title: Age and gender differences in objectively measured physical activity in youth.
abstract: OBJECTIVE
  The purpose of this study was to evaluate age and gender differences in objectively measured physical activity (PA) in a population-based sample of students in grades 1-12.
  
  
  METHODS
  Participants (185 male, 190 female) wore a CSA 7164 accelerometer for 7 consecutive days. To examine age-related trends, students were grouped as follows: grades 1-3 (N = 90), grades 4-6 (N = 91), grades 7-9 (N = 96), and grades 10-12 (N = 92). Bouts of PA and minutes spent in moderate-to-vigorous PA (MVPA) and vigorous PA (VPA) were examined.
  
  
  RESULTS
  Daily MVPA and VPA exhibited a significant inverse relationship with grade level, with the largest differences occurring between grades 1-3 and 4-6. Boys were more active than girls; however, for overall PA, the magnitudes of the gender differences were modest. Participation in continuous 20-min bouts of PA was low to nonexistent.
  
  
  CONCLUSIONS
  Our results support the notion that PA declines rapidly during childhood and adolescence and that accelerometers are feasible alternatives to self-report methods in moderately sized population-level surveillance studies.
authors.affiliation: School of Human Movement Studies, University of Queensland, Brisbane, Australia. strost@hms.uq.edu.au
authors.forename: Stewart G
authors.initials: SG
authors.lastname: Trost
authors.forename: Russell R
authors.initials: RR
authors.lastname: Pate
authors.forename: James F
authors.initials: JF
authors.lastname: Sallis
authors.forename: Patty S
authors.initials: PS
authors.lastname: Freedson
authors.forename: Wendell C
authors.initials: WC
authors.lastname: Taylor
authors.forename: Marsha
authors.initials: M
authors.lastname: Dowda
authors.forename: John
authors.initials: J
authors.lastname: Sirard
mesh_terms: D000203:Activities of Daily Living; D000293:Adolescent; D017677:Age Distribution; D002648:Child; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008019:Life Style; D008297:Male; D008404:Massachusetts / Q000453:epidemiology; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods*; D012574:Schools; D017678:Sex Distribution; D013177:Sports / Q000706:statistics & numerical data; D013334:Students / Q000706:statistics & numerical data*