The main goal of this pilot study is to find the best ways to use transcutaneous spinal cord stimulation (scTS) to improve hand function in children with spinal cord injuries (SCI). The investigators will start by exploring the best places and strengths for applying scTS on the neck, the added benefits of applying scTS on the lower back (T11-T12), and comparing the effects of using activity based upper extremity training (a control treatment) alone versus combining it with scTS to help children with chronic SCI regain hand function.

After learning about the study and potential risks, parents/legal guardians and their eligible children with SCI will sign consent and assent forms, respectively. For the first two aims of the study, the investigators will recruit and enroll 10 participants. In the first week, participants will undergo clinical assessments from day 1 to day 4 to categorize the severity and level of their injuries and assess their current arm and hand function. On day 5, eligible participants will have experimental assessments to measure hand grip and control, both with and without spinal cord stimulation (scTS) at one or two neck sites optimized to improve hand grip. On day 6, participants will have similar assessments, this time adding stimulation to the trunk area to help with upright sitting and study its impact on hand grip and control.

For the third aim, 4 participants who showed improved hand grip and control with stimulation in aims 1 and 2 will be selected on a first-come, first-served basis. They will undergo 20 sessions of activity-based upper extremity training, followed by 20 more sessions with the optimal stimulation sites identified from aims 1 and 2. After completing the training, participants will be asked to follow up and repeat experimental and clinical assessments to determine how long the improvements last.

Inclusion Criteria:

For aim 1 and 2, 10 participants with SCI:

1. age 7-12 years;
2. chronic (>6 months), acquired upper motor neuron SCI;
3. cervical SCI at or above C8 neurological level with motor score of 1-3 for finger flexors
4. Pediatric Neurorecovery scale score of ≥2B and ≤ 4C for impaired grip

For Aim 3, 4 participants with SCI who:

1. complete aim 1 and 2;
2. consent/assent for aim 3
3. demonstrate a minimum of 10% increase in HG force with scTS (aim1-2)
4. confirmed volitional activation in hand muscles during hang grip assessment without scTS

Exclusion Criteria:

For all 3 aims will include:

1. Botox use within past 3 months (for upper or lower extremity);
2. current oral baclofen (or pump);
3. musculoskeletal impairment limiting range of motion;
4. unhealed fracture or other medical condition limiting participation in AB-UET;
5. etiology of spina bifida;
6. total ventilator dependence.