Thyroidal changes associated with endurance training in women.

Area of Science:

• Endocrinology
• Exercise Physiology
• Sports Medicine

Background:

• The pituitary-thyroid axis plays a crucial role in regulating metabolism and responding to physiological stress.
• Endurance training is known to induce significant adaptations in body composition and hormonal profiles.
• Understanding the impact of progressive endurance exercise on thyroid function is essential for athletes and clinicians.

Purpose of the Study:

• To investigate the relationship between endurance training, changes in body composition, and the pituitary-thyroid axis in healthy young women.
• To assess hormonal changes in thyroid hormones (T4, T3, rT3) and thyroid-stimulating hormone (TSH) in response to increasing training loads.

Main Methods:

• 17 healthy young women underwent assessments of body composition and plasma thyroid hormone levels at baseline, after 48 km/week increase, and after 80 km/week increase in training distance.
• Measurements included T4, T3, rT3, resin T3 uptake, TSH, and TRH-stimulated TSH.
• Statistical analysis was performed to determine significant changes over time.

Main Results:

• Lean body mass significantly increased with training, while total body weight remained unchanged.
• Initial training (delta 48) showed mild thyroidal impairment with decreased T3 and rT3, and an exaggerated TSH response to TRH.
• Prolonged training (delta 48 to delta 80) led to increased T4, rT3, and unstimulated TSH, with decreased T4/rT3 and T3/rT3 ratios and blunted TSH response to TRH.

Conclusions:

• Progressive endurance training in young women leads to significant increases in lean mass and alters pituitary-thyroid axis function.
• The observed thyroidal changes with prolonged training resemble those seen in other non-thyroidal stress conditions.
• These findings highlight the complex interplay between exercise, body composition, and thyroid regulation.