According to Hennig (2000) the protective properties of shoes significantly deteriorate after 220 km wear. Sports shoes need to meet both the physical characteristics (biomechanics) of the athletes and the demands imposed by the sporting activities. In the research and design of new sports shoes certain parameters are taken into consideration. These include biomechanics of the sport and athlete which help develop properties including protection from overuse injury and performance enhancement. To produce a quality shoe, designers need a thorough grounding of foot morphology and anatomy, aetiology of commonly reported injuries, and the bioengineering of the lower extremity. Activity analysis entails time and frequency surveys of athletic activities which involves interviews with athletes, coaches, and medical staffs. Biomechanical measurements, performed during running, are essential in determining the influence of footwear construction on running style and loads to the human body. Rearfoot pronation, foot pressure patterns, and shock absorption properties have to be identified to determine shoe characteristics which will reduce the risk of overuse injuries. Rigorous field tests with many runners are necessary to evaluate shoe fit and comfort during running on varying terrain. Durability and long term performance of production shoes are evaluated through a final three month long wear test program. Only the combination of a technical test, biomechanical evaluation and subjective ratings by the athletes provides a complete picture for the quality of performance, protection and comfort needs of athletic shoes. Recent innovations have been the inclusion of dual density midsoles which are soft on the outside and hard on the inside. This provides lateral stability when the foot rolls over. Now sport surfaces and shoes are constructed in tandem with the intention to reduce excessive loading and optimise performance. The elastic response of the sport surface /shoe system is a critical variable for determining mechanical behaviour. The mechanical behaviour includes energy storage and return, frequency of energy return and cushioning. Original tracks and shoes were less efficient and had limited capacity to store and return energy. New combination estimate a 14 times improvement which converts to about 3% of the average energy expenditure per step during middle distance running. Elastomers used in sports shoes can deform elastically up to large strains and permit large volumetric changes due to their porous structure. Cellular elastomers exhibit under tension different material behaviour from compression. These are known as strain energy potential functions. Energy return and cushioning appear associated.
Hennig E M, 2000 Biomechanical methods for the evaluation of athletic footwear 2000 Pre-Olympic Congress Sports Medicine and Physical Education International Congress on Sport Science.