Multilevel correlates of physical activity for early, mid, and late adolescent girls.

Background: We examined associations among multilevel variables and girls' physical activity to determine whether they vary at different adolescent ages. Methods: All field sites of the Trial of Activity for Adolescent Girls contributed participants from 6th (n = 1576) and 8th grades (n = 3085). The Maryland site contributed an 11th grade sample (n = 589). Questionnaires were used to obtain demographic and psychosocial information (individual- and social-level variables); height, weight, and triceps skinfold to assess body composition; interviews and surveys for school-level data; and geographical information systems and self-report for neighborhood-level variables. Moderate to vigorous physical activity minutes (MVPA) were assessed from accelerometers. Mixed models (13 individual, 5 social, 15 school, 12 neighborhood variables) were used to determine multilevel associations. Results: Variables at individual, social, school, and neighborhood levels were associated with MVPA, but differed across grades. Lower percent body fat, higher social support from friends, and lower school math scores were associated with higher MVPA at 6th and 8th grade. Higher physical activity self-efficacy was associated with higher MVPA at 11th grade. Only lower physical activity barriers were associated with higher MVPA at all grades. Conclusion: MVPA is a complex behavior with fluid, multilevel correlates that differ among girls across middle and high school.