Previous paragraphs explain the hierarchy of our simulation framework. How to find the appropriate values for both the controller and muscle parameters is key to achieve stable performance of the locomotion. We here use the algorithm of Covariance Matrix Adaptation (CMA) to optimize the parameters. CMA is an evolutionary algorithm that is designed to solve nonlinear non-convex optimization problem. Existing works have applied this method to design the locomotion controller for virtual characters11,12,28.