Dorman Garrett R, Davis Kevin C, Peaden Allan W, Charles Steven K
Neuroscience Center, Brigham Young University , Provo, Utah.
Department of Mechanical Engineering, Brigham Young University , Provo, Utah.
J Neurophysiol. 2018 Oct 1;120(4):2138-2154. doi: 10.1152/jn.00449.2017. Epub 2018 Jun 27.
The musculoskeletal system can move in more ways than are strictly necessary, allowing many tasks to be accomplished with a variety of limb configurations. Why some configurations are preferred has been a focus of motor control research, but most studies have focused on shoulder-elbow or whole arm movements. This study focuses on movements involving forearm pronation-supination (PS), wrist flexion-extension (FE), and wrist radial-ulnar deviation (RUD) and elucidates how these three degrees of freedom (DOF) combine to perform the common task of pointing, which only requires two DOF. Although pointing is more sensitive to FE and RUD than to PS and could be easily accomplished with FE and RUD alone, subjects tend to involve a small amount of PS. However, why we choose this behavior has been unknown and is the focus of this paper. With the use of a second-order model with lumped parameters, we tested a number of plausible control strategies involving minimization of work, potential energy, torque, and path length. None of these control schemes robustly predicted the observed behavior. However, an alternative control scheme, hypothesized to control the DOF that were most important to the task (FE and RUD) and ignore the less important DOF (PS), matched the observed behavior well. In particular, the behavior observed in PS appears to be a mechanical side effect caused by unopposed interaction torques. We conclude that moderately sized pointing movements involving the wrist and forearm are controlled by ignoring forearm rotation even though this strategy does not robustly minimize work, potential energy, torque, or path length. NEW & NOTEWORTHY Many activities require us to point our hands in a given direction using wrist and forearm rotations. Although there are infinitely many ways to do this, we tend to follow a stereotyped pattern. Why we choose this pattern has been unknown and is the focus of this paper. After testing a variety of hypotheses, we conclude that the pattern results from a simplifying strategy in which we focus on wrist rotations and ignore forearm rotation.
肌肉骨骼系统的运动方式比严格所需的更多，这使得许多任务能够通过各种肢体配置来完成。为何某些配置更受青睐一直是运动控制研究的重点，但大多数研究都集中在肩肘或整个手臂的运动上。本研究聚焦于涉及前臂旋前 - 旋后（PS）、腕关节屈伸（FE）以及腕关节桡尺偏斜（RUD）的运动，并阐明这三个自由度（DOF）如何结合起来执行指向这一仅需两个自由度的常见任务。尽管指向对FE和RUD比对PS更敏感，并且仅通过FE和RUD就能轻松完成，但受试者往往会涉及少量的PS。然而，我们为何选择这种行为尚不清楚，这也是本文的重点。通过使用具有集中参数的二阶模型，我们测试了许多合理的控制策略，包括使功、势能、扭矩和路径长度最小化。这些控制方案均未能可靠地预测观察到的行为。然而，一种替代控制方案，假设其控制对任务最重要的自由度（FE和RUD）并忽略不太重要的自由度（PS），与观察到的行为匹配良好。特别是，在PS中观察到的行为似乎是由未被抵消的相互作用扭矩引起的机械副作用。我们得出结论，涉及手腕和前臂的适度大小的指向运动是通过忽略前臂旋转来控制的，尽管这种策略并不能可靠地使功、势能、扭矩或路径长度最小化。新内容与值得注意之处许多活动要求我们通过手腕和前臂的旋转将手指向给定方向。尽管有无数种方法可以做到这一点，但我们倾向于遵循一种刻板模式。我们为何选择这种模式尚不清楚，这也是本文的重点。在测试了各种假设之后，我们得出结论，这种模式源于一种简化策略，即我们专注于手腕旋转而忽略前臂旋转。
