Energy cost of activity assessed by indirect calorimetry and a 13CO2 breath test.

Abstract

The aim of this study was to assess the accuracy of a 13CO2 breath test for the prediction of short-duration energy expenditure. 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. 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. 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.