Delivering and evaluating digital therapeutic interventions to increase physical activity: Formative testing of engagement, compliance, and adherence

Background Digital therapeutics (DTx) allow for the deployment of real-world interventions on a broad scale, at a lower cost. However, using digital modalities for both intervention delivery and evaluation can become a concern if they unintentionally influence each other, as well as behavioral adherence. A DTx formative test to enhance affective response during physical activity (PA) examined intercorrelations between engagement with digital intervention strategies and compliance with digital assessment procedures. We also examined whether digital engagement and compliance were associated with behavioral adherence. Methods Adults (N = 37, M = 46.5, range: 25–75 years) participated in a 14-day DTx. Fitbit smartwatches assessed intervention mediators (e.g., affective response) and outcomes (e.g., PA) through ecological momentary assessment (EMA) and accelerometers, respectively. Digital compliance (e.g., EMA response rates, smartwatch wear time), digital engagement (e.g., completing weekly PA scheduling sessions, completing morning PA planning/goal sessions), and behavioral adherence (e.g., performing planned PA sessions, achieving PA goals) were assessed. Partial correlations controlling for age and body mass index examined person-level associations among compliance, engagement, and adherence variables. Results One component of digital engagement showed a moderate association with the random EMA component of digital compliance (r = .37). Some engagement components showed medium to strong associations with behavioral adherence (rs = .46−.84). Digital compliance was unrelated to behavioral adherence. Conclusion Digital engagement was largely unrelated to digital compliance. Digital engagement (but not digital compliance) was associated with behavioral adherence. Using similar digital modalities for intervention delivery and evaluation does not appear to pose serious methodological concerns for DTx to promote PA. The study is registered on clinicaltrial.gov under eMOTION Formative Study (TRN: NCT06125964) on 26 October 2023.