title: Field validation of the MTI Actigraph and BodyMedia armband monitor using the IDEEA monitor.
abstract: OBJECTIVE
  Accelerometers offer considerable promise for improving estimates of physical activity (PA) and energy expenditure (EE) in free-living subjects. Differences in calibration equations and cut-off points have made it difficult to determine the most accurate way to process these data. The objective of this study was to compare the accuracy of various calibration equations and algorithms that are currently used with the MTI Actigraph (MTI) and the Sensewear Pro II (SP2) armband monitor.
  
  
  METHODS
  College-age participants (n=30) wore an MTI and an SP2 while participating in normal activities of daily living. Activity patterns were simultaneously monitored with the Intelligent Device for Estimating Energy Expenditure and Activity (IDEEA) monitor to provide an accurate estimate (criterion measure) of EE and PA for this field-based method comparison study.
  
  
  RESULTS
  The EE estimates from various MTI equations varied considerably, with mean differences ranging from -1.10 to 0.46 METS. The EE estimates from the two SP2 equations were within 0.10 METS of the value from the IDEEA. Estimates of time spent in PA from the MTI and SP2 ranged from 34.3 to 107.1 minutes per day, while the IDEEA yielded estimates of 52 minutes per day.
  
  
  CONCLUSIONS
  The lowest errors in estimation of time spent in PA and the highest correlations were found for the new SP2 equation and for the recently proposed MTI cut-off point of 760 counts/min (Matthews, 2005). The study indicates that the Matthews MTI cut-off point and the new SP2 equation provide the most accurate indicators of PA.
authors.affiliation: Department of Health and Human Performance, 257 Forker Building, Iowa State University, Ames, IA 50011, USA. gwelk@iastate.edu
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Welk
authors.forename: James J
authors.initials: JJ
authors.lastname: McClain
authors.forename: Joey C
authors.initials: JC
authors.lastname: Eisenmann
authors.forename: Eric E
authors.initials: EE
authors.lastname: Wickel
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D002153:Calorimetry, Indirect; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D009043:Motor Activity / Q000502:physiology*; D013178:Sports Medicine / Q000379:methods; D016138:Walking