![]() ![]() Of note, metabolic simulators exclude biological variation, but the price to pay is a questionable transferability to human individuals, where expired gas concentrations, their temperature, and humidity may change throughout the test, as respiratory frequency and tidal volumes do, too. These studies applied either simulated testing via metabolic simulator or biological testing via exercise tests in humans. In the rare cases where inter-unit variability between two units of a particular device has been reported, a considerable variability of 0.4–2.1% was calculated. However, they are in fact generalized, assuming that a particular unit represents the whole “population” of the respective device. Interestingly, reliability of CPX devices has been determined in several studies, with differences ranging 0.12–8.15% for common respiratory variables, but these results are nearly always based on results obtained by a single apparatus. This will be called inter-device difference hereafter. A third measure used throughout this paper is the difference between two devices at a given intensity or stage. ![]() This will be called inter-unit reliability (i.e. ![]() As soon as more than one unit of a particular device is used–be that within one or in multiple labs–the variability between two or more CPX-units needs to be considered, too. This will be called intra-unit reliability (i.e. As for any scientific method, reliability is an important quality measure also for CPX devices and if testing is conducted within one laboratory and only one CPX-unit is applied, the overall variability of one unit between two or more trials is a key quality measure. Cardiopulmonary exercise (CPX) testing is frequently used to evaluate fitness in healthy and unhealthy populations in cross-sectional or longitudinal evaluations or studies, as underlined by 3357 hits on the search item “ V ˙ O 2 max testing” in pubmed within 5 years (Aug. ![]()
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