title: Post-activation depression in the human soleus muscle using peripheral nerve and transcutaneous spinal stimulation.
abstract: Transcutaneous stimulation of the human lumbar spine can be used to elicit root-evoked potentials (REPs). These sensory-motor responses display notable similarities to the monosynaptic H-reflex. The purpose of this study was to compare post-activation depression of the soleus REP to that of the H-reflex, when conditioned by either an H-reflex or an REP. Paired pulses were delivered 25-200ms apart and the recovery was characterized using three levels of stimulation. In all conditions, post-activation depression was reduced during contraction as compared to rest (P<0.001). REP doublets, delivered using an inter-pulse interval of 150ms, recovered to 68±8% of control during plantarflexion and 20±6% of control at rest. During contraction, recovery of a second REP was 65% of the corresponding recovery for a second H-reflex. The recovery of an H-reflex was equivalent, when conditioned by either an H-reflex or an REP, even though the spinal stimulus activated and/or engaged more afferent and efferent fibers. Our results suggest that the additional elements activated by the spinal stimulus did not affect the recovery of the H-reflex. However, the transcutaneous spinal stimulus produced more inhibition when it was assessed using two low-intensity REPs (P<0.05) suggesting that the pathway mediating the spinally-evoked response was more susceptible to being inhibited.
authors.affiliation: Department of Physiology, University of Alberta, Edmonton, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Andrews
authors.affiliation: Department of Physiology, University of Alberta, Edmonton, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Stein
authors.affiliation: Department of Surgery, University of Alberta, Edmonton, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada. Electronic address: francois.roy@ualberta.ca.
authors.forename: François D
authors.initials: FD
authors.lastname: Roy
mesh_terms: D005071:Evoked Potentials; D006181:H-Reflex; D006801:Humans; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D062187:Spinal Cord Stimulation; D013126:Spinal Nerve Roots / Q000502:physiology; D013979:Tibial Nerve / Q000502:physiology
keywords: H-reflex; Post-activation depression; Root evoked potential; Soleus; Transcutaneous spinal stimulation