Surface EMG signals were collected using a 64-channel 2-dimensional electrode array from the paretic and contralateral first dorsal interosseous (FDI) muscles of nine hemiparetic stroke subjects at different isometric discrete contraction

Recent advances in high density surface electromyogram (EMG) decomposition have made it a feasible task to discriminate single motor unit activity from surface EMG interference patterns, thus providing a noninvasive approach for examination of motor unit control properties. In the current study we applied high density surface EMG recording and decomposition techniques to assess motor unit firing behavior alterations post-stroke. Surface EMG signals were collected using a 64-channel 2-dimensional electrode array from the paretic and contralateral first dorsal interosseous (FDI) muscles of nine hemiparetic stroke subjects at different isometric discrete contraction levels between 2 N to 10 N with a 2 N increment step. Motor unit firing rates were extracted through decomposition of the high density surface EMG signals, and compared between paretic and contralateral muscles. Across the nine tested subjects, paretic FDI muscles showed decreased motor unit firing rates compared with contralateral muscles at different contraction levels. Regression analysis indicated a linear relation between the mean motor unit firing rate and the muscle contraction level for both paretic and contralateral muscles (p < 0.001), with the former demonstrating a lower increment rate (0.32 pulses per second (pps)/N) compared with the latter (0.68 pps/N). The coefficient of variation (CoV, averaged over the contraction levels) of the motor unit firing rates for the paretic muscles (0.21 ± 0.012) was significantly higher than for the Manuscript received xxxx xx, xxxx. This study was supported in part by the National Institutes of Health of the U.S. Department of Health and Human Services under Grant R24HD050821 and Grant R01NS080839, and in part by the National Natural Science Foundation of China under Grant 81271658. A. Holobar was supported by Slovenian Research Agency (programme P2-0041 (B) Computer Systems, Methodologies and Intelligent Services). M. Gazzoni and R. Merletti were supported by Compagnia di San Paolo and Fondazione CRT in Torino, Italy. Asterisk indicates corresponding author. X. Li is with the Department of Physical Medicine and Rehabilitation, University of Texas Health Science Center (UTHealth), and TIRR Memorial Hermann Research Center, Houston, Texas, 77030, USA (email: [email protected]). A. Holobar is with the Faculty of Electrical Engineering and Computer Science, the University of Maribor, 2000 Maribor, Slovenia (e-mail: [email protected]). M. Gazzoni and R. Merletti are with the Laboratory of Engineering of Neuromuscular System and Motor Rehabilitation (LiSIN), Department of Electronics, Politecnico di Torino, Torino, Italy (emails: [email protected]; [email protected]). W. Z. Rymer is with the Sensory Motor Performance Program, Rehabilitation Institute of Chicago, and with Departments of Physical Medicine and Rehabilitation, Physiology, and Biomedical Engineering, Northwestern University, Chicago, Illinois, 60611, USA (email: [email protected]). P. Zhou is with the Department of Physical Medicine and Rehabilitation, UTHealth, and TIRR Memorial Hermann Research Center, Houston, Texas, 77030, USA, and also with the Biomedical Engineering Program of the University of Science and Technology of China, Hefei, China (email: [email protected]; [email protected]; [email protected]). Copyright (c) 2013 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending an email to [email protected]. contralateral muscles (0.17 ± 0.014) (p < 0.05). This study provides direct evidence of motor unit firing behavior alterations post-stroke using surface EMG, which can be an important factor contributing to hemiparetic muscle weakness.