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
