After stroke, motor control is often negatively affected, leaving survivors with less muscle strength and coordination, increased tone, and abnormal synergies (coupled joint movements) in their affected upper extremity. Humeral internal and external rotation have been included in definitions of abnormal synergy but have yet to be studied in-depth. Determine the ability to generate internal and external rotation torque under different shoulder abduction and adduction loads in persons with chronic stroke (paretic and non-paretic arm) and uninjured controls. 24 participants, 12 with impairments after stroke and 12 controls, completed this study. A robotic device controlled abduction and adduction loading to 0, 25, and 50% of maximum strength in each direction. Once established against the vertical load, each participant generated maximum internal and external rotation torque in a dual-task paradigm. Four linear mixed-effects models tested the effect of group (control, non-paretic, and paretic), load (0, 25, 50% adduction or abduction), and their interaction on task performance; one model was created for each combination of dual-task directions (external or internal rotation during abduction or adduction). The protocol was then modeled using OpenSim to understand and explain the role of biomechanical (muscle action) constraints on task performance. Group was significant in all task combinations. Paretic arms were less able to generate internal and external rotation during abduction and adduction, respectively. There was a significant effect of load in three of four load/task combinations for all groups. Load-level and group interactions were not significant, indicating that abduction and adduction loading affected each group in a similar manner. OpenSim musculoskeletal modeling mirrored the experimental results of control and non-paretic arms and also, when adjusted for weakness, paretic arm performance. Simulations incorporating increased co-activation mirrored the drop in performance observed across all dual-tasks in paretic arms. Common biomechanical constraints (muscle actions) explain limitations in external and internal rotation strength during adduction and abduction dual-tasks, respectively. Additional non-load-dependent effects such as increased antagonist co-activation (hypertonia) may cause the observed decreased performance in individuals with stroke. The inclusion of external rotation in flexion synergy and of internal rotation in extension synergy may be over-simplifications.

中文翻译：

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慢性中风镜控制个体肩关节扭矩的耦合，在联合扭矩任务中具有额外的非负载依赖性负面影响

中风后，运动控制通常会受到负面影响，使幸存者的上肢肌肉力量和协调性降低，紧张度增加，协同作用异常（耦合关节运动）。肱骨内旋和外旋已包含在异常协同作用的定义中，但尚待深入研究。确定慢性中风患者（麻痹和非麻痹手臂）和未受伤对照者在不同的肩外展和内收负荷下产生内部和外部旋转扭矩的能力。24 名参与者完成了这项研究，其中 12 名中风后有损伤，12 名对照组完成了这项研究。机器人设备将外展和内收负荷控制在每个方向的最大强度的 0%、25% 和 50%。一旦建立了垂直负载，每个参与者在双重任务范例中产生最大的内部和外部旋转扭矩。四种线性混合效应模型测试了组（对照组、非麻痹组和麻痹组）、负荷（0%、25%、50% 内收或外展）及其相互作用对任务表现的影响；为双重任务方向（外展或内收期间的外部或内部旋转）的每个组合创建一个模型。然后使用 OpenSim 对该协议进行建模，以理解和解释生物力学（肌肉动作）约束对任务性能的作用。小组在所有任务组合中都很重要。分别在外展和内收过程中，麻痹手臂不太能够产生内部和外部旋转。在所有组的四种负荷/任务组合中的三种中，负荷有显着影响。负荷水平和组相互作用不显着，表明外展和内收负荷以类似的方式影响每个组。OpenSim 肌肉骨骼建模反映了控制和非麻痹手臂的实验结果，并且在针对无力、麻痹手臂表现进行调整时。结合增加的共同激活的模拟反映了在麻痹手臂的所有双重任务中观察到的性能下降。常见的生物力学约束（肌肉动作）分别解释了在内收和外展双重任务期间外旋和内旋强度的限制。额外的非负荷依赖性效应，例如增加的拮抗剂共激活（张力亢进）可能会导致观察到的中风患者表现下降。