Zettel John L, McIlroy William E, Maki Brian E
Center for Studies in Aging, Sunnybrook and Women's Health Sciences Center, University of Toronto, Ontario, M4N 3M5, Canada.
Exp Brain Res. 2002 Sep;146(1):38-47. doi: 10.1007/s00221-002-1150-5. Epub 2002 Jul 9.
This study used environmental restrictions on foot movement to challenge the capacity of the central nervous system (CNS) to counter the lateral instability that arises after foot-lift during rapid triggered stepping reactions evoked by unpredictable postural perturbation. The objective was to determine the extent to which lateral stability could be regulated via modulation of the mediolateral (m-l) anticipatory postural adjustment (APA) that precedes foot-lift. A high frontal obstacle was used to double the required swing duration, and thereby increase the potential for the center of mass (COM) to fall laterally toward the unsupported side, during forward-step reactions. The capacity to use lateral step placement to recover lateral stability was restricted by means of lateral barriers. Six healthy young adults were tested. In obstacle-only trials, the APA was insufficient to prevent increased lateral COM motion during the prolonged swing phase; hence, lateral step placement was necessitated. However, when lateral stepping was obstructed, the CNS was able to upregulate the APA amplitude so as to prevent this increase in lateral COM motion. The swing foot was placed medially, with no detriment to clearing the frontal obstacle or recovering equilibrium. There was no change in step timing or anteroposterior (a-p) COM motion. While previous studies have suggested that the a-p COM progression may determine the extent to which the m-l APA is expressed or truncated during triggered stepping reactions evoked by unpredictable perturbation, the present findings demonstrate that prior knowledge of environmental demands can lead to predictive efforts to modulate the APA during such reactions. An apparent preference to underscale anticipatory efforts when lateral step placement is permitted suggests that the CNS may be acting to avoid some potential risk or cost associated with the execution of a large APA.
本研究利用对足部运动的环境限制，来挑战中枢神经系统（CNS）应对在不可预测的姿势扰动引发的快速触发步反应中抬脚后出现的侧向不稳定的能力。目的是确定通过调节抬脚前的内外侧（m-l）预期姿势调整（APA），侧向稳定性能够在多大程度上得到调节。在向前迈步反应过程中，使用一个高的前方障碍物使所需的摆动持续时间加倍，从而增加质心（COM）向无支撑侧横向跌落的可能性。通过侧向障碍物限制利用侧向步幅放置来恢复侧向稳定性的能力。对六名健康的年轻成年人进行了测试。在仅设置障碍物的试验中，APA不足以防止在延长的摆动阶段COM的侧向运动增加；因此，需要进行侧向步幅放置。然而，当侧向迈步受到阻碍时，CNS能够上调APA幅度，以防止COM的侧向运动增加。摆动脚向内侧放置，这对越过前方障碍物或恢复平衡没有不利影响。步长时机或前后（a-p）COM运动没有变化。虽然先前的研究表明，在不可预测的扰动引发的触发步反应中，a-p COM的进展可能决定m-l APA表达或截断的程度，但目前的研究结果表明，对环境需求的先验知识可以导致在这种反应过程中对APA进行预测性调节。当允许进行侧向步幅放置时，明显倾向于缩小预期努力的规模，这表明CNS可能在采取行动避免与执行大的APA相关的一些潜在风险或成本。
