The validity of the Moxus Modular metabolic system during incremental exercise tests: impacts on detection of small changes in oxygen consumption

Research paper by Fernando G. Beltrami, Christian Froyd, Asgeir Mamen, Timothy D. Noakes

Indexed on: 30 Jan '14Published on: 30 Jan '14Published in: European Journal of Applied Physiology


We investigated the accuracy of the Moxus Modular Metabolic System (MOXUS) against the Douglas Bag Method (DBM) during high-intensity exercise, and whether the two methods agreed when detecting small changes in \(\dot{V}{\text{O}}_{2}\) between two consecutive workloads (\(\Delta {\dot{{V}}\text{O}}_{ 2}\)).Twelve trained male runners performed two maximal incremental running tests while gas exchange was analyzed simultaneously by the two systems using a serial setup for four consecutive intervals of 30 s on each test. Comparisons between methods were performed for \(\dot{V}{\text{O}}_{2}\), \({\dot{{V}}}_{\text{E}}\), fractions of expired O2 (FeO2) and CO2 (FeCO2) and \(\Delta {\dot{{V}}\text{O}}_{ 2}\).The MOXUS produced significant higher (mean ± SD, n = 54) readings for \(\dot{V}{\text{O}}_{2}\) (80 ± 200 mL min−1, p = 0.005) and \({\dot{{V}}}_{\text{E}}\) (2.9 ± 4.2 L min−1, p < 0.0001), but not FeO2 (−0.01 ± 0.09). Log-transformed 95 % limits of agreement for readings between methods were 94–110 % for \(\dot{V}{\text{O}}_{2}\), 97–108 % for \(\dot{V}_{\text{E}}\) and 99–101 % for FeO2. \(\Delta \dot{V}{\text{O}}_{2}\) for two consecutive measurements was not different between systems (120 ± 110 vs. 90 ± 190 mL min−1 for MOXUS and DBM, respectively, p = 0.26), but agreement between methods was very low (r = 0.25, p = 0.12).Although it was tested during high-intensity exercise and short sampling intervals, the MOXUS performed within the acceptable range of accuracy reported for automated analyzers. Most of the differences between equipments were due to differences in \(\dot{V}_{\text{E}}\). Detecting small changes in \(\dot{V}{\text{O}}_{2}\) during an incremental test with small changes in workload, however, might be beyond the equipment’s accuracy.