title: Validation study of Polar V800 accelerometer.
abstract: BACKGROUND
  The correct quantification of physical activity (PA) and energy expenditure (EE) in daily life is an important target for researchers and professionals. The objective of this paper is to study the validity of the Polar V800 for the quantification of PA and the estimation of EE against the ActiGraph (ActiTrainer) in healthy young adults.
  
  
  METHODS
  Eighteen Caucasian active people (50% women) aged between 19-23 years wore an ActiTrainer on the right hip and a Polar V800 on the preferred wrist during 7 days. Paired samples t-tests were used to analyze differences in outcomes between devices, and Pearson's correlation coefficients to examine the correlation between outcomes. The agreement was studied using the Bland-Altman method. Also, the association between the difference and the magnitude of the measurement (heteroscedasticity) was examined. Sensitivity, specificity and area under the receiver operating characteristic curve (ROC-AUC value) were calculated to evaluate the ability of the devices to accurately define a person who fulfills the recommendation of 10,000 daily steps.
  
  
  RESULTS
  The devices significantly differed from each other on all outcomes (P<0.05), except for Polar V800's alerts vs. ActiTrainer's 1 hour sedentary bouts (P=0.595) and Polar V800's walking time vs. ActiTrainer's lifestyle time (P=0.484). Heteroscedasticity analyses were significant for all outcomes, except for Kcal and sitting time. The ROC-AUC value was fair (0.781±0.048) and the sensitivity and specificity was 98% and 58%, respectively.
  
  
  CONCLUSIONS
  The Polar V800 accelerometer has a comparable validity to the accelerometer in free-living conditions, regarding "1 hour sedentary bouts" and "V800's walking time vs. ActiTrainer's lifestyle time" in young adults.
authors: Faculty of Health and Sport Science, University of Zaragoza, Huesca, Spain ;
authors: Adrián
authors: A
authors: Hernández-Vicente
authors: GIDFYS, European University Miguel de Cervantes, Valladolid, Spain; ; Research Institute of Hospital 12 de Octubre ("i+12"), Madrid, Spain;
authors: Alejandro
authors: A
authors: Santos-Lozano
authors: Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium ;
authors: Katrien
authors: K
authors: De Cocker
authors: Faculty of Health and Sport Science, University of Zaragoza, Huesca, Spain; ; GENUD, University of Zaragoza, Zaragoza, Spain.
authors: Nuria
authors: N
authors: Garatachea
keywords: Accelerometry; energy expenditure (EE); physical activity (PA); validity; young adults