| Research Abstract |
After daily heat exposure or exercise for 4-5 h limited to a fixed time for more than 5 consecutive days, body core temperature of rats drops before and during the period they were previously exposed to heat. To investigate the influence of exposure to heat or exercise performance, we measured the changes of hematological status, anaerobic threshold (AT : V-slope), maximal oxygen consumption (VO_2max), and sweat rate during exercise in long distance student runners before and after continuous heat exposure at tropical regions (Thailand). And after the core temperature is regard as oral temperature, when they wake up, their basal body temperature were measured. After then, they were measured 5 times everyday (before a breakfast, at resting time before and after an exercise, before a dinner, and before going to bed). The amount of sweat during exercise is measured as a sweat loss with the following equation. Sweat loss = (weight before during exercise + weight of drinking water) - weight
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after the exercise. The ambient temperature is measured with WBGT with a heat environment checker (Kyoto Electronics Manufacturing Co.,Ltd).
Changes in basal and resting core temperature (Tcor) during 12 experimental days in hot environment
In the case of staying in Japan, Tcor kept about 35.9℃ and in the case of Thailand, the Tcor shifted to the neighborhood of 36.4℃. After they came back to Japan, the Tcor kept 36.3℃ on the second day. In staying in Japan, the Tcor of resting after an exercise was always lower than that of resting before an exercise. On the other hand and in the case of Thailand, the result was opposite. Thus, our human basal temperature may be rise by repeating exercise in hot environment.
Although the sweat rate during exercise showed about 700g/h under cold environment of Japan, the sweat rate increased largely until the 5th day after the participant moved to Thailand, it decreased a little and kept about 1400g/h. When the subjects were 2 hour exercising in winter in Japan, the amount of drinking water was not observed, but the amount kept about 500g/h in Thailand. These result suggested that the raising of basal temperature after repeating exercise in hot environment is caused by dehydration.
The difference of physiological responses between pre- and post- heat exposure during maximal exercise, sweat rate during maximum exercise after 12 heat exposure.
The hematological data (RBC, Ht) and heart rate were significantly lower before heat-acclimation than after heat-acclimation. VO_2max and sweat rate were significantly higher before heat-acclimation than after heat-acclimation. These results indicate that maximal aerobic power may be increased by consecutive heat exposure. And this increased exercise performance is caused by plasma and blood volume. Less
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