Relationship of body mass index and psychosocial factors on physical activity in underserved adolescent boys and girls.

OBJECTIVE: Previous research indicates that body mass index (BMI) and sex are important factors in understanding physical activity (PA) levels. The present study examined the influence of BMI on psychosocial variables (self-efficacy, social support) and PA in underserved (ethnic minority, low income) boys in comparison with girls.
METHODS: Participants (N = 669; 56% girls; 74% African American) were recruited from the "Active by Choice Today" trial. MAIN OUTCOME MEASURES: BMI ʐ score was calculated from objectively collected height and weight data, and PA was assessed with 7-day accelerometry estimates. Self-report questionnaires were used to measure self-efficacy and social support (family, peers) for PA.
RESULTS: A 3-way interaction between BMI z score, sex, and family support on PA was shown such that family support was positively associated with PA in normal-weight but not overweight or obese boys, and was not associated with PA in girls. Self-efficacy had the largest effect size related to PA in comparison with the other psychosocial variables studied.
CONCLUSIONS: Self-efficacy was found to be an important variable related to PA in underserved youth. Future studies should evaluate possible barriers to PA in girls, and overweight youth, to provide more effective family support strategies for underserved adolescents' PA. (PsycINFO Database Record (c) 2010 APA, all rights reserved).