Yamagata Momoko, Falaki Ali, Latash Mark L
Department of Kinesiology, Rec.Hall-268N, The Pennsylvania State University, University Park, PA, 16802, USA.
Department of Human Health Science, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Exp Brain Res. 2018 May;236(5):1501-1517. doi: 10.1007/s00221-018-5239-x. Epub 2018 Mar 21.
We explored the relations between indices of mechanical stability of vertical posture and synergy indices under unexpected perturbations. The main hypotheses predicted higher posture-stabilizing synergy indices and higher mechanical indices of center of pressure stability during perturbations perceived by subjects as less challenging. Healthy subjects stood on a force platform and held in fully extended arms a bar attached to two loads acting downward and upward. One of the loads was unexpectedly released by the experimenter causing a postural perturbations. In different series, subjects either knew or did not know which of the two loads would be released. Forward perturbations were perceived as more challenging and accompanied by co-activation patterns among the main agonist-antagonist pairs. Backward perturbation led to reciprocal muscle activation patterns and was accompanied by indices of mechanical stability and of posture-stabilizing synergy which indicated higher stability. Changes in synergy indices were observed as early as 50-100 ms following the perturbation reflecting involuntary mechanisms. In contrast, predictability of perturbation direction had weak or no effect on mechanical and synergy indices of stability. These observations are interpreted within a hierarchical scheme of synergic control of motor tasks and a hypothesis on the control of movements with shifts of referent coordinates. The findings show direct correspondence between stability indices based on mechanics and on the analysis of multi-muscle synergies. They suggest that involuntary posture-stabilizing mechanisms show synergic organization. They also show that predictability of perturbation direction has strong effects on anticipatory postural adjustment but not corrective adjustments. We offer an interpretation of co-activation patterns that questions their contribution to postural stability.
我们探究了垂直姿势的机械稳定性指标与意外扰动下协同指标之间的关系。主要假设预测，在受试者认为挑战性较小的扰动过程中，姿势稳定协同指标和压力中心稳定性的机械指标会更高。健康受试者站在一个测力平台上，双臂完全伸展握住一根连接着两个上下作用负荷的杆。实验者意外释放其中一个负荷，从而引起姿势扰动。在不同的系列实验中，受试者知道或不知道两个负荷中的哪一个会被释放。向前的扰动被认为更具挑战性，并且主要的 agonist - antagonist 对之间会出现共同激活模式。向后的扰动导致肌肉的交互激活模式，并伴随着机械稳定性指标和姿势稳定协同指标，这些指标表明更高的稳定性。在扰动后 50 - 100 毫秒就观察到协同指标的变化，这反映了非自主机制。相比之下，扰动方向的可预测性对稳定性的机械指标和协同指标影响较弱或没有影响。这些观察结果在运动任务协同控制的分层方案以及关于参考坐标移动的运动控制假设中得到解释。研究结果表明基于力学和多肌肉协同分析的稳定性指标之间存在直接对应关系。它们表明非自主姿势稳定机制呈现协同组织。它们还表明扰动方向的可预测性对预期姿势调整有强烈影响，但对纠正调整没有影响。我们对共同激活模式的解释对它们对姿势稳定性的贡献提出了质疑。
