The effects of priming exercise on the V̇O₂ 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 (V̇O2SC) 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 (VHCON) and with prior exercise (VHEXP), to measure the cycling peak torque decrement. The V̇O2SC magnitude at 3 min (VHCON = 0.280 ± 0.234, VHEXP = 0.116 ± 0.109 L·min−1; p = 0.04) and the V̇O2SC trajectory were significantly lower for VHEXP (VHCON = 0.108 ± 0.042, VHEXP = 0.063 ± 0.031 L·min−2; p < 0.01), leading to a V̇O2SC 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 (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 VHCON and VHEXP, respectively, without significant differences between conditions. Regardless of the condition, there was a significant relationship between Δtorque and the V̇O2SC (R2: VHCON = 0.23, VHEXP = 0.25; p = 0.01). Considering that “priming” effects on the V̇O2SC 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 V̇O2SC.

Changes in VO2 Kinetics After Elevated Baseline Do Not Necessarily Reflect Alterations in Muscle Force Production in Both Sexes

“…A switch from the hyperbolic mode to the isokinetic mode happened instantaneously when required. This protocol was similar to previously used protocols (Cannon et al, 2011; de Souza et al, 2016; Hopker et al, 2016; do Nascimento Salvador et al, 2018) and considered as reliable (do Nascimento Salvador et al, 2018) (no differences were observed for both peak torque – intraclass correlation coefficient = 0.99, typical error = 3.7% and, peak power output – intraclass correlation coefficient = 0.99; typical error = 4.2% obtained during the pre-exercise assessments). Peak torque was assessed for each subject by a 5 s cycling sprint test in the isokinetic mode at 60 or 120 rpm.…”

“…The authors concluded that muscle fatigue is neither the primary determinant of the VO 2SC nor does it affect the τ of the fundamental phase. Recently, do Nascimento Salvador et al (2018) showed that prior VH cycling changed the VO 2SC and the trajectory of the VO 2SC in a subsequent VH cycling exercise, but did not alter MFP behavior. The present study is in line with these findings and challenges a “cause-effect” relationship between VO 2SC and muscle fatigue.…”

“…Beelen et al (1995) suggest that fatigue in this type of dynamic isokinetic exercise may be due to changes in the muscle itself and not due to failure of central drive. Considering that muscle fatigue measured by MIE recovers back to baseline values within 1–3 min (Beelen et al, 1995; Coelho et al, 2015; do Nascimento Salvador et al, 2018), it represents a tendency to indicate more the peripheral fatigue.…”

“…Furthermore, de Souza et al (2016) showed differences in the VO 2SC and τ despite a similar magnitude of muscle fatigue during VH cycling exercise. do Nascimento Salvador et al (2018) demonstrated that prior cycling exercise decreased the VO 2SC behavior, but did not modify the time-course of muscle torque production in a subsequent VH cycling bout.…”

“…Breath-by-breath data for each test were initially examined to exclude outlier values caused by sighs, swallowing and coughs (Lamarra et al, 1987). After that, for each exercise transition, the breath-by-breath data was processed and analyzed as described previously (do Nascimento et al, 2015; de Souza et al, 2016; do Nascimento Salvador et al, 2018). Non-linear regression techniques were used to fit the data after the onset of a fundamental phase with an exponential function (OriginPro 8; OriginLab).…”