Six male subjects were exposed to combined stress of heat and exercise, and their heart rate, blood pressure, oxygen uptake, skin temperature, esophageal temperature and body weight were measured. These observations were repeated 12 times for each subject under 4 levels of WBGT (Wet Bulb Globe Temperature) : 22, 26, 30, 32.5°C at rest and at 2 levels of exercise intensity : 150 W/m² (Ex. 150W) and 250 W/m² (Ex. 250 W) . The results obtained were as follows:
1. Significant differences were found in heart rate, oxygen pulse and rate pressure product at 32.5t WBGT and Ex. 150 W and at 30 and 32.5t WBGT and Ex. 250W compared with those at 22t WBGT.
2. Significant increases in esophageal temperature were observed at 32.5°C WBGT and Ex. 150 W and at 30 and 32.5t WBGT and Ex. 250 W.
3. The body weight loss at 26, 30 and 32.5 C WBGT was significantly higher than that at 22°C WBGT for both Ex. 150 W and 250 W.
4. These results suggest that there is a risk of heat exhaustion at WBGT higher than 30-32.5°C under mild exercise and above 26-30°C WBGT at a moderate exercise level. The upper limit for moderate exercise (Ex. 250W) is suggested to be 30°C WBGT.

Indexes to prevent heat casualties have been reported by many investigators based on different temperature scales including wet bulb temperature, wet bulb globe temperature, dry bulb temperature and so on. In this report, environmental temperature of an athletic field in Tokyo area was monitored in summer of 1981 to 1985, using natural wetbulb temperature (NWB), natural drybulb temperature (NDB), globe temperature (GT) and air velocity (A. V.) and WBGT (Wet Bulb Globe Temperature Index) was calculated, from NWB, GT and NDB on the result.
The highest temperature observed was 33.2°C in WBGT, 28.0°C in NWB and 37.5°C in GT. Highly significant correlations were obtained between WBGT and other parameters, than for A. V.
Based on the regression equation between WBGT and NWB, preventive measures for athletes in hot conditions were compared.

Deaths and morbidity due to heat disorders during physical activity were gleaned from newspaper reports between 1970 and 1990. The environmental temperatures (dry-bulb temperature and relative humidity) recorded at the closest meteorological observatory at the time of occurrence were used to calculate the wet-bulb temperature and WBGT (wet-bulb globe temperature), and the relationship between heat disorders and environmental temperature was analyzed.
During the 21-year period, 108 cases of heat disorders (91 deaths and 477 casualties) were reported in newspapers. Of the 91 deaths, 9 were in females and 82 were in males, and mean ages were 23.3 years, females and 19.0 years, males.
It was possible to record the environmental conditions at the time of the heat disorder in 99 cases. The results indicated that almost all disorders occurred at ranges higher than 25.5°C, dry-bulb temperature, and 20.0°C, wet-bulb temperature, 40% relative humidity, and 24.0°C, WBGT. The mean WBGT was 28°C at physiological intensities less than 12-RMR (Relative Metabolic Rate) and 25.8°C at RMR higher than 15.
The seasonal distribution was from April to November. In cases observed in April, May and November, abrupt rises in WBGT in the 1.2-3.4°C range were observed on the day of occurrence in comparison with the previous day, suggesting that the degree of heat acclimatization is olso an important factor in preventing heat disorders.

In this study, the danger of dehydration and heatstroke in a walking event in the summer was examined. Subjects were 64 males, 11 females, and the average age was 62.3±7.8 years old. The following were measured before and after 25 km walking : body weight, blood pressure, heart rate, tympanic temperature, and fluid intake. WBGT in the walking event was 22.6℃ mean value. Time of the 25 km walking was 5 hours 45 minutes, and the number of steps were 36,570±2,741 steps. The body weight loss by the walking was 1.36±0.57 kg, 2.24±0.96%. This body weight loss rate increased with the age. The fluid intake was 1,327±608 g, and sweat loss was 2,621±740 g in the walking. The tympanic temperature after walking was 38.02±0.60℃, and increased 0.99±0.67℃ from before walking. In the walking of middle-aged and elderly persons in the summer, there is danger of dehydration and heatstroke, therefore enough water and salt intakes are necessary.

The relationship between environmental conditions and water balance during training for baseball and American football was analyzed. The environmental conditions were assessed in terms of WBGT (wet-bulb globe temperature) based on NDB (natural dry-bulb temperature), NWB (natural wet-bulb temperature) and GT (globe temperature), as WBGT=0.7NWB+0.2GT+0.1NDB,
During baseball training, a commercially available sports drink was provided ad libitum, whereas during American football training, the effect of free water intake was compared between tap-water and sports drink. The sweat rate and the amount of water consumption were significantly correlated with WBGT under each experimental condition. Body weight loss was 0.2% body wt./h during baseball training, whereas during American football training, body weight loss was 0.5%/h with tap-water and 0.4%/h with sports drink on average, revealing a significantly higher value for tap-water.
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, although the loss is significantly higher when tap-water is provided.

Effects of drinking on body temperature during exercise and recovery in heat were studied in the field. Five healthy baseball players participated in baseball training with and without fluid re-placement on summer days, and rectal temperature, body weight loss, rating of thirst and the amount of water consumption were measured.
The rectal temperature was significantly lower throughout exercise when fluid replacements were allowed. The normalization of rectal temperature during rest periods was also significantly accelerated by fluid replacement. The rating of thirst was significantly correlated with the increase in rectal temperature and sweat loss, and also with the volume of fluid intake. Although full rehydration was not observed, body fluid replacement by drinking is suggested to be advantageous for body temperature regulation during exercise in heat.

The relationship between environmental conditions and water balance during training for baseball and American football was analyzed. The environmental conditions were assessed in terms of WBGT (wet-bulb globe temperature) based on NDB (natural dry-bulb temperature), NWB (natural wet-bulb temperature) and GT (globe temperature), as WBGT=0.7NWB+0.2GT+0.1NDB,
During baseball training, a commercially available sports drink was provided ad libitum, whereas during American football training, the effect of free water intake was compared between tap-water and sports drink. The sweat rate and the amount of water consumption were significantly correlated with WBGT under each experimental condition. Body weight loss was 0.2% body wt./h during baseball training, whereas during American football training, body weight loss was 0.5%/h with tap-water and 0.4%/h with sports drink on average, revealing a significantly higher value for tap-water.
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, although the loss is significantly higher when tap-water is provided.

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.