PURPOSE: Childhood obesity has multiple causes; however, physical activity (PA) is likely to provide a protective effect. Using a longitudinal observational design spanning 8 years of growth (age 5 to 13), we examined associations between PA and fat mass (FM) in a cohort of healthy children (n=398).

METHODS: A total of 188 boys and 210 girls participating in the Iowa Bone Development Study were assessed at least twice in 8 years. PA was measured by the Actigaph physical activity monitor and FM was assessed by dual x-ray absorptiometry (DXA). Data were analyzed using multilevel (random- and fixed-effects) regression models with adjustment for centered age (yr), centered age-squared (yr), height (cm), somatic maturity (0,1), TV viewing (1-5 scale), video gaming (1-5 scale). Quadratic age was included to allow for non-linear growth. Maturity was estimated using predictive equations by Mirwald (maturity offset). TV viewing and video gaming, markers of sedentary activity, were estimated from parent and child reports. The first-level of the models described the child-specific developmental change of FM over the course of the study (random effect). The predictor variables were added in a stepwise fashion as fixed effects to the second-level of the models. Likelihood ratio statistics were used to determine whether the effects of predictor variables were significant contributors to the models. All models were gender-specific and p < 0.05.

RESULTS: Throughout childhood, boys and girls who were the most active had the least amount of FM (inverse association). Beta coefficients indicated that if all other variables were held constant, 10 min of PA would result, on average, in .25 kg less FM. In addition, video gaming; but not TV viewing, was positively associated with FM.

CONCLUSION: These results provide evidence that greater amounts of everyday PA are associated with a healthy developmental profile for adiposity; whereas video gaming increases the likelihood of excessive adiposity. Increasing the level of PA is likely to be a safe and efficient strategy to counter obesity in children.

Supported by NIH Grants R01-DE 12101 and R01-DE09551.