title: Age group comparability of raw accelerometer output from wrist- and hip-worn monitors.
abstract: OBJECTIVE
  The study aims were to compare raw triaxial accelerometer output from ActiGraph GT3X+ (AG) and GENEActiv (GA) placed on the hip and the wrist and to develop regression equations for estimating energy expenditure.
  
  
  METHODS
  Thirty children (7-11 yr) and 30 adults (18-65 yr) completed eight activities (ranging from lying to running) while wearing one AG and one GA on the hip and the wrist. Oxygen consumption (V˙O2) was measured with indirect calorimetry. Analysis involved the use of ANOVA to examine the effect of activity, brand, and placement on the acceleration values, intraclass correlation coefficient to evaluate the agreement between the two brands and placements, and linear regression to establish intensity thresholds.
  
  
  RESULTS
  A significant difference in acceleration values between the hip and the wrist placement was found (P < 0.001). The output from the wrist placement was, in general, higher compared with that from the hip. There was no main effect of monitor brand in adults (P < 0.12) and children (P < 0.73), and the intraclass correlation coefficient showed a strong agreement (0.96-0.99). However, a three-way interaction and systematic error between the brands was found in children. Acceleration from both brands and placements showed a strong correlation with V˙O2. The intensity classification accuracy of the developed thresholds for both brands and placements was, in general, higher for adults compared with that for children and was greater for sedentary/light (93%-97%), and vigorous activities (68%-92%) than that for moderate activities (33%-59%).
  
  
  CONCLUSIONS
  Accelerometer outputs from AG and GA seem comparable when attached to the same body location in adults, whereas inconsistent differences are apparent between the two brands and placements in children, hence limiting the comparability between brands in this age group.
authors.affiliation: 1Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, NORWAY; 2MoveLab-Physical Activity and Exercise Research, Institute of Cellular Medicine, Newcastle University, Newcastle, UNITED KINGDOM; and 3Medical Research Council Epidemiology Unit, Institute of Metabolic Science, Cambridge, UNITED KINGDOM.
authors.forename: Maria
authors.initials: M
authors.lastname: Hildebrand
authors.forename: Vincent T
authors.initials: VT
authors.lastname: VAN Hees
authors.forename: Bjorge Hermann
authors.initials: BH
authors.lastname: Hansen
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
mesh_terms: D061725:Accelerometry / Q000295:instrumentation* / Q000379:methods; D000328:Adult; D000367:Age Factors; D000368:Aged; D000704:Analysis of Variance; D002648:Child; D004734:Energy Metabolism; D005260:Female; D006615:Hip; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D010101:Oxygen Consumption; D012044:Regression Analysis; D014953:Wrist; D055815:Young Adult