Examining the effects of a 12-week lifestyle modification intervention on physical activity and related psychological outcomes among overweight and obese adolescent girls

BACKGROUND: Adolescents typically experience sharp declines in physical activity. This is especially true for overweight and obese girls, whose efforts are often thwarted by feelings of guilt, shame, and failure. Therefore, interventions for improving physical activity behaviours among this population should also aim to promote favorable psychological outcomes. PURPOSE: Guided by Self-Determination Theory (SDT), this study examined the effects of a 12-week lifestyle modification intervention for overweight and obese adolescent girls on physical activity and related psychological variables. METHODS: Participants (N=54; mean age =14.8±2.25 years) were randomized to one of three groups; two intervention groups (G1 n= 24; G2 n=23) which undertook a 12-week intervention including supervised exercise, dietary counseling and behaviour-management, and one control group (Con n=7). Intervention groups differed by the type of dietary program followed. Leisure time physical activity (LTPA), exercise motivation, perceived competence, and physical self-perceptions were measured at 0 and 12 weeks. RESULTS: Significant time by group interactions were observed for LTPA (F(1,51)=4.3, p=0.019), physical self-worth (F(1,51)= 9.03, p