Wing A M, Flanagan J R, Richardson J
MRC Applied Psychology Unit, Cambridge, UK.
Exp Brain Res. 1997 Aug;116(1):122-30. doi: 10.1007/pl00005732.
The reactive forces and torques associated with moving a hand-held object between two points are potentially destabilising, both for the object's position in the hand and for body posture. Previous work has demonstrated that there are increases in grip force ahead of arm motion that contribute to object stability in the hand. Other studies have shown that early postural adjustments in the legs and trunk minimise the potential perturbing effects on body posture of rapid voluntary arm movement. This paper documents the concurrent evolution of grip force and postural adjustments in anticipation of dynamic and static loads. Subjects held a manipulandum in precision grasp between thumb and index finger and pulled or pushed either a dynamic or a fixed load horizontally towards or away from the body (the grasp axis was orthogonal to the line of the load force). A force plate measured ground reaction torques, and force transducers in the manipulandum measured the load (tangential) and grip (normal) forces acting on the thumb and finger. In all conditions, increases in grip force and ground reaction torque preceded any detectable rise in load force. Rates of change of grip force and ground reaction torque were correlated, even after partialling out a common dependence on load force rate. Moreover, grip force and ground reaction torque rates at the onset of load force were correlated. These results imply the operation of motor planning processes that include anticipation of the dynamic consequences of voluntary action.
在两点之间移动手持物体时所涉及的反作用力和扭矩，对手中物体的位置和身体姿势都可能产生不稳定影响。先前的研究表明，在手臂运动之前握力会增加，这有助于保持手中物体的稳定。其他研究则显示，腿部和躯干的早期姿势调整能将快速随意手臂运动对身体姿势的潜在干扰影响降至最低。本文记录了在预期动态和静态负荷时握力和姿势调整的同步变化情况。受试者用拇指和食指精确抓握一个操作手柄，然后水平地将动态或固定负荷拉向或推离身体（抓握轴与负荷力的方向正交）。一个测力板测量地面反作用力矩，操作手柄中的力传感器测量作用在拇指和手指上的负荷（切向）力和握力（法向）。在所有情况下，握力和地面反作用力矩的增加都先于负荷力的任何可检测到的上升。即使排除了对负荷力变化率的共同依赖，握力变化率和地面反作用力矩变化率仍具有相关性。此外，负荷力开始时的握力和地面反作用力矩变化率也具有相关性。这些结果意味着存在运动规划过程，其中包括对随意动作的动态后果的预期。
