Differences between sexes in rectal cooling rates after exercise-induced hyperthermia.
OBJECTIVE
We evaluated differences between sexes in core cooling rates during cold water immersion after exercise-induced hyperthermia.


METHODS
Ten male (M) and nine female (F) participants, matched for body surface area-to-mass ratio (AD/M) (F: 268 +/- 19 vs M: 261 +/- 16 cm2 x kg(-1)), were recruited for the study. Participants exercised until rectal temperature reached 39.5 degrees C and were subsequently immersed in a 2.0 degrees C circulated water bath until rectal temperature decreased to 37.5 degrees C. Rectal and mean skin temperatures and the relative rate of nonevaporative heat loss (W x m(-2)) were measured continuously during the immersion period.


RESULTS
Males were heavier, had a lower body fat percentage, and had a greater amount of lean body mass compared with females (P < or = 0.05). Significant differences were found in the overall cooling rate for rectal temperature (F: 0.22 +/- 0.07 vs M: 0.12 +/- 0.03 degrees C x min(-1), P = 0.001) and in the overall immersion times (F: 10.89 +/- 4.49 vs M: 18.13 +/- 4.47 min, P = 0.003). Mean skin temperature was lower in females compared with that in males during the immersion period (P < 0.001), although there were no differences between sexes in the rate of nonevaporative heat loss (P = 0.180).


CONCLUSIONS
Although females had a similar AD/M and greater body adiposity, they had approximately 1.7-fold greater rectal cooling rate. Because AD/M and body adiposity do not seem to influence rectal cooling rates in previously hyperthermic individuals, the greater cooling rates in females may be attributed to physical differences in lean body mass.
Lemire
Bruno B
BB
Laboratory of Human Bioenergetics and Environmental Physiology, School of Human Kinetics, Faculty of Health Sciences, University of Ottawa, Ottawa, Ontario, Canada.
Gagnon
Daniel
D
Jay
Ollie
O
Kenny
Glen P
GP
D000328:Adult; D001831:Body Temperature / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D005334:Fever / Q000628:therapy*; D006801:Humans; D007036:Hypothermia, Induced; D007101:Immersion; D008297:Male; D012007:Rectum; D012737:Sex Factors; D014867:Water; D055815:Young Adult
D014867:Water