Abstract
Standing and walking balance control in humans relies on the transformation of sensory information to motor commands that drive muscles. Here, we evaluated whether sensorimotor transformations underlying walking balance control can be described by task-level center of mass kinematics feedback similar to standing balance control. We found that delayed linear feedback of center of mass position and velocity, but not delayed linear feedback from ankle angles and angular velocities, can explain reactive ankle muscle activity and joint moments in response to perturbations of walking across protocols (discrete and continuous platform translations and discrete pelvis pushes). Feedback gains were modulated during the gait cycle and decreased with walking speed. Our results thus suggest that similar task-level variables, i.e. center of mass position and velocity, are controlled across standing and walking but that feedback gains are modulated during gait to accommodate changes in body configuration during the gait cycle and in stability with walking speed. These findings have important implications for modelling the neuromechanics of human balance control and for biomimetic control of wearable robotic devices. The feedback mechanisms we identified can be used to extend the current neuromechanical models that lack balance control mechanisms for the ankle joint. When using these models in the control of wearable robotic devices, we believe that this will facilitate shared control of balance between the user and the robotic device.
Highlights
Most humans are extremely good at standing and walking without falling even in uncertain environments
Reactive bi-lateral gluteus medius activity, which has an important contribution to foot placement, is correlated with center of mass (COM) kinematics [14, 17]. These results suggest that COM kinematics are important task-level variables driving the control of medio-lateral foot placement during perturbed walking [18]
We showed that (1) sensorimotor transformations underlying the ankle response to perturbations of standing and walking can largely be explained by task-level feedback of COM kinematics and not with delayed linear feedback of joint kinematics and (2) COM kinematics feedback gains are modulated within the gait cycle and with walking speed
Summary
Most humans are extremely good at standing and walking without falling even in uncertain environments. Continuous adaptations of muscle activity are needed to control the relatively high position of the center of mass (COM) above a small base of support This is achieved through sensorimotor transformations: the nervous system continuously receives sensory inputs, which are processed to generate descending motor commands to muscles [1]. Changes in muscle activity and joint moments in response to external mechanical perturbations of standing can be explained by delayed feedback from COM kinematics [4,5,6]. It is yet unclear whether COM kinematics feedback captures sensorimotor transformations during walking
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