Serum thyroid hormones, thyrotropin and thyroxine binding globulin during prolonged strength training

Area of Science:

• Exercise Physiology
• Endocrinology
• Sports Science

Background:

• Progressive strength training is a common method to enhance physical performance.
• The impact of prolonged, intensified training on endocrine function, particularly the pituitary-thyroid axis, requires further elucidation.

Purpose of the Study:

• To investigate the effects of 24 weeks of progressive strength training on maximal strength and pituitary-thyroid function in males.
• To examine the changes during a subsequent 12-week detraining period.

Main Methods:

• 21 male participants underwent 24 weeks of progressive strength training.
• Maximal strength and serum concentrations of thyroid hormones (total T4, free T4, triiodothyronine), thyrotropin, and thyroxine binding globulin were measured.
• Measurements were taken during the training period and a subsequent 12-week detraining period.

Main Results:

• Maximal strength significantly increased during training (p < 0.001) and decreased significantly during detraining (p < 0.001).
• Serum total thyroxine (T4) and free thyroxine (fT4) concentrations decreased during training (p < 0.05 and p < 0.01, respectively) and returned to baseline during detraining.
• A positive correlation was observed between changes in serum fT4 and maximal force during the most intense training phase (r = 0.56; p < 0.01). No significant changes were noted in triiodothyronine, thyrotropin, or thyroxine binding globulin.

Conclusions:

• Prolonged, intensified strength training can lead to minor reductions in serum total and free T4 concentrations.
• These observed hormonal changes are unlikely to have clinical significance and may have only marginal physiological relevance.
• The pituitary-thyroid axis appears largely resilient to the demands of this training regimen.