Physical activity and sedentary behaviour trajectories in middle childhood, and the association of these with adiposity.

Background: The prevalence of overweight/obesity increases substantially throughout the middle childhood years. The contribution of physical activity and sedentary behaviour to the development of overweight/obesity is unclear. It is also unknown whether the impacts of physical activity and sedentary behaviour on weight differ by sex. Purpose: To assess changes in physical activity and sedentary behaviour between the ages of 5-6 and 8-9 years, and the association of these changes with adiposity. Methods: Longitudinal investigation using an ethnically diverse sample of 1467 children. Separate multilevel linear regression models were constructed with the change in each physical activity/sedentary behaviour measure as the explanatory and follow-up adiposity as the outcome variable. Results: Physical activity decreased throughout the study period, whilst sedentary time increased. A decrease in moderate-vigorous physical activity (MVPA) was associated with an increase in all adiposity measures in the overall sample and in girls. An increase in TV viewing time was associated with an increase in BMI z-score in the overall sample. Conclusion: Preventing the decline in MVPA and the increase in TV viewing time during middle childhood could reduce the incidence of overweight/obesity in this age group