The distribution of physical activity in an after-school friendship network.

OBJECTIVE To examine whether a child's friendship network in an afterschool program influences his/her physical activity. METHODS Three waves of data were collected from school-aged children participating in aftercare (n = 81; mean [SD] age, 7.96 [1.74] years; 40% African American, 39% white, and 19% Latino) a name generator survey was used to map each child's social network, and accelerometers were used to measure physical activity. We applied stochastic actor-based modeling for social networks and behavior. RESULTS Children did not form or dissolve friendships based on physical activity levels, but existing friendships heavily influenced children's level of physical activity. The strongest influence on the amount of time children spent in moderate-to-vigorous activity in the afterschool hours was the activity level of their immediate friends. Children consistently made adjustments to their activity levels of 10% or more to emulate the activity levels of their peers (odds ratio [OR] = 6.89, P < .01). Age (OR = 0.92, P < .10) and obesity status (OR = 0.66, P < .10) had marginally significant and relatively small direct effects on the activity. Gender had no direct effect on activity. CONCLUSIONS These results suggest that friendship ties play a critical role in setting physical activity patterns in children as young as 5 to 12 years. Children's activity levels can be increased, decreased, or stabilized depending on the activity level of their immediate social network during a 12-week afterschool program. Network-based interventions hold the potential to produce clinically significant changes to children's physical activity.