Use of the ME-BYO Index, a Mobile Health App, During an Online Strength Training Program in Adults: Fidelity, Feasibility, and Acceptability Study.

Background: Although various apps have been developed to support health behaviors, they are mostly commercial, possibly limiting the number of users. The ME-BYO index was developed by Kanagawa Prefecture in 2019 to comprehensively and numerically measure and visualize an individual's current health status and future disease risk by quantifying data. The ME-BYO index is free of charge, so it can be made available to as many prefectural residents as possible for health promotion. Effective online strength training programs are being developed that, when combined with ME-BYO index measurements, will help with both exercise habits and health management. Objective: In this study, we aimed to validate the fidelity, feasibility, and acceptability of self-measurement using the ME-BYO index during the implementation of an online strength training program. Methods: Participants were 23 adults aged 40 years or older who did not regularly perform muscle strengthening exercises. The strength training program was performed twice a week for 8 weeks (16 sessions in total), and the ME-BYO index was explained to the participants so that they could self-measure the ME-BYO index with a smartphone on the day of the strength training program, before its implementation. The ME-BYO index during the study period was continuously collected from the app, and the ME-BYO index adherence rate was calculated. Questionnaires were used to assess the feasibility (difficulty of measurement and motivation to improve lifestyle) and acceptability (intention to maintain measurement and appropriate frequency of measurement) of implementing and continuing the ME-BYO index measurements. Changes in the ME-BYO index between the first and second halves of the program period, examination of items strongly related to changes in the ME-BYO index, and a comparison of physical fitness and health outcomes before and after the program period were conducted. Results: The mean ME-BYO index adherence rate during the strength training program was 89.4% (SD 17%). Regarding acceptability, the participants were highly motivated to continue measuring the ME-BYO index (77%), and the appropriate frequency of measurement was once a week and twice a week (31% and 31%, respectively). Panel data analysis of the self-measured ME-BYO index showed no significant change in the ME-BYO index score; however, it increased to a higher score. Examination of the items that increased the overall score indicated that systolic blood pressure, mental resilience, and Mini-Cog scores were the relevant factors. The pre- and postprogram measurements showed no significant changes in items other than physical fitness. Conclusions: The fidelity, feasibility, and acceptability of measuring the ME-BYO index during a regular online strength training program were high, suggesting that self-measurement of the ME-BYO index could be used to implement and maintain healthy behaviors. These findings suggest that the ME-BYO index can be recommended as a basic health app.