Zhang Wei, Zatsiorsky Vladimir M, Latash Mark L
Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
Exp Brain Res. 2006 Oct;175(1):68-82. doi: 10.1007/s00221-006-0521-8. Epub 2006 May 24.
We investigated the production of time profiles of the total moment of force produced in isometric conditions by the four fingers of a hand. We hypothesized that these tasks would be associated with multi-finger synergies stabilizing the time profile of the total moment across trials but not necessarily stabilizing the time profile of the total force produced by the fingers. We also expected the multi-finger synergies to prevent an increase in the moment variability with its magnitude. Seated subjects pressed on force sensors with the four fingers of the right hand and produced two time profiles of the total moment of force, starting from a certain pronation effort, leading to a similar supination effort, and back to the initial pronation effort. One of the profiles was a sequence of straight lines (M-Ramp) while the other was a smooth curve (M-Sine). The subjects showed an increase in the total force during each task. This was accompanied by an increase in the force produced by the fingers opposing the required direction of the total moment-antagonist fingers. Variability of the total force and of the total moment showed complex, non-monotonic changes with the magnitude of the force and moment, respectively. In both tasks, the subjects showed patterns of co-variation of commands to fingers that stabilized the required moment profile over trials. The time profile of the total force was stabilized to a lesser degree or not stabilized at all. The share of fingers with larger moment arms (index finger for pronation efforts and little finger for supination efforts) was higher when the fingers acted to produce moments in a required direction but not necessarily when they acted as antagonists. The results demonstrate the existence of multi-finger synergies stabilizing the combined rotational action. They fit a hypothesis that stabilization of rotational actions may be a default strategy conditioned by everyday experience. The data also suggest that the mechanical advantage hypothesis is valid for sets of effectors that act in the required direction but not for sets of effectors that act as antagonists.
我们研究了手部四指在等长条件下产生的总力矩随时间变化的情况。我们假设，这些任务会与多手指协同作用相关联，这种协同作用会在不同试验中稳定总力矩随时间变化的情况，但不一定会稳定手指产生的总力随时间变化的情况。我们还预期多手指协同作用会防止力矩变异性随其大小增加。坐着的受试者用右手的四指按压力传感器，并产生两个总力矩随时间变化的情况，从一定的旋前用力开始，达到类似的旋后用力，然后回到初始的旋前用力。其中一个情况是一系列直线（M - 斜坡），而另一个是平滑曲线（M - 正弦）。在每个任务中，受试者的总力都有所增加。这伴随着与总力矩所需方向相反的手指（拮抗手指）产生的力增加。总力和总力矩的变异性分别随力和力矩的大小呈现出复杂的、非单调的变化。在两个任务中，受试者都表现出手指指令的协变模式，这种模式在不同试验中稳定了所需的力矩情况。总力随时间变化的情况稳定程度较低或根本没有稳定。当手指朝着所需方向产生力矩时，具有较大力臂的手指（旋前用力时的食指和旋后用力时的小指）所占比例较高，但当它们作为拮抗肌时不一定如此。结果表明存在稳定联合旋转动作的多手指协同作用。它们符合这样一种假设，即旋转动作的稳定可能是一种由日常经验决定的默认策略。数据还表明，机械优势假说对于朝着所需方向起作用的效应器组是有效的，但对于作为拮抗肌起作用的效应器组则无效。
