The guidelines for the prevention of heat disorders during sports activities were established 13 years ago in Japan. Since then, various studies on preventive measures against heat disorders have been done, yielding new knowledge about its prevention. It has been reported that the incidence of heat disorders is high in children and the elderly, and heat acclimatization and clothing are the factors involved in this disorder. We proposed to lower the WBGT (wet-bulb globe temperature) limit for warning (discontinuation of hard exercise) from “28°C or more” to “25°C or more” (corresponding to an ambient temperature of 28°C) for non-acclimatized persons, children, the elderly, and persons wearing clothes covering the entire body. We also indicated that heat disorders can occur due to unpredictable causes, because the mechanism is very complicated.
