‘Precious’, N-of-1 smartphone trial for physical activity with biofeedback and digitalised elements from motivational interviewing

Background: Daily variability in physical activity (PA) and its psychological determinants should be examined within individuals to produce accurate evidence. Precious project developed an app that offers randomised intervention elements and studies the following fluctuation in activity, motivation, and engagement. Method: Fifteen participants used the Precious app and activity bracelet for six weeks during which they received repeated, randomised interventions of digitalised motivational interviewing features, prompts to conduct 24h measurements with Firstbeat heart-rate variability sensors, prompts to download the biofeedback, and daily questions on motivation, self-efficacy and perceived barriers. Exit interviews focused on feasibility and user perceptions of their motivation, self-regulation, PA, and the role of Precious app in these. Interview data was analysed with thematic analysis. The N-of-1 intervention effects on PA and goal setting were analysed with multilevel modelling and time-series analysis. Findings: All participants completed the intervention and most reported sustained motivation to track their well-being and progress. Participants found step tracking features most useful and motivational features least useful, potentially due to the high level of motivation to increase PA reported at baseline. Some participants wished the app offered more detailed PA prescriptions. Challenges relating to feasibility included smartphone notifications as a delivery method, as push notifications sometimes passed unnoticed. Discussion: Precious helped participants to understand their PA and self-regulation, and ways to improve these. Most insights were related to self-monitoring of steps and the activity logging. Testing the app among people with low baseline motivation for PA would allow better examining the motivational interviewing features.