title: Energy cost of activity assessed by indirect calorimetry and a 13CO2 breath test.
abstract: OBJECTIVE
  The aim of this study was to assess the accuracy of a 13CO2 breath test for the prediction of short-duration energy expenditure.
  
  
  METHODS
  Eight healthy volunteers walked at 1.5 km.h-1 for 60 min followed by 60-min recovery. During this time, the energy cost of physical activity was measured via respiratory calorimetry and a 13C bicarbonate breath test. A further eight subjects were tested using the same two methods during a 60-min cycle at 0.5 kp, 30 rpm followed by a 60-min recovery. The rate of appearance of 13CO2 (RaCO2) was measured and the mean ratio, VCO2/RaCO2, was used to calculate energy expenditure using the isotopic approach.
  
  
  RESULTS
  As would be expected, there was a significant difference in the energy cost of walking and cycling using both methods (P < 0.05). However, no significant differences were observed between respiratory calorimetry and the isotope method for measurement of energy expenditure while walking or cycling.
  
  
  CONCLUSIONS
  These data suggest that the 13C breath test is a valid method that can be used to measure the energy cost of short duration physical activity in a field setting.
authors.affiliation: School of Human Movement Studies, Faculty of Health, Queensland University of Technology, Brisbane, Queensland, Australia, 4059. ml.richards@qut.edu.au
authors.forename: M
authors.initials: M
authors.lastname: Leigh Richards
authors.forename: P S
authors.initials: PS
authors.lastname: Davies
mesh_terms: D000328:Adult; D001944:Breath Tests / Q000379:methods*; D002151:Calorimetry; D002247:Carbon Isotopes / Q000032:analysis; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D012680:Sensitivity and Specificity
chemical_list: D002247:Carbon Isotopes