Chumacero-Polanco Erik, Yang James
Human-Centric Design Research Lab,Department of Mechanical Engineering,Texas Tech University,Lubbock, TX 79409e-mail:
Fellow ASMEHuman-Centric Design Research Lab,Department of Mechanical Engineering,Texas Tech University,Lubbock, TX 79409e-mail:
J Biomech Eng. 2019 Nov 1;141(11). doi: 10.1115/1.4043563.
The study of upright posture (UP) stability is of relevance to estimating risk of falls, especially among people with neuromuscular deficits. Several studies have addressed this problem from a system dynamic approach based on parameter bifurcation analyses, which provide the region of stability (RoS) and the delimiting bifurcation curves (usually Hopf and pitchfork) in some parameter-spaces. In contrast, our goal is to determine the effect of parameter changes on the size of the basin of attraction (BoA) of the UP equilibrium and the amplitude of the limit cycle oscillations (LCOs) emerging from the Hopf bifurcations (HBs). The BoA is an indicator of the ability of the UP to maintain balance without falling, while LCOs may explain the sway motion commonly observed during balancing. In this study, a three degree-of-freedom model for a human balancing on a balance board (BB) was developed. Analysis of the model revealed the BoAs and the amplitude of the LCOs. Results show that physical parameters (time-delays and feedback control gains) have a large impact on the size of the BoA and the amplitude of the LCOs. Particularly, the size of the BoA increases when balancing on a rigid surface and decreases when either proprioceptive or combined visual and vestibular (V&V) feedback gain is too high. With respect to the LCOs, it is shown that they emerge from both the subcritical and supercritical HBs and increase their amplitudes as some parameters vary.
直立姿势（UP）稳定性的研究对于评估跌倒风险具有重要意义，尤其是对于患有神经肌肉缺陷的人群。一些研究从基于参数分岔分析的系统动力学方法来解决这个问题，该方法在某些参数空间中提供了稳定性区域（RoS）和界定分岔曲线（通常是霍普夫分岔和叉形分岔）。相比之下，我们的目标是确定参数变化对UP平衡吸引域（BoA）大小以及从霍普夫分岔（HBs）出现的极限环振荡（LCOs）幅度的影响。BoA是UP保持平衡而不跌倒能力的一个指标，而LCOs可以解释在平衡过程中常见的摇摆运动。在本研究中，开发了一个用于人体在平衡板（BB）上进行平衡的三自由度模型。对该模型的分析揭示了BoA和LCOs的幅度。结果表明，物理参数（时间延迟和反馈控制增益）对BoA的大小和LCOs的幅度有很大影响。特别是，在刚性表面上平衡时BoA的大小会增加，而当本体感觉或视觉与前庭联合（V&V）反馈增益过高时则会减小。关于LCOs，研究表明它们从亚临界和超临界HBs中出现，并随着某些参数的变化而增加其幅度。
