Abstract
To assess if the alteration of neuromuscular properties of knee extensors muscles during heavy exercise co-vary with the SCV ({dot{{rm{V}}}{rm{O}}}_{2} slow component), eleven healthy male participants completed an incremental ramp test to exhaustion and five constant heavy intensity cycling bouts of 2, 6, 10, 20 and 30 minutes. Neuromuscular testing of the knee extensor muscles were completed before and after exercise. Results showed a significant decline in maximal voluntary contraction (MVC) torque only after 30 minutes of exercise (−17.01% ± 13.09%; p < 0.05) while single twitch (PT), 10 Hz (P10), and 100 Hz (P100) doublet peak torque amplitudes were reduced after 20 and 30 minutes (p < 0.05). Voluntary activation (VA) and M-wave were not affected by exercise, but significant correlation was found between the SCV and PT, MVC, VA, P10, P100, and P10/P100 ratio, respectively (p < 0.015). Therefore, because the development of the SCV occurred mainly between 2–10 minutes, during which neuromuscular properties were relatively stable, and because PT, P10 and P100 were significantly reduced only after 20-30 minutes of exercise while SCV is stable, a temporal relationship between them does not appear to exist. These results suggest that the development of fatigue due to alterations of neuromuscular properties is not an essential requirement to elicit the SCV.
Highlights
To assess if the alteration of neuromuscular properties of knee extensors muscles during heavy exercise co-vary with the slow component of V O2 (SCV) (VO2 slow component), eleven healthy male participants completed an incremental ramp test to exhaustion and five constant heavy intensity cycling bouts of 2, 6, 10, 20 and 30 minutes
Neuromuscular properties of knee extensor muscles are sensitive to the accumulation of muscle metabolites such as adenosine diphosphate (ADP), inorganic phosphate (Pi), hydrogen ion (H+), and magnesium ion (Mg2+)
Since the SCV occurs during high-intensity exercise, and because high-intensity exercise is always associated with changes in metabolite concentration that may produce an alteration in neuromuscular properties of muscle filament, the latter may be considered a putative mediator of the SCV
Summary
To assess if the alteration of neuromuscular properties of knee extensors muscles during heavy exercise co-vary with the SCV (VO2 slow component), eleven healthy male participants completed an incremental ramp test to exhaustion and five constant heavy intensity cycling bouts of 2, 6, 10, 20 and 30 minutes. Using self-paced dynamic concentric extension/flexion of the knee and interleaving voluntary and electrically evoked contractions, Froyd and colleagues have shown, even without measuring directly VO2 kinetics, that fatigue progresses with similar dynamics to those expected of the SCV during an approximately 6-min time trial[18]. These findings do not show the mechanism linking the alteration of neuromuscular properties of knee extensors, per se, and the SCV. The hypothesis was that the SCV amplitude correlates with the change in neuromuscular properties of knee extensor muscles, depicted by a decrease in evoked peak torque
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