To clarify the effects of the polyester underwear for prevention of heat accumulation under the heat environment in baseball, two series of exercise experiments were carried out at an ambient temperature of 35℃, and 60% of relative humidity. In the first experiment, the thermoregulatory responses under three clothing conditions were compared: nude, 81% polyester baseball undershirt with tight clothing (PE), and 81% cotton baseball undershirt with loose clothing (CT) on the upper body and with common swimming pants, on the lower body. In the second experiment, the thermoregulatory responses under the corresponding three clothing conditions with baseball uniform and socks on the lower body were compared: nude on the upper body, the 81% polyester undershirt with layered wearing of baseball uniform (PE uniform), and the 81% cotton undershirt with layered wearing of baseball uniform (CT uniform) on the upper body. Heart rate (HR), rectal temperatures (Tre), skin temperatures, total sweat volume (TSV), effective sweat volume (ESV) and subject votes (thermal, comfort, skin humid sensations) were measured in each experimental condition. In Experiment 1, the Tre rose most in the CT condition than the other two conditions. This was due mainly to increased effective sweat rate (ESV/TSV) in the PE condition. On the other hand, in Experiment 2, the rise of Tre was not different between PE uniform and CT uniform conditions. Above results showed that the polyester undershirt with clothing pressure was effective in reducing the thermal load than the conventional cotton undershirt, but the effect disappeared with layered wearing. The layered wearing in baseball activity for prevention of the heat accumulation remained to be studied.

DESCENTE SPORTS SCIENCE Vol.26/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE