title: A prospective study of sedentary behavior in a large cohort of youth.
abstract: OBJECTIVE
  The study's purpose was to describe longitudinal patterns of objectively measured sedentary behavior from age 12 to 16.
  
  
  METHODS
  Children participating in the Avon Longitudinal Study of Parents and Children wore accelerometers for 1 wk at ages 12, 14, and 16. Participants included boys (n = 2591) and girls (n = 2845) living in a single geographic location in the United Kingdom (Bristol). Total minutes per day spent in sedentary behavior and time spent in blocks of sedentary behavior lasting 10-19, 20-29, and ≥ 30 min are described. Growth curve models were used to determine the rate of change in sedentary behavior from age 12 to 16.
  
  
  RESULTS
  At age 12, the boys and girls, on average, were sedentary for 418.0 ± 67.7 and 436.6 ± 64.0 min·d(-1), respectively, and sedentary behavior increased over time to 468.0 ± 74.3 and 495.6 ± 68.9 min·d(-1) at age 14 and to 510.4 ± 76.6 and 525.4 ± 67.4 min·d(-1) at age 16. Growth curve analyses found that total sedentary behavior increased at a rate of 19.5 ± 0.7 and 22.8 ± 0.7 min·d(-1)·yr for the boys and girls, respectively. The absolute mean increase in total sedentary behavior (+92.4 and +88.8 min·d(-1) for the boys and girls, respectively) closely matched the mean decrease in light physical activity (-82.2 and -82.9 min·d(-1) for the boys and girls, respectively) from age 12 to 16. Time spent in continuous sedentary behavior lasting ≥ 30 min increased by 121% from age 12 to 16.
  
  
  CONCLUSIONS
  Sedentary behavior increased with age, at the expense of light physical activity. The increase in sedentary behavior lasting ≥ 30 min in duration contributed greatly to the increase in total sedentary behavior.
authors.affiliation: Department of Exercise Science, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA. jmitch@mail.med.upenn.edu
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Mitchell
authors.forename: Russell R
authors.initials: RR
authors.lastname: Pate
authors.forename: Marsha
authors.initials: M
authors.lastname: Dowda
authors.forename: Calum
authors.initials: C
authors.lastname: Mattocks
authors.forename: Chris
authors.initials: C
authors.lastname: Riddoch
authors.forename: Andy R
authors.initials: AR
authors.lastname: Ness
authors.forename: Steven N
authors.initials: SN
authors.lastname: Blair
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000886:Anthropometry; D002648:Child; D002657:Child Development / Q000502:physiology*; D004739:England; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D018670:Monitoring, Ambulatory; D011446:Prospective Studies; D057185:Sedentary Behavior; D013997:Time Factors