Optimization of directional energy transfer in Adidas bounce tubes

Directional energy transfer quantifies the ratio of energy put into a system as a force acting in one direction to the energy returned as force acting in another direction. Directional energy transfer in sports shoes maximises conservative (recycled) energy and thus increases athletic performance in terms of running speed. The Adidas Bounce™ Concept uses tubes with a Θ-shaped cross section incorporated into the shoe sole. Directional energy transfer can be improved if the Bounce Tubes of Adidas shoes are rotated. The degree of rotation depends on the ratio of compressive to shear stiffness. The aim of this project was to analyse the structural properties (compressive and shear stiffness as a function of linear deflection) of Adidas Bounce Tubes and to optimise the degree of rotation. Maximal energy transfer from vertical to horizontal direction results from a Bounce Tube rotation of 18 degrees (counter clockwise, right view, running direction to the right) and with a tube length of 114 mm. The energy transfer with these conditions was 34%.