title: Validity and comparability of a wrist-worn accelerometer in children.
abstract: BACKGROUND
  Wrist-worn accelerometers may provide an alternative to hip-worn monitors for assessing physical activity as they are easier to wear and may thus facilitate long-term recordings. The current study aimed at a) assessing the validity of the Actiwatch (wrist-worn) for estimating energy expenditure, b) determining cut-off values for light, moderate, and vigorous activities, c) studying the comparability between the Actiwatch and the Actigraph (hip-worn), and d) assessing reliability.
  
  
  METHODS
  For validity, indirect calorimetry was used as criterion measure. ROC-analyses were applied to identify cut-off values. Comparability was tested by simultaneously wearing of the 2 accelerometers during free-living condition. Reliability was tested in a mechanical shaker.
  
  
  RESULTS
  All-over correlation between accelerometer output and energy expenditure were found to be 0.80 (P < .001).Based on ROC-analysis, cut-off values for 1.5, 3, and 6 METs were found to be 80, 262, and 406 counts per 15 s, respectively. Energy expenditure estimates differed between the Actiwatch and the Actigraph (P < .05). The intra- and interinstrument coefficient of variation of the Actiwatch ranged between 0.72% and 8.4%.
  
  
  CONCLUSIONS
  The wrist-worn Actiwatch appears to be valid and reliable for estimating energy expenditure and physical activity intensity in children aged 8 to 10 years.
authors.affiliation: Åstrand Laboratory of Work Physiology, The Swedish School of Sport and Health Sciences, Stockholm, Sweden.
authors.forename: Orjan
authors.initials: O
authors.lastname: Ekblom
authors.forename: Gisela
authors.initials: G
authors.lastname: Nyberg
authors.forename: Elin Ekblom
authors.initials: EE
authors.lastname: Bak
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
authors.forename: Claude
authors.initials: C
authors.lastname: Marcus
mesh_terms: D000054:Acceleration; D056044:Actigraphy / Q000295:instrumentation* / Q000592:standards*; D002153:Calorimetry, Indirect / Q000295:instrumentation; D002648:Child; D002669:Child Welfare; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D011237:Predictive Value of Tests; D012372:ROC Curve; D015203:Reproducibility of Results; D013223:Statistics as Topic; D014953:Wrist / Q000502:physiology*