Normalized estimated torques for random contraction. (red: measured, magenta: estimated by the model of GAS, green: estimated by the model of SOL, blue: sum of both models) (A) result obtained with the linear Hill model. (B) result obtained with the modified nonlinear Hill model. (C.1) result obtained with the multi-scale physiology based model. (C.2) The corresponding active muscle stiffness k
estimated with the proposed model.