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. 2021 Mar;44(2):212-220.
doi: 10.1080/10790268.2019.1576444. Epub 2019 Feb 27.

Validity of the Apple Watch® for monitoring push counts in people using manual wheelchairs

Kati S Karinharju  1   2 , Alexandra M Boughey  3 , Sean M Tweedy  1   4 , Kelly M Clanchy  5 , Stewart G Trost  6 , Sjaan R Gomersall  3
Affiliations

Validity of the Apple Watch® for monitoring push counts in people using manual wheelchairs

Kati S Karinharju et al. J Spinal Cord Med. 2021 Mar.

Abstract

Objective: A recent Apple Watch® activity-monitoring innovation permits manual wheelchair users to monitor daily push counts. This study evaluated the validity of the Apple Watch® push count estimate.Design: Criterion validity.Setting: Southern Finland and Southeast Queensland, Australia.Participants: Twenty-six manual wheelchair users from Finland and Australia were filmed completing a standardized battery of activities while wearing the Apple Watch® (dominant wrist).Outcome Measures: Wheelchair pushes as determined by the Apple Watch® were compared to directly observed pushes.Results: Agreement between Apple Watch® push counts and directly observed pushes was evaluated using Intraclass correlation coefficients (ICC), Pearson correlations and Bland-Altman analyses. Apple Watch® pushes and directly observed push counts were strongly correlated (ICC = 0.77, P < 0.01) (r = 0.84, P < 0.01). Bland Altman plots indicated that the Apple Watch® underestimated push counts (M = -103; 95% ULoA = 217; LLoA = -423 pushes). Mean absolute percentage error was 13.5% which is comparable to studies evaluating agreement between pedometer-based step counts and directly observed steps.Conclusion: Apple Watch® push-count estimates are acceptable for personal, self-monitoring purposes and for research entailing group-level analyses, but less acceptable where accurate push-count measures for an individual is required.

Keywords: Apple Watch®; Monitoring; Physical activity; Push counts; Wheelchair.

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Figures

Figure 1
Figure 1
Scatterplot of push counts recorded by Apple Watch® (x axis) vs. Direct observation (y axis); ρ = 0.84.
Figure 2
Figure 2
Bland-Altman plot for wheelchair pushes: the Apple Watch® compared with direct observation. Note: The solid line indicates the mean degree of underestimation by the Apple Watch® measured in push counts. The dashed lines represent the upper and lower limits of agreement (push counts). Figures have been rounded to the nearest whole push. LoA, limits of agreement; MD, mean difference.
See this image and copyright information in PMC

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