Sex-related differences in thermoregulatory responses while wearing protective clothing |
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Authors: | T M McLellan |
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Institution: | (1) Human Protection and Performance Sector, Defence and Civil Institute of Environmental Medicine, 1133 Sheppard Ave. W, PO Box 2000, Toronto, Ontario, Canada M3M 3B9, CA |
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Abstract: | This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In
total, 13 M mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5) kg, height␣1.79␣(0.06) m, surface area to mass ratio 2.46␣(0.18) m2 · kg−1 · 10−2, Dubois surface area 2.01 (0.16) m2, %body fatness 14.6 (3.9)%, V˙O2peak 49.0 (4.8) ml · kg−1 · min−1] and 17 F 23.2 (4.2) years, 62.4 (7.7) kg, 1.65 (0.07) m, 2.71 (0.14) m2 · kg−1 · 10−2, 1.68 (0.13) m2, 20.2 (4.8)%, 43.2 (6.6) ml · kg−1 · min−1, respectively] performed light intermittent exercise (repeated intervals of 15 min of walking at 4.0 km · h−1 followed by 15 min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical
protective clothing (0.29 m2 ·°C · W−1 or 1.88 clo, Woodcock vapour permeability coefficient 0.33 i
m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of
their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats · min−1 at 105 min (n = 13) compared with 145.1 (14.4) beats · min−1 for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature () was higher for F. The increase in rectal temperature (T
re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105 min compared with an increase of 1.37 (0.29)°C for
M. Tolerance times were significantly longer for M 142.9 (24.5) min] than for F 119.3 (17.3) min]. Partitional calorimetric
estimates of heat storage (S) revealed that although the rate of S was similar between genders 42.1 (6.6) and 46.1 (9.7) W · m−2 for F and M, respectively], S expressed per unit of total mass was significantly lower for F 7.76 (1.44) kJ · kg−1] compared with M 9.45 (1.26) kJ · kg−1]. When subjects were matched for body fatness (n = 8 F and 8 M), tolerance times 124.5 (14.7) and 140.3 (27.4) min for F and M, respectively] and S 8.67 (1.44) and 9.39 (1.05) kJ · kg−1 for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory
disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can
be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness.
Accepted: 31 October 1997 |
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Keywords: | Rectal temperature Heat storage Gender Body composition Aerobic fitness |
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