The purpose of this research is to test the effectiveness of a new therapy, called Brain-Computer Interface (BCI)-Transcutaneous Spinal Cord Stimulation (TSCS), for improving walking in people with an incomplete spinal cord injury (SCI).

Inclusion Criteria:

1. At least 18 years old and no older than 70 years old at the time of enrollment.
2. Traumatic incomplete spinal cord injury (neurological level at or above T10 spinal cord level; Abbreviated Injury Scale (AIS) C or D impairment grade for group 1, 3 and 4 and AIS B, C or D impairment grade for group 2), who are more than 6 months post-injury.
3. Has detectable motor function in at least 2 muscles per side confirmed by voluntary Electromyography (EMG) or detectable tibialis anterior (TA) muscle motor evoked potentials (MEPs) at the baseline assessment.
4. Able to commit to intensive training and assessment sessions over a maximum total duration of 6 months.
5. Could effectively walk overground for at least 10 meters with some assistance of a therapist and minimal body-weight support, with functional spasticity (by participant's self-report), functional range-of-motion of lower limb joints, and acceptable bone mass to enable body-weight support, confirmed by Dual-energy X-ray absorptiometry (DXA) scan.

Exclusion Criteria:

1. Has traumatic brain injury, stroke, multiple sclerosis, or other neuromuscular disorders that could affect neuromotor function and walking.
2. Has severe spasticity that could prevent stepping and walking function determined by the investigator.
3. Has major executive dysfunction, dementia, depression, neurocognitive impairments, or other major medical co-morbidities.
4. Has other contra-indications for transcranial magnetic stimulation (TMS) or Transcutaneous Spinal Cord Stimulation (TSCS).
5. Has a history of recent seizures or poorly managed autonomic dysreflexia that could be triggered by TMS or TSCS.
6. Has a history of prior intracranial surgery or known lesions that would limit TMS assessments and Brain-Computer Interface (BCI) recordings.
7. Individuals with metal implants in their head and other implantable devices in the body that could be affected by TMS or TSCS.
8. Has peripheral neuropathy (diabetic polyneuropathy, entrapment neuropathy, etc.).
9. Has urinary tract infection, unhealed fracture, contracture, and pressure sore (Braden Scale).
10. Has breakdown in skin area that will come into contact with electrodes.
11. Individuals who require therapy or other care that could interfere with participation in the study.
12. Individuals on investigational drugs or any other intervention known to have a potential impact on neuromotor function.
13. Individuals with substance disorders, including alcoholism and drug abuse.
14. Individuals who are pregnant, breastfeeding, or the desire to become pregnant during the study.
15. In the opinion of the investigators, the study is not safe or appropriate for the participant.