title: Tracking physical activity and sedentary behavior in childhood: a systematic review.
abstract: BACKGROUND
  To date, no reviews have investigated the evidence of tracking of physical activity and sedentary behavior specifically during early childhood (aged 0-5.9 years) or from early childhood to middle childhood (aged 6-12 years). It is important to review the evidence of tracking of these behaviors to determine their stability during the foundational early years of life.
  
  
  METHODS
  A literature search of studies was conducted in seven electronic databases (January 1980 to April 2012). Studies were compared on methodologic quality and evidence of tracking of physical activity or sedentary behavior. Tracking was defined as the stability (or relative ranking within a cohort) of behaviors, such as physical activity and sedentary behavior, over time.
  
  
  RESULTS
  Eleven studies met the inclusion criteria. All studies reporting physical activity outcomes had high methodologic quality; 71% of studies reporting sedentary behavior outcomes had high methodologic quality. Of the tracking coefficients for physical activity, 4% were large, 60% were moderate, and 36% were small. Of the tracking coefficients for sedentary behavior, 33% were large, 50% were moderate, and 17% were small. Overall, there was evidence of moderate tracking of physical activity during early childhood, and from early childhood to middle childhood, and of moderate-to-large tracking of sedentary behavior during early childhood and from early childhood to middle childhood.
  
  
  CONCLUSIONS
  This review highlights the importance of establishing recommended levels of physical activity and sedentary behavior during the early years of life. Based on this review, the following recommendations are made: (1) early childhood should be targeted as a critical time to promote healthy lifestyle behaviors through methodologically sound prevention studies; and (2) future tracking studies should assess a broad range of sedentary behaviors using objective measures.
authors.affiliation: Faculty of Education and Interdisciplinary Educational Research Institute, University of Wollongong, Wollongong, New South Wales, Astralia. rachelj@uow.edu.au
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Jones
authors.forename: Trina
authors.initials: T
authors.lastname: Hinkley
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Okely
authors.forename: Jo
authors.initials: J
authors.lastname: Salmon
mesh_terms: D002648:Child; D002675:Child, Preschool; D016208:Databases, Factual; D015444:Exercise; D005260:Female; D015438:Health Behavior; D006801:Humans; D007223:Infant; D008297:Male; D011159:Population Surveillance / Q000379:methods; D057185:Sedentary Behavior