NTT Communication Science Laboratories, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa, 243-0198, Japan.
Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, Japan.
Sci Rep. 2020 Dec 18;10(1):22333. doi: 10.1038/s41598-020-79526-1.
The movement in a joint is facilitated by a pair of muscles that pull in opposite directions. The difference in the pair's muscle force or reciprocal activity results in joint torque, while the overlapping muscle force or the cocontraction is related to the joint's stiffness. Cocontraction knowingly adapts implicitly over a number of movements, but it is unclear whether the central nervous system can actively regulate cocontraction in a goal-directed manner in a short span of time. We developed a muscle interface where a cursor's horizontal position was determined by the reciprocal activity of the shoulder flexion-extension muscle pair, while the vertical position was controlled by its cocontraction. Participants made goal-directed movements to single and via-point targets in the two-dimensional muscle space, learning to move the cursor along the shortest path. Simulations using an optimal control framework suggest that the reciprocal activity and the cocontraction may be controlled independently by the CNS, albeit at a rate orders of magnitude slower than the muscle's maximal activation speed.
关节的运动是由一对朝相反方向牵拉的肌肉来完成的。这对肌肉的肌力差或交互活动导致关节产生扭矩，而肌肉的重叠力或共同收缩与关节的刚度有关。共同收缩在许多运动中是自动适应的，但尚不清楚中枢神经系统是否能够在短时间内以目标导向的方式主动调节共同收缩。我们开发了一种肌肉界面，其中光标水平位置由肩部屈伸肌对的交互活动决定，而垂直位置由其共同收缩控制。参与者在二维肌肉空间中进行了针对单个和多点目标的目标导向运动，学习沿着最短路径移动光标。使用最优控制框架的模拟表明，尽管 CNS 的控制速度比肌肉的最大激活速度慢几个数量级，但 CNS 可能会独立控制交互活动和共同收缩。
