title: A review of preschool children's physical activity and sedentary time using objective measures.
abstract: BACKGROUND
  Identifying current physical activity levels and sedentary time of preschool children is important for informing government policy and community initiatives. This paper reviewed studies reporting on physical activity and time spent sedentary among preschool-aged children (2-5 years) using objective measures.
  
  
  METHODS
  Databases were searched for studies published up to and including April 2013 that reported on, or enabled the calculation of, the proportion of time preschool children spent sedentary and in light- and moderate to vigorous-intensity physical activity. A total of 40 publications met the inclusion criteria for physical activity and 31 met the inclusion criteria for sedentary time. Objective measures included ActiGraph, Actiwatch, Actical, Actiheart, and RT3 accelerometers, direct observation, and Quantum XL telemetry heart rate monitoring. Data were analyzed in May 2013.
  
  
  RESULTS
  Considerable variation in prevalence estimates existed. The proportion of time children spent sedentary ranged from 34% to 94%. The time spent in light-intensity physical activity and moderate to vigorous-intensity physical activity ranged from 4% to 33% and 2% to 41%, respectively.
  
  
  CONCLUSIONS
  The considerable variation of prevalence estimates makes it difficult to determine the "true" prevalence of physical activity and sedentary time in preschool children. Future research should aim to reduce inconsistencies in the employed methodologies to better understand preschoolers' physical activity levels and sedentary behavior.
authors.affiliation: School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Victoria. Electronic address: j.hnatiuk@deakin.edu.au.
authors.forename: Jill A
authors.initials: JA
authors.lastname: Hnatiuk
authors.affiliation: School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Victoria.
authors.forename: Jo
authors.initials: J
authors.lastname: Salmon
authors.affiliation: School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Victoria.
authors.forename: Trina
authors.initials: T
authors.lastname: Hinkley
authors.affiliation: Interdisciplinary Education Research Centre, University of Wollongong, Wollongong, New South Wales.
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Okely
authors.affiliation: School of Human Movement Studies , University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Stewart
authors.initials: S
authors.lastname: Trost
mesh_terms: D002675:Child, Preschool; D006801:Humans; D009043:Motor Activity / Q000502:physiology*; D015995:Prevalence; D057185:Sedentary Behavior; D013997:Time Factors