A simple mechanical model was used to represent the characteristics of running leg and shoe sole. The model consists of a concentrated mass supported by a damped spring which represents the dynamic property of leg, and 3 elements of spring damper which represent shoe sole. The system was modelled as a 3-DOF system. The physical properties of the spring damper of the leg was obtained from ground contact time. The coefficients of spring damper of shoe sole were experimentally identified for existing shoe and modification were sought by numerical optimization to improve running performance. In this system, intermittent motion due to different elements of shoe sole was solved by introducing the unit step logical function. The results of motion analysis have shown agreeable similarity with experimental data.
The optimal mechanical propereties of shoe sole were investigated using the gradient projection method, in order to minimize the energy loss of this model or maximum reaction force. In the former case, the solution was found to have low damping and proper range of stiffness 130-180 KN/m. Also in the latter case, low damping in shoe sole except high damping in heel part was suggested to minimize maximum ground reaction force. Low stiffness in the mid part of the shoe sole was recommended in both case.
