title: Week-to-week differences of children's habitual activity and postural allocation as measured by the ActivPAL monitor.
abstract: BACKGROUND
  Quantification of sitting and standing is possible with the ActivPAL accelerometer, using algorithms to classify activity into time spent sitting, standing and stepping. The purpose of this study was to determine children's week-to-week differences in time spent sitting/lying and standing along with other measures as provided by the ActivPAL accelerometer during continuous wearing of the ActivPAL monitor.
  
  
  METHODS
  Fifty-six children (age 10.2±0.9 years, mean±SD) were recruited from 30 urban schools in Auckland, New Zealand. Children wore the monitor for 24h per day up to 14 days. Analyses were performed with mixed modeling. Reliability was expressed as change in the mean from week to week, intraclass correlation coefficient (ICC) and standard error of measurement (SEM).
  
  
  RESULTS
  Mean week-to-week differences in percent time spent sitting/lying, standing and stepping on week days and weekend days for girls and boys were typically small. Step and sit-to-stand counts differences were small and unclear respectively. ICC values ranged from 0.40 to 0.79 during week days and 0.25-0.60 during weekends. SEM for time spent sitting/lying, standing and stepping were ∼3.5%, ∼2.5% and ∼1.5% respectively.
  
  
  CONCLUSIONS
  The ActivPAL showed moderate to low week-to-week reliability for habitual activity and postural allocation under free living conditions in boys and girls. Interventions aimed at a moderate reduction in sitting time (∼5% of the day) will require modest sample sizes for adequate precision.
authors.affiliation: Centre for Physical Activity and Nutrition, Centre for Child Health Research, Institute of Public Health and Mental Health, Auckland University of Technology, Private Bag 92006, Auckland, New Zealand. Electronic address: erica.hinckson@aut.ac.nz.
authors.forename: Erica A
authors.initials: EA
authors.lastname: Hinckson
authors.forename: Will G
authors.initials: WG
authors.lastname: Hopkins
authors.forename: Saeideh
authors.initials: S
authors.lastname: Aminian
authors.forename: Kara
authors.initials: K
authors.lastname: Ross
mesh_terms: D061725:Accelerometry / Q000295:instrumentation*; D000203:Activities of Daily Living; D000465:Algorithms; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D009043:Motor Activity / Q000502:physiology*; D009520:New Zealand; D011187:Posture; D015203:Reproducibility of Results; D057185:Sedentary Behavior
keywords: Accelerometer; ICC; Physical activity; Reliability; SEM; Sedentary