Decline in physical activity during adolescence is not associated with changes in mental health.

Background: The majority of studies investigating associations between physical activity and mental health in adolescents have been cross-sectional in design. Potential associations between physical activity and mental health may be better examined longitudinally as physical activity levels tend to decrease in adolescence. Few studies have investigated these associations longitudinally in adolescents and none by measuring physical activity objectively.
Methods: A total of 158 Dutch adolescents (mean age 13.6 years, 38.6% boys, grades 7 and 9 at baseline) participated in this longitudinal study. Physical activity, depressive symptoms and self-esteem were measured at baseline and at the 1-year follow-up. Physical activity was objectively measured with an ActivPAL3™ accelerometer during one full week. Depressive symptoms were measured with the Center for Epidemiologic Studies Depression Scale (CES-D) and self-esteem was assessed with the Rosenberg Self-Esteem Scale (RSE). Results were analysed using structural equation modelling.
Results: Physical activity levels decreased 15.3% over a 1-year period (p < .001), with significantly (p = .001) greater decreases during grade 7 (-20.7%) than during grade 9 (-5.0%). Overall, depressive symptoms decreased (-12.1%, p < .001) over a 1-year period, while self-esteem did not change significantly (+2.9%, p = .066). Higher levels of depressive symptoms at baseline predicted a greater decline in depressive symptoms (β = -.51, p < .001) and higher levels of self-esteem at baseline predicted a smaller increase in self-esteem (β = -.48, p < .001). The decline in physical activity did not appear to predict any change in depressive symptoms and self-esteem.
Conclusion: The decline in physical activity over a 1-year period during adolescence is not associated with a change in mental health. Further studies in adolescents aiming to investigate whether a change in physical activity is associated with a change in mental health should control for baseline levels of mental health and academic year differences.