Effect of acceleration on optimization of Adidas Bounce shoes

Directional energy transfer is a term used to describe the phenomenon where energy is returned as force acting in a direction other than the direction in which energy was put into the system. Directional energy transfer in running shoes increases athletic performance as running speed by transferring energy to the direction of locomotion. The concept can be applied to the Adidas Bounce™ style shoe. The shoe uses tubes with a Θ-shaped cross section incorporated into the shoe sole. Directional energy transfer can be optimized if the Bounce tubes of Adidas shoes are rotated and the overall stiffness changed (by altering the tube length). There are a number of parameters that relate to directional energy transfer. These parameters are: energy transferred (as a percentage of vertical input energy); energy transferred (absolute quantity); energy returned in the horizontal direction and total system energy. The aim of this paper was to investigate whether the optimum solution changed if the runner accelerated during a stride. The simulations showed that there is very little change in optimum design angle and that if additional rearward deflection of the bounce tube is permissible performance (energy transferred and returned) actually improves when the runner accelerates.