Feasibility of a mobile health intervention to motivate adolescent fitness and high-intensity exercise adherence (Motivating Adolescent Fitness (MOTAFIT)): protocol for a randomised controlled trial

INTRODUCTION: Most adolescents fail to achieve recommended levels of vigorous-intensity physical activity, despite the established benefits for cardiorespiratory fitness and vascular health. Supervised interventions can be effective, but are resource-intensive and lack scalability. Mobile health (mHealth) technologies may provide a cost-effective and accessible approach to support structured, individualised training for adolescents. The Motivating Adolescent Fitness (MOTAFIT) trial will assess the feasibility and acceptability of an mHealth-supported exercise intervention for adolescents to inform the design of a definitive randomised controlled trial (RCT). METHODS AND ANALYSIS: MOTAFIT is a three-arm feasibility RCT targeting 120 adolescents aged 13-16 years from the Okanagan Valley, British Columbia. Participants will be randomised (1:1:1) to: (1) MOTAFIT, (2) active control or (3) control group. The 12-week intervention targets ≥40 min/week of vigorous-intensity exercise (≥80% HRmax), co-designed with an exercise specialist and supported by mHealth technology. Primary outcomes for feasibility, including recruitment, retention, adherence, fidelity and acceptability, will be assessed as part of a process evaluation. Secondary measures (cardiorespiratory fitness, vascular health and blood pressure) will provide preliminary estimates to guide future sample size calculations. ETHICS AND DISSEMINATION: The study has received approval from the University of British Columbia Clinical Research Ethics Board (H22-03183) and the University of Victoria Human Research Ethics Board. Parental consent and adolescent assent will be obtained prior to participation. Findings will be disseminated via peer-reviewed publications, conferences and community engagement. TRIAL REGISTRATION NUMBER: NCT06409793.