Hypohydration effects on thermoregulation during moderate exercise in the cold

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Human Physiology

Background:

• Hyperosmotic hypovolemia is known to impair vasoconstriction during sedentary cold exposure.
• Understanding the impact of hypohydration on physiological responses during exercise in cold environments is critical for athletes and military personnel.

Purpose of the Study:

• To investigate whether hypohydration alters thermoregulation and cardiovascular responses during moderate-intensity exercise in cold air.
• To compare physiological responses between hypohydrated and euhydrated states in both cold and temperate conditions.

Main Methods:

• Eight healthy males performed 60-minute walks at 50% maximal oxygen uptake (VO(2max)) in 4°C (Cold) and 25°C (Temperate) environments.
• Participants were tested in both hypohydrated (-4% body mass) and euhydrated states.
• Measurements included rectal temperature (T(re)), mean weighted skin temperature, heart rate (HR), cardiac output (CO), and stroke volume (SV).

Main Results:

• Mean weighted skin temperature was lower in the cold compared to temperate conditions, but not different between hydration states.
• Rectal temperature (T(re)) was not significantly different between hypohydrated and euhydrated conditions during cold exposure.
• Cardiac output (CO), stroke volume (SV), and heart rate (HR) showed no significant differences between hydration states or between cold and temperate environments.

Conclusions:

• Moderate-intensity exercise in the cold while hypohydrated does not alter metabolic heat production, skin temperatures, or heat loss.
• Hypohydration does not increase thermoregulatory or cardiovascular strain during exercise in cold air.
• These findings suggest that moderate hypohydration may not significantly impair physiological function during cold-weather exercise.