Spinal excitability following sensory electrical stimulation of the upper limb

The purpose of the study was to determine if sensory electrical stimulation (SES), below motor threshold, would reduce spinal excitability via reciprocal inhibition (RI) and determine if any changes were sex-related. Eighteen healthy participants (11 males and 7 females) participated in a pre-post comparison study. The Hoffmann (H-) reflex was elicited to assess the spinal excitability of Flexor Carpi Radialis (FCR) and the influence of RI from Extensor Carpi Radialis Longus (ECRL) on FCR using a paired conditioning pulse paradigm. A 15-min bout of SES (4 pulse bursts at 100 Hz) was applied to ECRL, and the H-reflexes were measured at 0- and 20-min post SES. A linear mixed model regression analysis was performed to evaluate the effects of stimulus order, conditioning, sex, and time on the FCR H-reflex. All participants experienced RI from the conditioning pulses, with females having significantly greater suppression than males (mean difference; MD = 0.026). For males, SES produced a depression in FCR excitability (MD = 0.023 at time 0; MD = 0.015 at 20 min post-SES) with no changes in RI. SES had no effect on FCR excitability or RI in females. The potential for SES to produce changes in antagonist excitability was sex-related, which may have important rehabilitation considerations.