Predictors of change in children's physical activity over 20 months - Variations by gender and level of adiposity

Background: Physical activity declines during childhood and determinants of this decline are poorly understood, The purpose of this prospective stud! was to examine modifiable psychological and social correlates of physical a ctivity change over 20 months, Subjects: 370 girls and 362 boys in public schools, studied through the 4th and 5th grades. Measures: A physical activity index was computed from child reports, parent reports, and objective activity monitoring. Predictor variables were asses sed by child and I,arent surveys. Results: In multiple regressions, after adjustment for demographic variable s, psychological variables explained 4% of the variance in boys' physical a ctivity change, parent variables explained 8%, and interactions with skinfo lds explained 3%, for a total of 15% (unadjusted), Regarding change in girl s' physical activity, psychological variables explained 3%, parent variable s explained 1.5%, and interactions with skinfold explained 1.5%, for a tota l of 6% explained variance (unadjusted). There were differences in predicto rs among children with high and low levels of body fat. Conclusions: Children's preferences for physical activity and frequency of parents transporting children to activity locations explained significant p roportions of variance for girls and boys. The results support a dynamic mo del of the determinants of children's physical activity, but most of the va riance was left unexplained. (C) 1999 American Journal of Preventive Medici ne.