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.

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.

In this study, we investigated total sweat rate per unit area of body surface per hour (TSR), the percentage of total sweat loss to initial body weight (%TSL) and the percentage of fluid intake volume to total sweat loss (%FIV) in children (during baseball or basketball practice), young adults (during softball or baseball practice), and the elderly (during gateball practice) in summer. During the practice all participants were given access to drink sports drink or Japanese tea ad libitum. In the basketball group of children no sex difference was observed in TSR, %TSL and %FIV. Although TSR and %TSL in the baseball group of children were significantly higher than in the basketball group due to a higher WBGT, there was no group difference for %FIV. Children drank sports drinks (with carbohydrate-electrolyte) of the similar volume with total sweat loss. The baseball group of children showed a significantly greater %FIV compared to the young adult group regardless of simi lar %TSL, when they drank sports drinks. Children showed a significantly higher %FIV in sports drinks than in Japanese tea, whereas the %FIV of young adults was not affected by the type of beverage. The TSR, %TSL and %FIV of the elderly group were significantly lower than in young adults and children. These results suggest that children can prevent voluntary dehydration by con-suming sports drinks with carbohydrate-electrolyte ad libitum regardless of sex and WBGT, and that periodic drinking should be actively encouraged for the elderly because of their blunted rehydration ability, to prevent heat disorders during sports activity in summer.

The effects of fencing uniforms (U) on thermoregulatory responses were analyzed in both practical field investigation (PFI) and laboratory experiment (LE) . In PFI, six fencers (college-aged) performed regular fencing practice wearing U and wearing a short-sleeved shirt and pants (T) in summer. Rectal temperature (Tr), chest skin temperature (Tch), mask temperature (Tmk), heart rate (HR) and sweat rate (SR) were measured during fencing practice. In LE, seven male college-aged subjects performed three sessions of 20-min cycling at light intensity (250 W/m²) in a room temperature maintained at 28 WBGT (wet bulb globe temperature) . Esophageal temperature (Tes), mean skin temperature (Tsk), mean body temperature (Tb), HR, and SR were measured during exercise wearing U and in a semi-nude condition (N) . In both PFI and LE, increases in Tch, Tsk, Tb, Tes, Tr and SR were significantly (p<0.001) greater when wearing U than when wearing T and N. In PFI, the maximal value of Tr correlated significantly with the maximal values of Tch (r=0.513, p<0.001) and SR (r=0.635, p<0.001) during practice wearing U and T. In LE, positive correlations between Tsk and Tes (r=0.797, p<0.001), and between Tb and SR (r=0.658, p<0.02) were found at the end of exercise wearing U and N. In PFI, although the Tsk decreased within a few minutes of a decrease in Tmk, a significant relationship between the decrease in Tmk and Tsk or Tr was not observed during fencing practice. These results demonstrate that when wearing U, a higher skin temperature induces core temperature elevation, and higher skin and core temperatures are associated with increases in SR and HR during exercise in a hot environment. Thus, wearing light clothing during exercise, and taking off the fencing jacket and mask during rest periods would be recommended to reduce the heat stress during fencing practice in hot environments.

To clarify the effect of sports wear on exercise-heat stress, we analyzed quantitative differences in thermoregulatory responses among baseball uniforms (BB), soccer uniforms (SC), and swimming trunks (NU) during exercise in a hot environment. Eight male subjects performed three sessions of 20-min cycling at light intensity (250W/m²) wearing BB, SC and NU in a room maintained at 28°C (wet-bulb globe temperatures, WBGT) . Esophageal (Tes), mean skin (Tsk), and mean body temperatures (Tb), heart rate (HR), thermal sensation (TS), and total sweat loss (m_SW) were measured during the exercise. Increases in Tes, Tsk, Tb, HR, and TS during exercise were significantly (p<0, 05) higher, and m_SW, was significantly (p<0.001) greater for BB than SC and NU. The increase in Tes at the end of the exercise was 3.0 times higher for BB than NU ; and also 2.0 times higher for SU than NU. Under all conditions, the increase in Tes significantly correlated with Tsk (r=0.634, p<0, 001) and HR (r=0.854, p<0.001) ; m_SW also significantly correlated with Tb (r=0.683, p<0.001) at the end of the exercise. These findings suggest that quantitative differences regarding the increase in Tes among BB, SC and NU relate to Tsk elevation due to attenuation of heat dissipation depending on sports wear ; body temperature elevation also relates to the increase in HR and m_SW during light exercise in a hot environment.

To clarify the effects of varying skin temperature due to several types of clothing on temperature responses and heat-stress during exercise, we analyzed thermoregulatory responses while wearing various types of sportswear including soccer (SC), baseball (BB), and fencing uniforms (FU), and while wearing water-perfused suits (WS) and vests (WV) during exercise in a hot environment. We also compared these results with those obtained under a semi-nude condition (NU). Eight male subjects performed three 20-min cycling sessions at light intensity (250W/m²) in a room maintained at 28°C (wet-bulb globe temperature, WBGT). The experiment was performed under ten conditions, with six sets of clothing, WS and WV at 14°C (WS14, WV14), 20°C (WS20, WV20) and 26°C (WS26, WV26), and FU, SC, BB or NU. While wearing sport-swear, increases in esophageal (ΔTes), mean skin (Tsk), mean body (Tb) temperature, heart rate (HR), thermal sensation (TS) at the end of exercise, and total sweat loss (m_{sw, tot}) during exercise were significantly (p<0.01) higher in BB and FU than in NU. In comparison to WS or WV conditions, ΔTes was significantly (p<0.01) higher under WV conditions than under NU, while there was no significant difference in ΔTes between WS and NU. Tsk, Tb, HR, TS and m_{sw, tot} tended to be lower in WS14 and 20, and higher in WV26 than in NU. Under all conditions at the end of exercise, the ΔTes markedly increased when Tsk exceeded 34°C ; and ΔTes was significantly correlated with Tsk (r=0.861, p<0.01) for all conditions except WS14 and 20. For Tsk less than 34°C, however, ΔTes remained constant. ΔTes, Tsk, and Tb significantly correlated with HR (r=0.932, p<0.001), TS (r=0.888, p<0.001), and m_{sw, tot} (r=0.961, p<0.001), respectively. These results show that during light exercise under hot conditions, 1) in several types of clothing, a critical level of skin temperature causing core temperature elevation may exist, 2) cooling the skin temperature can alleviate heat-stress due to body temperature elevation, and 3) the semi-nude condition is the simplest method of alleviating core temperature elevation without using body cooling materials such as WS or WV.

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.