title: Tracking of activity and sedentary behaviors in childhood: the Iowa Bone Development Study.
abstract: BACKGROUND
  Physical activity tracking studies can determine when children settle into activity patterns and their risk for maintaining sedentary behaviors. This study examined the tracking of activity and sedentary behavior in relation to adiposity during middle childhood.
  
  
  METHODS
  Activity intensities and patterns were examined during a 3-year interval in a population-based study of children using accelerometry and survey methods. Data were collected and analyzed from 1998 to 2004. Participants (n = 379) were, on average, 5.6 (standard deviation [SD] +/- 0.5) years at baseline and 8.6 (SD +/- 0.5) years at follow-up. Adiposity was measured with whole-body, dual-energy x-ray absorptiometry. Correlation coefficients and odds ratios were used to assess tracking. The association of activity with adiposity was tested using the Wilcoxon rank-sum test.
  
  
  RESULTS
  Over the 3-year interval, Spearman rank-order correlation coefficients between baseline and follow-up activity measures were low to moderate (r = 0.18 to 0.39). Sedentary behavior was more predictable than overall activity, and tended to be more stable (r = 0.37 to 0.52), with the exception of video playing in boys (r = 0.18). Children maintaining a high degree of vigorous activity and low levels of TV viewing were less likely than peers to be in the upper quartile for adiposity at follow-up, and were less likely to gain adiposity during the study period.
  
  
  CONCLUSIONS
  Sedentary behavior, including TV viewing, is moderately stable during middle childhood. Health promotion programs that specifically target maintaining high levels of vigorous activity and low levels of TV viewing may help reduce the increasing prevalence of childhood obesity.
authors.affiliation: Department of Health and Sport Studies, University of Iowa, Iowa City, 52242, USA. kathleen-janz@uiowa.edu
authors.forename: Kathleen F
authors.initials: KF
authors.lastname: Janz
authors.forename: Trudy L
authors.initials: TL
authors.lastname: Burns
authors.forename: Steven M
authors.initials: SM
authors.lastname: Levy
mesh_terms: D015502:Absorptiometry, Photon; D050154:Adiposity; D000886:Anthropometry / Q000379:methods; D001846:Bone Development; D002648:Child; D002675:Child, Preschool; D003625:Data Collection; D015444:Exercise; D005260:Female; D015438:Health Behavior; D006801:Humans; D007484:Iowa; D008297:Male; D011159:Population Surveillance