title: A cohort-sequential latent growth model of physical activity from ages 12 to 17 years.
abstract: BACKGROUND
  Despite serious public health implications of decreased physical activity during adolescence, few longitudinal studies have been conducted to determine the trajectory and important correlates of physical activity change during this period.
  
  
  OBJECTIVE
  This study examines change in physical activity from ages 12 to 17 years and the influences of personal, family, peer, and demographic factors on activity patterns.
  
  
  METHODS
  Data were from 371 youth. The sample was 50.1% female, 76% White, 12% African American, 4% Hispanic, 2% Asian, 2% American Indian, and 4% other or mixed races. Mean age was 12.05 years (SD = 1.63) at Time 1. Multivariate latent growth curve modeling (LGM), a cohort-sequential design, and a multiple-group design by sex were employed.
  
  
  RESULTS
  Youth physical activity declined significantly from ages 12 to 17. Boys had higher initial levels of physical activity than girls. Efficacy to overcome barriers, physically active friends, and friend social support all played roles in reducing the decline in physical activity. Early maturing boys, although more physically active initially, experienced a greater decline in physical activity compared to later maturing boys.
  
  
  CONCLUSIONS
  These findings encourage further research on the etiology and development of youth physical activity using procedures such as LGM to better understand the risk and protective factors associated with youth physical activity decline.
authors.affiliation: Oregon Research Institute, Eugene, OR 97403, USA. sued@ori.org
authors.forename: Susan C
authors.initials: SC
authors.lastname: Duncan
authors.forename: Terry E
authors.initials: TE
authors.lastname: Duncan
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Strycker
authors.forename: Nigel R
authors.initials: NR
authors.lastname: Chaumeton
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D002657:Child Development; D015331:Cohort Studies; D015444:Exercise / Q000523:psychology*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008960:Models, Psychological; D015233:Models, Statistical; D015999:Multivariate Analysis; D015205:Northwestern United States; D010379:Peer Group; D011627:Puberty / Q000523:psychology; D013223:Statistics as Topic