Abstract
Objective: This study examined the activation difference of muscles innervated by cervical cord 5-6 (C5-C6) and cervical cord 8- thoracic cord 1 (C8-T1) in upper limb flexion synergy after stroke.Methods: Surface electromyography (sEMG) signals were collected during elbow flexion in stroke patients and healthy controls. The study compared normalized activation of two pairs of muscles that could cause similar joint movement but which dominated different spinal cord segments (clavicular part of the pectoralis major, PC vs. Sternocostal part of the pectoralis major, PS; Flexor carpi radialis, FCR vs. Flexor carpi ulnaris, FCU). In each muscle pair, one muscle was innervated by the same spinal cord segment (C5-C6), dominating the elbow flexion and the other was not. The comparison of the activation of the same muscle between patients and healthy controls was undertaken after standardization based on the activation of the biceps brachii in elbow flexion.Results: There was no difference between the PC and PS's normalized activation in healthy controls while the PC's normalized activation was higher than PS in stroke patients during elbow flexion. Similarly, there was no significant difference in normalized activation between FCR and FCU in healthy controls, and the same is true for stroke patients. However, the standardized activation of both FCR and FCU in stroke patients was significantly lower than that in healthy controls.Conclusion: After stroke, the activation of the distal muscles of the upper limb decreased significantly regardless of the difference of spinal cord segments; while the activation of the proximal muscles innervated by the same spinal cord segment (C5-C6) dominating the elbow flexion showed higher activation during flexion synergy. The difference in muscle activation based on spinal cord segments may be the reason for the stereotyped joint movement of upper limb flexion synergy.
Highlights
Hemiplegia is the most common sequela of a stroke and the leading cause of disability [1, 2]
No difference was found between the normalized activation of patients and healthy controls (PC) and PS in healthy controls during elbow flexion (PC: 0.104 ± 0.018 vs. PS: 0.080 ± 0.018; Z = −1.381, P = 0.167)
As for the standardized activation, no significant difference in both PC and PS was found between stroke patients and healthy controls (PC: controls 0.541 ± 0.114 vs. patients 0.779 ± 0.161; Z = −1.851, P = 0.064; PS: controls 0.392 ± 0.079 vs. patients 0.435 ± 0.092; Z = −0.675, P = 0.500; Figure 3C)
Summary
Hemiplegia is the most common sequela of a stroke and the leading cause of disability [1, 2]. A considerable number of patients have chronic hemiplegia in the affected upper limb, characterized by synergistic movements [3]. It is generally believed that decreased descending inhibitory signals or an imbalance between the inhibitory and excitatory descending signals after stroke leads to an increase in the excitability of spinal motor neurons. Overactive spinal motor neurons are sensitive to the obscured signals from the remaining pyramidal tract or extrapyramidal pathway [7], such as the reticular spinal tract [8], activating the muscles to participate in the synergistic movements [9]. There remains an unanswered question as to why some muscles participate in synergistic movements, while other muscles are only involved to a small extent. An investigation of the differences in the activation of different muscles in synergistic movements may help develop rehabilitation strategies to break the synergy
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
