Abstract
BACKGROUND: Physical inactivity is a global health concern. mHealth interventions have become increasingly popular, but to date, principles of effective communication from Self-Determination Theory have not been integrated with behavior change techniques to optimize app effectiveness. We outline the development of the START app, an app combining SDT principles and 17 purposefully chosen BCTs to support inactive office employees to increase their walking during a 16-week randomized controlled trial. We also explored acceptability, engagement with, associations between app usage and behavioral engagement, and perceived impact of the app in supporting behavior change. METHODS: Following development, fifty insufficiently physically active employees (M age = 44.21 ± 10.95 years; BMI = 29.02 ± 5.65) were provided access and instructions on use of the app. A mixed methods design was used to examine feasibility of the app, including the User Mobile App Rating Scale, app engagement data, step counts, and individual interviews. Linear mixed modeling and inductive thematic analysis were used to analyze quantitative and qualitative data, respectively. RESULTS: Walkers rated the app quality favorably (M = 3.68 out of 5). Frequency of entering step counts (i.e., frequency of self-monitoring) on a weekly basis positively predicted weekly step counts measured via Fitbits at both the between-and within-individual levels. App features (entering daily step counts, reminders, and motivational messages) were perceived to assist walkers in fostering goal achievement by building competence and via self-monitoring. CONCLUSIONS: The START app may be a useful component of walking interventions designed to increase walking in the workplace. Apps designed to promote walking behavior may be effective if they target users' competence and integrate BCTs. TRIAL REGISTRATION: This study was part of a pilot larger randomized controlled trial, in which a component of the intervention involved the use of the mobile app. The trial was retrospectively registered with the Australian and New Zealand Clinical Trials Registry (ACTRN12618000807257) on 11 May 2018 https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=375049&isReview=true .