Hypohydration and acclimation: effects on hormone responses to exercise/heat stress

Area of Science:

• Exercise Physiology
• Environmental Stress
• Endocrinology

Background:

• Dehydration significantly impacts physiological responses during exercise.
• Heat acclimation is known to alter stress hormone profiles.
• Understanding these interactions is crucial for performance and health in demanding environments.

Purpose of the Study:

• To investigate the combined effects of hypohydration and heat acclimation on plasma cortisol (PC) and growth hormone (GH) during exercise.
• To compare responses in hot-wet versus hot-dry environmental conditions.

Main Methods:

• Participants underwent exercise protocols in controlled hot-wet and hot-dry environments.
• Body weight was monitored to induce hypohydration (-5% body weight).
• Plasma cortisol and growth hormone levels were measured before and during exercise intervals.

Main Results:

• Hypohydration significantly increased plasma cortisol levels during exercise in both environments.
• Heat acclimation did not alter PC levels in euhydrated states but attenuated the PC response in hypohydrated, hot-wet conditions.
• Hypohydration generally elevated growth hormone levels compared to euhydration, with inconsistent effects of acclimation.

Conclusions:

• Hypohydration to -5% body weight generally elevates circulating stress hormones (PC and GH) during exercise.
• Heat acclimation did not consistently reduce these stress hormone responses to exercise under the tested conditions.