Fig. 1

Control parameter identification. We estimated the control parameters of a model without (blue) and with (green) additional feedback of whole body center of mass (COM) velocity by minimizing the difference between the experimental ankle moment and the ankle moment simulated with the neuromechanical model (representative example in A). Control parameters of each model were estimated by tracking eight steady-state and 16 perturbed gait cycles in one optimization problem. Perturbations were applied at toe-off of the contralateral leg while the subjects walked at 0.62 m/s. The root mean square error (RMSE) between experimental and simulated ankle moments was smaller in the model with additional COM feedback for (B) steady-state walking, (C) perturbed walking, and (D) a validation perturbation trial that was not used in the parameter estimation (the dots represent the RMSE in each of the five subjects and the bar represents the average across subjects). The lower RMSE for the model with COM feedback compared to the default model reflects the simulated change in ankle moment in response to pelvis push and pull perturbations (F) that is in agreement with experimental observations (G), whereas the default reflex model without COM feedback cannot capture the experimental data (E). (E–G contains data of one representative subject with the two-trial average response of each unique perturbation)