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

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.