School-based physical exercise intervention for adolescents' mental health: An adaptation of the 'ActTeens Program' cluster RCT.

Background: Although there is evidence on the associations between physical activity practice and adolescents' mental health, there is still a lack of information on randomized controlled studies carried out in the school environment, and factors of the dose of PA still need to be better explored. Aims: To analyze the effects of a school-based physical exercise intervention on adolescents' mental health. Methods and materials: A 12-week cluster randomized controlled study was conducted in two public schools in Brazil. The intervention included structured physical exercise sessions within Physical Education classes, twice a week, for 20 minutes per lesson. The intensity of the exercises was monitored via heart rate sensor. The Depression, Anxiety and Stress Scale - Short Form (DASS-21) was used to measure symptoms of depression, anxiety, and stress. Multilevel linear mixed models were used to evaluate the effects of the intervention on mental health indicators. Results: A total of 131 adolescents were included in the analysis (52.7% female; age 13.2 ± 0.90). No significant group × time interaction effects were observed for depression (interaction effect: 0.71; 95% CI -0.98 to 2.40; p = 0.412), anxiety (interaction effect: 0.27; 95% CI -0.92 to 1.46; p = 0.655), or stress (interaction effect: 0.39; 95% CI -0.92 to 1.71; p = 0.557). Conclusion: The intervention was not effective in improving adolescents' mental health indicators. Future research are warranted to investigate whether higher doses of PA may yield positive effects on mental health among adolescents.