Acclimation Training Improves Endurance Cycling Performance in the Heat without Inducing Endotoxemia

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Immunology

Background:

• Endurance athletes use heat training to adapt for competition.
• The immune system's response to acute heat training is not well understood.
• This study investigates heat training's effects on performance and immune markers.

Purpose of the Study:

• To examine the impact of short-term heat training on endurance performance.
• To assess changes in immune system biomarkers (interleukin-6, immunoglobulin M, lipopolysaccharide) following heat exposure.
• To determine if heat training poses an acute challenge to the immune system.

Main Methods:

• 24 moderately-fit males were randomized into HOT (heat), NEUTRAL (neutral), or CON (control) groups.
• HOT and NEUTRAL groups completed 7 cycling sessions over 18 days.
• Participants underwent heat stress tests (HST) with serum sample analysis before and after.

Main Results:

• Both HOT and NEUTRAL groups improved 5 km time trial performance significantly.
• The HOT group showed further performance gains in later heat stress tests.
• Interleukin-6 levels increased post-exercise, but immunoglobulin M and lipopolysaccharide remained unchanged.

Conclusions:

• Short-term heat training enhances cycling performance by ~6%, comparable to neutral conditions.
• Additional heat sessions provided a further ~3% performance improvement.
• Heat training did not present a significant acute challenge to the immune system.