The goal of this study is to identify the effect of different types of noninvasive spinal stimulation on spasticity (involuntary muscle activity), muscle strength, and pain in people with spinal cord injury. The spinal stimulation consists of electrical stimulation applied through one electrode over the skin of the lower back and two electrodes over the stomach. Testing will include participating in measurements before the intervention, during intervention, and immediately after the intervention. This study requires participants to come into Shepherd Center 4 consecutive days a week for 2-3 hours per day across 2-3 weeks.

Transcutaneous spinal stimulation (TSS) is a noninvasive electrical stimulation that is applied over the skin of the low back and stomach. In prior research studies, TSS has reduced spasticity without the negative side effects of drug therapies. Although research in TSS is growing, the best dosage of TSS remains unknown. The investigators want to further advance the effects of TSS by comparing three different frequencies. Frequency is the number of electrical pulses that are delivered over a period of time. Frequency can affect the activation of nerves and therefore affect the outcome of TSS. Participation in this study includes testing of the participants' spasticity, strength, and pain before and after 30 minutes of TSS.

Inclusion Criteria:

• Participants must agree to allow use of health information.
• Participants should be 16 years old or older.
• Participants must have had a spinal cord injury (SCI) of any severity (AIS A, B, C, or D) that happened at least 3 months ago.
• Objectively measurable spasticity in your legs.
• Participants must inform the investigators if there is a change in medications during the study.
• Participants must be able to follow instructions.
• Participants must be able to communicate if pain or discomfort is experienced.

Exclusion Criteria:

• People with spinal issues that are getting worse, such as degenerative or progressive vascular disorders.
• People neurological problems other than SCI.
• People with an injury level is below T12.
• People with un-treated or uncontrolled heart problems that the lead investigator believes could be affected by stimulation or affected by an increase in blood pressure.
• People with bone or joint problems that would make it hard to follow the study plan.
• Women who are pregnant or actively trying to become pregnant.
• People with implanted stimulators (like a baclofen pump, spinal stimulator, heart defibrillator, or diaphragmatic pacemaker)
• People with infection.
• People with skin that is broken or wounds in the area of the body where stimulation is applied.
• People who have or had certain types of cancer in the area of the body where stimulation will be applied.
• People who have had botulinum toxin or numbing shots in the test leg or spine in the last 6 months
• People who have had permanent spasticity treatment in the test leg or spine (like a certain type of surgery).
• Other health issues that the lead investigator things could make it unsafe for you to join the study.