Prior exercise speeds pulmonary oxygen uptake kinetics and increases critical power during supine but not upright cycling

Abstract

Critical power (CP) is a fundamental parameter defining high-intensity exercise tolerance and is related to the time constant of phase II pulmonary oxygen uptake kinetics (τ_V̇O2). To test the hypothesis that this relationship is causal we determined the impact of prior exercise ("priming") on CP and τ_V̇O2 in the upright and supine positions. 17 healthy men were assigned to either upright or supine exercise groups, whereby CP, τ_V̇O2 and muscle deoxyhaemoglobin kinetics (τ_[HHb]) were determined via constant-power tests to exhaustion at four work-rates with (primed) and without (control) priming exercise at ∼31%Δ. During supine exercise, priming reduced τ_V̇O2 (control: 54 ± 18 vs. primed: 39 ± 11 s; P < 0.001), increased τ_[HHb] (control: 8 ± 4 vs. primed: 12 ± 4 s; P = 0.003) and increased CP (control: 177 ± 31 vs. primed: 185 ± 30 W, P = 0.006) compared to control. However, priming exercise had no effect on τ_V̇O2 (control: 37 ± 12 vs. primed: 35 ± 8 s; P = 0.82), τ_[HHb] (CON: 10 ± 5 s vs. PRI: 14 ± 10; P = 0.10), or CP (control: 235 ± 42 vs. primed: 232 ± 35 W; P = 0.57) during upright exercise. The concomitant reduction of τ_V̇O2 and increased CP following priming in the supine group, effects that were absent in the upright group, provides the first experimental evidence that τ_V̇O2 is mechanistically related to critical power. The increased τ_[HHb] suggests that this effect was mediated, at least in part, by improved oxygen availability.

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