FIT FIRST Teen - School Intervention Study

The goal of this cluster randomised controlled trial is to investigate the effects of the FIT FIRST Teen program on adolescents' physical fitness, motivation, and well-being, as well as the implementation of such a program within schools. The main questions it aims to answer are: Research Question 1: Does the FIT FIRST Teen program improve cardiorespiratory fitness, body composition, and muscle strength among adolescents? Research Question 2: Does the FIT FIRST Teen program improve well-being, motivation towards physical activity, and body image among adolescents? Research Question 3: What are the challenges that teachers and schools will face regarding the implementation of the FIT FIRST Teen program? The research team will compare the FIT FIRST Teen program to a control (usual physical education curricula) to see if such a program improves adolescents' physical fitness, motivation, and well-being. Participating schools will: * Participate in a training course, where the core principles of the FIT FIRST Teen program will be delivered. * Implement the FIT FIRST Teen program for a full school year (three 45-minute lessons a week). * Keep a logbook where the weekly practised activities will be reported.