title: Modulation of spinal inhibitory reflexes depends on the frequency of transcutaneous electrical nerve stimulation in spastic stroke survivors.
abstract: Neurophysiological studies in healthy subjects suggest that increased spinal inhibitory reflexes from the tibialis anterior (TA) muscle to the soleus (SOL) muscle might contribute to decreased spasticity. While 50 Hz is an effective frequency for transcutaneous electrical nerve stimulation (TENS) in healthy subjects, in stroke survivors, the effects of TENS on spinal reflex circuits and its appropriate frequency are not well known. We examined the effects of different frequencies of TENS on spinal inhibitory reflexes from the TA to SOL muscle in stroke survivors. Twenty chronic stroke survivors with ankle plantar flexor spasticity received 50-, 100-, or 200-Hz TENS over the deep peroneal nerve (DPN) of the affected lower limb for 30 min. Before and immediately after TENS, reciprocal Ia inhibition (RI) and presynaptic inhibition of the SOL alpha motor neuron (D1 inhibition) were assessed by adjusting the unconditioned H-reflex amplitude. Furthermore, during TENS, the time courses of spinal excitability and spinal inhibitory reflexes were assessed via the H-reflex, RI, and D1 inhibition. None of the TENS protocols affected mean RI, whereas D1 inhibition improved significantly following 200-Hz TENS. In a time-series comparison during TENS, repeated stimulation did not produce significant changes in the H-reflex, RI, or D1 inhibition regardless of frequency. These results suggest that the frequency-dependent effect of TENS on spinal reflexes only becomes apparent when RI and D1 inhibition are measured by adjusting the amplitude of the unconditioned H-reflex. However, 200-Hz TENS led to plasticity of synaptic transmission from the antagonist to spastic muscles in stroke survivors.
authors.affiliation: a Department of Rehabilitation , Kawamura Hospital , Gifu , Japan ;|b Faculty of Rehabilitation, School of Health Sciences, Fujita Health University , >Aichi > , Japan.
authors.forename: Soichiro
authors.initials: S
authors.lastname: Koyama
authors.affiliation: b Faculty of Rehabilitation, School of Health Sciences, Fujita Health University , >Aichi > , Japan.
authors.forename: Shigeo
authors.initials: S
authors.lastname: Tanabe
authors.affiliation: a Department of Rehabilitation , Kawamura Hospital , Gifu , Japan ;
authors.forename: Kazuya
authors.initials: K
authors.lastname: Takeda
authors.affiliation: b Faculty of Rehabilitation, School of Health Sciences, Fujita Health University , >Aichi > , Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Sakurai
authors.affiliation: b Faculty of Rehabilitation, School of Health Sciences, Fujita Health University , >Aichi > , Japan.
authors.forename: Yoshikiyo
authors.initials: Y
authors.lastname: Kanada
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009128:Muscle Spasticity / Q000209:etiology* / Q000628:therapy*; D018482:Muscle, Skeletal; D009433:Neural Inhibition / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D020521:Stroke / Q000150:complications* / Q000401:mortality / Q000628:therapy; D017741:Survivors; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods*
keywords: Neurorehabilitation; Transcutaneous electrical nerve stimulation; spasticity