![]() However, there remains an unanswered question as to why some muscles participate in synergistic movements, while other muscles are only involved to a small extent. 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). 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. The synergistic movements are partially voluntary yet not completely under control ( 5, 6). It is difficult to break upper limbs' synergic pattern and to induce isolated movement with practical value ( 4). A considerable number of patients have chronic hemiplegia in the affected upper limb, characterized by synergistic movements ( 3). Hemiplegia is the most common sequela of a stroke and the leading cause of disability ( 1, 2). The difference in muscle activation based on spinal cord segments may be the reason for the stereotyped joint movement of upper limb flexion synergy. However, the standardized activation of both FCR and FCU in stroke patients was significantly lower than that in healthy controls.Ĭonclusion: 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. Similarly, there was no significant difference in normalized activation between FCR and FCU in healthy controls, and the same is true for stroke patients. 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. 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. 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. Sternocostal part of the pectoralis major, PS Flexor carpi radialis, FCR vs. 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. Methods: Surface electromyography (sEMG) signals were collected during elbow flexion in stroke patients and healthy controls. 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. 2Department of Rehabilitation Medicine, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.1Department of Rehabilitation Medicine, Huashan Hospital, Fudan University, Shanghai, China. ![]() Gang Liu 1 † Chin-hsuan Chia 2 † Wei-ning Wang 1 † Yue Cao 1 Shan Tian 1 Xue-yan Shen 1 Ying Chen 1 Rong-rong Lu 1 Jun-fa Wu 1 Yu-lian Zhu 1 Yi Wu 1 *
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