The effects of priming exercise on the <i>V</i>O₂ slow component and the time-course of muscle fatigue during very-heavy-intensity exercise in humans

Abstract

We hypothesized that prior exercise would attenuate the muscle fatigue accompanied by oxygen uptake slow-component (V̇O_2SC) behavior during a subsequent very-heavy (VH)-intensity cycling exercise. Thirteen healthy male subjects performed tests to determine the critical power (CP) and the fixed amount of work above CP ([Formula: see text]) and performed 6 square-wave bouts until 3 or 8 min, each at a work rate set to deplete 70% [Formula: see text] in 8 min, with a maximal isokinetic effort before and after the conditions without (VH_CON) and with prior exercise (VH_EXP), to measure the cycling peak torque decrement. The V̇O_2SC magnitude at 3 min (VH_CON = 0.280 ± 0.234, VH_EXP = 0.116 ± 0.109 L·min^-1; p = 0.04) and the V̇O_2SC trajectory were significantly lower for VH_EXP (VH_CON = 0.108 ± 0.042, VH_EXP = 0.063 ± 0.031 L·min^-2; p < 0.01), leading to a V̇O_2SC magnitude at the eighth minute that was significantly lower than VH_CON (VH_CON = 0.626 ± 0.296 L·min^-1, VH_EXP = 0.337 ± 0.179; p < 0.01). Conversely, peak torque progressively decreased from pre-exercise to 3 min (Δtorque = 21.5 ± 7.7 vs. 19.6 ± 9.2 Nm) and to 8 min (Δtorque = 29.4 ± 15.8 vs. 27.5 ± 12.0 Nm) at VH_CON and VH_EXP, respectively, without significant differences between conditions. Regardless of the condition, there was a significant relationship between Δtorque and the V̇O_2SC (R²: VH_CON = 0.23, VH_EXP = 0.25; p = 0.01). Considering that "priming" effects on the V̇O_2SC were not accompanied by the muscle force behavior, these findings do not support the hypothesis of a "causal" relationship between the time-course of muscle fatigue and V̇O_2SC.