title: Objectively measured physical activity and sedentary time in youth: the International children's accelerometry database (ICAD).
abstract: BACKGROUND
  Physical activity and sedentary behaviour in youth have been reported to vary by sex, age, weight status and country. However, supporting data are often self-reported and/or do not encompass a wide range of ages or geographical locations. This study aimed to describe objectively-measured physical activity and sedentary time patterns in youth.
  
  
  METHODS
  The International Children's Accelerometry Database (ICAD) consists of ActiGraph accelerometer data from 20 studies in ten countries, processed using common data reduction procedures. Analyses were conducted on 27,637 participants (2.8-18.4 years) who provided at least three days of valid accelerometer data. Linear regression was used to examine associations between age, sex, weight status, country and physical activity outcomes.
  
  
  RESULTS
  Boys were less sedentary and more active than girls at all ages. After 5 years of age there was an average cross-sectional decrease of 4.2% in total physical activity with each additional year of age, due mainly to lower levels of light-intensity physical activity and greater time spent sedentary. Physical activity did not differ by weight status in the youngest children, but from age seven onwards, overweight/obese participants were less active than their normal weight counterparts. Physical activity varied between samples from different countries, with a 15-20% difference between the highest and lowest countries at age 9-10 and a 26-28% difference at age 12-13.
  
  
  CONCLUSIONS
  Physical activity differed between samples from different countries, but the associations between demographic characteristics and physical activity were consistently observed. Further research is needed to explore environmental and sociocultural explanations for these differences.
authors.affiliation: Centre for Exercise, Nutrition and health Sciences, School for Policy Studies, University of Bristol, Bristol, UK. ashley.cooper@bristol.ac.uk.|National Institute for Health Research Bristol Biomedical Research Unit in Nutrition, Diet and Lifestyle, Bristol, UK. ashley.cooper@bristol.ac.uk.
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Cooper
authors.affiliation: Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK. anna.goodman@lshtm.ac.uk.
authors.forename: Anna
authors.initials: A
authors.lastname: Goodman
authors.affiliation: Centre for Exercise, Nutrition and health Sciences, School for Policy Studies, University of Bristol, Bristol, UK. a.s.page@bristol.ac.uk.
authors.forename: Angie S
authors.initials: AS
authors.lastname: Page
authors.affiliation: School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UK. l.b.sherar@lboro.ac.uk.
authors.forename: Lauren B
authors.initials: LB
authors.lastname: Sherar
authors.affiliation: School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UK. dale.esliger@lboro.ac.uk.
authors.forename: Dale W
authors.initials: DW
authors.lastname: Esliger
authors.affiliation: MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge, Cambridge, UK. ev234@medschl.cam.ac.uk.
authors.forename: Esther M F
authors.initials: EM
authors.lastname: van Sluijs
authors.affiliation: Centre for Research in Childhood Health, Exercise Epidemiology Unit, Department of Sport Sciences and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark. lboandersen@health.sdu.dk.
authors.forename: Lars Bo
authors.initials: LB
authors.lastname: Andersen
authors.affiliation: Department of Sport Medicine, Norwegian School of Sport Sciences, Oslo, Norway. s.a.anderssen@nih.no.
authors.forename: Sigmund
authors.initials: S
authors.lastname: Anderssen
authors.affiliation: Department of Movement and Sport Sciences, University of Ghent, Ghent, Belgium. greet.cardon@ugent.be.
authors.forename: Greet
authors.initials: G
authors.lastname: Cardon
authors.affiliation: Centre for Research & Action in Public Health, Health Research Institute, University of Canberra, Canberra, ACT 2617, Australia. rachel.davey@canberra.edu.au.
authors.forename: Rachel
authors.initials: R
authors.lastname: Davey
authors.affiliation: Centre for Research in Childhood Health, Exercise Epidemiology Unit, Department of Sport Sciences and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark. kfroberg@health.sdu.dk.
authors.forename: Karsten
authors.initials: K
authors.lastname: Froberg
authors.affiliation: Federal University of Pelotas, Pelotas, RS, Brazil. prchallal@gmail.com.
authors.forename: Pedro
authors.initials: P
authors.lastname: Hallal
authors.affiliation: Department of Health and Human Physiology, University of Iowa, Iowa, USA. kathleen-janz@uiowa.edu.
authors.forename: Kathleen F
authors.initials: KF
authors.lastname: Janz
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, UK. kasia.kordas@bristol.ac.uk.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kordas
authors.affiliation: Institute of Social and Preventive Medicine, University of Zurich, Zürich, Switzerland. susi.kriemler@unibas.ch.
authors.forename: Susi
authors.initials: S
authors.lastname: Kreimler
authors.affiliation: Department of Exercise Science, University of South Carolina, Columbia, USA. rpate@mailbox.sc.edu.
authors.forename: Russ R
authors.initials: RR
authors.lastname: Pate
authors.affiliation: Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland. jardena.puder@chuv.ch.
authors.forename: Jardena J
authors.initials: JJ
authors.lastname: Puder
authors.affiliation: School of Psychological Sciences and Health, University of Strathclyde, Glasgow, Scotland. john.j.reilly@strath.ac.uk.
authors.forename: John J
authors.initials: JJ
authors.lastname: Reilly
authors.affiliation: Centre for Physical Activity and Nutrition Research, Deakin University, 221 Burwood Highway, Burwood, VIC 3125, Australia. jo.salmon@deakin.edu.au.
authors.forename: Jo
authors.initials: J
authors.lastname: Salmon
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculty of Human Kinetics, University of Lisbon, Lisbon, Portugal. lsardinha@fmh.utl.pt.
authors.forename: Luis B
authors.initials: LB
authors.lastname: Sardinha
authors.affiliation: Centre for Physical Activity and Nutrition Research, Deakin University, 221 Burwood Highway, Burwood, VIC 3125, Australia. anna.timperio@deakin.edu.au.
authors.forename: Anna
authors.initials: A
authors.lastname: Timperio
authors.affiliation: Department of Sport Medicine, Norwegian School of Sport Sciences, Oslo, Norway. ulf.ekelund@nih.no.
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
mesh_terms: D061725:Accelerometry / Q000706:statistics & numerical data*; D000293:Adolescent; D017677:Age Distribution; D001835:Body Weight; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D016208:Databases, Factual; D005190:Family; D005260:Female; D006801:Humans; D038622:Internationality; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity; D050177:Overweight; D057185:Sedentary Behavior; D057566:Self Report; D017678:Sex Distribution; D013997:Time Factors