title: Between-monitor differences in step counts are related to body size: implications for objective physical activity measurement.
abstract: BACKGROUND
  The quantification of the relationships between walking and health requires that walking is measured accurately. We correlated different measures of step accumulation to body size, overall physical activity level, and glucose regulation.
  
  
  METHODS
  Participants were 25 men and 25 women American Indians without diabetes (Age: 20-34 years) in Phoenix, Arizona, USA. We assessed steps/day during 7 days of free living, simultaneously with three different monitors (Accusplit-AX120, MTI-ActiGraph, and Dynastream-AMP). We assessed total physical activity during free-living with doubly labeled water combined with resting metabolic rate measured by expired gas indirect calorimetry. Glucose tolerance was determined during an oral glucose tolerance test.
  
  
  RESULTS
  Based on observed counts in the laboratory, the AMP was the most accurate device, followed by the MTI and the AX120, respectively. The estimated energy cost of 1000 steps per day was lower in the AX120 than the MTI or AMP. The correlation between AX120-assessed steps/day and waist circumference was significantly higher than the correlation between AMP steps and waist circumference. The difference in steps per day between the AX120 and both the AMP and the MTI were significantly related to waist circumference.
  
  
  CONCLUSIONS
  Between-monitor differences in step counts influence the observed relationship between walking and obesity-related traits.
authors.affiliation: Diabetes Epidemiology and Clinical Research Section, National Institute of Diabetes and Digestive and Kidney Diseases, Phoenix, Arizona, United States of America. jeremy.pomeroy@nih.gov
authors.forename: Jeremy
authors.initials: J
authors.lastname: Pomeroy
authors.forename: Søren
authors.initials: S
authors.lastname: Brage
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Curtis
authors.forename: Pamela D
authors.initials: PD
authors.lastname: Swan
authors.forename: William C
authors.initials: WC
authors.lastname: Knowler
authors.forename: Paul W
authors.initials: PW
authors.lastname: Franks
mesh_terms: D000328:Adult; D004734:Energy Metabolism; D005260:Female; D006304:Health Status; D006801:Humans; D007198:Indians, North American; D008297:Male; D009043:Motor Activity