Exploring the feasibility of combining transcutaneous electrical spinal cord stimulation and overground robotic exoskeleton for gait rehabilitation in patients with spinal cord injury

Marina Algaba Vidoy^1,2Soraya Pérez Nombela^3,4Álvaro Megía Carpintero^3,4,5Cristina Montero-Pardo⁶Carolina Redondo Galán⁷Ana De Los Reyes-Guzmán^8,9Diego Serrano Muñoz^3,4Julio Gómez-Soriano^3,4Antonio J. del-Ama¹⁰Juan Camilo Moreno^1,11*

• ¹BioRobotics Group, Centre for Automation and Robotics (CAR) CSIC-UPM, Arganda del Rey, Madrid, Spain
• ²E.T.S. Ingenieros de Telecomunicación, Universidad Politécnica de Madrid, Madrid, Spain
• ³Toledo Physiotherapy Research Group (GIFTO). Faculty of Physiotherapy and Nursing. Universidad de Castilla-La Mancha, Toledo, Spain
• ⁴Toledo Physiotherapy Research Group (GIFTO). Instituto de Investigación Sanitaria de Castilla-La Mancha (IDISCAM), Toledo, Spain
• ⁵Unit of Neurorehabilitation, Biomechanics and Sensorimotor Function (HNP-SESCAM). Associated Unit of R&D&I to the CSIC, Madrid, Spain
• ⁶Neural Engineering Lab, Cajal Institute (CSIC), Madrid, Spain
• ⁷Biomechanical and Technical Aids Unit, National Hospital for Paraplegics, Toledo, Spain
• ⁸Unit of Neurorehabiliation, Biomechanics and Sensorimotor Function (HNP-SESCAM). Associated Unit of R&D&I to the CSIC, Madrid, Spain
• ⁹Biomechanics and Technical Aids Unit, National Hospital for Paraplegics, Toledo, Spain
• ¹⁰Bioengineering Systems and Technologies Research Group (BeST). Rey Juan Carlos University, Móstoles, Madrid, Spain
• ¹¹Unit of Neurorehabilitation, Biomechanics and Sensorimotor Function (HNP-SESCAM), Associated Unit of R&D&I to the CSIC, Madrid, Spain

Introduction: Spinal cord injury (SCI) is a traumatic condition that causes severe sensory and mobility impairments, including gait dysfunction. Combining exoskeleton-assisted gait training (EGT) with transcutaneous spinal cord stimulation (tSCS) may enhance motor recovery in SCI patients. This study explores the feasibility and immediate effects of combining these two neurorehabilitation strategies, without pursuing clinical benefits. Methods: We present a 3-of-1 case series of incomplete SCI patients (AIS C-D) who participated in two walking sessions: tSCS-assisted gait, then combined with the robotic exoskeleton Exo-H3. Each session included three phases of 3 minutes each: before, during and after tSCS. Surface electromyography (EMG) was recorded to analyze muscle activation and the level of effort generated using root mean square (RMS) and integrated EMG (iEMG). Functional outcomes were assessed with the Timed Up and Go (TUG) test, Visual Analog Scale (VAS) for discomfort and fatigue and distance covered. Results: Immediate effects varied among patients. Participant 1 showed increased muscle activation and effort without the Exo-H3 after tSCS, particularly in the Rectus Femoris (ReFe) muscle, along with improved TUG performance and walking speed. However, during the combined tSCS-Exo session, muscle activation did not decrease, but effort was significantly reduced, masking the tSCS effects seen without the exoskeleton. Walking speed and TUG also worsened. Participant 2 exhibited reduced RMS and iEMG in both conditions, especially in the ReFe, with no notable improvement in TUG score or distance covered. In contrast, Participant 3 appeared to benefit from both sessions, showing increased activation and exertion in the tibialis anterior and upper leg (biceps femoris and ReFe). TUG did not improve in the non-exoskeleton session after tSCS but showed significant improvement when combined with Exo-H3. None of the participants reported abnormal discomfort or fatigue beyond the levels typically associated with exoskeleton use. Discussion: The combined use of tSCS and EGT appears technically feasible and safe, whereas the responses were highly individualized. Knee extensors muscles showed the greatest responsiveness to tSCS during gait. Synergistic effects may depend on the user's proficiency with the exoskeleton. Further analysis and larger studies are needed to better identify SCI who may benefit the most.