More than half of U.S. high-school students do not meet the moderate and vigorous physical activity (MVPA) 5 hours per week recommendation. The purpose of this study was to determine how individual dimensions (motivation and planning) mediate the relationship of social context with physical activity by integrating available measures of personal characteristic including internal/external motivations (derived from Self-Determination Theory -SDT]) for MVPA, MVPA planning, peer MVPA, and parental support to better understand adolescent MVPA.

Survey responses of a nationally representative cohort of 11^th graders (N = 2439) in the NEXT Generation Health Study were analyzed with structural equation modeling.

Adolescent MVPA was directly, significantly associated with MVPA planning (β = 0.17), peer MVPA (β = 0.21), and internal motivation (β = 0.50). Internal motivation was associated with peer MVPA (β = 0.31), parental support for MVPA (β = 0.16), and external motivation (β = 0.40). A significant relation between parental support and external motivation (β = 0.31) was also found.

Adolescents with higher internal motivation and more active friends were more likely to engage in MVPA. The results are consistent with SDT and suggest that planning is an important construct for adolescent MVPA.