The energetics of running and running shoes

It has been suggested that elastic energy storage and recovery in the cushioning system of an athletic shoe ('energy return') is a desirable quality that can enhance performance. However, comparing the energetics of a running shoe cushioning system with other passive energy exchange mechanisms in the running athlete suggests that the potential benefits of energy return are limited. The energetics of running shoe cushioning systems have been studied using a multiple-element, non-linear viscoelastic model to analyse the effect on the shoe of plantar pressure distributions recorded in vivo. The running shoe is a net dissipator of energy but small quantities of strain energy, of the order of 10J, are stored and recovered during a running step. The actual energy exchanges depend on the cushioning material properties and the runner's plantar pressure distribution. Energy storage and recovery occurs throughout the step in different regions of the shoe midsole. Energy dissipation is confined almost entirely, both spatially and temporally, to the impact phase of ground contact. Thus the proportion of input energy recovered from the shoe is higher than that predicted by mechanical tests which stimulate only the impact phase of the step. Energy storage and recovery in the model shoe are large enough to have local effects on the energetics of the foot and lower leg but modest when compared with passive energy transfer within and between body segments or strain energy storage and recovery in the lower limb. Similarly, differences in the energy dissipated by well-designed shoes are predicted to be small and unlikely to have a direct effect on the energetics of the body as a whole. The possibility of indirect, kinematically mediated effects remains open, however.