Studies of Interactions between Limbs in Humans Subjected to Noninvasive Electrical Stimulation of the Spinal Cord

Abstract

The effects of activation of spinal locomotor centers at the cervical and lumbar levels on interlimb synergies were studied in humans. Subjects were placed on a biomechanical trainer in the supine position and carried out voluntary rhythmic leg movements, moving the carriage of the walking device of the trainer, or performing voluntary arm movements moving the levers of the trainer, or making simultaneous leg and arm movements. In the resting state, sequential transcutaneous stimulation of the spinal cord at three levels (cathode positioned between vertebrae C4/C5, T12/L1, or L1/L2) did not induce leg movements in most subjects, though performance of arm movements in combination with stimulation initiated low-amplitude (less than 10°) movements in all the leg joints. Stimulation of the spinal cord and simultaneous arm movements induced facilitation of the performance of voluntary leg movements, which was apparent as an increase in the integral characteristic of muscle electrical activity and an increase in movement amplitude at the hip joint. The results obtained here may be useful for developing a neurorehabilitation method for patients with impaired motor function.