title: Measuring physical activity using accelerometry in 13-15-year-old adolescents: the importance of including non-wear activities.
abstract: OBJECTIVE
  The present study aimed to examine the impact of non-wear activities registered in diaries when using accelerometers to assess physical activity (PA) in young adolescents.
  
  
  METHODS
  Data arise from a large-scale cross-sectional study on PA. PA was objectively assessed using Actigraph™ accelerometers (Actigraph MTI, Manufacturing Technology Inc., Pensacola, FL, USA) during seven consecutive days. Non-wear time activity diaries were provided to register the activities for which the accelerometer was removed. After correction to deal with over-reporting, the registered minutes of PA were used to replace periods of non-wear time measured by the accelerometer.
  
  
  METHODS
  Between October 2008 and May 2009 adolescents were recruited by home visits in Ghent (Belgium).
  
  
  METHODS
  Young adolescents (n 513; 48·6% boys) aged 13 to 15 years.
  
  
  RESULTS
  Of the total sample, 49·9% registered at least one activity of moderate to vigorous intensity in the non-wear time activity diary. More adolescents registered an activity performed on a weekday than on a weekend day and the registered mean number of minutes of moderate to vigorous PA were higher on weekend days. Repeated-measures (M)ANOVA tests revealed a significant difference between the mean minutes with and without non-wear activities for all PA intensities, regardless of adolescents' socio-economic status or gender. More adolescents achieved the PA recommendations after inclusion of the non-wear activities irrespective of accelerometer thresholds used.
  
  
  CONCLUSIONS
  The collection of information regarding non-wear time by non-wear time activity diaries when using accelerometers in 13-15-year-old adolescents can lead to different PA outcomes at the individual level and therefore can improve the ability to accurately measure PA.
authors.affiliation: Department of Movement and Sport Sciences, Faculty of Medicine and Health Sciences, Ghent University, Watersportlaan 2, B-9000 Ghent, Belgium. Femke.DeMeester@UGent.be
authors.forename: Femke
authors.initials: F
authors.lastname: De Meester
authors.forename: Ilse
authors.initials: I
authors.lastname: De Bourdeaudhuij
authors.forename: Benedicte
authors.initials: B
authors.lastname: Deforche
authors.forename: Charlene
authors.initials: C
authors.lastname: Ottevaere
authors.forename: Greet
authors.initials: G
authors.lastname: Cardon
mesh_terms: D056044:Actigraphy; D000293:Adolescent; D001530:Belgium; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D012959:Socioeconomic Factors