A switched optimal control strategy in human balancing on a harmonically moving platform

Postural balance is crucial for human daily activities, and understanding the neural-motor control mechanisms underlying balance performance is essential for improving diagnosis and intervention strategies for balance disorders. This study focuses on the human standing balance task on a harmonically moving platform with anterior-posterior translation, exploring the neural-motor control logic using a switched control strategy. It is hypothesized that humans switch between optimal energy gains and optimal decay gains to maintain balance in a safe and energy-efficient manner with the usage of optimal decay gains being closely related to balancing ability. A two-stage identification process is employed to determine switching time instances, starting with the adjoint method to estimate control gains and followed by the enumeration of gain switching instances. The proposed postural stability assessment indices, Control Strategy Ratio and Control Switch Frequency, offer clear physical interpretations and dynamic insights, demonstrating better consistency and sensitivity compared to some stabilometry parameters. These indices show potential for early diagnosis and intervention in balance disorders.