Activation deficit correlates with weakness in chronic stroke: Evidence from evoked and voluntary EMG recordings

Abstract

Objective To use evoked (M-wave) and voluntary (during maximal voluntary contraction (MVC)) EMG recordings to estimate the voluntary activation level in chronic stroke. Methods Nine chronic hemiparetic stroke subjects participated in the experiment. M-wave (EMGM-wave) and MVC (EMGMVC) EMG values of the biceps brachii muscles were recorded. Results Peak torque was significantly smaller on the impaired than non-impaired side. EMGM-wave was also significantly smaller on the impaired than non-impaired side. However, the normalized EMGM-wave/TorqueMVC ratio was not significantly different between two sides. In contrast, both absolute EMGMVC and normalized EMGMVC/TorqueMVC were smaller on the impaired than non-impaired side. The voluntary activation level, EMGMVC/M-wave, was also smaller on the impaired than non-impaired side. The voluntary activation level on the impaired side was highly correlated with weakness (R=0.72), but very low (R=0.32) on the non-impaired side. Conclusion Collectively, our findings suggest that both peripheral and central factors contribute to post-stroke weakness, but activation deficit correlates most closely with weakness as estimated from maximum voluntary torque generation.

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