title: Associations of objectively assessed sleep and physical activity in 11-year old children.
abstract: OBJECTIVE
  Objective methods were used to evaluate children's sleep and physical activity over several days in order to test the hypotheses that: (1) low average sleep duration and/or sleep efficiency are linked to a low amount of physical activity; and (2) a reduction in sleep quantity and/or sleep efficiency during the night is followed by a decrease in physical activity the following day.
  
  
  METHODS
  This is a multi-centre, observational study involving 276 children, aged 10.5-12 years, from diverse urban settings in Croatia, Slovenia and the US. Sleep and activity were monitored for 2-6 days (median = 4) using the Sensewear Armband™ multi-sensor body monitor.
  
  
  RESULTS
  While average sleep duration and efficiency were unrelated to physical activity, within-subjects associations revealed that an extra hour spent in bed during the night was followed by a 16-minute decrease in moderate-to-vigorous physical activity (p < 0.001). This was accompanied by a 4.5 kJ/kg and 5.9 kJ/kg lower total daily energy expenditure in boys and girls, respectively (p < 0.001).
  
  
  CONCLUSIONS
  This study found no evidence for a link between short sleep and low or reduced physical activity.
authors.affiliation: Faculty of Kinesiology, University of Zagreb , Croatia .
authors.forename: Maroje
authors.initials: M
authors.lastname: Sorić
authors.forename: Gregor
authors.initials: G
authors.lastname: Starc
authors.forename: Katarina T
authors.initials: KT
authors.lastname: Borer
authors.forename: Gregor
authors.initials: G
authors.lastname: Jurak
authors.forename: Marjeta
authors.initials: M
authors.lastname: Kovač
authors.forename: Janko
authors.initials: J
authors.lastname: Strel
authors.forename: Marjeta
authors.initials: M
authors.lastname: Mišigoj-Duraković
mesh_terms: D002648:Child; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D017286:Polysomnography; D012890:Sleep / Q000502:physiology*
keywords: Adolescence; inactivity; multi-level modelling; short sleep