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

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.

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.

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).

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.