Postural control of a musculoskeletal model against multidirectional support surface translations

Abstract

The human body is a complex system driven by hundreds of muscles, and its control mechanisms are not sufficiently understood. To understand the mechanisms of human postural control, neural controller models have been proposed by different research groups, including our feed-forward and feedback control model. However, these models have been evaluated under forward and backward perturbations, at most. Because a human body experiences perturbations from many different directions in daily life, neural controller models should be evaluated in response to multidirectional perturbations, including in the forward/backward, lateral, and diagonal directions. The objective of this study was to investigate the validity of an NC model with FF and FB control under multidirectional perturbations. We developed a musculoskeletal model with 70 muscles and 15 degrees of freedom of joints, positioned it in a standing posture by using the neural controller model, and translated its support surface in multiple directions as perturbations. We successfully determined the parameters of the neural controller model required to maintain the stance of the musculoskeletal model for each perturbation direction. The trends in muscle response magnitudes and the magnitude of passive ankle stiffness were consistent with the results of experimental studies. We conclude that the neural controller model can adapt to multidirectional perturbations by generating suitable muscle activations. We anticipate that the neural controller model could be applied to the study of the control mechanisms of patients with torso tilt and diagnosis of the change in control mechanisms from patients’ behaviors.

A Neural Controller Model Considering the Vestibulospinal Tract in Human Postural Control

“…The task was to maintain an upright standing posture for 5,000 ms using the musculoskeletal model. This posture was chosen on the basis of a previous study (Kaminishi et al, 2019). As this model has many DOF and muscles, it is suitable for representing the function of the VST, which sends different signals to each muscle type and maintains the body in a vertical position.…”

“…This model was based on the musculoskeletal model from a previous study, with four DOF (pitch, roll) added to the neck and 24 additional muscles to control these movements. The previous study had considered the upper part of the body to be a single rigid unit (Jiang et al, 2016(Jiang et al, , 2017Kaminishi et al, 2019Kaminishi et al, , 2020, and therefore these additional DOFs and muscles were necessary because our model included the vestibular sense, which is greatly influenced by head movements.…”

“…q 1 -q 18 represent the DOF, where black is the sagittal plane, yellow is the frontal plane, and blue is the horizontal plane. The model is based on one developed in a previous study, but q 1 -q 4 degrees of freedom have been added to the neck (Kaminishi et al, 2019).…”

“…Computational modeling studies have also been conducted using musculoskeletal models, which have more DOF than the inverted pendulum model (Jiang et al, 2016;Kaminishi et al, 2019Kaminishi et al, , 2020Koelewijn and Ijspeert, 2020). These models better represent the human anatomical structure, and they include muscle control.…”

“…By introducing visual and vestibular FB control, it was possible to verify the relationship between sensory information and muscle tone (Jiang et al, 2017). The simulator has since been improved by Kaminishi et al to investigate postural control when there is some disturbance (Kaminishi et al, 2019(Kaminishi et al, , 2020.…”