Increasing adolescents' physical activity levels through a comprehensive school-based physical activity program: study protocol of the cluster randomized controlled trial Active School.

Background: The positive effects of regular physical activity on children and adolescents' physical and mental health are well-established. Despite these health benefits, most Swiss adolescents do not meet WHO's recommended level of physical activity, which includes a daily minimum of 60 min of moderate-to-vigorous physical activity. Due to their inclusivity, schools are identified as a key setting to promote physical activity.