Non-invasive estimation of muscle oxygen uptake kinetics with pseudorandom binary sequence and step exercise responses

PURPOSE: The aim of the study was to test for significant differences in non-invasively estimated muscle oxygen uptake ([Formula: see text]) kinetics, assessed by a square-wave exercise protocol (STEP) as well as by a time series approach with pseudorandom binary sequence (PRBS) work rate (WR) changes.

METHODS: Seventeen healthy and active individuals (10 women, 7 men; 23 ± 2 years old; height 175 ± 11 cm; body mass 73 ± 14 kg [mean ± SD]) completed five repetitions of WR transitions from 30 to 80 W for the STEP approach and two sequences of pseudorandom binary WR changes between 30 and 80 W for the PRBS approach. Pulmonary oxygen uptake ([Formula: see text]) was measured breath by breath. [Formula: see text] kinetics were estimated during phase II [Formula: see text] in the STEP approach and during the pseudorandom binary sequence WR changes in the PRBS approach.

RESULTS: No significant differences were observed between different models of the STEP and the PRBS approach for estimation of [Formula: see text] kinetics (p > 0.05). In addition, a very high variability between the models was determined for [Formula: see text] kinetics [mean time constants (τ) difference: - 2.5 ± 11.4 s]. A significant correlation for τ of [Formula: see text] between the STEP approach with experimentally determined phase I [Formula: see text] lengths and the PRBS approach was noticed (r = 0.536; p < 0.05).

CONCLUSIONS: Both approaches (STEP and PRBS) are not significantly different for estimating the [Formula: see text] kinetics, but the very high variability impairs the predictability between the models. However, the determination of the length of phase I [Formula: see text] should be as appropriate as possible because predefined duration lengths can result in overestimations in [Formula: see text] kinetics.