Energy cost of activity assessed by indirect calorimetry and a (CO2)-C-13 breath test

Purpose: The aim of this study was to assess the accuracy of a (CO2)-C-13 b reath 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 m easured via respiratory calorimetry and a C-13 bicarbonate breath test. A f urther eight subjects were tested using the same two methods during a 60-mi n cycle at 0.5 kp. 30 ipm followed by a 60-min recovery. The rate of appear ance of (CO2)-C-13, (RaCO2) was measured and the mean ratio, (V) over dot C O2/RaCO2 was used to calculate energy expenditure using the isotopic approa ch. Results: As would be expected, there was a significant difference in th e 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 C-13 breath test is a valid method that can be used to measure the energy cost of short duration physical activity in a field setting.