KIDS OUT! Protocol of a brief school-based intervention to promote physical activity and to reduce screen time in a sub-cohort of Finnish eighth graders

Background Adolescents’ physical activity (PA) is decreasing and sedentary behavior (SB) increasing alarmingly. Insufficient PA and excessive SB are both related to various health risks indicating that interventions to promote adolescents’ PA and to reduce their SB are needed. Schools have a great potential to reach most adolescents, and in Finland health education (HE) as stand-alone subject provides an excellent platform for health promotion. This paper describes the protocol and evaluation (RE-AIM) of an intervention developed for three HE lessons to increase PA and reduce SB during leisure among 8th graders.