Abstract: By applying evoked and voluntary surface electromyography (EMG) recordings, motor unit changes in paretic hypothenar muscles of stroke survivors were examined. Eleven stroke subjects participated in the study. The maximum M waves and voluntary surface EMG signals at different muscle contraction levels were recorded from the hypothenar muscles bilaterally in each subject. The motor unit number index (MUNIX) values were estimated from the mathematical model describing the relation between the surface EMG signal and the ideal motor unit number count derived from M wave and surface EMG measurements. A decrease in both the maximum M wave amplitudes and the estimated MUNIX values was observed in paretic muscles of the stroke subjects compared with the contralateral muscles. But no significance was found. The ratio between the maximum voluntary EMG to compound muscle action potential was significantly deceased in paretic muscles compared with the contralateral side. These findings, in combination with previous simulation and experiment outcomes, provide evidence of muscle activation deficiency and complex neuromuscular changes post stroke, thus helping understand complicated determinants of paretic muscle weakness for stroke rehabilitation.

Key words: surface electromyography (EMG), stroke, paretic muscle, motor unit (MU)