![]() In upper limb movement, the muscle activity can be fully characterized by a relatively limited number of muscle synergies among various motor tasks (d'Avella and Lacquaniti, 2013). (2008) demonstrated that synergies represented a generalized control strategy in postural control of cats and rhesus macaques. For example, Ting and Macpherson (2005) and Overduin et al. The hypothesis of muscle synergy has been explored by many previous studies. Neural control of movements can be accomplished by a hierarchal framework where muscle synergies are at the bottom and the task-related conceptual parameters are manipulated by higher neural centers ( Loeb et al., 1999 Scott, 2004 Todorov et al., 2005). Muscle synergy hypothesis, which describes muscle activation of a set of muscles contributing to a particular movement, has been proposed to simplify the motor control (d'Avella et al., 2003). As each joint of the musculoskeletal system can afford up to 6 degrees of freedom movement, it makes the motor control extremely delicate. However, the organization of human movement is not straightforward, as it involves complex cooperative interactions between the central nervous system (CNS) and the musculoskeletal system. We can perform various daily tasks almost effortless. Movement is one of the basic skills of human beings. The synergies of stroke survivors at Brunnstrom Stage IV–III gradually diverged from those of control group, but the activation coefficients remained the same after stroke, irrespective of the recovery level. Furthermore, the similarity of muscle synergies was significantly correlated with the Brunnstrom Stage ( R = 0.52, p < 0.01). By comparing the structure of muscle synergies and the similarity of activation coefficients across groups, we can validate the increasing activation of pectoralis major muscle and the decreasing activation of elbow extensor of triceps in stroke groups. Muscle synergies were extracted from the activity of 7 upper-limb muscles via nonnegative matrix factorization under the criterion of 95% variance accounted for. We collected electromyographic (EMG) data from 35 stroke survivors, ranging from Brunnstrom Stage III to VI, and 25 age-matched control subjects. In this paper, the alterations of muscle synergies in subacute stroke survivors were examined during the voluntary reaching movement. Motor cortical impairments, such as stroke and spinal cord injuries, disrupt the orchestration of the muscle synergies and result in abnormal movements. Motor system uses muscle synergies as a modular organization to simplify the control of movements. 3School of Electronic and Electrical Engineering, University of Leeds, Leeds, United Kingdom.2Rehabilitation Department, Peking University First Hospital, Beijing, China.1Sensor Network and Application Research Center, School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China.Bingyu Pan 1 Yingfei Sun 1 Bin Xie 2 Zhipei Huang 1 * Jiankang Wu 1 Jiateng Hou 1 Yijun Liu 2 Zhen Huang 2 * Zhiqiang Zhang 3
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