Salivary cortisol response to post-exercise infrared sauna declines over time

Area of Science:

• Sports Science
• Exercise Physiology
• Heat Therapy

Background:

• Post-exercise heat exposure may aid recovery but increases physiological stress.
• Infrared sauna (IRS) is a heat therapy modality with potential recovery benefits.
• Understanding the adrenal and autonomic nervous system (ANS) responses to IRS is crucial for athlete well-being.

Purpose of the Study:

• To investigate the effects of post-exercise infrared sauna (IRS) on adrenal and autonomic nervous system (ANS) responses in female athletes.
• To examine the adaptation of these physiological responses over a 6-week training intervention.
• To compare IRS effects against passive recovery (CON).

Main Methods:

• Forty female team-sport athletes were pair-matched into IRS and control (CON) groups.
• Participants underwent jumping exercises followed by IRS (10 min, 50 °C) or passive recovery.
• Physiological assessments included nocturnal heart rate, heart rate variability, salivary cortisol, muscle soreness, and perceived recovery, measured in the first (EX1) and last (EX2) weeks of a 6-week intervention.

Main Results:

• The IRS group showed elevated morning cortisol after EX1 compared to CON (p=0.017).
• A greater pre-post cortisol change was observed in EX1 (4.6 nmol/l) versus EX2 (-1.8 nmol/l) in the IRS group.
• The IRS group had higher post-session heart rate in EX1 (61 bpm vs. 55 bpm; p=0.019), and less muscle soreness at 36h post-exercise in EX2 compared to CON.

Conclusions:

• Post-exercise IRS initially elevates physiological stress markers in female athletes.
• Six weeks of regular IRS use leads to adaptation in ANS balance and cortisol response.
• These findings suggest effective physiological adjustment to heat intervention within six weeks, potentially enhancing recovery.