Popularity and Friendships and Their Relationship to Physical Activity Before and After Transition to a Higher School Grade

Background This study investigated the relationships between children's friendship ties and their physical activity (PA) both before and after their transition to a new school year. Methods In 2011-2012, children in grades 5-8 attending a Canadian urban middle-school completed web-based health and friendship surveys two times before (pre-transition) and three times after (post-transition) they moved up in school grade. Cross-sectional associations between an average daily frequency of >= 60 min/day of moderate-to-vigorous intensity PA (MVPA) and characteristics of children's friendships were estimated for pre-transition (n = 191) and post-transition (n = 255) data. Sociodemographic-adjusted linear regression (beta) estimated associations between a child's MVPA and friendship characteristics. Results We found positive associations between a child's MVPA and the average MVPA of their friends at post-transition only (beta = 0.61, 95% CI 0.10 to 1.13) and the number of sent friendships at pre-transition (beta = 0.03, 95% CI 0.01 to 0.05) and post-transition (beta = 0.02, 95% CI 0.01 to 0.04). A statistically significant interaction between popularity and friends' average PA at pre-transition was also found. Conclusions The PA of friends and the number of school friends that a child identified are positively associated with MVPA. The estimated associations between MVPA and aspects of children's friendships are similar for boys and girls.