Cold Acclimation Does Not Alter Physiological or Perceptual Responses During Subsequent Exercise in the Heat

Area of Science:

• Environmental Physiology
• Military Medicine
• Human Adaptation to Extreme Environments

Background:

• Warfighters frequently train in cold environments, potentially leading to inadvertent cold acclimatization and body heat retention.
• Rapid environmental shifts (cold to hot or hot to cold) pose a risk for hyperthermia in cold-acclimatized individuals during strenuous activity.
• Current evidence is lacking on the impact of cold acclimatization on subsequent exercise in heat.

Purpose of the Study:

• To investigate the effect of repeated cold water immersion on physiological and perceptual responses during exercise in a hot environment.
• To determine if cold acclimatization increases the risk of hyperthermia in warfighters exposed to heat stress after cold exposure.

Main Methods:

• Twelve healthy subjects underwent a baseline trial of treadmill walking in 40°C/40% relative humidity.
• Subjects completed a cold acclimation protocol involving seven 90-minute immersions in 10°C water, separated by 24 hours.
• A second heat trial was conducted 24 hours after the final cold immersion to assess physiological and perceptual responses.

Main Results:

• Cold acclimation resulted in decreased skin temperature and attenuated shivering and lactate responses, indicating successful insulative-hypothermic adaptation.
• No significant differences were observed in core temperature, skin temperature, or perceptual responses between the pre- and post-cold acclimation heat trials.
• Findings suggest that cold acclimatization does not alter the body's response to exercise in the heat.

Conclusions:

• Cold acclimatization, induced by repeated cold water immersion, does not appear to increase the risk of hyperthermia during subsequent exercise in hot environments for military personnel.
• Warfighters accustomed to cold environments are unlikely to face heightened thermal strain when transitioning to hot conditions for physical activity.
• The study provides evidence that cold acclimatization does not exacerbate hyperthermia risk during exercise in heat.