Thermoregulation during cold exposure: effects of prior exercise

Area of Science:

• Environmental Physiology
• Exercise Physiology

Background:

• Maintaining thermal balance is crucial for human survival and performance.
• Understanding how acute exercise affects thermoregulation during subsequent cold exposure is important for safety in cold environments.

Purpose of the Study:

• To investigate if acute exercise impairs the body's ability to maintain thermal balance during subsequent cold air exposure.
• To compare thermal responses following exercise-induced heating versus passive heating before cold exposure.

Main Methods:

• Ten healthy men underwent a cold-air test (4.6°C) after two conditions: 60 minutes of cycling exercise (Ex) at 55% peak oxygen uptake or passive heating (Heat).
• Exercise was performed in 35°C water immersion, while passive heating was in 38.2°C water immersion, adjusted to achieve similar end-immersion rectal temperatures.
• Thermal variables including rectal temperature, heat flow, insulation, and metabolic heat production were measured during the cold-air test.

Main Results:

• Following exercise, rectal temperature was significantly lower (40-120 min) compared to passive heating.
• Mean weighted heat flow and insulation were significantly higher after exercise, indicating increased heat loss.
• Metabolic heat production, including shivering response, was not significantly different between the two conditions.

Conclusions:

• Acute exercise may compromise the body's capacity to maintain thermal balance during subsequent cold exposure.
• Prior exercise appears to increase susceptibility to heat loss and core temperature decline in cold environments.
• The studied exercise protocol did not impair the shivering response to cold exposure.