Alterations to neuromuscular properties of skeletal muscle are temporally dissociated from the oxygen uptake slow component

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 30minutes. 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 30minutes of exercise (-17.01% +/- 13.09%; p<0.05) while single twitch (PT), 10Hz (P10), and 100Hz (P100) doublet peak torque amplitudes were reduced after 20 and 30minutes (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 2-10minutes, during which neuromuscular properties were relatively stable, and because PT, P10 and P100 were significantly reduced only after 20-30minutes 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.