Sex-based differences in body core temperature response across repeat work bouts in the heat

Area of Science:

• Environmental Physiology
• Human Performance
• Occupational Health

Background:

• Heat strain during repeated work bouts is a concern, especially in demanding environments like military operations.
• Understanding sex-based differences in thermoregulation is crucial for optimizing heat exposure protocols.

Purpose of the Study:

• To examine how repeated work bouts in heat affect peak body core temperature.
• To investigate potential sex-based differences in physiological responses to heat during exercise.

Main Methods:

• Fourteen males and fifteen females completed four alternating heavy and moderate work bouts in hot conditions (32.5°C WBGT) with intermittent rest.
• Participants wore military combat uniforms with a 10 kg load during work, with protective gear removed during rest.
• Body core temperature was monitored throughout the trial.

Main Results:

• Body core temperature rose faster during the first work bout compared to subsequent bouts.
• Initial heat strain was similar between sexes, but females maintained significantly lower body core temperatures in later work bouts.
• A reduction in heat storage occurred across successive exercise bouts.

Conclusions:

• Repeated work bouts in heat did not lead to cumulative heat strain as expected.
• Physiological adaptations, such as reduced heat storage, mitigated increasing heat strain in subsequent exercise bouts.
• Sex-based differences in thermoregulation emerged after the initial heavy work bout, with females exhibiting lower core temperatures.