Differences between Sexes in Rectal Cooling Rates after Exercise-Induced Hyperthermia


Medicine & Science in Sports & Exercise: August 2009 - Volume 41 - Issue 8 - pp 1633-1639
doi: 10.1249/MSS.0b013e31819e010c
Basic Sciences

Purpose: 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·kg−1), were recruited for the study. Participants exercised until rectal temperature reached 39.5°C and were subsequently immersed in a 2.0°C circulated water bath until rectal temperature decreased to 37.5°C. Rectal and mean skin temperatures and the relative rate of nonevaporative heat loss (W·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 ≤ 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°C·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 ∼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.

Laboratory of Human Bioenergetics and Environmental Physiology, School of Human Kinetics, Faculty of Health Sciences, University of Ottawa, Ottawa, Ontario, CANADA

Address for correspondence: Glen P. Kenny, Ph.D., University of Ottawa, School of Human Kinetics, 125 University, Montpetit Hall, Room 367, Ottawa, Ontario, Canada K1N 6N5; E-mail: gkenny@uottawa.ca.

Submitted for publication November 2008.

Accepted for publication January 2009.

© 2009 American College of Sports Medicine