Department of Biomedical Engineering, University of Texas, Austin, TX 78712, USA.
J Biomech. 2011 Feb 24;44(4):644-9. doi: 10.1016/j.jbiomech.2010.11.007. Epub 2010 Nov 20.
Understanding how humans remain stable during challenging locomotor activities is critical to developing effective tests to diagnose patients with increased fall risk. This study determined if different continuous low-amplitude perturbations would induce specific measureable changes in measures of dynamic stability during walking. We applied continuous pseudo-random oscillations of either the visual scene or support surface in either the anterior-posterior or mediolateral directions to subjects walking in a virtual environment with speed-matched optic flow. Floquet multipliers and short-term local divergence exponents both increased (indicating greater instability) during perturbed walking. These responses were generally much stronger for body movements occurring in the same directions as the applied perturbations. Likewise, subjects were more sensitive to both visual and mechanical perturbations applied in the mediolateral direction than to those applied in the anterior-posterior direction, consistent with previous experiments and theoretical predictions. These responses were likewise consistent with subjects' anecdotal perceptions of which perturbation conditions were most challenging. Contrary to the Floquet multipliers and short-term local divergence exponents, which both increased, long-term local divergence exponents decreased during perturbed walking. However, this was consistent with specific changes in the mean log divergence curves, which indicated that subjects' movements reached their maximum local divergence limits more quickly during perturbed walking. Overall, the Floquet multipliers were less sensitive, but reflected greater specificity in their responses to the different perturbation conditions. Conversely, the short-term local divergence exponents exhibited less specificity in their responses, but were more sensitive measures of instability in general.
了解人类在挑战性的运动活动中如何保持稳定对于开发有效的测试以诊断增加跌倒风险的患者至关重要。本研究旨在确定不同的连续低幅度扰动是否会在行走时的动态稳定性的测量中引起特定的可测量变化。我们在具有速度匹配视流的虚拟环境中向受试者施加视觉场景或支撑面的连续伪随机前后或左右方向的摆动，以施加连续的伪随机摆动。在受到干扰的行走过程中，弗洛奎特乘数和短期局部散度指数都增加（表明不稳定性增加）。这些响应对于与施加的扰动方向相同的身体运动通常要强得多。同样，与施加在前-后方向的扰动相比，受试者对施加在中-侧方向的视觉和机械扰动更为敏感，这与先前的实验和理论预测一致。这些响应同样与受试者对哪些扰动条件最具挑战性的轶事感知一致。与弗洛奎特乘数和短期局部散度指数都增加相反，在受到干扰的行走过程中，长期局部散度指数减小。然而，这与平均对数发散曲线的特定变化一致，这表明在受到干扰的行走过程中，受试者的运动更快地达到其最大局部发散极限。总体而言，弗洛奎特乘数的敏感性较低，但对不同扰动条件的响应具有更大的特异性。相反，短期局部散度指数的响应特异性较低，但通常是不稳定性的更敏感度量。
