Implementing resistance training in secondary schools: a cluster randomized controlled trial

PURPOSE: Guidelines recommend that young people engage in muscle-strengthening activities on at least three days per week. The purpose of this study was to examine the impact of a school-based intervention focused on resistance training (RT) for adolescents. METHODS: The 'Resistance Training for Teens' intervention was evaluated using a cluster randomized controlled trial with 607 adolescents (50.1% female; 14.1±0.5 years) from 16 secondary schools. Teachers were trained to deliver the intervention, which included: (i) an interactive student seminar; (ii) a structured physical activity program, focused on RT; (iii) lunchtime fitness sessions; and, (iv) web-based smartphone apps. The primary outcome was muscular fitness (MF) and secondary outcomes included body mass index (BMI), RT skill competency, flexibility, physical activity, self-efficacy and motivation. Assessments were conducted at baseline, 6- (post-program; primary end-point) and 12-months (follow-up). Outcomes were assessed using linear mixed models, with three potential moderators tested using interaction terms (and sub-group analyses where appropriate). RESULTS: For the primary outcome (MF), a group-by-time effect was observed at 6-months for upper body (2.0 repetitions, 95% confidence interval [CI]: 0.8 to 3.2), but not lower body (-1.4cm, 95% CI: -4.7 to 1.9). At 6-months, there were intervention effects for RT skill competency and self-efficacy, but no other secondary outcomes. Effects for upper body MF and RT skill competency were sustained at 12-months. Despite overall no effect for BMI, there was a group-by-time effect at 12-months among students who were overweight/obese at baseline (-0.55 kg/m, 95% CI: -1.01 to -0.08). CONCLUSIONS: The school-based RT intervention resulted in immediate and sustained improvements in upper body MF and RT skill competency, demonstrating an effective and scalable approach to delivering RT within secondary schools.