Self-Efficacy Moderates the Relation Between Declines in Physical

Objective To test whether self-efficacy for overcoming barriers to physical activity has direct, indirect (i.e., mediated), or moderating relations with naturally occurring change in perceived social support and declines in physical activity during high school. Methods Latent growth modeling was used with measures completed in the 8th, 9th, and 12th grades by a cohort of 195 Black and White girls. Results Self-efficacy was stable and moderated the relation between changes in physical activity and perceived social support. Girls who maintained a perception of strong social support had less of a decline in physical activity if they also had high self-efficacy. However, girls having high self-efficacy had a greater decline in physical activity if they perceived declines in social support. Conclusions Randomized controlled trials of physical activity interventions based on social cognitive theory should consider that the influence of girls ’ perceptions of social support on their physical activity may differ according to their efficacy beliefs about barriers to physical activity. Key words adolescents; growth curve analysis; health behavior; race/ethnicity. Insufficient physical activity among adolescent girls is a public health concern in the United States, especially as it relates to increasing incidence of obesity and type 2 diabetes (Ogden, Carroll, & Flegal, 2003; Wang & Dietz, 2002) and the risk of sedentary adult behavior (Campbell et al., 2001). Girls have twice the rate of decline in physical activity during high school compared to boys. Nearly two of three girls and three of four boys in the United States participate in sufficient vigorous physical activity when they are in the 9th grade, but by the 12th grade, only 46 % of girls are sufficiently active compared to 64 % of boys (Grunbaum et al., 2004). Population estimates indi-cate that participation in leisure time physical activity among girls declines by about 45 % between ages 12 an