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 (τV̇O2). To test the hypothesis that this relationship is causal we determined the impact of prior exercise (“priming”) on CP and τV̇O2 in the upright and supine positions. 17 healthy men were assigned to either upright or supine exercise groups, whereby CP, τV̇O2 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 τV̇O2 (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 τV̇O2 (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 τV̇O2 and increased CP following priming in the supine group, effects that were absent in the upright group, provides the first experimental evidence that τV̇O2 is mechanistically related to critical power. The increased τ[HHb] suggests that this effect was mediated, at least in part, by improved oxygen availability

Hyperoxia speeds pulmonary oxygen uptake kinetics and increases critical power during supine cycling

“…Despite our recent data (Goulding et al., , , b), stronger evidence for a determining effect of on critical power would arguably come from the establishment of a relationship between the changes in critical power (ΔCP) and () between two conditions where would be expected to differ. However, a valid assessment of this relationship requires the precise characterization of the value of via repeated, identical exercise transitions in each set of conditions (Lamarra, Whipp, Ward, & Wasserman, ; Whipp, Ward, Lamarra, Davis, & Wasserman, ).…”

“…Conversely, inspired hyperoxic air has the potential to reduce , at least during supine exercise where O 2 delivery is rate limiting (Macdonald, Pedersen, & Hughson, ). However, unlike our previously imposed interventions (Goulding et al., , , b), hyperoxia does not require a prolonged wash‐out period before the physiological responses to further exercise can be considered as being normal. Hence, during supine exercise, hyperoxia represents a convenient means by which to manipulate , observe any effect on critical power and characterize precisely via bouts of moderate‐intensity exercise undertaken shortly before the criterion bouts that determine critical power.…”

“…Absolute concentrations of muscle and microvascular deoxyhaemoglobin + deoxymyoglobin ([HHb + Mb]), oxyhaemoglobin + oxymyoglobin ([HbO 2 + MbO 2 ]) and total haemoglobin + total myoglobin ([THb + Mb]) were determined using a frequency‐domain multidistance near‐infrared spectroscopy (NIRS) system (OxiplexTS; ISS, Champaign, IL, USA). This technique has been described in detail previously (Broxterman, Wilcox, Schlup, Craig, & Barstow, ; Goulding et al., ). Briefly, this device consists of one detector fibre bundle and eight light‐emitting diodes (LEDs) operating at wavelengths of 690 and 830 nm (four LEDs per wavelength), with LED‐detector fibre bundle separation distances of 2.25, 2.75, 3.25 and 3.75 cm.…”

“…At the onset of muscular work, pulmonary kinetics increase in a near‐exponential fashion, with a time constant () that closely approximates that of muscle (Grassi et al., ). A strong inverse relationship has been observed between and critical power during upright cycle exercise (Goulding, Roche, & Marwood, , ; Murgatroyd, Ferguson, Ward, Whipp, & Rossiter, ), suggesting that these parameters might be related causally. In support of this, we recently showed that a prior bout of heavy‐intensity ‘priming’ exercise reduced and increased critical power (Goulding et al., ).…”

“…A strong inverse relationship has been observed between and critical power during upright cycle exercise (Goulding, Roche, & Marwood, , ; Murgatroyd, Ferguson, Ward, Whipp, & Rossiter, ), suggesting that these parameters might be related causally. In support of this, we recently showed that a prior bout of heavy‐intensity ‘priming’ exercise reduced and increased critical power (Goulding et al., ). However, the concomitant improvements in critical power and might have been attributable to the enhanced O 2 availability that attended priming exercise, rather than a dependence of critical power on per se .…”