Using self-determination theory as a framework, the purpose of this study was to test a structural model of hypothesized relationships among perceived need support from physical education teachers (autonomy support, competence support, and relatedness support), psychological need satisfaction (autonomy, competence, and relatedness), intrinsic motivation, and physical activity. Participants were 286 middle school students in the southeastern U.S. They completed previously validated questionnaires assessing their perceived need support from teachers, need satisfaction, intrinsic motivation, and physical activity. The hypothesized model demonstrated a good fit with the data (RMSEA = 0.08; CFI = 0.97; NFI = 0.96 GFI = 0.96). Need satisfaction and intrinsic motivation mediated the relationship between need support and physical activity. The constructs of perceived autonomy, competence, and relatedness represent the nutriments that facilitate students' intrinsic motivation and ultimately positively predict students' physical activity. The findings supported the theoretical tenets of self-determination theory. (Contains 1 table and 3 figures.)