Oxygen Uptake Kinetics During Supra V·O_2max Treadmill Running in Humans

Abstract

Accurate classification of V·O₂ kinetics is essential to correctly interpret its control mechanisms. The purpose of this study was to examine V·O₂ kinetics in severe and supra-maximal intensity running exercise using two modelling techniques. Nine subjects (mean ± S.D: age, 27 ± 7 years; mass, 69.8 ± 9.0 kg; V·O_2max, 59.1 ± 1.8 mL · kg · min^-1) performed a series of “square-wave” exercise transitions to exhaustion at running speeds equivalent to 80 % of the difference between the V·O₂ at LT and V·O_2max (Δ), and at 100 %, 110 % and 120 % V·O_2max. The V·O₂ response was modelled with an exponential model and with a semi-logarithmic transformation, the latter assuming a certain steady state V·O₂. With the exponential model there was a significant reduction in the “gain” of the primary component in supra-maximal exercise (167 ± 5 mL · kg^-1 · km^-1 at 80 % Δ to 142 ± 5 mL · kg^-1 · km^-1 at 120 % V·O_2max, p = 0.005). The time constant of the primary component also reduced significantly with increasing intensity (17.8 ± 1.1 s at 80 % Δ to 12.5 ± 1.2 s at 120 % V·O_2max, p < 0.05). However, in contrast, using the semi-log model, the time constant significantly increased with intensity (30.9 ± 13.5 s at 80 % Δ to 72.2 ± 23.9 s at 120 % V·O_2max, p < 0.05). Not withstanding the need for careful interpretation of mathematically modelled data, these results demonstrate that neither the gain nor the time constant of the V·O₂ primary component during treadmill running are invariant across the severe and supra-maximal exercise intensity domains when fit with an exponential model. This suggests the need for a reappraisal of the V·O₂/work rate relationship in running exercise.

Key words

Exponential modelling - semi-logarithmic transformation - exercise intensity domains - time to exhaustion

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