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

<b>Objective:</b> 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. <b>Design:</b> Criterion validity. <b>Setting</b>: Southern Finland and Southeast Queensland, Australia. <b>Participants</b>: Twenty-six manual wheelchair users from Finland and Australia were filmed completing a standardized battery of activities while wearing the Apple Watch^® (dominant wrist). <b>Outcome Measures:</b> Wheelchair pushes as determined by the Apple Watch^® were compared to directly observed pushes. <b>Results:</b> 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, <i>P</i> r = 0.84, <i>P</i> ® 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. <b>Conclusion:</b> 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.