Late facilitation of the human soleus H reflex induced by sustained isometric maneuver.
Studying the effect of spinal cord reinforcement maneuvers (SCRMs) on H reflex assists in understanding aspects of motor control. Our objective was as follows: (1) to elucidate the effects of four neck positions (neck resting at neutral position (control); passive hyperflexion of the neck; hyperextension of the neck with simultaneous abdominal contraction; and sustained active neck hyperflexion); (2) to evaluate the temporal changes of soleus H reflexes repeatedly evoked after a period of sustained neck flexion. We used a prospective, intrinsically controlled trial of the effects of these SCRMs on the H reflexes and M-responses in ten healthy volunteers. Pre- and postmaneuver measures included H reflex and M-response latencies and amplitudes, H/M maximum amplitude ratio, and H threshold. The four maneuvers showed no significant effect on the H reflex or M-response measures. To investigate temporal changes in the H reflex amplitude, H reflexes were repeatedly evoked at two-minute intervals after a one-minute period of active neck flexion. The amplitude of the H reflex was enhanced (P = 0.0356; analysis of variance), and the post hoc least significant difference test was significant at four minutes postmaneuver. Peak magnitude of the H reflex occurred at four minutes after relaxation, and the response returned to pretest baseline at eight minutes. The results of this study document the time course of repeated H reflexes after SCRM, and the timing of the H reflex was found to be a contributing variable that should be considered in future study designs.
Chuang
T Y
TY
Department of Physical Medicine and Rehabilitation, Veterans General Hospital Taipei, Taiwan, Republic of China.
Chiou-Tan
F Y
FY
Pinzon
E G
EG
Tuel
S M
SM
D000222:Adaptation, Physiological; D000328:Adult; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation*; D009333:Neck / Q000502:physiology*; D010812:Physical Stimulation; D011187:Posture / Q000502:physiology*; D011446:Prospective Studies; D013997:Time Factors