Exploring changes in physical activity, sedentary behaviors and hypothesized mediators in the NEAT girls group randomized controlled trial

Objective: To evaluate the impact of a 12-month school-based multi-component program on adolescent girls’ physical activity and sedentary behaviors, and hypothesized mediators of physical activity behavior change. Design: Group randomized controlled trial with 12-month follow-up. Methods: The intervention, guided by Social Cognitive Theory, involved 357 adolescent girls (13.2 ± 0.5 years) from 12 secondary schools (6 intervention schools, 6 control schools) in low-income communities in the Hunter and Central Coast regions of New South Wales, Australia. The intervention included enhanced school sport, lunchtime physical activity sessions, interactive seminars, student handbooks, nutrition workshops, pedometers, parent newsletters and text messages to encourage physical activity and healthy eating, and a decrease in sedentary behavior. Outcomes were assessed at baseline and 12-months and included: physical activity (accelerometers), sedentary behaviors (questionnaire and accelerometers), and social-cognitive mediators of physical activity (questionnaire). Results: There were significant between group differences in favor of the intervention group for self-reported recreational computer use (−26.0 min; 95% CI, −46.9 to −5.1), and sedentary activities summed (−56.4 min; 95% CI, −110.1 to −2.7), however objective sedentary behavior showed no differences. There were no group-by-time effects for any of the physical activity outcomes or hypothesized mediators. Conclusions: A school-based intervention tailored for adolescent girls from schools located in low-income communities significantly reduced time spent in sedentary activities. However, improvements in physical activity and hypothesized mediators of physical activity behavior were not observed. Future studies are encouraged to explore alternative mechanisms of behavior change derived from integrated and socio-ecological theories.