An athlete trains daily in hot humid conditions for six weeks. Compared with her pre-acclimatization state, which combination of adaptations is EXPECTED?

• A Earlier onset of sweating with reduced sweat sodium concentration ✓
• B Later onset of sweating with reduced sweat sodium concentration
• C Earlier onset of sweating with increased sweat sodium concentration
• D Unchanged sweat rate with markedly expanded plasma volume

Explanation

Heat acclimatization produces two cardinal changes: sweating begins at a lower core temperature and reaches much higher maximal rates, and aldosterone-mediated upregulation of ductal sodium reabsorption lowers sweat sodium concentration, conserving salt. Expanded plasma volume supports cardiovascular stability and sustains the increased sweat output. Later onset of sweating would worsen heat storage, and saltier sweat would predispose to heat cramps, so those combinations contradict the physiology. These adaptations develop over one to two weeks and explain improved performance and reduced risk of exertional heat illness.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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