Background Commercial off-the-shelf activity trackers (eg, Fitbit) allow users to self-monitor their daily physical activity (PA), including the number of steps, type of PA, amount of sleep, and other features. Fitbits have been used as both measurement and intervention tools. However, it is not clear how they are being incorporated into PA intervention studies, and their use in specific age groups across the life course is not well understood. Objective This narrative review aims to characterize how PA intervention studies across the life course use Fitbit devices by synthesizing and summarizing information on device selection, intended use (intervention vs measurement tool), participant wear instructions, rates of adherence to device wear, strategies used to boost adherence, and the complementary use of other PA measures. This review provides intervention scientists with a synthesis of information that may inform future trials involving Fitbit devices. Methods We conducted a search of the Fitabase Fitbit Research Library, a database of studies published between 2012 and 2018. Of the 682 studies available on the Fitabase research library, 60 interventions met the eligibility criteria and were included in this review. A supplemental search in PubMed resulted in the inclusion of 15 additional articles published between 2019 and 2020. A total of 75 articles were reviewed, which represented interventions conducted in childhood; adolescence; and early, middle, and older adulthood. Results There was considerable heterogeneity in the use of Fitbit within and between developmental stages. Interventions for adults typically required longer wear periods, whereas studies on children and adolescents tended to have more limited device wear periods. Most studies used developmentally appropriate behavior change techniques and device wear instructions. Regardless of the developmental stage and intended Fitbit use (ie, measurement vs intervention tool), the most common strategies used to enhance wear time included sending participants reminders through texts or emails and asking participants to log their steps or synchronize their Fitbit data daily. The rates of adherence to the wear time criteria were reported using varying metrics. Most studies supplemented the use of Fitbit with additional objective or self-reported measures for PA. Conclusions Overall, the heterogeneity in Fitbit use across PA intervention studies reflects its relative novelty in the field of research. As the use of monitoring devices continues to expand in PA research, the lack of uniformity in study protocols and metrics of reported measures represents a major issue for comparability purposes. There is a need for increased transparency in the prospective registration of PA intervention studies. Researchers need to provide a clear rationale for the use of several PA measures and specify the source of their main PA outcome and how additional measures will be used in the context of Fitbit-based interventions.

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BACKGROUND Commercial off-the-shelf activity trackers (e.g., Fitbit) allow users to self-monitor their daily activity, including number of steps, type of PA, and amount of sleep, among other features. Fitbits have been used as both measurement and intervention tools. However, it is not clear how they are being incorporated into PA intervention studies, and differences in use protocols across the life course (e.g., models, strategies to boost wear time) are not known. OBJECTIVE This paper aimed to review the use of Fitbit devices in PA intervention research across the life course in order to provide intervention scientists with a synthesis of information that may inform their future trials involving Fitbit devices. METHODS We conducted a search of the Fitabase Fitbit Research Library. Of the 682 studies available on the Fitabase Fitbit Research Library, 79 interventions met the eligibility criteria for this review and 44 were selected for inclusion, representing interventions conducted in childhood, adolescence, early, middle, and older adulthood. RESULTS Most studies used developmentally appropriate behavior change techniques and wear time instructions. Device wear instructions differed substantially across studies, ranging from a specific number of hours over a given assessment period to daily wear for the duration of the intervention. Strategies to boost wear time included daily reminders through texts and syncing Fitbit data. Minimum wear time criteria differed considerably, both within and between developmental stages. Additionally, rates of adherence to wear time criteria were reported using varying metrics. Most studies supplemented the use of Fitbits with additional objective or self-report measures for PA. CONCLUSIONS Future work should focus on developing standardized protocols for using commercially available devices, especially the most popular ones, in the context of research.