title: Early determinants of physical activity in adolescence: prospective birth cohort study.
abstract: OBJECTIVE
  To examine the effects of early social, anthropometric, and behavioural variables on physical activity in adolescence.
  
  
  METHODS
  Prospective birth cohort study.
  
  
  METHODS
  Pelotas, southern Brazil.
  
  
  METHODS
  4453 adolescents aged 10-12 years participating in the Pelotas 1993 birth cohort study (follow-up rate 87.5%).
  
  
  METHODS
  Sedentary lifestyle (< 300 minutes of physical activity per week) and median physical activity score (minutes per week).
  
  
  RESULTS
  The prevalence of a sedentary lifestyle at age 10-12 years was 58.2% (95% confidence interval 56.7% to 59.7%). Risk factors for a sedentary lifestyle in adolescence were female sex, high family income at birth, high maternal education at birth, and low birth order. Weight gain variables at ages 0-1, 1-4, and 4-11 years and overweight at age 1 or 4 years were not significant predictors of physical activity. Levels of physical activity at age 4 years, based on maternal report, were inversely related to a sedentary lifestyle at age 10-12 years.
  
  
  CONCLUSIONS
  Physical activity in adolescence does not seem to be programmed by physiological factors in infancy. A positive association between birth order and activity may be due to greater intensity of play in childhood and adolescence. Tracking of physical activity from age 4 to 10-12 years, however, suggests that genetic factors or early habit formation may be important.
authors.affiliation: Postgraduate Program in Epidemiology, Federal University of Pelotas, Duque de Caxias 250 3## piso 96030-002 Pelotas-RS, Brazil. prchallal@terra.com.br
authors.forename: Pedro C
authors.initials: PC
authors.lastname: Hallal
authors.forename: Jonathan C K
authors.initials: JC
authors.lastname: Wells
authors.forename: Felipe F
authors.initials: FF
authors.lastname: Reichert
authors.forename: Luciana
authors.initials: L
authors.lastname: Anselmi
authors.forename: Cesar G
authors.initials: CG
authors.lastname: Victora
mesh_terms: D001938:Brazil; D002648:Child; D002652:Child Behavior / Q000502:physiology; D015331:Cohort Studies; D004522:Educational Status; D015444:Exercise; D005260:Female; D006801:Humans; D008019:Life Style; D008297:Male; D009035:Mothers / Q000706:statistics & numerical data; D011446:Prospective Studies; D012044:Regression Analysis; D012959:Socioeconomic Factors