The purpose of this study is to determine the effect of water temperature and swimming velocity on sweat loss and body temperature during swimming. Five male college swimmers swam 1,500 m free style swim at three submaximal velocities (90%, 95%, and 97.5%) of their best record in the water temperatures of 26.4℃ and 29.2℃. Swimming time, body temperature (oral), heart rate, RPE (rating of perceived exertion), and sweat loss were measured. The sweat loss (g/kg) was calculated from the body weight measured before and after swimming [(body weight after swimming - body weight before swimming)×1,000/body weight before swimming].
　Body temperature changes at 90%, 95%, and 97.5% was 0.34±0.09℃, 0.56±0.14℃, 0.96±0.07℃ in the water temperature of 26.4℃, and 0.34±0.07℃, 0.70±0.05℃, 0.88±0.08℃ in 29.2℃, respectively. Sweat loss at 90%, 95%, and 97.5% was 2.73±0.45g/kg, 4.43±0.79g/kg, 5.04±1.03g/kg in 26.4℃, and 4.32±0.84g/kg, 7.09±1.57g/kg, 7.16±1.95g/kg in 29.2℃, respectively. Heart rate, RPE, and body temperature change was significantly increased according to swimming velocity, but there was no significant difference in the values between the water temperature of 26.4℃ and 29.2℃. Sweat loss was significantly increased according to rise in swimming velocity and water temperature.
　In conclusion, body temperature change during swimmimg relates to swimming velocity. Sweat loss during swimming relates to both swimming velocity and water temperature. It is considered that swimmer should take fluid during intensive swimming to prevent dehydration and body temperature rise around 30.0℃ or warmer water.

DESCENTE SPORTS SCIENCE Vol.17/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE