Balance maintenance in response to a perturbation could be affected by the predictability of the magnitude of the body disturbance. We investigated anticipatory (APAs) and compensatory (CPAs) postural adjustments in response to perturbations of predictable and unpredictable magnitudes. Twenty young adults received series of perturbations of small or large magnitudes the order of which was varied. Electromyographic activity of six leg and trunk muscles and displacements of the center-of-pressure (COP) were recorded. The muscle onset time, integrals of muscle activity, and COP displacements in the anterior–posterior direction were analyzed during the APA and CPA phases. The results indicated that when the participants were exposed to the repeated perturbation magnitude, it became predictable and they generated APAs more precisely according to the magnitudes of the perturbation. Moreover, when the magnitude of perturbation changed unpredictably, the participants overestimated or underestimated the magnitudes of the perturbation, as they generated APAs based on their prior experience of dealing with the perturbation. The optimal adjustment of APAs occurred after five trials of repeated perturbations. The findings imply that the process of APAs and CPAs generation depends on the accuracy of the predictability of perturbation magnitudes.

响应扰动的平衡维持可能会受到身体扰动幅度的可预测性的影响。我们研究了预期（APA）和补偿（CPA）姿势调整，以应对可预测和不可预测程度的扰动。二十名年轻人接受了一系列或大或小的扰动，扰动的顺序各不相同。记录了六个腿部和躯干肌肉的肌电活动以及压力中心（COP）的位移。在 APA 和 CPA 阶段分析肌肉起始时间、肌肉活动积分和前后方向 COP 位移。结果表明，当参与者暴露于重复的扰动幅度时，它变得可预测，并且他们根据扰动的幅度更精确地生成 APA。此外，当扰动的幅度发生不可预测的变化时，参与者会高估或低估扰动的幅度，因为他们根据之前处理扰动的经验生成了 APA。经过五次重复扰动试验后，APA 得到了最佳调整。研究结果表明，APA 和 CPA 的生成过程取决于扰动幅度可预测性的准确性。