One-year changes in physical activity and sedentary behavior among adolescents: the Croatian Physical Activity in Adolescence Longitudinal Study (CRO-PALS).

Background Little is known about the concurrent change in physical activity (PA), sedentary behavior (SB) and sport participation (SP) during adolescence. The main purpose of this prospective and partly objective study was to simultaneously investigate PA, SBs and SP changes between the 1st and 2nd grades of high school in urban adolescents. Methods In this 1-year follow-up study, the participants were 81 secondary-school students (28 boys and 53 girls) aged 15.5 years at the baseline. PA was assessed with the SenseWear Armband multi-sensor activity monitor, while SBs were assessed by using School Health Action, Planning and Evaluation System (SHAPES) PA questionnaire. The SHAPES questionnaire was supplemented with two questions inquiring about SP in organized sports in school and outside of school. Results PA decreased markedly in both genders between the 1st and 2nd grades of high school. Total energy expenditure (TEE) was reduced by 13 kcal/kg/day on average in boys and by 10 kcal/kg/day in girls (p for both <0.001), while mean daily active energy expenditure (AEE) decreased by 7 kcal/kg/day (p < 0.001) and 3 kcal/kg/day (p = 0.04) in boys and girls, respectively. Similarly, the amount of moderate PA declined by 49 min/day in boys and 21 min/day in girls (p for both <0.001). At the same time vigorous PA was cut by 14 min/day (p < 0.001) and 3 min/day (p = 0.003) in boys and girls, respectively. Conversely, time spent in SBs did not show any change. Conclusion In conclusion, a decline in PA between the 1st and 2nd grades of high school was marked but was not accompanied with an increase in SBs. Policies aimed at increasing PA should be targeting the period of entering secondary school to offset the observed drop in PA.