The purpose of this study was to test the accuracy of a new portable spirometric-telemetric device (Oxycon Mobile®) over a wide range of exercise intensities against an accurate stationary apparatus (Oxycon Pro®). Therefore, fifteen endurance-trained subjects (V·O2peak: 58.8 ± 5.2 ml · min-1 · kg-1) performed an incremental as well as an endurance exercise test on two different occasions. Gas exchange variables were measured by the two ergospirometric devices simultaneously. For this purpose, a special face mask was designed which allowed respiratory gas sampling with both devices at exactly the same time. Compared to the Oxycon Pro® as an accurate reference system, the Oxycon Mobile® showed significantly lower values for V·O2 at 200 and 250 W during the incremental exercise test. For V·CO2 no significant differences were found although the Oxycon Mobile® seemed to systematically measure higher values. With regard to RER the Oxycon Mobile® showed significantly higher values at all workloads tested. We therefore dissuade from comparing gas exchange variables collected by the Oxycon Mobile® with data measured under laboratory conditions by an accurate reference system like the Oxycon Pro®. Furthermore, the extrapolation of information about substrate utilization during different exercise durations and intensities from data measured by the Oxycon Mobile® seems inappropriate.
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