Dynamic stability of passive dynamic walking on an irregular surface
Dynamic stability of passive dynamic walking on an irregular surface
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DOI：
10.1115/1.2800760
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发表时间：
2007-12-01
影响因子：
1.7
通讯作者：
Dingwell, Jonathan B.
中科院分区：
文献类型：
--
作者：
Su, Jimmy Li-Shin;Dingwell, Jonathan B.
行走时发生的福尔斯是一个严重的健康问题。解决这个问题的最大障碍之一是没有一种明显“正确”的方法来量化行走稳定性。虽然许多人使用变异性作为稳定性的代表，但变异性的测量并不能量化运动系统对扰动的反应。本研究的目的是确定步行表面的变化如何影响运动变异性和稳定性的变化。我们修改了一个不可约的简单模型的步行应用随机扰动，模拟行走在一个不规则的表面。由于模型的全局吸引域保持不变，增加所施加扰动的幅度直接增加了模型中的坠落风险。我们在六个扰动幅度中的每一个上生成了300个连续步幅的十个模拟，所述扰动幅度从零（即，光滑连续的表面）直到模型可以容忍的最大水平而不翻倒。轨道稳定性定义了系统如何响应小的（即，“局部”）扰动，并通过计算模型的最大Floquet乘数来量化。局部稳定性定义了系统在真实的时间内对相似扰动的响应，并通过计算模型的短期和长期局部指数发散率来量化。随着扰动幅度的增加，轨道稳定性（r（2）=2.43%; p=0.280）或长期局部不稳定性（r（2）=1.0%; p=0.441）没有变化。这些措施基本上反映了这样一个事实，即模型在我们的任何模拟过程中从未真正“下降”。相反，步行者运动学的变异性呈指数增加（r（2）>= 99.6%; p
Falls that occur during walking are a significant health problem. One of the greatest impediments to solve this problem is that there is no single obviously "correct" way to quantify walking stability. While many people use variability as a proxy for stability, measures of variability do not quantify how the locomotor system responds to perturbations. The purpose of this study was to determine how changes in walking surface variability affect changes in both locomotor variability and stability. We modified an irreducibly simple model of walking to apply random perturbations that simulated walking over an irregular surface. Because the model's global basin of attraction remained fixed, increasing the amplitude of the applied perturbations directly increased the risk of falling in the model. We generated ten simulations of 300 consecutive strides of walking at each of six perturbation amplitudes ranging from zero (i.e., a smooth continuous surface) up to the maximum level the model could tolerate without falling over. Orbital stability defines how a system responds to small (i.e., "local") perturbations from one cycle to the next and was quantified by calculating the maximum Floquet multipliers for the model. Local stability defines how a system responds to similar perturbations in real time and was quantified by calculating short-tern and long-term local exponential rates of divergence for the model. As perturbation amplitudes increased no changes were seen in orbital stability (r(2)=2.43%; p=0.280) or long-term local instability (r(2)=1.0%; p=0.441). These measures essentially reflected the fact that the model never actually "fell" during any of our simulations. Conversely, the variability of the walker's kinematics increased exponentially (r(2)>= 99.6%; p