Spinal Reflex Excitability of Lower-Limb Muscles Using Transcutaneous Spinal Cord Stimulation - The Study of Development for Longitudinal Test

Abstract

The purpose of this study was to examine reproducibility of recruitment properties of the spinal reflexes evoked by a transcutaneous spinal cord stimulation （tSCS） between days. Twenty males （25.8 ± 3.4 years） participated in this study. Experiments were conducted while the subjects were in the supine position. Recruitment curves were obtained from the spinal reflexes evoked by tSCS in two consecutive days. A paired-pulse stimulation with 50 ms inter-pulse interval was delivered to confirm that responses were caused by activation of the sensory fibers. Surface electromyography （EMG） of eight muscles in the lower-limbs （i.e., foot, shank, and thigh muscles） was recorded. Peak-to-peak EMG amplitudes of the first response was calculated for each muscle when no response was observed in the second response. Threshold intensity of the responses was defined as the minimum stimulation intensity that produced the responses, and maximal slope of the responses was determined by fitting six-order polynomial function to the recruitment curve. Inter-day reproducibility of the recruitment parameters was quantified using intraclass correlation coefficients （ICC）. ICCs of threshold intensity for each muscle ranged between 0.487 and 0.874, and ICCs of maximal slope ranged between 0.474 and 0.964. These results suggest moderate to high reproducibility of the parameters of the recruitment curve of spinal reflexes in lower-limbs. Therefore, spinal reflexes evoked by tSCS could be useful in longitudinal neurophysiological studies.