Multisite Transspinal Stimulation for Augmenting Recovery in Spinal Cord Injury

Soleus H-reflex recruitment curve

Investigators will deliver single pulses of 1 ms duration every 5 seconds at increasing intensities to the posterior tibial nerve behind the knee to assemble the soleus H-reflex recruitment curve. At least 50 responses will be recorded. From the recruitment curve, the investigators will estimate changes in the slope and stimulation intensities for reflex threshold.

Soleus H-reflex rate-dependent depression

Soleus H-reflexes following posterior tibial nerve of the right leg behind the knee with a 1-ms pulse randomly at 1, 3, 5, 8, and 10 s inter-pulse intervals will be recorded. At each inter-pulse interval, 15 responses will be recorded. Stimulation will be delivered via a ball shape electrode and responses will be recorded from leg muscles with surface electrodes. The smaller the soleus H-reflex amplitude when evoked every 1 second the larger the spinal inhibition. Recovery of spinal inhibition will be considered when the soleus H-reflex depression at 1 second is statistically significant different before and after the intervention.

Soleus H-reflex phase-dependent modulation during stepping

Each participant will step with the assistance of the Lokomat, and the investigators will record soleus H-reflexes randomly across 16 equal time bins into which each step cycle is divided. The posterior tibial nerve behind the knee will be stimulated at motor threshold. Stimulations will be triggered based on the foot switch signal. Under physiological conditions, the soleus H-reflex during walking largely is facilitated during the stance phase and inhibited during the swing phase. Recovery of spinal locomotor circuits will be based on the amplitude of the soleus H-reflex during the stance and swing phases of gait, and how much is facilitated and inhibited during the stance and swing phases after intervention compared to before intervention for each participant.

Leg transspinal evoked potentials recruitment curves

The investigators will deliver single 1 ms pulses every 5 seconds at increasing intensities with a surface electrode to the low back to assemble the recruitment curves of transspinal evoked potentials recorded from leg muscles with surface electrodes. Participants will lay on their back on a treatment table. From the recruitment curve, the slope and excitation threshold will be established and the intervention will be considered effective when statistical significant differences on their amplitude between before and after values is established.

2-Minute Walk Test

The 2-Minute Walk Test is a physical assessment measuring aerobic capacity and endurance. Participants will walk with or without assistive devices as far as possible for two minutes in a hallway. The total distance walked is recorded, and will be compared to normative values for the participant's age and gender to identify potential limitations or track progress over time. There is currently no single established Minimal Clinically Important Difference for the 2-minute walk test in people with spinal cord injury. However, a recent study showed that in the subacute phase of rehabilitation a 2-Minute Walk Test Minimal Clinically Important Difference is considered when the increase is 31 meters. However, other research studies indicate that the Minimal Clinically Important Difference can vary significantly depending on the specific patient population, rehabilitation stage, disability level, and age.

10-Meter Walk Test

The 10-Meter Walk Test is a performance measure and assesses the walking speed in meters per second over a short duration. Participants will walk 10 meters and the time needed to cover the 10 meters will be recorded. The minimal clinically important difference for the 10-meter walk test in spinal cord injury is approximately 0.13 m/s, a value established for individuals with incomplete SCI within one year of injury. This means that recovery of walking ability will be based on when the speed is improved by 0.13 m/s.

Sexual function

Participants will complete a brief questionnaire on sexual function before and after intervention. The questionnaire is the International Spinal Cord Injury sexual function for male and female. The answers to the questions include: normal, reduced/altered, absent, and unknown/not applicable. Improvement from the intervention will be considered when more "normal" answers replace the "reduced-absent or absent" answers.

Bladder function

The Overactive Bladder Symptom Score (OABSS) questionnaire will be answered by the participants before and after intervention to establish recovery or changes of the bladder function. The maximum score is 15 and the minimum score is 0. The smaller the score the better the outcome.