Comparative studies on thermoregulatory responses to heat between Japanese Brazilians and Japanese

Eight male Japanese Brazilians (20-32 yrs) and 11 male Japanese (22-24 yrs) volunteered for this study. The Brazilians had been staying for about 2-21 weeks in Japan. Their physical characteristics are not significantly different from those of the Japanese. Each one of them sat on a chair for 45 min at 40 degrees C (R.H. 50%) in a climatic chamber. Then, they exercised using a bicycle ergometer in a semi-reclining position for 45 min at 40% of maximal oxygen uptake. Forearm blood flow (FBF), oxygen uptake (VO2), heart rate (HR), skin temperature (Tsk), sweat rate (SR) at chest region and body weight loss (delta Wt) were measured. Thermal sensation and thermal comfort were also measured. Thermal and comfort sensation confirmed that Japanese Brazilians felt cooler and more comfortable in 40 degrees C environment than the Japanese. VO2, SR and delta Wt for both groups were not significantly different. FBF and HR for Brazilians were significantly lower than those for Japanese. Tsk at chest region for Brazilians was found to be significantly higher than that for Japanese. Thus the thermoregulatory responses observed in Japanese Brazilians may be largely attributed to the climate in their native places located on the Tropic of Capricorn.