Clinical Investigation to Validate the Safety and Performance of Integrating Functional Electrical Stimulation Into the ABLE Exoskeleton

Inclusion Criteria: * 18 to 80 years old * Diagnosis of acquired brain injury, spinal cord injury (neurological level between C5 and L2, AIS B to AIS D), or multiple sclerosis * Currently undergoing physiotherapy treatment, either as an inpatient or outpatient at the investigating center * Ability to provide informed consent Exclusion Criteria: * Significant osteoporosis that may increase the risk of fracture * Unresolved fractures in the pelvis or limbs, or a history of fragility fractures in the lower limbs within the past 2 years * Spinal instability (or use of spinal orthoses, unless medically approved) * Deterioration \>3 points of the total in the motor score of the International Standards for the Neurological Classification of Spinal Cord Injury (ISNCSCI) in the last 4 weeks. Loss of sensation and/or motor activity above the level of injury detected that has not been evaluated by a doctor. * Severe spasticity: Level 4 on the Modified Ashworth Scale * Orthostatic hypotension: Inability to tolerate at least 10 minutes in an upright position * Uncontrolled autonomic dysreflexia * Medical instability * Unstable cardiovascular condition, hemodynamic instability, untreated hypertension (SBP \> 140 mmHg, DBP \> 90 mmHg), deep vein thrombosis (DVT), or uncontrolled autonomic dysreflexia * Severe comorbidities, including any condition deemed inappropriate by the investigator for using the ABLE Exoskeleton or for completing the study * Pressure ulcers Grade I or higher (as defined by the European Pressure Ulcer Advisory Panel - EPUAP) in areas that will be in contact with the device * Anthropometric measurements incompatible with the ABLE Exoskeleton, specifically height outside the 1.5-1.9 m range or weight exceeding 100 kg * Anatomical constraints (such as leg length differences, users unable to position themselves inside the device) that are incompatible with the device * Range of motion restrictions preventing normal gait or sit-to-stand transitions, including: Ankle: ability to achieve at least neutral (0°) position; Knee: ability to extend to at least -10°; Hip: bilateral hip flexion of at least 100° and extension of at least 0° * Heterotopic ossification * Pregnant or breastfeeding women * Cognitive impairment that results in the inability to follow simple instructions, particularly psychological or cognitive problems that do not allow a participant to follow study procedures * Requires assisted ventilation. * Scoliosis \>40-50º Cobb angle. * Presence of pacemakers, defibrillators, or other non-compatible electronic implants. * Open wounds, infections, or active irritation at the electrode placement sites. * Severe dermatological conditions in the stimulation area. * Uncontrolled active epilepsy. * Malignant tumors in the area of application. * Severe loss of sensation in the areas where electrodes are to be placed. * Medical conditions where electrical stimulation is contraindicated by physician recommendation. * Inability to communicate pain, discomfort, or adverse reactions during stimulation. * Venous thrombosis, thrombophlebitis, or severe arterial obstruction. * Chronic venous insufficiency with significant varicosities. * Hemophilia. * Ongoing infectious process or fever. * Presence of metallic implants in the flow area between the electrodes