Beer R F, Dewald J P, Rymer W Z
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, IL 60611, USA.
Exp Brain Res. 2000 Apr;131(3):305-19. doi: 10.1007/s002219900275.
This study provides a detailed analysis of disturbances in the kinematics and dynamics of the acceleration phase of multijoint arm movements in six patients with chronic hemiparesis. Movements of the dominant and nondominant limbs were also examined in three control subjects. Subjects performed rapid movements from a central starting point to 16 targets located equidistantly around the circumference of a circle. Support of the upper limb was provided by an air-bearing apparatus, which allowed very low friction movements in the horizontal plane. We found that patients retained the capacity to modulate, in response to target direction, the initial direction of movements performed with the paretic limb. However, in comparison to the nonparetic limb or control subjects, movements of the paretic limb were misdirected systematically. An inverse dynamics analysis revealed an abnormal spatial tuning of the muscle torque at the elbow used to initiate movements of the paretic limb. Based on electromyographic recordings, similar spatial abnormalities were also apparent in the initial activations of elbow muscles. We argue that these spatial abnormalities result from a systematic disturbance in the control signal to limb muscles that cannot be attributed to previously identified mechanisms such as weakness, spasticity mediated restraint, or stereotypic muscle activation patterns (muscle synergies). Instead, our analysis of movement dynamics and simulation studies demonstrate that the spatial abnormalities are consistent with an impaired feedforward control of the passive interaction torques which arise during multijoint movements. This impaired control is hypothesized to reflect a degradation of the internal representation of limb dynamics that occurs either as a primary consequence of brain injury or secondary to disuse.
本研究详细分析了6例慢性偏瘫患者多关节手臂运动加速阶段的运动学和动力学紊乱情况。还对3名对照受试者的优势肢体和非优势肢体运动进行了检查。受试者从中央起始点向等距分布在圆周上的16个目标进行快速运动。上肢由气垫装置支撑，该装置允许在水平面内进行极低摩擦的运动。我们发现，患者能够根据目标方向调节患侧肢体运动的初始方向。然而，与健侧肢体或对照受试者相比，患侧肢体的运动存在系统性的方向偏差。逆动力学分析显示，用于启动患侧肢体运动的肘部肌肉扭矩存在异常的空间调谐。基于肌电图记录，肘部肌肉的初始激活中也明显存在类似的空间异常。我们认为，这些空间异常是由于向肢体肌肉的控制信号出现系统性紊乱所致，而不能归因于先前确定的机制，如无力、痉挛介导的约束或刻板的肌肉激活模式（肌肉协同作用）。相反，我们对运动动力学的分析和模拟研究表明，空间异常与多关节运动期间出现的被动相互作用扭矩的前馈控制受损一致。这种受损的控制被认为反映了肢体动力学内部表征的退化，这要么是脑损伤的主要后果，要么是废用的继发结果。
