Shared feedback control principles across standing and walking

Feedback control is required to maintain stability in both walking and standing, whereas the control parameters may differ due to the inherently different characteristics of these tasks. How feedback is adapted between tasks is unclear. To address this, we applied a unified feedback model, relating preceding center of mass position and velocity information to corrective ground reaction forces, to estimate and compare the control parameters between walking and standing. 15 healthy young participants (21{+/-} 4 yrs, 63 {+/-} 9 kg, 1.70 {+/-} 0.10 m, 13 females, 2 males) participated, they walked at 4.5 km/h for 5 minutes, and performed 3 different standing tasks: normal standing, unipedal standing, and step posture for 1 minute, repeated 5 times. Whole-body kinematics and ground reaction forces were collected and used to fit the feedback model and estimate feedback delay and gains. Results showed good model fits for both walking and standing with mean R2-values higher than 0.69. The feedback delay was significantly longer in walking than in standing. While the feedback position gains and velocity gains varied significantly across tasks and directions, position gains were mostly above critical stiffness and velocity gains all at under-damped level, with as only exception that position gains in the AP direction in walking, which were slightly below critical stiffness. The ratio of position to velocity gains in all tasks remained consistently close to the eigenfrequency [Formula] as predicted by the extrapolated center of mass concept. Our findings suggest a robust control strategy in which the sensorimotor system maintains a relative consistent weighting between position and velocity feedback for walking and standing.