Which of the following is a sign of adequate heat acclimation in a trained individual?

• A. Lower plasma volume
• B. Higher heart rate for a given workload
• C. Earlier onset of sweating
• D. Decreased evaporative cooling capacity

Answer: (C)

The key idea is that heat acclimation makes the body's cooling and cardiovascular responses more efficient. The most telling sign is that sweating starts earlier during exercise. Beginning sweating at a lower core temperature means evaporation begins sooner, which cools the body more effectively and helps keep core temperature in check as work continues. This earlier cooling reduces the need for the heart to compensate with large increases in rate, so trained individuals typically show a lower heart rate for the same workload and, overall, better maintenance of performance in heat.

In contrast, lower plasma volume would hinder heat dissipation and stroke volume, not reflect adaptation (plasma volume tends to rise with acclimation). A higher heart rate for the same workload indicates poorer adaptation, not adequate acclimation. Decreased evaporative cooling capacity would opposite reflect improved cooling, whereas acclimation actually enhances evaporative cooling through more efficient sweating.