Abnormal intermuscular coordination limits the motor capability of stroke-affected upper limbs. By evaluating the intermuscular coordination in the affected limb under various biomechanical task constraints, the impact of a stroke on motor control can be analyzed and intermuscular coordination-based rehabilitation strategies can be developed. In this study, we investigated upper limb intermuscular coordination after a stroke during isokinetic movements. Sixteen chronic stroke survivors and eight neurologically intact individuals were recruited. End-point forces and electromyographic activities of the shoulder and elbow muscles were measured while the participants performed isokinetic upper limb movements in a three-dimensional space. Intermuscular coordination of the stroke survivors and the control participants was quantified in the form of muscle synergies. Then, we compared the number, composition, and activation coefficients of muscle synergies and the end-point force between the groups. The correlation between the alteration of muscle synergies and the level of motor impairment was investigated. Four and five muscle synergies in the stroke and control groups were observed, respectively. The composition of muscle synergies was comparable between the groups, except that the three heads of the deltoid muscle were co-activated and formed one synergy in the stroke group, whereas those muscles formed two synergies in the control group. When the number of muscle synergies between the groups matched, the comparable composition of muscle synergies was observed in both groups. Alternatively, the modulation of synergy activation coefficients was altered after a stroke. The severity of motor impairments was negatively correlated with the similarity of the post-stroke synergies with respect to the mean control synergies. Stroke-affected upper limbs seemed to modularize the activation of the shoulder and elbow muscles in a fairly similar way to that of neurologically intact individuals during isokinetic movements. Compared with free (i.e., unconstrained) movement, exercise under biomechanical constraints including the isokinetic constraint might promote the activation of muscle synergies independently in stroke survivors. We postulated the effect of biomechanical constraints on the intermuscular coordination and suggested a possible intermuscular coordination-based rehabilitation protocol that provides the biomechanical constraint appropriate to a trainee throughout the progress of rehabilitation.

中文翻译：

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中风后等速运动肌肉间协调性的改变及其对神经康复的影响

异常的肌间协调限制了受中风影响的上肢的运动能力。通过评估在各种生物力学任务约束下受影响肢体的肌肉间协调，可以分析中风对运动控制的影响，并可以制定基于肌肉间协调的康复策略。在这项研究中，我们调查了在等速运动过程中中风后的上肢肌肉协调性。招募了 16 名慢性中风幸存者和 8 名神经系统完好的个体。当参与者在三维空间中进行等速上肢运动时，测量了肩部和肘部肌肉的终点力和肌电活动。中风幸存者和对照参与者的肌肉间协调以肌肉协同作用的形式进行量化。然后，我们比较了组间肌肉协同作用和终点力的数量、组成和激活系数。研究了肌肉协同作用的改变与运动障碍水平之间的相关性。在中风组和对照组中分别观察到四块和五块肌肉协同作用。除了三角肌的三个头被共同激活并在中风组中形成一个协同作用，而这些肌肉在对照组中形成两个协同作用外，各组之间肌肉协同作用的组成具有可比性。当组间肌肉协同作用的数量匹配时，在两组中观察到肌肉协同作用的可比组成。或者，在中风后改变协同激活系数的调制。运动障碍的严重程度与中风后协同作用与平均控制协同作用的相似性呈负相关。在等速运动中，受中风影响的上肢似乎以与神经功能完好的个体非常相似的方式将肩部和肘部肌肉的激活模块化。与自由（即无约束）运动相比，在包括等速约束在内的生物力学约束下的运动可能会独立地促进中风幸存者肌肉协同作用的激活。