Milner Theodore E
School of Kinesiology, Simon Fraser University, Burnaby, B.C. V5A 1S6, Canada.
Exp Brain Res. 2002 Apr;143(4):515-9. doi: 10.1007/s00221-002-1049-1. Epub 2002 Mar 1.
This study investigates the ability to maintain a stable position of the hand when confronted with environmental instability. Subjects were required to hold the hand inside a 0.4-mm square while counteracting the destabilizing effect of a force field, which pushed the hand away from a line in the horizontal plane. The endpoint stiffness of the relaxed arm proved to be a reliable predictor of stability. Subjects were most successful in stabilizing hand position when the direction of the force field was aligned with the direction of greatest endpoint stiffness. They were least successful when the force field was aligned in the orthogonal direction, the direction of least endpoint stiffness. Subjects increased their endpoint stiffness as the strength of the force field was increased, but when the force field was in the direction of least stiffness they eventually failed in stabilizing the hand at the highest force field strength. In contrast, they were as successful in stabilizing the hand at the highest force field strength as at the lowest, when the force field was aligned with the direction of greatest stiffness. With the elbow flexed, endpoint stiffness of the relaxed arm becomes more uniform than with the elbow extended. This was reflected in subjects' performance, which improved considerably compared to the extended elbow posture, as force field strength was increased in the direction of lesser stiffness. The results indicate that posture was more effective than joint stiffness in stabilizing hand position.
本研究调查了在面对环境不稳定时保持手部稳定位置的能力。受试者需要将手放在一个0.4毫米见方的区域内，同时抵消力场的不稳定作用，该力场会将手从水平面内的一条直线推开。结果表明，放松手臂的端点刚度是稳定性的可靠预测指标。当力场方向与端点刚度最大的方向一致时，受试者在稳定手部位置方面最为成功。当力场方向与端点刚度最小的正交方向一致时，他们最不成功。随着力场强度的增加，受试者会增加其端点刚度，但当力场方向为刚度最小时，他们最终会在最高力场强度下无法稳定手部。相比之下，当力场方向与刚度最大的方向一致时，他们在最高力场强度下稳定手部的成功率与在最低力场强度下相同。当肘部弯曲时，放松手臂的端点刚度比肘部伸展时更加均匀。这反映在受试者的表现上，随着力场强度在刚度较小的方向上增加，与肘部伸展姿势相比，受试者的表现有了显著改善。结果表明，在稳定手部位置方面，姿势比关节刚度更有效。
