Investigate the changes of motor unit recruitment pattern after stroke using surface EMG

Stroke is a major contributor of functional disability in adults. Muscle weakness and slowness are the impairments that affect motor control primarily. Previous studies show rate-coding pattern of motor units (MUs) altered after stroke, which may cause slowness and weakness of muscle. However, the recruitment pattern of MU hasn’t been well studied due to instrumental limitations. We previously developed a new method to investigate MU recruitment using surface EMG and turns-amplitude analysis (TAA). In this study, we used TAA to investigate changes in MU recruitment in individuals with stroke. Six stroke subjects and 6 control subjects (1 female) were recruited. The sEMG were collected from tibialis anterior muscle during steady-hold and rapid isometric ankle dorsiflexion. sEMG signals were analyzed offline using TAA. The maximal recruitment threshold (MaxRT) between groups was compared to determine changes in MU recruitment pattern. Results showed that MaxRT for tibialis anterior during steady-hold contractions in stroke and control subjects were at 40% and 50% MVC, respectively. These MaxRTs were significantly lower compared to young subjects (70% MVC). During rapid contractions, the MaxRT of both groups decreased to less than 20% MVC, which is also relatively lower than young subjects. To conclude, the MU recruitment pattern is altered after stroke.