A Behavior Genetic Study of Activity Levels and Internalizing Problems Across Childhood

This study used a twin and triplet sample to investigate the influence of preschoolers’ physical activity levels and internalizing problems on subsequent health outcomes (body-mass index, internalizing behavior problems, household health behaviors) in middle childhood. The potential influence of stressors salient in childhood (household chaos, socioeconomic status, stressful life events) on the hypothesized relationship between physical activity and internalizing on health was also explored. A specific focus was placed on examining the underlying genetic and environmental influences of children’s physical activity levels, as assessed by both temperamental (parent-reported) activity levels and observed (in-lab) motor behavior, using a behavioral genetic approach. By measuring physical activity in these two ways, this project also investigated the validity of the observational coding scheme developed for the current study to assess preschoolers’ overt motor behavior during laboratory testing. Data from 65 families (n = 134 children) included in the Southern Illinois Twins/Triplets and Siblings Study (SITSS) were examined from age 5 (physical activity levels, internalizing problems, and household chaos) to follow-up (body-mass index, internalizing problems, household health behavior, socioeconomic status, and stressful life events) when children were age 7-13 years old. Findings indicated that observed motor behavior and temperamental activity were not significantly correlated, suggesting that these measures assess different aspects of preschoolers’ physical activity levels. Additionally, results supported the reliability and validity of the newly developed observational coding scheme, which underscores the utility of this measure; employing this methodological tool in future studies focused on investigating motor behavior in childhood may be particularly fruitful. Genetic analyses demonstrated that approximately 66% and 34% of the variance in observed motor behavior was accounted for by additive genetic and non-shared environmental influences, respectively, whereas the variance in temperamental activity was attributable to dominant genetic effects (72%) and non-shared environmental influences (28%). These results suggest that differences in age 5 physical activity levels are largely due to genetic differences. Finally, longitudinal analyses showed that health outcomes at follow-up were significantly influenced by 5-year-old temperamental activity and internalizing problems, as well as follow-up socioeconomic status and stressful life events: 1) children who were older, were boys, and lived in a low socioeconomic status household had a higher body-mass index at follow-up; 2) children with higher age 5 internalizing problems and concurrent stressful life events had greater internalizing problems at follow-up; 3) boys and children with higher age 5 temperamental activity had lower scores for household health behaviors. The present project provides greater insight into childhood health (body-mass index, internalizing, household health behaviors) by examining factors relevant to health (physical activity levels, internalizing problems, stress) across development (i.e., from age 5 to ages 7-13 years)