Describe the main features of heat acclimation, including physiological changes.

• A. Delayed sweating response
• B. Higher plasma volume
• C. Early sweating response, larger plasma volume, more efficient cardiovascular response, improved evaporative cooling capacity, lower core temperature for a given heat load.
• D. Lower sweat rate and higher heart rate

Answer: (C)

Heat acclimation produces a set of physiological adjustments that make thermoregulation during heat exposure more efficient. A key feature is an earlier sweating response, where sweating begins sooner as heat exposure starts. This starts the evaporative cooling process earlier and helps keep the core temperature lower during heat stress. At the same time, plasma volume expands with repeated heat exposure, which improves venous return and allows a higher stroke volume. With a greater stroke volume, the heart can pump the same amount of blood with a lower heart rate, reducing cardiovascular strain during heat stress.

The cardiovascular system becomes more efficient at directing blood to the skin for heat loss, while evaporative cooling capacity is enhanced through greater and more effective sweating. The net result is better heat dissipation and a lower core temperature for a given heat load.

Choosing this combination captures the full range of adaptations seen with heat acclimation: earlier sweating, increased plasma volume, a more efficient cardiovascular response, improved evaporative cooling, and a lower core temperature under heat stress. Delayed sweating, a lower sweat rate, or a higher heart rate would indicate less adaptation and poorer thermoregulation.