title: Improving physical activity assessment in prepubertal children with high-frequency accelerometry monitoring: a methodological issue.
abstract: OBJECTIVE
  The aim of this study was to examine the duration of physical activity (PA) bouts in prepubertal children with high-frequency accelerometry monitoring.
  
  
  METHODS
  Thirteen boys and thirteen girls (aged 8-10 years) from one school in North of France had their PA recorded during 7 days using a uniaxial Actigraph accelerometer. To examine PA behavior patterns, the epoch was set at 2 s. Times spent in light (LPA), moderate (MPA), vigorous (VPA) and very high (VHPA) intensity activity and the daily number of PA bouts of different durations (from 2 to 1200 s) were calculated for each intensity level. Data were collected in 2004.
  
  
  RESULTS
  The mean duration of PA bouts was 70.8+/-13.2 s for LPA, 9.0+/-2.8 s for MPA, 4.7+/-1.2 s for VPA and 3.9+/-1.6 s for VHPA. For the whole population, 80% of MPA, 93% of VPA and 96% of VHPA lasted less than 10 s. Although times spent in VPA and VHPA represented 2.4% of the total PA time, VPA and VHPA bouts accounted for 36.1+/-5.8% of the total amount of PA.
  
  
  CONCLUSIONS
  Children's PA pattern is highly transitory and intermittent whatever its intensity. Physical activity assessed with a sampling interval related to children's behavior may improve our understanding of their PA patterns.
authors.affiliation: Laboratory of Human Movement Studies EA 3608, Faculty of Sport Sciences and Physical Education, University of Lille 2, 9 rue de l'Université 59790, Ronchin, France. georges.baquet@univ-lille2.fr
authors.forename: Georges
authors.initials: G
authors.lastname: Baquet
authors.forename: Gareth
authors.initials: G
authors.lastname: Stratton
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Van Praagh
authors.forename: Serge
authors.initials: S
authors.lastname: Berthoin
mesh_terms: D000054:Acceleration; D000367:Age Factors; D002648:Child; D005260:Female; D015438:Health Behavior; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000379:methods*; D009043:Motor Activity / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D011627:Puberty; D012307:Risk Factors; D012737:Sex Factors