Threshold position control of arm movement with anticipatory increase in grip force
Threshold position control of arm movement with anticipatory increase in grip force
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DOI：
10.1007/s00221-007-0901-8
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发表时间：
2007-07-01
影响因子：
2
通讯作者：
Feldman, Anatol G.
中科院分区：
文献类型：
--
作者：
Pilon, Jean-Francois;De Serres, Sophie J.;Feldman, Anatol G.
在手指之间保持物体的抓握力通常在手臂运动之前或与手臂运动同时增加，从而防止物体滑动。我们基于以下概念对这种预期行为进行了实验分析和模拟。(1)为了将手臂移动到一个新的位置，神经系统改变了手臂肌肉开始被招募的阈值位置。偏离其激活阈值后，手臂肌肉会产生活动和力量，这些活动和力量往往会通过将手臂带到新位置来最大限度地减少这种偏差。(2)为了产生抓握力，无论是否有手臂运动，神经系统都会改变手的阈值配置。该过程定义适当手指的阈值（参照物）孔径（R-a）。实际孔径（Q（a））受夹在手指之间的物体的尺寸约束，而在参考位置R-a中，手指实际上穿透物体。由于物体偏离它们的激活阈值，手部肌肉产生与Q（a）和R-a之间的差距成比例的活动和抓握力。因此，由于物体阻止手指到达参考位置，因此出现抓握力。(3)根据以前的经验，系统知道当进行手臂运动时物体倾向于从手指上滑落，并且为了防止滑动，它与参考手臂位置的变化的开始同时或稍微在参考手臂位置的变化的开始之前开始使参考孔径变窄。(4)手指和物体之间的相互作用是通过指尖上的弹性垫来实现的。垫不仅由于夹持力而被压缩，而且由于从物体沿沿着臂轨迹作用在垫上的切向惯性力（“负载”）而被压缩。在负载力的压缩下，垫在指骨和物体之间的差距中来回移动，从而不可避免地改变握力的法向分量，与负载力同步并成比例。基于这些概念，我们模拟实验肘部运动和握力时，迅速改变手肘角度，同时举行的食指和拇指之间的对象。它的结论是，预期增加的抓地力与或不相关的切向负荷在手臂运动过程中，可以解释在神经生理学和生物力学方面，而不依赖于编程的抓地力的基础上的内部模型。
The grip force holding an object between fingers usually increases before or simultaneously with arm movement thus preventing the object from sliding. We experimentally analyzed and simulated this anticipatory behavior based on the following notions. (1) To move the arm to a new position, the nervous system shifts the threshold position at which arm muscles begin to be recruited. Deviated from their activation thresholds, arm muscles generate activity and forces that tend to minimize this deviation by bringing the arm to a new position. (2) To produce a grip force, with or without arm motion, the nervous system changes the threshold configuration of the hand. This process defines a threshold (referent) aperture (R-a) of appropriate fingers. The actual aperture (Q(a)) is constrained by the size of the object held between the fingers whereas, in referent position R-a, the fingers virtually penetrate the object. Deviated by the object from their thresholds of activation, hand muscles generate activity and grip forces in proportion to the gap between the Q(a) and R-a. Thus, grip force emerges since the object prevents the fingers from reaching the referent position. (3) From previous experiences, the system knows that objects tend to slide off the fingers when arm movements are made and, to prevent sliding, it starts narrowing the referent aperture simultaneously with or somewhat before the onset of changes in the referent arm position. (4) The interaction between the fingers and the object is accomplished via the elastic pads on the tips of fingers. The pads are compressed not only due to the grip force but also due to the tangential inertial force ("load") acting from the object on the pads along the arm trajectory. Compressed by the load force, the pads move back and forth in the gap between the finger bones and object, thus inevitably changing the normal component of the grip force, in synchrony with and in proportion to the load force. Based on these notions, we simulated experimental elbow movements and grip forces when subjects rapidly changed the elbow angle while holding an object between the index finger and the thumb. It is concluded that the anticipatory increase in the grip force with or without correlation with the tangential load during arm motion can be explained in neurophysiological and biomechanical terms without relying on programming of grip force based on an internal model.