The relationship between environmental factors and water balance during training of baseball, handball, soccer and American football was analyzed. The environmental factor was assessed in terms of WBGT (wet-bulb globe temperature).
　During physical training, a commercially available sports drink was provided. The sweat rate and the amount of water intake were significantly correlated with WBGT in each physical training. By replenishing body fluid with water intake body weight was well maintained irrespective of WBGT. Body weight loss was significantly decreased with the increase of rehydration rate (fluid intake / sweat loss).
　The effect of free fluid intake on the rate of rehydration was compared between sucking through a straw and drinking out of a cup during fencing training : the rate of rehydration was 59.3% with cup and 36.6% with straw on averages.
　These results indicate that both sweat loss and water intake during exercise increase with WBGT, and that body weight loss is maintained at a fairly constant level during exercise with free water intake. The results indicate that rate of rehydration is influenced by the accessibility to fluid, along with the pattern of physical training and the tools to provide fluid together with the knowledge on the importance of fluid replacement to maintain work performance and to prevent heat casualty.

DESCENTE SPORTS SCIENCE Vol.16/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE