During intense exercise in a hot environment, which thermoregulatory mechanism accounts for the greatest proportion of heat loss from the body surface?
- A Evaporation of sweat ✓
- B Radiation
- C Convection
- D Conduction
Correct answer: A. Evaporation of sweat
Explanation
At rest in a thermoneutral environment, radiation accounts for ~60% of heat loss, convection ~12%, and evaporation ~25%. However, during intense exercise or in hot environments where ambient temperature approaches or exceeds skin temperature, radiation and convection become ineffective (and may even add heat). Evaporation of sweat then becomes the dominant — effectively the only — heat loss mechanism, capable of removing up to 10 kcal/min when sweat rate is maximal. Each gram of sweat evaporation dissipates approximately 0.58 kcal.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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