title: A calibration protocol for population-specific accelerometer cut-points in children.
abstract: OBJECTIVE
  To test a field-based protocol using intermittent activities representative of children's physical activity behaviours, to generate behaviourally valid, population-specific accelerometer cut-points for sedentary behaviour, moderate, and vigorous physical activity.
  
  
  METHODS
  Twenty-eight children (46% boys) aged 10-11 years wore a hip-mounted uniaxial GT1M ActiGraph and engaged in 6 activities representative of children's play. A validated direct observation protocol was used as the criterion measure of physical activity. Receiver Operating Characteristics (ROC) curve analyses were conducted with four semi-structured activities to determine the accelerometer cut-points. To examine classification differences, cut-points were cross-validated with free-play and DVD viewing activities.
  
  
  RESULTS
  Cut-points of ≤ 372, >2160 and >4806 counts • min(-1) representing sedentary, moderate and vigorous intensity thresholds, respectively, provided the optimal balance between the related needs for sensitivity (accurately detecting activity) and specificity (limiting misclassification of the activity). Cross-validation data demonstrated that these values yielded the best overall kappa scores (0.97; 0.71; 0.62), and a high classification agreement (98.6%; 89.0%; 87.2%), respectively. Specificity values of 96-97% showed that the developed cut-points accurately detected physical activity, and sensitivity values (89-99%) indicated that minutes of activity were seldom incorrectly classified as inactivity.
  
  
  CONCLUSIONS
  The development of an inexpensive and replicable field-based protocol to generate behaviourally valid and population-specific accelerometer cut-points may improve the classification of physical activity levels in children, which could enhance subsequent intervention and observational studies.
authors.affiliation: Faculty of Education, Community and Leisure, Liverpool John Moores University, Liverpool, United Kingdom. k.a.mackintosh@2009.ljmu.ac.uk
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Mackintosh
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Fairclough
authors.forename: Gareth
authors.initials: G
authors.lastname: Stratton
authors.forename: Nicola D
authors.initials: ND
authors.lastname: Ridgers
mesh_terms: D002138:Calibration; D002648:Child; D019719:Diagnostic Equipment / Q000592:standards*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*