title: Motivation and planning as mediators of the relation between social support and physical activity among U.S. adolescents: a nationally representative study.
abstract: BACKGROUND
  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.
  
  
  METHODS
  Survey responses of a nationally representative cohort of 11th graders (N=2439) in the NEXT Generation Health Study were analyzed with structural equation modeling.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Health Behavior Branch, Eunice Kennedy Shriver National Institute of Child Health & Human Development, 6100 Executive Blvd, Bethesda, MD 20892-7510, USA. Kaigang.li@nih.gov.
authors.forename: Kaigang
authors.initials: K
authors.lastname: Li
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Iannotti
authors.forename: Denise L
authors.initials: DL
authors.lastname: Haynie
authors.forename: Jessamyn G
authors.initials: JG
authors.lastname: Perlus
authors.forename: Bruce G
authors.initials: BG
authors.lastname: Simons-Morton
mesh_terms: D000293:Adolescent; D002648:Child; D003430:Cross-Sectional Studies; D003710:Demography; D005260:Female; D033062:Friends; D006801:Humans; D008297:Male; D009042:Motivation; D009043:Motor Activity; D015999:Multivariate Analysis; D010379:Peer Group; D026684:Personal Autonomy; D012931:Social Environment; D012944:Social Support; D013334:Students; D014481:United States