A comparative study on different methods for the determination of energy expenditure

In order to determine energy expenditure, the Douglas Bag technique (DB) and Kofranyi-Michaelis respirometers (KM) have been widely used under field conditions for several decades. Some years ago the Oxylog (OX) method was developed, measuring simultaneously the difference of partial oxygen pressure in inspired and expired air (PO2 diff.) by two polarographic oxygen sensors. In order to compare these three methods laboratory experiments (3 test subjects, 5 different bicycle ergometer work loads, 180 measurements per apparatus) were performed. Oxygen uptake (VO2) varied between about 0.9 to 3.0 l/min. The VO2 data obtained by the DB method, which were used as a reference, and those obtained by the KM method agreed fairly well. The recorded data of OX underestimated VO2 up to 21%, with the deviation increasing with work intensity. A sufficient accuracy of recorded VO2 was observed only up to moderate work intensity. OX data calculated from ventilation volume of inspired air per minute (VI) and PO2 diff., measured by OX, were always about 19% higher than those recorded by OX. This means that the calculated VO2 values of the OX corresponded fairly well with DB values at heavy work loads. The reason for the differences between recorded and calculated OX data is still unknown. Further research is urgently needed.