Goal feedback from whom? A physical activity intervention using an N-of-1 RCT

Objective: Adolescents are not meeting the recommended guidelines for physical activity. Social support and self-regulatory skills are two factors known to impact physical activity and sedentary behaviour. The study sought to examine how targeting feedback as part of a self-regulatory process could increase physical activity, and the individual who should be providing the feedback. Design: The study utilised an aggregated N-of-1 RCT which allows for an iterative process of intervention development, and examines variability within participants to answer the question for whom did the intervention work. Ten adolescents (ages 13–18) set a daily physical activity goal. Adolescents received a SMS text message providing feedback on goal attainment daily from a parent, peer, behavioural health specialist; or no text message (control). Main Outcome Measures: A bioharness heart rate monitor assessed heart rate as proxy for goal attainment. Adolescents also self-monitored their physical activity in the Calorie Counter and Diet Tracker by MyFitnessPal^TM app (commercially available). Results: Intervention demonstrated a significant effect for 30% of the sample in increasing MVPA (M_increase = 52 min), with no significant effect on sedentary behaviour. Conclusion: A single occasion of text messaging from the right person can produce changes, however, careful consideration should be given to who provides the feedback.