title: The Role of Self-Efficacy and Friend Support on Adolescent Vigorous Physical Activity.
abstract: Physical activity, including some form of vigorous activity, is a key component of a healthy lifestyle in young people. Self-efficacy and social support have been identified as key determinants of physical activity; however, the mechanism that reflects the interplay of these two factors is not well understood. The aim of the current study was to test social cognitive theory's notion that self-efficacy relates to intention that translates into behavior and to investigate whether friend support and self-efficacy synergize, interfere, or compensate for one another to predict vigorous physical activity in adolescents-a population at risk of rapid decreases in physical activity.
  
  
  
  A survey at two points in time was conducted in 226 students aged 12 to 16 years. In a conditional process analysis, friend support and physical activity self-efficacy were specified as interacting predictors of intention. The latter was specified as a mediator between self-efficacy and later vigorous physical activity, controlling for sex and age.
  
  
  
  Self-efficacy emerged as the dominant predictor of intention, followed by friend support, and an interaction between support and self-efficacy. In adolescents with high self-efficacy, intention was independent of support. In those with low self-efficacy, receiving friend support partly compensated for lack of self-efficacy. The effect of self-efficacy on vigorous physical activity was mediated by intention.
  
  
  
  Adolescent vigorous physical activity was indirectly predicted by self-efficacy via intention, and this mediation was further moderated by levels of friend support, indicating that friend support can partly buffer lack of self-efficacy.
authors.affiliation: 1 Griffith University, Brisbane, Queensland, Australia.|2 Curtin University, Perth, Western Australia, Australia.
authors.forename: Kyra
authors.initials: K
authors.lastname: Hamilton
authors.affiliation: 3 Freie Universität Berlin, Germany.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Warner
authors.affiliation: 4 Australian Catholic University, Strathfield, New South Wales, Australia.|5 University of Social Sciences and Humanities, Wroclaw, Poland.
authors.forename: Ralf
authors.initials: R
authors.lastname: Schwarzer
mesh_terms: D000293:Adolescent; D002648:Child; D015444:Exercise / Q000523:psychology*; D005260:Female; D033062:Friends / Q000523:psychology*; D015438:Health Behavior; D006801:Humans; D008297:Male; D020377:Self Efficacy; D012944:Social Support; D066269:Social Theory; D011795:Surveys and Questionnaires
keywords: buffer effect; exercise; intention; peer support; self-efficacy; social cognitive theory