Is replacing time spent in one type of physical activity with another associated with health in children?

Altering the proportion of total physical activity time accumulated while participating in different types of physical activity may influence health. Our objective was to use observational data to estimate whether replacing time from one physical activity type with another is associated with physical and mental health indicators among children. Participants were 385 children aged 10-13 years. They wore a Global Positioning System watch and accelerometer and completed an activity log for 7 days. Data from these instruments was used to estimate time spent in outdoor active play, organized sport, curriculum-based physical activity at school, and active transportation. A cardiometabolic risk factor score was created from body fat, resting heart rate, and resting blood pressure measures. An internalizing symptoms score was created using anxiety and depression symptom questionnaire items. Isotemporal substitution models estimated if health indicators changed when time in one type of physical activity was replaced with equivalent time from another. The results indicated that time spent in all types of physical activity combined was associated with the cardiometabolic risk factor and internalizing symptom scores. Replacing active transportation with outdoor active play was associated with an increase in the internalizing symptoms score but a decrease in the cardiometabolic risk factor score. The internalizing symptoms score decreased when active transportation was replaced by equivalent time in organized sport. Other time substitutions were not significant. In conclusion, the total time spent participating in physical activity and not a specific type of physical activity was the most consistent correlate of the health indicators.