Evidence for a time-invariant phase variable in human ankle control

Human locomotion is a rhythmic task in which patterns of muscle activity are modulated by state-dependent feedback to accommodate perturbations. Two popular theories have been proposed for the underlying embodiment of phase in the human pattern generator: a time-dependent internal representation or a time-invariant feedback representation (i.e., reflex mechanisms). In either case the neuromuscular system must update or represent the phase of locomotor patterns based on the system state, which can include measurements of hundreds of variables. However, a much simpler representation of phase has emerged in recent designs for legged robots, which control joint patterns as functions of a single monotonic mechanical variable, termed a phase variable. We propose that human joint patterns may similarly depend on a physical phase variable, specifically the heel-to-toe movement of the Center of Pressure under the foot. We found that when the ankle is unexpectedly rotated to a position it would h...

人类步行运动是一项节律性任务，其肌肉活动模式可通过状态依赖反馈进行调节，以适配外界扰动。针对人类运动模式发生器内相位的内在实现机制，目前已提出两种主流理论：一类是时变内部表征，另一类是时不变反馈表征（即反射机制）。无论采用何种理论，神经肌肉系统都需基于系统状态更新或表征运动模式的相位，而系统状态可涵盖数百项变量的测量数据。然而，近年来腿式机器人的设计中已出现一种更为简洁的相位表征方案：将关节运动模式控制为单个单调机械变量的函数，该变量被称为相位变量（phase variable）。我们提出，人类的关节运动模式或许同样依赖于某一物理相位变量，具体即足底压力中心（Center of Pressure）的足跟至趾部移动过程。我们发现，当踝关节被意外旋转至其本应处于的某一位置时……