Estimulación Espinal con Entrenamiento de la Marcha para Mejorar la Recuperación Motora de las Extremidades Inferiores en la Lesión de la Médula Espinal (CIMELocomotion)

Participants with spinal cord injury (SCI) classified as AIS A-D will receive sham transcutaneous spinal cord stimulation (tSCS) combined with robotic-assisted, treadmill, or overground gait training. The sham stimulation will reproduce the sensory sensation of active tSCS without eliciting effective spinal activation, ensuring participant blinding.

The type of gait training will be determined based on the severity of the injury and the participant's ability to generate voluntary or assisted locomotor movements. Each participant will complete 20 training sessions, delivered four times per week over approximately five weeks.

The gait training sessions will be individualized and task-specific, emphasizing repetitive stepping practice to promote locomotor learning and engage spinal and supraspinal networks involved in walking.

The training will be conducted using either the G-EO System (ReHa Technology) or a treadmill/overground with participants secured by a bodyweight support system (Biodex) to reduce bodyweight and prevent falls. Participants will complete 20 training sessions over a periode of 5 to 6 weeks. Each session will last up to 40 minutes, with rest periods if needed in case of performance decline.

Each session will begin with a warm-up phase (5 minutes) to evaluate the condition of the participant and to ensure safety. On the G-EO System, this consists of using Passive Mode, which fully compensates for the participant's motor deficits. On the treadmill, the warm-up involves full hand assistance to guide gait.

In sham-group, participants will combined gait training with a sham stimulation sets at sensory threshold, providing the perception of stimulation without activating locomotor spinal circuits.

Participants with spinal cord injury (SCI) classified as AIS A-D will receive active transcutaneous spinal cord stimulation (tSCS) combined with robotic-assisted, treadmill, or overground gait training. The stimulation intensity will be individually adjusted to facilitate voluntary movement generation and enhance activation of spinal circuits involved in locomotion.

The type of gait training will be determined based on the severity of the injury and the participant's ability to generate locomotor movements. Each participant will complete 20 training sessions, delivered four times per week over approximately five weeks.

The gait training sessions will be individualized and task-specific, emphasizing repetitive stepping practice to promote locomotor learning and engage spinal and supraspinal networks responsible for walking.

The training will be conducted using either the G-EO System (ReHa Technology) or a treadmill/overground with participants secured by a bodyweight support system (Biodex) to reduce bodyweight and prevent falls. Participants will complete 20 training sessions over a periode of 5 to 6 weeks. Each session will last up to 40 minutes, with rest periods if needed in case of performance decline.

Each session will begin with a warm-up phase (5 minutes) to evaluate the condition of the participant and to ensure safety. On the G-EO System, this consists of using Passive Mode, which fully compensates for the participant's motor deficits. On the treadmill, the warm-up involves full hand assistance to guide gait.

In experimental group, participants will combined gait training with tSCS at T11-L2, sets to individualized parameters determined to facilitate lower limbs movement generation.

Lower Extremity Motor Score (LEMS), derived from the ASIA Impairment Scale, is scored from 0 to 50, with higher scores indicating better motor function.

The transspinal evoked potentials (TEPs) are muscle responses (Soleus, Tibialis Anterior, Vastus Lateralis and Biceps Femoris) recorded by electromyography (EMG) after tSCS.

For each muscle, the resting motor threshold (RMT), the lowest intensity to elicit a motor response, will be measured. Additionally, normalized TEPmax (TEPmax/Mmax ratio) will be calculated to quantify the proportion of the maximal muscle response elicited by tSCS relative to the maximal direct motor response (Mmax). This ratio provides an index of spinal excitability and the effectiveness of stimulation in activating motor circuits.

Transcranial magnetic stimulation (TMS) over the motor cortex will be used to assess corticospinal tract excitability. The latency and amplitude of motor evoked potentials (MEPs), as well as the active and resting motor threshold of the Tibialis Anterior muscle, will be measured.

Muscle strength will be evaluated using a handheld dynamometer (MicroFET), with measurements expressed in kilograms (kg). Higher values indicate greater muscle strength. Nine movements will be tested bilaterally : hip abduction, hip extension, hip flexion, knee extension, knee flexion, ankle dorsiflexion, ankle eversion, ankle inversion and ankle plantarflexion.

Spasticity in the lower limbs will be assessed after the intervention using the Modified Ashworth Scale by a trained physical therapist. The examiner will passively move the limb through its full range of motion at a constant speed and rate the resistance encountered. The test is scored on a 6-point ordinal scale ranging from 0 (no increase in muscle tone) to 4 (affected part rigid in flexion or extension), with higher scores indicating greater levels of spasticity.

Sensory function will be assessed using the sensory component of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI). Light touch and pinprick sensations will be tested bilaterally across key dermatomes and scored on an ordinal scale. The total sensory score ranges from 0 to 56 (each for light touch and pinprick), with higher scores indicating better preserved sensory function.

Light touch and protective sensation will be assessed using Semmes-Weinstein monofilaments. Monofilaments of varying thickness will be applied perpendicularly to specific sites on the plantar surface of the foot or other areas of interest, until the filament bends. Participants will indicate whether they can perceive the touch. Each site will be tested multiple times to ensure reliability. The presence of sensation at thinner filaments indicates better sensory function, whereas inability to detect thicker filaments suggests sensory loss.

Balance will be assessed using the Modified Functional Reach Test (MFRT). Participants will be asked to reach forward as far as possible without taking a step or losing their balance, while sitting. The distance (in centimeters) reached is measured from the starting position of the fingertips to the maximal forward reach. Each trial will be performed three times and the average distance will be recorded. Higher reach distances indicate better dynamic balance and postural stability.

Tibial nerve stimulation will be applied and responses will be recorded by electroencephalogram (EEG) prior to and following the intervention. Evaluation of the latency and amplitude of somatosensory evoked potential (SSEP) will be realized.

The investigators aim to evaluate if combining transcutaneous spinal cord stimulation with task-specific gait training is feasible early after the lesion is safe and feasible.

For safety, the investigators are going to monitored adverse events and all participants will fill a qualitative questionnaire. This questionnaire will notably evaluate how the participant felt safe during the whole study (assessments and training sessions). Feasibility is assessed through recruitment and retention rates, % completion of expected number of sessions.