Influence of midsole bending stiffness on joint energy and jump height performance.

PURPOSE: A substantial amount of rotational energy is lost at the metatarsophalangeal joint during running and jumping. We hypothesized that the lost energy could be decreased by increasing the bending stiffness of shoe midsoles. The purposes of this investigation were to determine the influence of stiff shoe midsoles on changes in lower extremity joint power during running and jumping and to determine the influence of stiff shoe midsoles on vertical jump performance.
METHODS: Carbon fiber plates were inserted into shoe midsoles and data were collected on five subjects during running and vertical jumping.
RESULTS: The data showed that energy generation and absorption at each of the ankle, knee, and hip joints was not influenced by the stiffness of the shoe midsole. The stiff shoes with the carbon fiber plates did not increase the amount of energy stored and reused at the metatarsophalangeal joint; however, they reduced the amount of energy lost at this joint during both running and jumping. Vertical jump height was significantly higher (average, 1.7 cm for a group of 25 subjects) while wearing the stiff shoes.
CONCLUSIONS: Increasing the bending stiffness of the metatarsophalangeal joint reduced the amount of energy lost at that joint and resulted in a corresponding improvement of performance.