High-Density Surface EMG Assessment of Motor Unit Alterations After Stroke

In the NeuroMyo Engineering for Rehabilitation Laboratory at the TIRR Memorial Hermann Research Center, investigators led by Ping Zhou, PhD, are studying the use of noninvasive high-density surface electromyography (EMG) to enhance their understanding of muscle weakness following stroke. The researchers expect their findings to contribute to the development of rehabilitation strategies – including therapies and devices – that will help restore normal muscle function in stroke patients.

"This novel form of noninvasive EMG is helping us understand the neural mechanisms that contribute to the impairment of voluntary movement in patients with neurological injury,” says Dr. Zhou, who is director of the NeuroMyo Engineering for Rehabilitation Laboratory and an associate professor in the department of Physical Medicine and Rehabilitation at McGovern Medical School at UTHealth. “By using the most recent advances in high-density EMG recording and processing techniques, we hope understand the complicated origins of muscle weakness after a hemispheric stroke, and also to explore the origins of associated muscle fiber loss, contracture and other intrinsic property changes of the spastic-paretic muscles.”

In an article published in IEEE Transactions on Biomedical Engineering in December 2014,¹ Dr. Zhou and his colleagues presented their preliminary findings from a pilot study involving 12 stroke patients. The R01 study is funded by the National Institutes of Health from August 2014 to July 2018, and will ultimately enroll 90 survivors of stroke. A second article in the same publication, published in April 2015, reported on motor unit firing behavior in nine additional patients, for the first time providing direct evidence from surface EMG of motor unit control property alterations.²

“Our primary reliance on surface EMG offers practical benefits for patients because it is noninvasive and, unlike needle EMG, induces minimal discomfort and can be performed quickly,” Dr. Zhou says. “It allows us to estimate the number of motor units remaining in a muscle following stroke, and also to examine structural and functional changes in the remaining motor units. Preliminary results using the technology provide clear evidence of motor unit firing behavior alterations after stroke, which can be an important contributing factor to hemiparetic muscle weakness. Quantifying the factors that cause muscle weakness after stroke will ultimately help physicians and therapists improve therapeutic interventions.”

The Investigators also aim to assess whether there is active motoneuron degeneration or signs of impending motoneuron death by examining patterns of spontaneous discharge in resting paretic muscles of stroke survivors. In addition, they will examine muscle fiber atrophy and denervation and reinnervation changes post stroke using a range of novel quantitative motor unit action potential analyses.

“Neuromuscular change after stroke is complex,” Dr. Zhou says. “What works to quantify weakness after stroke in one patient may not work with others. Our preliminary studies show that EMG is a powerful and effective technique. Several other pilot studies are planned to gather as much useful information as possible for an improved understanding of motor unit properties in stroke.”

Ping Zhou, PhD, is an associate editor for the Journal of Neuroengineering and Rehabilitation and a reviewer for more than 40 journals. He has published more than 70 articles in peer-reviewed journals and has served as principal investigator on grants from the National Institutes of Health, the U.S. Department of Education and other organizations. His research has been recognized with numerous awards, including the Best Clinical Research Award at the XVIII Congress of the International Society of Kinesiology and Electrophysiology held in Denmark in 2010. Dr. Zhou has been a senior member of the Institute of Electrical and Electronic Engineers since 2007. His research interests include biomedical signal processing, in particular EMG; motor unit pathophysiology and electrodiagnosis; myoelectric control; and assistive devices for neurorehabilitation.

¹Li X, Liu J, Li S, Wang Y-C, Zhou P. Examination of Hand Muscle Activation and Motor Unit Indices Derived from Surface EMG in Chronic Stroke. IEEE Transactions on Biomedical Engineering. 2014 Dec;61(12):2891-98.

²Li X, Holobar A, Gazzoni M, Merletti R, Rymer WZ, Zhou P. Examination of Post-stroke Alteration in Motor Unit Firing Behavior Using High Density Surface EMG Decomposition. IEEE Transactions on Biomedical Engineering. 2015 May;62(5):1242-52.