Diverse motor unit alterations underlying muscle weakness: a case study with chronic stroke patients

This study assessed both motor unit population and firing behavior alterations of the first dorsal interosseous (FDI) muscle in six individuals with stroke, toward better understanding muscle weakness after stroke. Motor unit population was estimated using the F wave based motor unit number estimation (MUNE) technique, while motor unit firing behavior was extracted through high-density surface electromyography (EMG) decomposition. Inspection of individual subject data disclosed different patterns of motor unit changes associated with post-stroke weakness. Four subjects concurrently demonstrated loss of functioning motor units and reduced motor unit firing rates in the paretic muscle compared with the contralateral muscle. For the remaining two subjects, one showed remarkable decrease of motor unit number but similar firing rates in the paretic muscle, while on the contrary the other subject demonstrated remarkable decrease in motor unit firing rates but similar motor unit number counts in the paretic muscle, compared with the contralateral muscle. Findings from this study add insights in understanding complexity of post-stroke muscle weakness and help development of appropriate interventions in stroke rehabilitation targeting specific motor unit impairment. • Alterations in motor unit population and firing behavior were assessed post-stroke. • Different motor unit alteration patterns were associated with post-stroke weakness. • Appropriate intervention should target specific motor unit impairment.