The validity of the Moxus Modular metabolic system during incremental exercise tests: impacts on detection of small changes in oxygen consumption.
OBJECTIVE
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 [Formula: see text] between two consecutive workloads ([Formula: see text]).


METHODS
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 [Formula: see text], [Formula: see text], fractions of expired O2 (FeO2) and CO2 (FeCO2) and [Formula: see text].


RESULTS
The MOXUS produced significant higher (mean ± SD, n = 54) readings for [Formula: see text] (80 ± 200 mL min(-1), p = 0.005) and [Formula: see text] (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 [Formula: see text], 97-108 % for [Formula: see text] and 99-101 % for FeO2. [Formula: see text] 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).


CONCLUSIONS
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 [Formula: see text]. Detecting small changes in [Formula: see text] during an incremental test with small changes in workload, however, might be beyond the equipment's accuracy.
UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town and Sports Science Institute of South Africa, Boundary Road, Newlands, 7700, South Africa, fernando.beltrami@uct.ac.za.
Fernando G
FG
Beltrami
Christian
C
Froyd
Asgeir
A
Mamen
Timothy D
TD
Noakes
D000293:Adolescent; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange