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Contribution of M-Waves and H-Reflexes to Contractions Evoked by Tetanic Nerve Stimulation in Humans

Centre for Neuroscience, and Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada

Submitted 19 July 2005; accepted in final form 4 April 2006

Tetanic neuromuscular stimulation evokes contractions by depolarizing motor axons beneath the stimulating electrodes. However, we have shown that extra torque can develop due to the discharge of spinal neurons recruited by the evoked sensory volley. The present experiments investigated whether extra torque in the ankle plantar- and dorsiflexors was associated with enhanced H-reflexes. The tibial and common peroneal nerves were stimulated using 7-s trains (20 Hz for 2 s, 100 Hz for 2 s, 20 Hz for 3 s). Extra torque was defined as significantly more torque during 20-Hz stimulation after the 100-Hz burst (time₂) than before it (time₁). In 9 of 11 subjects, extra plantarflexion torque developed during stimulation just above motor threshold. In these nine subjects, torque increased from 8 to 13% MVC (time₁ to time₂), the soleus H-reflex increased from 13 to 19% M_max and the M-wave of 2% M_max did not change significantly. To evoke extra dorsiflexion torque, greater stimulation intensities were required. In 6 of 13 subjects, extra torque developed at intensities that evoked an M-wave of 5–20% M_max at time_1. In these six subjects, torque doubled from 2 to 4% MVC (time₁ to time₂), whereas tibialis anterior (TA) H-reflexes and M-waves did not change significantly (H-reflex from 0.8 to 2% M_max; M-wave from 12 to 14% M_max). In 7 of 13 subjects, extra torque developed at higher stimulation intensities (35–65% M_max). In these seven subjects, torque increased from 13 to 20% MVC, whereas TA H-reflexes and M-waves were not significantly different (H-reflex from 0.7 to 1% M_max; M-wave from 49 to 54% M_max). Thus enhanced H-reflexes contributed to extra plantarflexion, however, other factors generated extra dorsiflexion.

This article has been cited by other articles:

				J. C. Dean, L. M. Yates, and D. F. Collins Turning on the central contribution to contractions evoked by neuromuscular electrical stimulation J Appl Physiol, July 1, 2007; 103(1): 170 - 176. [Abstract] [Full Text] [PDF]