Training of spinal interneuronal networks may offer a means for re-establishing movements such as locomotion in patients with spinal injury. Sensory feedback in the pattern which results from the leg movement is hypothesized to be the critical component for training spinal networks. This protocol will address the basic assumption underlying such training: can a specific pattern of sensory input modify the strength of a spinal cord circuit? We will test whether peripheral nerve stimulation can modify the strength of the spinal reflex mediating reciprocal inhibition between ankle flexor and extensor muscles in normal subjects, comparing patterned and unpatterned stimulation.