Effects of arranging gel materials in the sole of running shoes on shock-absorbing and foot-stabilizing functions

Abstract

Running is one of the popular sports in Japan. But it is sometimes difficult for a lot of runners to continue it due to running-induced injuries. To prevent such injuries, running shoes have two different functions such as shock absorption and foot stabilization in the midsole, which contradict each other unfortunately. Then the effects of midsole’s structure and material on these functions have been investigated intensively. But with respect to gel materials recently used in the midsole, their functional effects have yet to be studied sufficiently. Then we studied how gel stiffness and arrangement in the midsole affect the afore-mentioned functions, by means of a motion analysis and a sensory test. Shock absorption and foot stabilization were evaluated in terms of midsole deformation as well as plantar pressure and the eversion computed from the relative orientation between the shoes and the thigh, respectively. Experiments using five subjects, all long-distance runners belonging to a track and field club, demonstrated that shock absorption could be improved by locating a low- stiffness gel in the lateral midsole, while stability could be improved by locating a low-stiffness gel and a high-stiffness gel in the lateral and medial midsole, respectively. Sensory test revealed that softness was affected by the elasticity of gel material located in lateral midsole as well as the deformation of the lateral midsole. All these findings suggested that the two functions of the midsole could be controlled objectively by the stiffness and midsole arrangement of gel material.