The association of objectively determined physical activity behavior among adolescent female friends.

The purpose of this study was to examine the extent to which physical activity among adolescent female friends is interdependent. The participants were 318 adolescent girls with a mean age of 16.0 years (range: 15-18 years). Pedometry was used to assess physical activity over 4 days. The relationship between an individual girl and her first-nominated reciprocal friend's physical activity level was moderate (r = 0.45, 90% confidence interval = 0.31, 0.56), when the friendship was nonreciprocal it was trivial (r = -.06, 90% confidence interval = -.36 .25). Friends'physical activity levels explained between 27% and 32% of an individual's pedometer-determined physical activity level. Reciprocity of friendship is an important variable to consider when understanding the relationship between adolescent female friends' physical activity. When friendships are reciprocal, there is a stronger relationship between friends' physical activity.