Physical activity, physical fitness and self-rated health: cross-sectional and longitudinal associations in adolescents.

Objectives: To evaluate the independent associations of physical activity and physical fitness with self-rated health in adolescents. Methods: Data from a 2-year observational study (2013-2015) were used (n=256, 58% girls, 13.7±0.3 years at baseline). Self-rated health was assessed with a questionnaire, physical activity by an accelerometer and a questionnaire, and physical fitness via the measurements included in the Finnish national Move! monitoring system for physical functional capacity and their z-score average (fitness index). Results: Self-reported physical activity had cross-sectional associations with self-rated health (girls β 0.213, p=0.006, β 0.221 boys p=0.021) while accelerometer-based moderate-to-vigorous physical activity did not. Higher self-reported physical activity at baseline was associated with higher self-rated health at follow-up in boys (β 0.289, p<0.001), but not in girls (β -0.056, p=0.430). Accelerometer-based moderate-to-vigorous physical activity had positive longitudinal associations with future self-rated health in boys, but some of these similar associations were negative in girls. Fitness index had a positive cross-sectional association with self-rated health in boys (β 0.282 or β 0.283, p=0.002), but not in girls (β 0.162 or β 0.161, p=0.051). Physical fitness was not longitudinally associated with self-rated health. Conclusions: Self-reported physical activity showed potential to explain current and future self-rated health better than accelerometer-based physical activity or physical fitness. We recommended to consider self-reported physical activity as an adequate metric of adolescent health in the population-level surveillance systems.