Neural-mechanical feedback control scheme can generate physiological ankle torque fluctuation during quiet standing: A comparative analysis of contributing torque components

We have recently demonstrated in simulations and experiments that a proportional and derivative (PD) feedback controller, which uses the body kinematics to regulate the active ankle torque during quiet stance, can stabilize the body despite a long sensory-motor time delay. The purpose of the present study was to implement the PD controller in a neural-mechanical control scheme of quiet stance and to determine whether the ankle torque elicited by the mechanical and neural controllers can match the total ankle torque modulation intrinsic to quiet stance. Fourteen young subjects were asked to stand still on a force platform to acquire data for model optimization and validation. During two trials of 30 s each, the fluctuation of the body angle, the electromyogram of the right soleus muscle, and the ankle torque were recorded. Using these data, the parameters of the neural-mechanical control scheme were optimized to achieve potential matching between the measured and predicted ankle torque fluctuation. The modelpsilas performance was finally validated with a new set of data. Our results indicate that the ankle torque modulation observed in healthy individuals can, in fact, be generated by the proposed control scheme. Taking our previous findings into account, we conclude that a PD control strategy is a legitimate model for the strategy that the central nervous system of healthy individuals applies to regulate the active ankle torque during quiet stance in spite of a long sensory-motor time delay.