Optimal control and biomechanics of ambulation with spring-loaded crunches

Standard underarm or forearm crutches have some drawbacks induced by their rigid legs. Spingloaded crutches can reduce the impact effect. However, whether or not they also improve propulsion is an open problem. We formulate a problem of the optimal performance of spring-loaded crutches and propose a numerical approach to solve the problem. Then, the numerical optimal values are incorporated to the innovative design of a pair of spring-loaded crutches. To evaluate the crutches' performance, we have conducted standard biomechanical experiments for a number of male subjects under two conditions: walking with standard crutches and with spring-loaded crutches. Three dimensional kinematic data and ground reaction force were recorded and analysed. It was observed that optimized spring-loaded crutches can efficiently propel the crutch walkers, which conforms to the theory.