The present study investigated location specificity of middle latency (~ 80−110 ms, MLR) cutaneous reflexes in the soleus (Sol) and tibialis anterior (TA) following nonnoxious electrical stimulation (2.0 times perceptual threshold, 5 pulses at 333 Hz) on different locations of the plantar foot. Subjects were 14 neurologically intact volunteers (13 male, 1 female) who gave informed consent. Electrical stimulation was given to the fore-medial (f-M), fore-lateral (f-L) and heel (HL) regions of the plantar surface of the right foot while the subjects performed isometric dorsiflexion or plantarflexion while sitting and standing upright. In Sol, an excitatory effect was observed following HL simulation, but it turned into an inhibitory one following f-M or f-L stimulation. TA showed a reciprocal pattern in contrast to Sol. In some cases, the slope of the regression line between the magnitude of MLR and background electromyographic activity was significantly decreased while standing compared to that while sitting. Our findings suggest that reflex effects from cutaneous nerves in the plantar foot on the motoneurons innervating the lower leg muscles is organized in a highly topographically specialized manner in humans. These reflex organizations may suit the behavioral demands of a standing posture.

DESCENTE SPORTS SCIENCE Vol.27/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE