Thyroid hormonal responses to intensive interval versus steady-state endurance exercise sessions

Area of Science:

• Exercise Physiology
• Endocrinology
• Sports Science

Background:

• Thyroid hormones (T₄, T₃, rT₃) are crucial for metabolic regulation.
• Exercise intensity and duration influence hormonal responses.
• Understanding these responses is key for optimizing training and preventing overtraining.

Purpose of the Study:

• To compare the acute thyroid hormonal and cortisol responses to high-intensity interval exercise (IE) versus steady-state endurance exercise (SEE) in highly trained males.
• To investigate the recovery kinetics of these hormones up to 12 hours post-exercise.

Main Methods:

• Fifteen highly trained males underwent three conditions: IE, SEE, and a control (CON) session.
• IE involved intense intervals (100-110% VO₂max) with active recovery.
• SEE involved continuous moderate-intensity exercise (60-65% VO₂max). Blood samples were analyzed for free T₄, free T₃, reverse T₃, and cortisol at pre-, immediate post-, and 12-hour post-exercise.

Main Results:

• Both IE and SEE significantly elevated hormones immediately post-exercise compared to CON.
• At 12 hours post-exercise, IE showed significantly reduced free T₃ and elevated reverse T₃ compared to SEE and CON.
• Correlations indicated that higher cortisol post-IE was associated with greater reverse T₃ and lower free T₃ at 12 hours post-exercise.

Conclusions:

• High-intensity interval exercise impairs peripheral conversion of thyroxine to triiodothyronine, suggesting a need for extended recovery compared to steady-state endurance exercise.
• These findings inform training program design, emphasizing recovery needs to prevent overreaching and overtraining syndrome.