EMG activity and knee joint torque evoked by microstimulation of the cat L6 spinal cord

The knee extensor and flexor EMG activity evoked by microstimulation of the cat L6 spinal cord were recorded while simultaneously monitoring the knee joint extension and flexion torques. Single fine-tipped (200 to 400 μm² surface area) activated iridium microelectrode was implanted in the left side of the L6 spinal cord. Large extension torque was produced by microstimulation in the ventral horn and small flexion torque was produced by microstimulation in the dorsal horn. The extensor EMG was much larger than the flexor EMG when large extension torque was produced. The flexor EMG was just slightly larger than the extensor EMG and both were small when small flexion torque was produced. When extension torque was generated, the extensor EMG increased rapidly with increasing stimulus intensity while the flexor EMG remained at almost the same level. These results showed that the L6 spinal cord of the cat is more effective in generating extension torque than flexion torque and that hindlimb flexor and extensor EMG is correlated with torque. Microstimulation of the spinal cord is a potential method to restore the low limb function for patients with spinal cord injuries