We compared voluntary oscillatory sway for eight subjects tested in 1.8g and 1g gravito-inertial force (GIF) levels of parabolic flight. Subjects performed voluntary forward-backward (FB) and lateral left-right (LR) swaying as the forces and moments under the soles of each foot were measured. We calculated the experimental values of three parameters - two ankle stiffness parameters K_S^AP and K_S^ML acting in orthogonal FB and LR directions, and one parameter K_ED related to leg pivot shifting. Simulations of the Engaged Leg Model (Bakshi et al. 2019a; b) correctly predicted the experimentally determined stability bounds of upright balance and also the scaling of the postural parameters as a function of GIF magnitude. The effective stiffness, K_S^AP, at the ankles played the primary role to prevent falling in FB swaying and both model predictions and experimental data showed K_S^AP to scale up in proportion to GIF magnitude. For LR swaying, the model predicted a 3:4 scaling of AP stiffness to change in GIF magnitude, which was borne out by the experimental data. Simulations predict stability (non-falling) not to depend on lateral stiffness, K_S^ML, which was experimentally found not to depend on the GIF magnitude. Both model and experiment showed that the geometry dependent pivot shift parameter K_ED was invariant to a change in GIF magnitude. Thus the ELM explains voluntary sway and balance in altered GIF magnitude conditions, rotating environments with Coriolis perturbations of sway, as well as normal terrestrial conditions.

中文翻译：

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超重力对直立平衡和自主摇摆的影响

我们比较了在 1.8 克和 1 克重力惯性力 (GIF) 水平抛物线飞行中测试的八名受试者的自愿振荡摇摆。在测量每只脚底下的力和力矩时，受试者进行自愿前后 (FB) 和横向左右 (LR) 摇摆。我们计算了三个参数的实验值 - 两个踝关节刚度参数 K _S ^AP和 K _S ^ML作用于正交 FB 和 LR 方向，以及一个参数 K _ED与腿枢轴移位有关。Engaged Leg Model 的模拟 (Bakshi et al. 2019a; b) 正确预测了直立平衡的实验确定的稳定性界限，以及作为 GIF 幅度函数的姿势参数的缩放。脚踝处的有效刚度 K _S ^AP在防止 FB 摇晃中起主要作用，模型预测和实验数据均显示 K _S ^AP与 GIF 幅度成比例地增加。对于 LR 摇摆，该模型预测 AP 刚度的比例为 3:4，以改变 GIF 幅度，这得到了实验数据的证实。模拟预测稳定性（非坠落）不依赖于横向刚度，K _S ^ML，实验发现它不依赖于 GIF 大小。模型和实验都表明几何相关的轴移参数 K _ED对 GIF 幅度的变化是不变的。因此，ELM 解释了在改变的 GIF 幅度条件、带有科里奥利摇摆的旋转环境以及正常的陆地条件下的自愿摇摆和平衡。