The Effect of Transcutaneous Electrical Spinal Cord Stimulation on the Functional Activity of Spinal Inhibition in the System of Synergistic Muscles of the Lower Leg in Humans

Abstract: The effect of 20-minute transcutaneous electrical spinal cord stimulation (tESCS) on the severity of nonreciprocal and recurrent inhibition of spinal α-motoneurons in humans at rest and during a weak muscular effort was studied. It was found that during the entire time of exposure to tESCS at rest, the nonreciprocal and recurrent inhibition of the α-motoneurons of the synergist muscle (m. soleus) weakened, inverting to nonreciprocal and recurrent facilitation. Nonreciprocal facilitation of the soleus α-motorneurons was maintained throughout the entire after effect and recurrent facilitation was inverted to recurrent inhibition, which increased up to 20 min after the end of stimulation. The retention of a weak muscular effort during spinal cord stimulation was accompanied by an increase in nonreciprocal and recurrent inhibition of α-motoneurons of the synergist muscle. This post-activation effect lasted up to 20 min after electrical stimulation of the spinal cord. The activity of recurrent inhibition was more pronounced during spinal cord stimulation when performing a weak voluntary effort, and the post-activation effect was manifested by similar changes in the severity of recurrent and nonreciprocal inhibition: their enhancement occurred within 10 min and weakening at 20 min after the end of stimulation to background values. The reflex mechanisms of descending supraspinal and ascending peripheral influences on the functional activity of nonreciprocal and recurrent inhibition in the system of lower leg synergistic muscles in humans based on the effects of tESCS are discussed. © 2022, Pleiades Publishing, Inc.