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Differences between sexes in rectal cooling rates after exercise-induced hyperthermia
Bruno B Lemire1, Daniel Gagnon, Ollie Jay
1Laboratory of Human Bioenergetics and Environmental Physiology, School of Human Kinetics, Faculty of Health Sciences, University of Ottawa, Ottawa, Ontario, Canada.
Medicine and Science in Sports and Exercise
|July 2, 2009
Summary
Females exhibited significantly faster rectal cooling rates during cold water immersion post-exercise hyperthermia compared to males. This enhanced cooling in females, despite similar body surface area-to-mass ratios, may be linked to differences in lean body mass.
Area of Science:
- Exercise Physiology
- Thermoregulation
- Environmental Medicine
Background:
- Understanding sex-based differences in thermoregulation is crucial for optimizing heat stress management.
- Exercise-induced hyperthermia significantly elevates core body temperature, necessitating effective cooling strategies.
- Cold water immersion is a common method for rapid body cooling, but its efficacy may vary between sexes.
Purpose of the Study:
- To investigate and compare the core cooling rates between males and females following exercise-induced hyperthermia.
- To determine if sex differences exist in the physiological responses during cold water immersion.
- To explore the influence of body composition and surface area-to-mass ratio on cooling efficacy.
Main Methods:
- Ten males and nine females, matched for body surface area-to-mass ratio, underwent exercise to induce hyperthermia (rectal temperature of 39.5°C).
- Participants were then immersed in a 2.0°C water bath until their rectal temperature decreased to 37.5°C.
- Continuous measurements of rectal temperature, mean skin temperature, and non-evaporative heat loss rate were recorded.
Main Results:
- Females demonstrated a significantly higher overall rectal cooling rate (0.22°C/min) compared to males (0.12°C/min).
- Immersion times were shorter for females (10.89 min) than for males (18.13 min).
- Despite lower mean skin temperatures, females and males exhibited no significant difference in the rate of non-evaporative heat loss.
Conclusions:
- Females experienced approximately 1.7 times greater rectal cooling rates than males after exercise-induced hyperthermia.
- Body surface area-to-mass ratio and body adiposity did not appear to be primary determinants of rectal cooling rates in this context.
- Greater lean body mass in females may be a key factor contributing to their enhanced cooling efficiency during cold water immersion.
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