Guidelines recommend that young people engage in muscle-strengthening activities on at least 3 d·wk−1. The purpose of this study was to examine the effect 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% girls; 14.1 ± 0.5 yr) from 16 secondary schools. Teachers were trained to deliver the intervention, which included the following: (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, RT skill competency, flexibility, physical activity, self-efficacy, and motivation. Assessments were conducted at baseline, 6 months (postprogram; primary end point), and 12 months (follow-up). Outcomes were assessed using linear mixed models, with three potential moderators tested using interaction terms (and subgroup analyses where appropriate).Results
For the primary outcome (MF), a group–time effect was observed at 6 months for the upper body (2.0 repetitions; 95% confidence interval (CI), 0.8–3.2), but not the lower body (−1.4 cm; 95% CI, −4.7–1.9). 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 body mass index, there was a group–time effect at 12 months among students who were overweight/obese at baseline (−0.55 kg·m−2; 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.