Heat reactions of male and female Caucasians’ C. H. WYNDHAM, J. F. MORRISON, AND C. G. WILLIAMS Human Sciences Laboratory, Transvaal and Orange Free State Chamber of Mines, Johannesburg, South Africa WYNDHAM, C. H., J. F. MORRISON, AND C. G. WILLIAMS. Heat reactions of male and female Caucasians. J. Appl. Physiol. 20(3) : 357-364. 1965. -Thirty male and twenty-six female Caucasians were tested at work levels of I .o liters 02 consump- tion in go F wet-bulb temperature, 93 F dry-bulb temperature, and 80 ft/min air velocity for comparative heat reactions in the unacclimatized state. The females had more severe physi- ological and psychological reactions. Rectal temperatures of 104 F and heart rates of 180 beat/min were reached more rapidly than in the male. The females sweated less and their oxygen consumptions were lower than those of the males. Ten males and four females were then acclimatized to the same extent at the same work rate in 93 F wet-bulb tempera- ture. At the end of the period their reactions were closely similar, although the females responded slower to the ac- climatization procedure. Both groups ended with heart rates of 140 beat/min and rectal temperatures of 102 F. The fe- males, however, continued to sweat less. In a retest at go F wet-bulb temperature, both groups had heart rates of I 30-140 beat/min and rectal temperatures of IO I F. Females still sweated less. The results demonstrate the fact that females react more severely on exposure to severe heat and work con- ditions. Once acclimatized, however, the temperature and circulatory reactions of both sexes are closely similar, but the females sweat less than males. acclimatization of Caucasians to heat Caucasians- acclimatization to heat sex differences -heat reactions physiological reactions to heat 0 UR PRESENT KNOWLEDGE of the physiological re- sponses to heat and of the mechanisms of acclimatiza- tion have been derived from experiments on male subjects. Very little is known of the physiological re- sponses of the female to heat, and even less of her ability to acclimatize to heat. This knowledge is important. Men from the temperate, industrialized countries are turning their attention, increasingly, to the hot, humid and hot, desert regions to exploit their natural resources as those in the temperate regions become exhausted. In this age of equality, the female, undoubtedly, will be Received for publication 14 September 1964. 1 This paper is published with the permission of the Transvaal and Orange Free State Chamber of Mines, Johannesburg, South Africa. expected to follow the male into these regions and to work and live under stressful conditions. The only study we are aware of on the heat reactions of females during acclimatization was reported by Hertig and Sargent (2) to the Leiden Temperature Regulation Symposium at the end of I 962. It is an outstanding con- tribution to knowledge in this field. It has, however, two limitations. One is that the degree of heat stress used was rather mild and does not test fully the ability of the female to adapt to heat. The other is that no parallel study has been done on males under the same stress conditions. No comparison can be made with the reactions of the male and, therefore, it is not yet known whether the extensive data on the male is applicable to the female. Differences between males and females in reaction to heat might be expected. They differ in certain anthro- pometric characteristics which might influence heat transfer, such as surface areas, height/weight ratios, and skinfold thickness; they differ also in endocrine constitu- tion and in the distribution and number of sweat glands in different areas (3). Because of the great practical importance of knowl- edge on this subject a start was made in 1960 on a study of the reactions of unacclimatized females under the same heat stress conditions as those under which 20 unacclimatized male Bantu and 30 Caucasians had been compared (5). A total of 26 females were studied in the unacclimatized state. In December 1962, 4 of 7 female 2nd-yr medical student volunteers were suc- cessfully acclimatized under severe heat stress conditions similar to those in which IO male Caucasians and 18 Bantu had been acclimatized previously. The results of both studies are given in this report. METHODS Subjects commenced with the 4-hr work period in the climatic tent at approximately 8: 30 AM each day. They were in the postabsorptive state and had rested for I hr before the study commenced. Rectal temperatures were measured with clinical thermometers, calibrated to o. I F by the National Physical Laboratory. Body weights, rectal temperatures, and heart rates were measured before commencing work and at the end 357358 WYNDHAM, MORRISON, AND WILLIAMS TABLE I. Anthropological measurements for male and female Caucasians Caucasian males, unacclimatized Caucasian males, acclimatized Caucasian females, unacclimatized Caucasian females, acclimatized 30 IO 26 4 - Height, cm 174.6 (6.54) 163.03 (6.50’ > 163.36 (2.302) Weight, kg 70.24 (7.016) 69934 6972) 59.4 (10.02) 59.7 (9*19> Surf ace Skinfold, Area, rn2 mm I .86 bI3d I .83 (0.122) I .63 (0. ‘42) I .65 (0.101) 8.09 (2.994) 8.27 (2.621) II .I2 (3.2’6) 10.08 (3.512) of each hour. Subject were encouraged to drink water as often as possible. Water intake and urine output vol- umes were recorded. Approximately 3 min before the end of each hour heart rates were recorded while stepping, after which the sub- jects stopped work for the recording of rectal tempera- tures and body weights. Male subjects wore shorts and female subjects, bikini- type clothing; both groups dispensed with these when they wished. Subjects were withdrawn from the climatic tent when
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