This study is a new subproject in The Childhood Health, Activity, and Motor Performance School (CHAMPS) Study Denmark, also known as the Svendborg Project. The project has a well-defined cohort with originally 1515 school students who since 2007 have been divided into two groups: schools with extra exercise during school hours and matched traditional schools. CHAMPS-DK aims to investigate the effect of increased physical activity on current and future health of children and adolescents.