title: Measuring reliability and validity of the ActiGraph GT3X accelerometer for children with cerebral palsy: a feasibility study.
abstract: OBJECTIVE
  The purposes of this study were to: 1) establish inter-instrument reliability between left and right hip accelerometer placement; 2) examine procedural reliability of a walking protocol used to measure physical activity (PA); and 3) confirm concurrent validity of accelerometers in measuring PA intensity as compared to the gold standard of oxygen consumption measured by indirect calorimetry.
  
  
  METHODS
  Eight children (mean age: 11.9; SD: 3.2, 75% male) with CP (GMFCS levels I-III) wore ActiGraph GT3X accelerometers on each hip and the Cosmed K4b<formula>^{2}</formula> portable indirect calorimeter during two measurement sessions in which they performed the six minute walk test (6MWT) at three self-selected speeds (comfortable/slow, brisk, fast). Oxygen consumption (VO2) and accelerometer step and activity count data were recorded.
  
  
  RESULTS
  Inter-instrument reliability of ActiGraph GT3X accelerometers placed on left and right hips was excellent (ICC=0.96-0.99, CI<formula>_{95}</formula>: 0.81-0.99). Reproducibility of the protocol was good/excellent (ICC=0.75-0.95, CI<formula>_{95}</formula>: 0.75-0.98). Concurrent validity of accelerometer count data and VO2 was fair/good (rho=0.67, p< 0.001). The correlation between step count and VO2 was not significant (rho=0.29, p=0.2).
  
  
  CONCLUSIONS
  This preliminary research suggests that ActiGraph GT3X accelerometers are reliable and valid devices to monitor PA during walking in children with CP and may be appropriate in rehabilitation research and clinical practice. ActiGraph GTX3 step counts were not valid for this sample and further research is warranted.
authors.affiliation: Department of Physical Therapy and Rehabilitation Sciences, College of Nursing and Health Professions, Drexel University, Philadelphia, PA, USA.
authors.forename: Margaret E
authors.initials: ME
authors.lastname: O'Neil
authors.affiliation: Franciscan Hospital for Children, Research Center for Children with Special Health Care Needs, Brighton, MA, USA.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Fragala-Pinkham
authors.affiliation: Department of Pediatric Rehabilitation Medicine, Franciscan Hospital for Children, Brighton, MA, USA.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Forman
authors.affiliation: Queensland Institute of Technology, Institute of Health and Biomedical Innovation, St Lucia, QLD, Australia.
authors.forename: Stewart G
authors.initials: SG
authors.lastname: Trost
mesh_terms: D061725:Accelerometry / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D056044:Actigraphy / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D000293:Adolescent; D002547:Cerebral Palsy / Q000503:physiopathology*; D002648:Child; D004734:Energy Metabolism / Q000502:physiology; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D015203:Reproducibility of Results; D016138:Walking
keywords: Physical activity measurement; accelerometry; cerebral palsy