Evaluation of a temperate environment test to predict heat tolerance

Area of Science:

• Environmental Physiology
• Human Adaptation
• Thermoregulation

Background:

• A prior heat tolerance test (HTT) was developed to differentiate heat-acclimatized individuals from those with a history of heat stroke.
• Understanding the sensitivity of screening tools to detect physiological adaptations is crucial for heat stress management.

Purpose of the Study:

• To evaluate the heat tolerance test's (HTT) capacity to measure acute individual changes in heart rate (HR) and core body temperature (Tre) responses.
• To assess the utility and sensitivity of HTT as a heat tolerance screening procedure following classical heat acclimation.

Main Methods:

• Fourteen healthy males underwent an initial heat tolerance test (HTT) in a temperate environment.
• Subjects then participated in a 9-day heat acclimation protocol involving treadmill exercise in a hot environment (41.2°C db, 28.4°C wb).
• The HTT was repeated on day 10 to assess changes in physiological responses and composite scores.

Main Results:

• Heat acclimation led to significant decreases in mean heart rate (HR), core body temperature (Tre), and perceived exertion, with plasma volume expansion.
• While mean HR during the repeated HTT was similar, mean Tre significantly decreased.
• The group mean HTT composite score did not change significantly, and individual scores indicated HTT failed to accurately track HR and Tre trends in 6 of 14 subjects.

Conclusions:

• The heat tolerance test (HTT) demonstrated limited sensitivity in detecting individual physiological adaptations to heat acclimation.
• The findings suggest that HTT may not be a sufficiently sensitive screening procedure for assessing acute changes in thermoregulatory responses in normal individuals.