Sweat rate and sweat composition during heat acclimation.

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Human Adaptation

Background:

• Heat acclimation (HA) improves thermoregulation through physiological adaptations.
• Understanding the time course and retention of these adaptations is crucial for optimizing training protocols.

Purpose of the Study:

• To quantify local sweat rate (LSR) and sweat composition changes during a 10-day HA protocol.
• To investigate the time course of sudomotor adaptations during HA.
• To examine the retention of HA adaptations following a 28-day decay and subsequent heat re-acclimation (HRA).

Main Methods:

• Ten days of controlled hyperthermia (cycling to 38.5°C rectal temperature in 33°C/65% RH).
• Measurement of LSR and sweat electrolyte (sodium, chloride, lactate, potassium) concentrations on arm and back.
• Assessment of adaptation decay over 28 days and restoration with 5 days of HRA.

Main Results:

• LSR significantly increased by day 10 of HA (arm: +58%, back: +36%).
• Sweat sodium, chloride, and lactate concentrations decreased significantly (~60%) by day 10.
• Adaptations began early in HA (e.g., sodium/chloride conservation from day 3), with some evidence of retention after decay and restoration after HRA.

Conclusions:

• Ten days of exercise-induced HA effectively increases LSR and reduces sweat electrolyte concentrations.
• Sudomotor adaptations occur progressively during HA, with varying induction times.
• HA-induced adaptations show partial conservation after a decay period and can be restored with HRA.