Dept. of Integrative Physiology, Univ. of Colorado, Boulder, CO 80309-0354, USA.
J Neurophysiol. 2012 Apr;107(7):1952-61. doi: 10.1152/jn.00983.2010. Epub 2012 Jan 11.
Our daily movements exert forces upon the environment and also upon our own bodies. To control for these forces, movements performed while standing are usually preceded by anticipatory postural adjustments (APAs). This strategy is effective at compensating for an expected perturbation, as it reduces the need to compensate for the perturbation in a reactive manner. However, it can also be risky if one anticipates the incorrect perturbation, which could result in movements outside stability limits and a loss of balance. Here, we examine whether the margin for error defined by these stability limits affects the amount of anticipation. Specifically, will one rely more on anticipation when the margin for error is lower? Will the degree of anticipation scale with the margin for error? We took advantage of the asymmetric stability limits (and margins for error) present in the sagittal plane during upright stance and investigated the effect of perturbation direction on the magnitude of APAs. We also compared anticipatory postural control with the anticipatory control observed at the arm. Standing subjects made reaching movements to multiple targets while grasping the handle of a robot arm. They experienced forward or backward perturbing forces depending on the target direction. Subjects learned to anticipate the forces and generated APAs. Although subjects had the biomechanical capacity to adapt similarly in the forward and backward directions, APAs were reduced significantly in the backward direction, which had smaller stability limits and a smaller margin for error. Interestingly, anticipatory control produced at the arm, where stability limits are not as relevant, was not affected by perturbation direction. These results suggest that stability limits modulate anticipatory control, and reduced stability limits lead to a reduction in anticipatory postural control.
我们的日常活动对环境和自身身体都会产生力量。为了控制这些力量，站立时的动作通常会先进行预期的姿势调整（APAs）。这种策略在补偿预期的扰动时非常有效，因为它减少了以反应方式补偿扰动的需要。然而，如果预测错误的扰动，这也可能是有风险的，因为这可能导致超出稳定性限制的运动和失去平衡。在这里，我们研究这些稳定性限制定义的误差幅度是否会影响预期的量。具体来说，当误差幅度较低时，人们是否会更多地依赖于预期？预期的程度是否会随误差幅度而变化？我们利用了直立姿势中矢状面的不对称稳定性限制（和误差幅度），并研究了扰动方向对 APAs 幅度的影响。我们还比较了手臂的预期姿势控制和预期控制。站立的受试者在抓住机器人手臂的手柄的同时向多个目标进行伸手动作。他们根据目标方向体验到向前或向后的扰动力。受试者学会了预测力并产生了 APAs。尽管受试者在向前和向后方向上具有类似的适应生物力学能力，但向后方向上的 APAs 显著减少，因为向后方向的稳定性限制较小，误差幅度较小。有趣的是，在手臂上产生的与稳定性限制不相关的预期控制不受扰动方向的影响。这些结果表明，稳定性限制调节了预期控制，而稳定性限制的降低导致预期姿势控制的减少。
