Cold Tolerance of Japanese Assessed by the Lower Critical Temperature and so on

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Five male Japanese adults were exposed to 10°C, 20°C, 25°C and 28°C ambient for 2 hr. The mean skin temperature, rectal temperature and heat production were measured during each exposure. In addition the electromyogram was led for monitor of the shivering. These results were compared with others from Japanese and some ethnical groups.The mean skin temperature decreased significantly with decreased ambient temperature. The amount of decrese was less than that of Caucasian and Bantu groups. The rectal temperature was independent of the ambient temperature, although it showed increment for Caucasians and decrement for Bantu with decreased ambient temperature. Significant increase in heat production during cold exposure was less than that for Caucasians and was about the same for Bantu. The severity of shivering was coincident well with heat production. The ratio of increase in heat production to decrease in mean skin temperature was caliculated as a parameter of cold tolerance. The ratio for this group was larger than that for other Japanese group. The discrepancy was interpreted as to be caused by the different experimental procedure. Although no difference was noticed in the ratio between this group and Caucasians, a difference in the response to cold was discussed. The lower critical temperature that was caliculated by the intercept method was 22.0°C for this group, and the average for this group from individual estimations was 21.7°C. These were lower than those for other ethnical groups. The difference among them was discussed from view points of the experimental procedure and human adaptability to cold.