Modeling and stability analysis of human normal walking with implications for the evolution of the foot

This paper formulates the mathematical model of a biped that is capable of dynamic walking gaits. The model consists of hip actuation, segmented legs, flat feet and torsional spring based passive ankle stiffness. Using numerical simulations on the proposed model, we find that from the view of stability, there is optimal foot-ankle ratio of the flat-foot bipeds. The results indicate that the human foot proportion is indeed better optimized for dynamic bipedal walking than that of apes, further suggesting the current state of human foot is to some extent the product of positive selection for more stable bipedal locomotion during the evolution of the foot.