Time-efficient intervention to improve older adolescents’ cardiorespiratory fitness: findings from the ‘Burn 2 Learn’ cluster randomised controlled trial

Abstract

BackgroundCardiorespiratory fitness (CRF) is an important marker of current and future health status. The primary aim of our study was to evaluate the impact of a time-efficient school-based intervention on older adolescents’ CRF.MethodsTwo-arm cluster randomised controlled trial conducted in two cohorts (February 2018 to February 2019 and February 2019 to February 2020) in New South Wales, Australia. Participants (N=670, 44.6% women, 16.0±0.43 years) from 20 secondary schools: 10 schools (337 participants) were randomised to the Burn 2 Learn (B2L) intervention and 10 schools (333 participants) to the control. Teachers in schools allocated to the B2L intervention were provided with training, resources, and support to facilitate the delivery of high-intensity interval training (HIIT) activity breaks during curriculum time. Teachers and students in the control group continued their usual practice. The primary outcome was CRF (20 m multi-stage fitness test). Secondary outcomes were muscular fitness, physical activity, hair cortisol concentrations, mental health and cognitive function. Outcomes were assessed at baseline, 6 months (primary end-point) and 12 months. Effects were estimated using mixed models accounting for clustering.ResultsWe observed a group-by-time effect for CRF (difference=4.1 laps, 95% CI 1.8 to 6.4) at the primary end-point (6 months), but not at 12 months. At 6 months, group-by-time effects were found for muscular fitness, steps during school hours and cortisol.ConclusionsImplementing HIIT during curricular time improved adolescents’ CRF and several secondary outcomes. Our findings suggest B2L is unlikely to be an effective approach unless teachers embed sessions within the school day.Trial registration numberAustralian New Zealand Clinical Trials Registry (ACTRN12618000293268).

Process Evaluation of a School-Based High-Intensity Interval Training Program for Older Adolescents: The Burn 2 Learn Cluster Randomised Controlled Trial

“…Almost 70% of students reported their intention to participate in HIIT over the next two months. However, findings for CRF at 12 months [40] may be in part explained by students not engaging in self-directed HIIT sessions. Once the structured curriculum-time sessions were discontinued after Phases 1 and 2, students' CRF improvements were lost [40].…”

“…However, it may be unrealistic to expect students that are not necessarily motivated to exercise at high intensity for an extended period of time. Having said this, our published outcomes paper [40] identified a number of meaningful intervention effects, despite HIIT session intensity being lower than intended. Our research demonstrates both the exercise intensity that can be expected when translating HIIT into a real-world school context, and the outcomes that can be achieved with this level of exercise intensity.…”

“…Burn 2 Learn (B2L) is a school-based physical activity program designed to improve older adolescents' CRF [37][38][39][40]. The intervention provides students in their final two years of schooling with a new opportunity to be physically active during the school day, via teacher-facilitated HIIT sessions during curricular time.…”

“…The B2L program was guided by the Consolidated Framework for Implementation Research (CFIR) [44] and we utilised a range of strategies to ensure the intervention was implemented as intended. We recently evaluated the B2L program in a cluster randomised controlled trial (RCT) in 20 secondary schools with 670 older adolescents [40]. Relative to those in the control group, participants in the intervention group improved their CRF and upper body muscular endurance, and reduced their stress (i.e., assessed using hair cortisol concentrations) [37,40].…”

“…We recently evaluated the B2L program in a cluster randomised controlled trial (RCT) in 20 secondary schools with 670 older adolescents [40]. Relative to those in the control group, participants in the intervention group improved their CRF and upper body muscular endurance, and reduced their stress (i.e., assessed using hair cortisol concentrations) [37,40]. We also observed improvements in students' on-task behaviour and subjective vitality immediately following participation in a B2L session [45], indicating beneficial acute effects.…”