The purpose of this study was to investigate the effects of temperature on the shock absorbing characteristics of two kinds of viscoelastic polymer sponges (EVA and RB) which were usually used for the running shoe midsoles. Changes in the temperature inside the midsole during running 10 km (200m・min⁻¹) were recorded using a thermistor for various environmental conditions. The hardness and viscoelasticity of the midsole materials exposed to temperatures between -10 and 60 degrees (C) were measured by means of a dynamic viscoelasticity measurement system (Rheovibron) and a rubber hardness tester. In addition, impact testing (Ht=4 cm) on shoes with varying midsole hardness was conducted using 4 subjects. An accelerometer was used to monitor the shock wave to the leg.
　It was found that the midsole temperature during running ranged between approximately 2 degrees (C) in winter and 53 degrees in summer. The difference in the peak shock to the leg between the two seasons was estimated to be about 20 m・sec⁻², indicating the difference in shock value was large enough to cause various problems to the runners' bodies. As far as the tested materials concerned, the RB sponge appeared to be more effective in shock absorption for high temperature conditions than the EVA.

DESCENTE SPORTS SCIENCE Vol.6/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE