title: Classification of physical activity intensities using a wrist-worn accelerometer in 8-12-year-old children.
abstract: BACKGROUND
  Population-specific accelerometer cut-points are required to accurately determine the accumulation of physical activity of various intensities.
  
  
  OBJECTIVE
  A calibration study was conducted (i) to determine the cut-points for the ActiGraph GT3X+, non-dominant, wrist-mounted accelerometer in children aged 8-12 years and (ii) to compare classification accuracies among the accelerometer's three axes and vector magnitude (VM) values.
  
  
  METHODS
  Forty-five children aged 8-12 years performed up to seven activities while wearing accelerometers on their non-dominant wrist. Activities were performed in a summer day camp setting, represented free-living activities, and lasted for 10 min with minutes 5-8.5 used for analysis. Direct observation and percentage of heart rate reserve were used to determine activity intensity.
  
  
  RESULTS
  Receiver operator characteristic (ROC) analyses resulted in area under the curve values of all three axes and VM ranging 0.82-0.89, 0.80-0.83, 0.62-0.67 and 0.86-0.89 for light, moderate, vigorous and moderate-to-vigorous activity intensities. Additionally, regression analyses resulted in prediction equations with R2 values ranging from 0.70 to 0.77.
  
  
  CONCLUSIONS
  Results found comparable activity intensity classification accuracies from the ActiGraph GT3X+ wrist-worn accelerometer to previously published studies. Based on ROC and regression analyses, activity intensities can be distilled from this accelerometer using axis 1, axis 2 or VM values with similar classification accuracy.
authors.affiliation: Department of Exercise Science, University of South Carolina, Columbia, SC, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Chandler
authors.affiliation: Department of Exercise Science, University of South Carolina, Columbia, SC, USA.
authors.forename: K
authors.initials: K
authors.lastname: Brazendale
authors.affiliation: Department of Exercise Science, University of South Carolina, Columbia, SC, USA.
authors.forename: M W
authors.initials: MW
authors.lastname: Beets
authors.affiliation: Department of Exercise Science, University of South Carolina, Columbia, SC, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Mealing
mesh_terms: D061725:Accelerometry / Q000295:instrumentation* / Q000379:methods; D002138:Calibration; D002648:Child; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D012372:ROC Curve; D012044:Regression Analysis; D013022:South Carolina / Q000453:epidemiology; D014953:Wrist
keywords: Accelerometry; activity; calibration; children