Using HD-EMG to Assess Motor Units in Vastus Lateralis With the Lokomat: A Pilot Study With Young, Elderly and Individuals Post-Stroke

High-Density Electromyography (HD-EMG) shows strong potential in research, but its translation into clinical rehabilitation remains limited. This pilot study explores the feasibility of integrating a portable HD-EMG system into a standardized rehabilitation test using the Lokomat, a robotic gait trainer widely employed in neurorehabilitation. By decomposing EMG signals and analyzing Motor Unit (MU) properties, this study aims to assess neuromuscular differences related to age and post-stroke conditions. Three groups (healthy young, healthy elderly, and chronic stroke survivors) performed isometric sub-maximal knee extensions at 30%, 50%, and 70% of their maximum force. EMG signals were recorded from the Vastus Lateralis muscle using a 64-channel electrode grid. Conventional EMG parameters (e.g., envelope and median frequency) failed to differentiate among groups. In contrast, MU-level analysis revealed fewer detected MUs and lower discharge rates in elderly participants, along with stroke-related alterations in MU recruitment and muscle relaxation. These findings demonstrate both the feasibility and added diagnostic value of HD-EMG in routine clinical robotic rehabilitation. HD-EMG offers objective, detailed insights into neuromuscular functions and could support the optimization of rehabilitation strategies. Further research is needed to validate its clinical applicability in larger populations and promote the adoption of HD-EMG as a standard diagnostic tool.