Abstract
Whether stroke-induced paretic muscle changes vary across different distal and proximal muscles remains unclear. The objective of this study was to compare paretic muscle changes between a relatively proximal muscle (the biceps brachii muscle) and two distal muscles (the first dorsal interosseous muscle and the abductor pollicis brevis muscle) following hemisphere stroke using clustering index (CI) analysis of surface electromyograms (EMGs). For each muscle, surface EMG signals were recorded from the paretic and contralateral sides of 12 stroke subjects versus the dominant side of eight control subjects during isometric muscle contractions to measure the consequence of graded levels of contraction (from a mild level to the maximal voluntary contraction). Across all examined muscles, it was found that partial paretic muscles had abnormally higher or lower CI values than those of the healthy control muscles, which exhibited a significantly larger variance in the CI via a series of homogeneity of variance tests (p < 0.05). This finding indicated that both neurogenic and myopathic changes were likely to take place in paretic muscles. When examining two distal muscles of individual stroke subjects, relatively consistent CI abnormalities (toward neuropathy or myopathy) were observed. By contrast, consistency in CI abnormalities were not found when comparing proximal and distal muscles, indicating differences in motor unit alternation between the proximal and distal muscles on the paretic sides of stroke survivors. Furthermore, CI abnormalities were also observed for all three muscles on the contralateral side. Our findings help elucidate the pathological mechanisms underlying stroke sequels, which might prove useful in developing improved stroke rehabilitation protocols.
Highlights
Muscle weakness is the most common clinical symptom of many neuromuscular diseases and it greatly impacts the day-to-day quality of life for patients and their caregivers [1, 2]
In the clustering index (CI)-area plots, we observed that all the control data were distributed over the normal area, while some epochs from the paretic and contralateral muscles were scattered outside the normal range
Of all the control subjects, the Z-scores derived from the biceps brachii (BB) muscle (0.00 ± 1.00, mean ± SD), the first dorsal interosseous (FDI) muscle (0.00 ± 1.00), and the abductor pollicis brevis (APB) muscle (−0.13 ± 0.99) scored within the predefined normal range from −2.5 to +2.5
Summary
Muscle weakness is the most common clinical symptom of many neuromuscular diseases (such as stroke and spinal cord injury) and it greatly impacts the day-to-day quality of life for patients and their caregivers [1, 2]. Paretic Muscle Changes following Stroke coordination [3] This contributes to impaired motor control [4]. Surface EMG studies in stroke patients have been previously performed through an EMG-force relation [18,19,20], peak amplitude distribution [21], and power spectral analysis [22]. These studies have reported mixed observations, suggesting that there are a variety of complex neural and muscular changes collectively contributing to muscle weakness following a stroke [23,24,25]
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