Time-efficient physical activity intervention for older adolescents: the Burn 2 Learn cluster randomised controlled trial

Introduction: Time-efficient physical activity interventions are needed for older adolescents (≥16 years) in the senior school years (i.e., Grades 11 and 12) where there is a heavy focus on academic performance and physical education is not mandatory. The aim of our study was to evaluate the impact of a time-efficient school-based intervention designed to improve older adolescents’ cardiorespiratory fitness (CRF) by integrating high-intensity activity breaks into curriculum time. Methods: We evaluated the Burn 2 Learn (B2L) intervention using a cluster randomised controlled trial with older adolescents (N=670) from 20 secondary schools in New South Wales, Australia. We utilised a range of implementation strategies to support teachers to facilitate the delivery of 2-3 high intensity interval training (HIIT) sessions/week during lesson-time. The B2L intervention included the following: (i) information seminar for students delivered by school champions, (ii) school-based HIIT sessions delivered during lesson time, (iii) purpose-built smartphone application (app) and heart rate monitors designed to quantify individual and group heart rate and support self-monitoring, and (iv) information newsletters for parents. The HIIT sessions involved a combination of aerobic and muscle-strengthening exercises, designed to be enjoyable and vigorous in nature. Teachers and students in the control group continued with their usual practice. Outcomes were assessed at baseline, 6 and 12-months. The primary outcome was CRF (multi-stage fitness test). Secondary outcomes included physical activity (ActiGraph GT9X Link accelerometers), hair cortisol concentrations, muscular fitness (push-up and standing long jump tests), body composition (body mass index), mental health and HIIT self-efficacy (questionnaires). Data were analysed using linear mixed models, accounting for clustering of effects at the class level. Potential moderators of effects were identified a priori and sub-group analyses were conducted if interaction tests were significant (p<0.1). Results: At the primary endpoint (6-months), we found a significant difference between groups (in favour of B2L) for the primary outcome CRF [4.0 laps (95% CI, 1.7 to 6.4)] and a range of secondary outcomes. Moderator analyses revealed reduced stress and internalising problems among adolescents in the intervention group who were identified as ‘at-risk’ of poor mental health at baseline. Discussion: Implementing high intensity breaks during curricular time improved CRF and muscular endurance among the full sample of older adolescents, and mental health among the ‘at-risk’ sub-sample. Our findings highlight the health benefits of re-allocating a small amount of curriculum time to physical activity during the final years of secondary school. Trial registration: ACTRN12618000293268 My co-authors and I acknowledge that we have no conflicts of interest of relevance to the submission of this abstract.