Koshland Gail F, Galloway James C, Farley Becky
Department of Physiology, University of Arizona, Tucson, AZ, 85724, USA.
Exp Brain Res. 2005 Jul;164(2):133-47. doi: 10.1007/s00221-005-2218-9. Epub 2005 Mar 15.
A fundamental issue in the neuromotor control of arm movements is whether the nervous system can use distinctly different muscle activity patterns to obtain similar kinematic outcomes. Although computer simulations have demonstrated several possible mechanical and torque solutions, there is little empirical evidence that the nervous system actually employs fundamentally different muscle patterns for the same movement, such as activating a muscle one time and not the next, or switching from a flexor to an extensor. Under typical conditions, subjects choose the same muscles for any given movement, which suggests that in order to see the capacity of the nervous system to make a different choice of muscles, the nervous system must be pushed beyond the normal circumstances. The purpose of this study, then, was to examine an atypical condition, reaching of cervical spinal cord injured (SCI) subjects who have a reduced repertoire of available distal arm muscles but otherwise a normal nervous system above the level of lesion. Electromyography and kinematics of the shoulder and elbow were examined in the SCI subjects performing a center-out task and then compared to neurologically normal control subjects. The findings showed that the SCI-injured subjects produced reaches with typical global kinematic features, such as straight finger paths, bell-shaped velocities, and joint excursions similar to control subjects. The SCI subjects, however, activated only the shoulder agonist muscle for all directions, unlike the control pattern that involved a reciprocal pattern at each joint (shoulder, elbow, and wrist). Nonetheless, the SCI subjects could activate their shoulder antagonist muscles, elbow flexors, and wrist extensor (extensor carpi radialis) for isometric tasks, but did not activate them during the reaching movements. These results demonstrate that for reaching movements, the SCI subjects used a strikingly different pattern of intact muscle activities than control subjects. Hence, the findings imply that the nervous system is capable of choosing either the control pattern or the SCI pattern. We would speculate that control subjects do not select the SCI pattern because the different choice of muscles results in kinematic features (reduced fingertip speed, multiple shoulder accelerations) other than the global features that are somehow less advantageous or efficient.
手臂运动神经肌肉控制中的一个基本问题是，神经系统是否能够使用明显不同的肌肉活动模式来获得相似的运动学结果。尽管计算机模拟已经展示了几种可能的机械和扭矩解决方案，但几乎没有实证证据表明神经系统在进行相同运动时实际采用了根本不同的肌肉模式，比如这次激活一块肌肉而下次不激活，或者从屈肌切换到伸肌。在典型情况下，受试者在进行任何给定运动时都会选择相同的肌肉，这表明为了观察神经系统做出不同肌肉选择的能力，必须使神经系统超出正常情况。那么，本研究的目的是考察一种非典型情况，即颈脊髓损伤（SCI）受试者的伸手动作，这些受试者可用的远端手臂肌肉种类减少，但损伤水平以上的神经系统在其他方面正常。在进行中心向外任务的SCI受试者中检测了肩部和肘部的肌电图和运动学，然后与神经功能正常的对照受试者进行比较。研究结果表明，SCI损伤受试者的伸手动作具有典型的整体运动学特征，比如手指路径笔直、速度呈钟形以及关节活动范围与对照受试者相似。然而，与每个关节（肩部、肘部和腕部）都采用交互模式的对照模式不同，SCI受试者在所有方向上仅激活肩部主动肌。尽管如此，SCI受试者能够在等长任务中激活肩部拮抗肌、肘部屈肌和腕部伸肌（桡侧腕长伸肌），但在伸手动作过程中并未激活它们。这些结果表明，对于伸手动作，SCI受试者使用的完整肌肉活动模式与对照受试者明显不同。因此，研究结果意味着神经系统能够选择对照模式或SCI模式。我们推测对照受试者不选择SCI模式是因为肌肉的不同选择会导致除整体特征之外的运动学特征（指尖速度降低、多次肩部加速），而这些特征在某种程度上不太有利或高效。
