title: Changes in children's physical activity over 12 months: longitudinal results from the SPEEDY study.
abstract: OBJECTIVE
  We measured physical activity changes among 10-year-old British children over 12 months and assessed biological and demographic determinants.
  
  
  METHODS
  Physical activity was measured with accelerometers (counts per minute) over ≥3 days at baseline and 1 year later in a prospective study of 844 children (41.6% male; mean±SD baseline age: 10.2±0.3 years) from 92 schools. Meeting physical activity recommendations was defined as ≥60 minutes/day at ≥2000 counts per minute. Biological (height, weight, and fat percentage) and demographic factors (gender, rural/urban home location, and socioeconomic status) were assessed at baseline. Associations between physical activity changes and multiple factors were studied.
  
  
  RESULTS
  Physical activity decreased over 1 year (baseline: 665.7±209.8 counts per minute; follow-up: 623.2±179.2 counts per minute; P<.001), with 70.4% of children meeting physical activity recommendations at the baseline evaluation and 65.8% at the follow-up evaluation (P<.001). The decrease occurred mainly on weekends (-47.2±395.8 counts per minute; P=.002), with no significant change on weekdays (8.0±201.6 counts per minute; P=.20). Girls (P<.001), participants with greater body fat percentage (P=.001), and participants of higher socioeconomic status (P=.008) were more likely to exhibit physical activity decreases.
  
  
  CONCLUSIONS
  Physical activity decreased over 1 year among children in primary school, predominantly during the weekend. Because these children were relatively active at baseline, prevention of physical activity decreases in childhood, particularly among girls and on weekends, may be a suitable health promotion target.
authors.affiliation: MRC Epidemiology Unit, Institute of Metabolic Science, Box 285, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 0QQ, United Kingdom. kirsten.corder@mrc-epid.cam.ac.uk
authors.forename: Kirsten
authors.initials: K
authors.lastname: Corder
authors.forename: Esther M F
authors.initials: EM
authors.lastname: van Sluijs
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Jones
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Griffin
mesh_terms: D002648:Child; D015331:Cohort Studies; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory; D012959:Socioeconomic Factors