In this study, we estimated the multi-directional ankle mechanical impedance in two degrees-of-freedom (DOF) during standing, and determined how the stiffness, damping, and inertia vary with ankle angle and ankle torque at different postures. Fifteen subjects stood on a vibrating instrumented platform in four stationary postures, while subjected to pulse train perturbations in both the sagittal and frontal planes of motion. The four stationary postures were selected to resemble stages within the stance phase of the gait cycle: including post-heel-strike during the loading response, mid-stance, post-mid-stance, and just before the heel rises from the ground in terminal-stance phase. In general, the ankle stiffness and damping increased in all directions as the foot COP moved forward, and more torque is generated in plantarflexion. Interestingly, the multi-directional ankle impedance during standing showed a similar shape and major tilt axes to the results of non-loaded scenarios. However, there were notable differences in the impedance amplitude when the ankle was not under bodyweight loading. Last, the stiffness during standing had similar amplitudes ranges to the time-varying ankle stiffness during the stance phase of dynamic walking estimated in previous studies. These results have implications on the design of new, less physically intense, biomechanics experiments aimed at people with neuromuscular disorders or other physical impairments who cannot complete a standard gait test.

中文翻译：

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站立姿势中的多方向踝阻抗

在这项研究中，我们估计了站立过程中两个自由度（DOF）下的多方向踝机械阻抗，并确定了在不同姿势下，刚度，阻尼和惯性如何随踝角度和踝转矩而变化。15名受试者以四个固定姿势站立在振动仪器平台上，同时在矢状和前额运动平面上受到脉冲串的扰动。选择了四个固定姿势，使其与步态周期的站立阶段相似：包括加载响应期间的后跟打击，中间姿势，中间姿势后以及脚跟从终站地面抬起之前立场阶段。通常，随着脚COP向前移动，踝关节的刚度和阻尼在所有方向上都会增加，并且在plant屈中会产生更多的扭矩。有趣的是 站立期间的多向踝阻抗显示出与无载荷情况相似的形状和主倾斜轴。但是，当脚踝不在体重负荷下时，阻抗幅度存在明显差异。最后，站立时的僵硬具有与先前研究中估计的动态步行站立阶段时变的踝关节僵硬相似的幅度范围。这些结果对旨在针对无法完成标准步态测试的神经肌肉疾病或其他身体障碍患者的新的，强度较小的生物力学实验的设计产生了影响。当脚踝不在体重负荷下时，阻抗幅度存在显着差异。最后，站立时的僵硬具有与先前研究中估计的动态步行站立阶段时变的踝关节僵硬相似的幅度范围。这些结果对旨在针对无法完成标准步态测试的神经肌肉疾病或其他身体障碍患者的新的，强度较小的生物力学实验的设计产生了影响。当脚踝不在体重负荷下时，阻抗幅度存在显着差异。最后，站立时的僵硬具有与先前研究中估计的动态步行站立阶段时变的踝关节僵硬相似的幅度范围。这些结果对旨在针对无法完成标准步态测试的神经肌肉疾病或其他身体障碍患者的新的，强度较小的生物力学实验的设计产生了影响。