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

Abstract

Purpose

The aim of the study was to test for significant differences in non-invasively estimated muscle oxygen uptake ( \(\dot {V}_{2{\text{musc}}}}\) ) 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 ( \(\dot {V}_{2{\text{pulm}}}}\) ) was measured breath by breath. \(\dot {V}_{2{\text{musc}}}}\) kinetics were estimated during phase II \(\dot {V}_{2{\text{pulm}}}}\) 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 \(\dot {V}_{2{\text{musc}}}}\) kinetics (p > 0.05). In addition, a very high variability between the models was determined for \(\dot {V}_{2{\text{musc}}}}\) kinetics [mean time constants (τ) difference: − 2.5 ± 11.4 s]. A significant correlation for τ of \(\dot {V}_{2{\text{musc}}}}\) between the STEP approach with experimentally determined phase I \(\dot {V}_{2{\text{pulm}}}}\) 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 \(\dot {V}_{2{\text{musc}}}}\) kinetics, but the very high variability impairs the predictability between the models. However, the determination of the length of phase I \(\dot {V}_{2{\text{pulm}}}}\) should be as appropriate as possible because predefined duration lengths can result in overestimations in \(\dot {V}_{2{\text{musc}}}}\) kinetics.

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