title: Friendship networks and physical activity and sedentary behavior among youth: a systematized review.
abstract: BACKGROUND
  Low levels of physical activity and increased participation in sedentary leisure-time activities are two important obesity-risk behaviors that impact the health of today's youth. Friend's health behaviors have been shown to influence individual health behaviors; however, current evidence on the specific role of friendship networks in relation to levels of physical activity and sedentary behavior is limited. The purpose of this review was to summarize evidence on friendship networks and both physical activity and sedentary behavior among children and adolescents.
  
  
  METHODS
  After a search of seven scientific databases and reference scans, a total of thirteen articles were eligible for inclusion. All assessed the association between friendship networks and physical activity, while three also assessed sedentary behavior.
  
  
  RESULTS
  Overall, higher levels of physical activity among friends are associated with higher levels of physical activity of the individual. Longitudinal studies reveal that an individual's level of physical activity changes to reflect his/her friends' higher level of physical activity. Boys tend to be influenced by their friendship network to a greater extent than girls. There is mixed evidence surrounding a friend's sedentary behavior and individual sedentary behavior.
  
  
  CONCLUSIONS
  Friends' physical activity level appears to have a significant influence on individual's physical activity level. Evidence surrounding sedentary behavior is limited and mixed. Results from this review could inform effective public health interventions that harness the influence of friends to increase physical activity levels among children and adolescents.
authors.forename: Keri Jo
authors.initials: KJ
authors.lastname: Sawka
authors.affiliation: Department of Community Health Sciences, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. gmccorma@ucalgary.ca.
authors.forename: Gavin R
authors.initials: GR
authors.lastname: McCormack
authors.forename: Alberto
authors.initials: A
authors.lastname: Nettel-Aguirre
authors.forename: Penelope
authors.initials: P
authors.lastname: Hawe
authors.forename: Patricia K
authors.initials: PK
authors.lastname: Doyle-Baker
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D016208:Databases, Factual; D005260:Female; D033062:Friends / Q000523:psychology*; D015438:Health Behavior; D006801:Humans; D007899:Leisure Activities; D008297:Male; D009043:Motor Activity; D057185:Sedentary Behavior; D012944:Social Support; D012959:Socioeconomic Factors