Statement
©Grant Abt, James Bray, Amanda Clare Benson. Originally published in JMIR Cardio (, 28.02.2018.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR Cardio, is properly cited. The complete bibliographic information, a link to the original publication on, as well as this copyright and license information must be included.

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