Prediction and compensation by an internal model for back forces during finger opening in an overarm throw
Prediction and compensation by an internal model for back forces during finger opening in an overarm throw
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DOI：
10.1152/jn.1999.82.3.1187
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发表时间：
1999-09-01
影响因子：
2.5
通讯作者：
Tweed, D
中科院分区：
文献类型：
--
作者：
Hore, J;Watts, S;Tweed, D
以前的研究表明，在上臂投掷中，手指张开的时间可能是中央控制的，可能是通过手部轨迹的内部模型。目前的目标是将投掷的研究扩展到考察手指张开的动力学。投掷重球和投掷轻球大概需要不同的神经指令，因为球的重量会影响手臂的机械结构，尤其是手指的机械结构。然而，手指控制对于上臂投掷的准确性至关重要。我们假设，在上臂抛掷中，手指张开是由一个中央机制控制的，该机制使用一个内部模型来预测和补偿手指上依赖于运动的背力。为了测试这一想法，我们确定了手指运动是否受到背力的影响，即更大的背力是否会导致更大的手指伸展。通过让受试者以相同的快速速度投掷不同重量(14、55和196克)的网球大小的球，背力是不同的。使用搜索线圈技术记录手臂和手指关节的旋转；使用力传感器测量中指上的力。记录显示，在放球过程中，中指在投掷较重的球时，会经历更大的背力。然而，大多数受试者表现为近侧指间关节伸展，较重的球没有变化或实际上较小。这是第一次投球的情况，以及随后所有投球都有新重量的情况。这表明，手指屈肌通过在手指伸展时施加较大的扭矩来补偿较大的背力。支持这一观点的是，在释放球的那一刻，由于手指屈肌现在没有相对的扭矩，所有的手指关节都突然弯曲，这种弯曲的幅度与球的重量成正比。我们的结论是，在用不同重量的球进行的上臂投掷中，中枢神经系统预测不同的球的背力，并相应地调整手指屈肌扭矩。这与上臂投掷中手指张开是由运动装置的内部模型和外部负荷控制的观点是一致的。
Previous studies have indicated that timing of finger opening in an overarm throw is likely controlled centrally, possibly by means of an internal model of hand trajectory. The present objective was to extend the study of throwing to an examination of the dynamics of finger opening. Throwing a heavy ball and throwing a light ball presumably require different neural commands, because the weight of the ball affects the mechanics of the arm, and particularly, the mechanics of the finger. Yet finger control is critical to the accuracy of an overarm throw. We hypothesized that finger opening in an overarm throw is controlled by a central mechanism that uses an internal model to predict and compensate for movement-dependent back forces on the fingers. To test this idea we determined whether finger motion is affected by back forces, i.e., whether larger back forces cause larger finger extensions. Back forces were varied by having subjects throw, at the same fast speed, tennis-sized balls of different weights (14, 55, and 196 g). Arm- and finger-joint rotations were recorded with the search-coil technique; forces on the middle finger were measured with force transducers. Recordings showed that during ball release, the middle finger experienced larger back forces in throws with heavier balls. Nevertheless, most subjects showed proximal interphalangeal joint extensions that were unchanged or actually smaller with the heavier balls. This was the case for the first throw and for all subsequent throws with a ball of a new weight. This suggests that the finger flexors compensated for the larger back forces by exerting larger torques during finger extension. Supporting this view, at the moment of ball release, all finger joints flexed abruptly due to the now unopposed torques of the finger flexors, and the amplitude of this flexion was proportional to ball weight. We conclude that in overarm throws made with balls of different weights, the CNS predicts the different back forces from the balls and adjusts finger flexor torques accordingly. This is consistent with the view that finger opening in overarm throws is controlled by means of an internal model of the motor apparatus and the external load.