Neuromodulation to Reduce Muscle Stiffness Following Spinal Cord Injury

The primary questions to be addressed are whether the intervention reduces muscle stiffness and spasms and alters spinal reflexes: * Using a 100-Hz (a measure of frequency) transcutaneous spinal stimulation is better than using a 50-Hz. * Transcutaneous spinal stimulation at 50 Hz differs from a single dose of baclofen. * Transcutaneous spinal stimulation at 50 Hz differs from a single dose of tizanidine. * Combining the 50 Hz stimulation with either baclofen or tizanidine decreases spasticity more than just taking the medicine alone. Participants will visit the Methodist Rehabilitation Center in Jackson, Mississippi, six times over a period of 3 to 5 weeks. During the first visit, the overall health and motor and sensory functions will be assessed following a spinal cord injury. For the next five visits, participants will take a study medication (tizanidine, baclofen, or a placebo). After an hour, they will receive a continuous 30-minute transcutaneous spinal stimulation at either 50 Hz, 100 Hz, or sham. The spinal reflexes and clinical assessments will be evaluated before, during, and after each intervention.