Capturing Objective Functional Measures Using Smartphone Inertial Sensors: Feasibility and Usability Study With Older Adults.

Background: Digital platforms and smartphone apps have the potential to help patients with musculoskeletal conditions receive targeted interventions and physiotherapy support at home. As musculoskeletal conditions are much more prevalent in older adults, it is important to determine whether these technologies are accessible and acceptable to this demographic, who may possess lower levels of digital literacy compared to younger adults. Objective: The study aims to evaluate the feasibility and usability of completing functional assessments while recording the activity using smartphone inertial sensors in adults 60 years or older. Methods: Participants (N=21) were recruited from a range of community settings to complete a 4-week home-based trial, recording unsupervised sit-to-stand and single-leg balance activities at least once per week using their smartphone. We analyzed the data quality and adherence by number of assessments per week from the uploaded datasets. Feedback on usability was assessed using interviews and the System Usability Score. Results: Inductive content analysis was used to identify 5 top-level categories: app, device, task, time, and personal perception. The mean System Usability Scale score was 81.2 (SD 17.5). The proportion of valid data uploads was 63.8% (81/127) for single-leg balance and 93.5% (58/62) for sit-to-stand measures. Adherence was high, with no significant deviations in the mean number of sessions completed or duration between sessions. Conclusions: Smartphone-based monitoring of functional activities can facilitate unsupervised, remote assessments, thus reducing burden on physiotherapy services and increasing the ability to monitor progress objectively. Activities should be considered for complexity and, where necessary, increase in difficulty over time. App-based feedback is essential to inform users of the progress and adherence to the activities.