Department of Robotics, Brain and Cognitive Sciences, Istituto Italiano di Tecnologia, Genoa, Italy.
Department of Informatics, Bioengineering, Robotics, and System Engineering, University of Genoa, Genoa, Italy.
PLoS One. 2019 Mar 21;14(3):e0213870. doi: 10.1371/journal.pone.0213870. eCollection 2019.
In the study of balance and postural control the (Single) Inverted Pendulum model (SIP) has been taken for a long time as an acceptable paradigm, with the implicit assumption that only ankle rotations are relevant for describing and explaining sway movements. However, more recent kinematic analysis of quiet standing revealed that hip motion cannot be neglected at all and that ankle-hip oscillatory patterns are characterized by complex in-phase and anti-phase interactions, suggesting that the SIP model should be substituted by a DIP (Double Inverted Pendulum) model. It was also suggested that DIP control could be characterized as a kind of optimal bi-axial active controller whose goal is minimizing the acceleration of the global CoM (Center of Mass). We propose here an alternative where active feedback control is applied in an intermittent manner only to the ankle joint, whereas the hip joint is stabilized by a passive stiffness mechanism. The active control impulses are delivered to the ankle joint as a function of the delayed state vector (tilt rotation angle + tilt rotational speed) of a Virtual Inverted Pendulum (VIP), namely a pendulum that links the ankle to the CoM, embedded in the real DIP. Simulations of such DIP/VIP model, with the hybrid control mechanism, show that it can reproduce the in-phase/anti-phase interaction patterns of the two joints described by several experimental studies. Moreover, the simulations demonstrate that the DIP/VIP model can also reproduce the measured minimization of the CoM acceleration, as an indirect biomechanical consequence of the dynamic interaction between the active control of the ankle joint and the passive control of the hip joint. We suggest that although the SIP model is literally false, because it ignores the ankle-hip coordination, it is functionally correct and practically acceptable for experimental studies that focus on the postural oscillations of the CoM.
在平衡和姿势控制的研究中，（单）倒立摆模型（SIP）长期以来一直被视为一种可接受的范例，其隐含假设是只有脚踝旋转对于描述和解释摆动运动是相关的。然而，最近对安静站立的运动学分析表明，髋关节运动根本不能忽略，并且脚踝-髋关节的振荡模式具有复杂的同相和反相相互作用，这表明 SIP 模型应该被 DIP（双倒立摆）模型所取代。有人还建议，DIP 控制可以被描述为一种优化的双轴主动控制器，其目标是最小化全局 CoM（质心）的加速度。我们在这里提出了一种替代方案，即仅以间歇方式将主动反馈控制应用于踝关节，而髋关节则由被动刚度机制稳定。主动控制脉冲作为虚拟倒立摆（VIP）的延迟状态向量（倾斜旋转角度+倾斜旋转速度）的函数被传递到踝关节，即一个将脚踝与 CoM 连接起来的摆，嵌入在实际的 DIP 中。具有混合控制机制的这种 DIP/VIP 模型的模拟表明，它可以再现几个实验研究所描述的两个关节的同相/反相相互作用模式。此外，模拟表明，DIP/VIP 模型还可以再现 CoM 加速度的测量最小化，这是脚踝关节主动控制和髋关节被动控制之间动态相互作用的间接生物力学后果。我们建议，尽管 SIP 模型从字面上说是错误的，因为它忽略了脚踝-髋关节的协调，但对于专注于 CoM 姿势振荡的实验研究来说，它在功能上是正确的，在实践上是可以接受的。
