Transcutaneous (non-invasive) spinal cord stimulation (tSCS) has been shown to facilitate volitional motor activity in patients with spinal cord injury. tSCS is known to activate the same neural structures as invasive SCS, meaning it may have the potential for functional restoration without an expensive surgical implant. Functional electrical stimulation (FES) is also used in therapy for patients with spinal cord injury to locally activate paralyzed or weakened muscles. There is evidence that combining FES and tSCS may elicit greater muscle activation than either modality alone.

The objective of this study is to quantify the torque at the ankle joint generated by tSCS, by FES, and by tSCS + FES. Additionally, ultrasound images will be collected during stimulation to provide a metric of muscle activity. The correlation between ultrasound and torque will be assessed to determine if ultrasound is a useful modality for quantifying tSCS-elicited muscle activity.

Inclusion Criteria:

• Between 18 and 60 years of age
• Weight less than 220 lb
• Healthy and able to walk at preferred speed without an assistive device
• Able to tolerate functional electrical stimulation and tSCS.

Exclusion Criteria:

• Active infection
• history of cancer,
• broken skin, sores, or areas of acute eczema near the electrode sites
• metal implants, such as staples or pins, near the electrode sites
• any neurological disorders
• difficulty walking or an orthopedic condition that would impede walking normally without assistance
• absent sensation in the lower extremities or trunk (torso),
• allergies to adhesive skin tapes and/or ultrasound gels,
• heart conditions
• an implanted electronic device such as a pacemaker
• current pregnancy
• having no physiological response to FES and/or tSCS.

IPD will not be shared outside of this research group. However, selected data may be published in academic journals, conference papers, or other publications. This data will be de-identified, and will not include the full set of data.