The effects of priming exercise on the (V)over dotO(2) 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 ((V)over dotO(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 (W') and performed 6 square-wave bouts until 3 or 8 min, each at a work rate set to deplete 70% W' in 8 min, with a maximal isokinetic effort before and after the conditions without (VHCON) and with prior exercise (VHEXP), to measure the cycling peak torque decrement. The (V)over dotO(2SC) magnitude at 3 min (VHCON = 0.280 +/- 0.234, VHEXP, = 0.116 +/- 0.109 L.min(-1) ;p = 0.04) and the (V)over dotO(2SC) trajectory were significantly lower for VHEXP (VHCON = 0.108 +/- 0.042, VHEXP= 0.063 +/- 0.0311:min(-2);p < 0.01), leading to a (V)over dotO(2SC) magnitude at the eighth minute that was significantly lower than VHCON (VHCON = 0.626 +/- 0.296 L.min(-1), VHEXP = 0.337 +/- 0.179; p < 0.01). Conversely, peak torque progressively decreased from pre-exercise to 3 min (Delta torque = 21.5 +/- 7.7 vs. 19.6 +/- 9.2 Nm) and to 8 min (Delta torque = 29.4 +/- 15.8 vs. 27.5 +/- 12.0 Nm) at V-CON and VHEXP, respectively, without significant differences between conditions. Regardless of the condition, there was a significant relationship between Delta torque and the (V)over dotO(2SC) (R-2 : VHCON = 0.23. VHEXP = 0.25; p = 0.01). Considering that priming effects on the (V)over dotO(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 (V)over dotO(2SC).