Effect of repetitive afferent electrical stimulation of the lower limb on corticomotor excitability and implications for rehabilitation.

Despite the extensive work published on the effects of electrical stimulation on corticomotor excitability, very few studies have focused on lower limb muscles. The aim of the present study was to determine the effect of high-frequency afferent electrical stimulation of the anterior thigh area on the corticomotor excitability of lower limb muscles. Twenty-two healthy subjects (mean age 23 ± 7 years) participated in the study. Electrical stimulation was applied for 60 minutes on the anterior thigh area (frequency 100 Hz, pulse duration 60 μs, intensity below motor threshold). Motor-evoked potentials (MEP) of the rectus femoris (RF) and biceps femoris (BF) muscles were recorded before, and after, the electrical stimulation paradigm with a Magstim 200 stimulator. Analyses revealed a significant modulation in MEP amplitude for the RF but not for the BF muscle. Specifically, there was a significant reduction in MEP amplitude for the RF muscle immediately, 15 minutes and 30 minutes after the end of electrical stimulation when compared with baseline. Our results indicate that a 60-minute high-frequency electrical stimulation protocol applied on the anterior thigh area decreases the corticomotor excitability of the RF muscle. Although the exact duration remains unknown, the pattern of modulation observed indicates that the inhibitory effect lasts for more than 30 minutes after the end of stimulation, giving enough time for clinicians to work on the desired motor task during rehabilitation.