Li, X.; Suresh, A.; Zhou, P.; Rymer, W.
Volume: PP, Issue: 99
People surviving from a stroke are usually unable to maintain their strength in the affected limb. The origins of muscle weakness after a stroke are still unclear. In this study, we examined electrical activity, i.e. electromyogram (EMG) signals, from 14 stroke subjects to help understand motor unit alterations underlying their muscle weakness. Motor unit contains an alpha motor neuron, its axon and all the muscle fibers it innervates. It is the basic functional component that our brain uses to manage force generation.
For each stroke subject, EMG signals were recorded using a surface electrode from affected and contralateral hand muscles, respectively, when the subject generated a series of isometric contraction. We developed a method to automatically detect the peaks of surface EMG and performed a quantitative comparison of the peak amplitude distribution at the same force levels between affected and contralateral muscles.
We found a striking redistribution of the surface EMG peak amplitude in affected muscles compared with contralateral muscles. In 9 stroke subjects we observed a broader peak amplitude distribution with a shift towards larger amplitude for the affected muscles when compared with the contralateral muscles, most likely induced by motor neuron degeneration, or impairments in motor unit control properties. The remaining 5 subjects displayed a narrower peak amplitude distribution with a shift towards smaller amplitudes for the affected muscles, primarily due to muscle fiber atrophy, increased activation of low-threshold motor units, or a selective loss of large motor units.
The developed identification of motor unit determinants for muscle weakness after a stroke is important for development of appropriate therapy or rehabilitation strategies. Moreover, our method was based on regular surface EMG recording, which is more convenient compared with traditional methods such as those relying on needle EMG recording and electrical stimulation.