Eccentric Muscle Training, Stimulation, and Biomarkers in SCI

The investigators are studying a new rehabilitation treatment for individuals trying to recover walking after spinal cord injury (SCI). The investigators will test conditions in the blood and spinal fluid to determine the best time to start this new training program. This will include checking for certain features called biomarkers by testing participants' spinal fluid and blood and compare these features to individuals without SCI. These features will help investigators determine when to start the new training program, either right away or waiting for 3 months. The new training program uses walking downhill on a slight slope on a treadmill while muscles that are not working normally are stimulated to contract using low levels of electricity. Adding this stimulation will allow people to practice walking and other skills even though full muscle control has not recovered. This new program will be in addition to any other rehabilitation therapy and will not replace standard rehabilitation. The hope is to see if downhill training with muscle stimulation, when delivered at the most ideal time, will improve trunk and leg movement, walking, and overall function. This recovery of movement and function will be compared to people with SCI receiving standard rehabilitation alone. Certain regions of the brain and spinal cord will also be studied using MRI scans to determine if these are affected by the training and compare to individuals without SCI. The total length of the study for SCI participants will be up to 16 weeks if in the standard of care group and up to 33 weeks if in the trained group. Healthy control participants will be involved for 1-2 visits.