Predictors of physical activity change during adolescence: a 3·5-year follow-up

OBJECTIVE: To investigate the predictors of change in physical activity (PA) from early to mid adolescence in a cohort of adolescents. DESIGN: Prospective, population-based birth cohort study. PA level was evaluated by means of questionnaire, and was analysed in continuous form (min/week) and as a trajectory (inactive–inactive, inactive–active, active–inactive, active–active) based on the cut-off point of 300 min/week. SETTING: Pelotas, a city of 340 000 inhabitants in southern Brazil. SUBJECTS: Adolescents (n 4120) followed from 11 to 15 years of age. RESULTS: Maternal PA change and more exposure to outdoors were directly associated with a positive change in PA level (min/week) for both genders. Higher maturation status (among boys) and later menarche were also associated with positive PA change in min/week. Predictors to remain inactive were: maternal PA change (inverse association), more exposure to outdoors, higher socio-economic level, fear of living in the neighbourhood and non-overweight girls. Predictors to become inactive were higher socio-economic level among boys and increase in screen time among girls. CONCLUSIONS: The study demonstrates that social, family, biological, behavioural and environmental factors exert an important role in the PA change among youngsters as they move into adolescence. These findings may be relevant to the design of policies and intervention programmes aimed at promoting PA in teenagers.