Date of Award


Document Type

Campus Access Thesis




Clinical-Community Psychology

First Advisor

Dawn K. Wilson


Previous research has shown that interventions to increase physical activity (PA) in adolescents, while statistically significant, have demonstrated only modest effects and have failed to identify mechanisms for change. Social Cognitive Theory (SCT) and Self-Determination Theory (SDT) identify social context and intrinsic motivation, respectively, as important factors to consider in understanding PA behavior. This study expands on previous research by examining intrinsic motivation as a mediator of the relationship between peer social support and moderate-to-vigorous PA (MVPA, measured by 7-day accelerometry) in underserved adolescents (low income, minorities). While SCT supports a relationship between peer social support and MVPA, SDT expands by suggesting the social contextual influences on behavior operate by increasing intrinsic motivation. In the current study, peer social support is hypothesized to positively effect intrinsic motivation (theoretically via positive social context) and, in turn, MVPA. Baseline data from the Active by Choice Today (ACT) Trial were analyzed using the product-as-coefficients methods of estimating a mediation relationship (n = 1421, mean age 11.3 years, 54% female, 72% African American, 71% reduced lunch). Adolescents self-reported peer social support and intrinsic motivation. Multiple imputations were used to handle missing data, and BMI and sex were covariates. Results showed steps for establishing mediation and a mediation effect (tested using the first order test; B = 1.63, se = 0.65, T (1420) = 2.53, p < .05) were statistically significant. Secondary analyses examined sex differences using moderated mediation and found the mediation effect did not significantly differ for boys versus girls. Results of the current study are the first to demonstrate that intrinsic motivation mediates the relationship been peer support and MVPA in underserved adolescents. While more research is needed to better understand the social conditions that influence intrinsic motivation, results of the current study suggest that these factors may be important in future interventions in underserved populations.