An Evaluation Method of Flexibility for Running Shoes based on Sole Curvature Distribution

Flexibility is one of the important properties of running shoes. This function has been evaluated by the bending stiffness of the shoe sole. However, this evaluation method seems to be insufficient because it cannot consider the deformation behaviors of the human foot and the shoe sole. The human foot can flex at the metatarsophalangeal joint only. This indicates that deformation of shoe sole must be considered. In this study, a new evaluation method for the flexibility of running shoes based on shoe sole deformation is proposed. In this method, curvature distributions of the plantar surface and shoe soles were measured at heel 100 mm up. The proposed flexibility is evaluated from the comparison. The influences of groove position and depth upon the sole curvature distribution were measured by both the experiment and the finite element method. Then, based on the analytical results, several shoes were made and these were evaluated by sensory evaluation test. From these results, it is suggested that matching the maximum flexion point of the shoe sole with that of plantar surface is important.