The H-reflex is one of the most common and useful techniques in the field of motor control. However, the H-reflex technique also involves difficulty in data interpretation when stimulus intensity is high enough to stimulate both sensory and motor fibers (antidromic current). On the other hand, transcutaneous stimulation applied on the spinous processes is able to stimulate the dorsal root, resulting in selective stimulation of only sensory fibers without evoking a direct motor response and antidromic current on the motor fibers. The purpose of this study was to compare the maximal reflex responses that can be elicited in the lower leg muscles using traditional tibial nerve stimulation (TS) and transcutaneous spinal stimulation (SS). Fifteen subjects participated in the study. EMG signals were recorded from triceps surae (the soleus, medial gastrocnemius, lateral gastrocnemius muscles) in the prone position. Using SS and TS, H-max amplitudes of triceps surae muscles were measured and standardized with M-max. H-max values elicited by SS were significantly greater than those by TS in each muscle. It is suggested that SS is able to evoke the H-reflex without a direct motor response and the traditional method (TS) which administers electric stimulation in the mixed nerve underestimates H-max values. Additionally, the SS protocol was used to reassess post-activation depression in the soleus and anterior tibialis muscles. The inter-stimulus intervals were set at 40, 80, 120, 160, and 200 ms and stimulus intensity was set to evoke H-reflexes of 10% M-max in each muscle. The results showed a significant interaction between muscles and intervals (F(4,32) = 2.72, p < 0.05). Post-hoc tests revealed that the depression ratios significantly differed at each interval between the muscles. In the tibialis anterior muscle, moreover, the depression was significantly greater at the 40 ms interval compared with other intervals whereas no significant difference among the depression ratios was found in the soleus. It is suggested that recovery occurs earlier in the tibialis anterior than in the soleus and spinal mechanisms involved in post-activation depression differ between the soleus and tibialis anterior muscles. Overall, electrical stimulation applied in the spinous processes is able to selectively stimulate the dorsal root and to evoke H-reflexes. The measurements obtained by the SS method are valid and this method can extend research areas, such as in measuring H-reflex properties which are impossible to study due to the deeper location of the mixed nerves.
|Advisor:||Koceja, David M., Prieto, Anne L.|
|Commitee:||Heath, Matthew D., Stager, Joel M.|
|Department:||School of Health, Physical Education and Recreation|
|School Location:||United States -- Indiana|
|Source:||DAI-B 72/10, Dissertation Abstracts International|
|Keywords:||H-reflex, Homosynaptic depression, Post-activation depression, Spinal cord|
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