tSCS in Children and Young People With HCP

Standardised photographs of the back will be obtained at each time point and reviewed by an independent clinician (not part of the study team). A skin reaction is defined as any visible erythema at/near the electrode site and will be recorded on a Yes/No erythema scale (0 = No erythema; 1 = Yes erythema). Results will be reported as the number and proportion of participants with ≥1 skin reaction during the session and by time point.

Heart rate will be measured immediately before and after tSCS using an OMRON M3 device. For each participant, a blinded independent clinician will classify the post-stimulation change relative to Baseline as one of three categories: Increased, Decreased, or No Apparent Change. Study results will be summarised as the number and proportion of participants in each category and described narratively.

Handgrip and pinch strength will be measured with handheld dynamometers (adjustable handle/pads; peak-hold). At each time point, participants perform 3 maximal attempts per measure; the average (mean) is calculated for handgrip and for pinch. Results will be summarised as mean (SD) by timepoint and change from pre to post within each session (Post - Pre). Component means (handgrip and pinch) will be presented descriptively as supportive information.

Hand function will be assessed with the Jebsen-Taylor Hand Function Test (JTHFT). The protocol includes three subtests: (1) picking up small common objects; (2) stacking checkers; (3) lifting large light and large heavy cans (~1 lb). Each subtest is timed to completion. Testing is administered with the less affected hand first, then the more affected hand; the primary outcome is the Total Score for the more affected hand. Results will be summarised as mean (SD) seconds by timepoint and change from pre to post within each session (Post - Pre). (Scores for the less affected hand may be presented descriptively as supportive data.)

Muscle activity will be assessed with surface EMG (Delsys Trigno). Sensors will be placed on the more affected arm over the abductor pollicis brevis, flexor carpi radialis, and extensor carpi radialis longus. Single spinal pulses (1 ms biphasic square-wave) will be delivered every ~5 s using a Digitimer DS8R. For each muscle at each time point, the motor threshold is defined as the lowest stimulation amplitude (mA) that produces an evoked sEMG response ≥50 µV. The participant-level outcome is the mean motor threshold (mA) across the three muscles. Results will be summarised as mean (SD) mA by timepoint and change from Baseline to Post.

Spasticity will be assessed with the Modified Ashworth Scale (MAS), scored 0, 1, 1+, 2, 3, 4 (0 = no increase in tone; 4 = rigid; higher scores indicate worse spasticity). The following muscles on the more affected upper limb will be tested in a fixed order: elbow flexors, wrist flexors, finger flexors. At each timepoint, the primary outcome is the worst (highest) MAS score across the tested muscles. Results will be summarised as median by timepoint and change from Pre to Post within each session (Post - Pre).

Systolic blood pressure will be measured immediately before and after tSCS using an OMRON M3 device. For each participant, a blinded independent clinician will classify the post-stimulation change relative to Baseline as one of three categories: Increased, Decreased, or No Apparent Change. Study results will be summarised as the number and proportion of participants in each category and described narratively.

Diastolic blood pressure will be measured immediately before and after tSCS using an OMRON M3 device. For each participant, a blinded independent clinician will classify the post-stimulation change relative to Baseline as one of three categories: Increased, Decreased, or No Apparent Change. Study results will be summarised as the number and proportion of participants in each category and described narratively.

A project-specific Participant Feedback Questionnaire (PFQ-tSCS), completed by the participant or caregiver, will capture experience with stimulation across predefined domains: comfort, ease of participation, sensations during the session, skin reactions, discomfort/adverse effects, and overall satisfaction. Items use ordered categorical response options (e.g., None/Mild/Moderate/Severe or Strongly disagree → Strongly agree), plus optional free-text. Outcome data will be reported as the number and proportion of participants in each response category for each item; free-text responses will be summarised narratively.

Manual ability will be assessed with the ABILHAND-Kids Questionnaire (21 items; response options: Impossible = 0, Difficult = 1, Easy = 2). The total raw score is the sum across items (higher scores indicate better manual ability). The questionnaire may be completed by the participant or a caregiver proxy per instrument guidance. Results will be summarised as mean (SD) total score by timepoint and change from Pre to Post within each session (Post - Pre)