Background: This study examined how prolonged, exhaustive exercise affects: (1) thyroid hormones, and (2) the interrelationship of cortisol and prolactin responses to such exercise on thyroid hormones.
Material and methods: Male subjects performed a treadmill run at their individual ventilatory threshold until exhaustion. Blood samples were taken before exercise at rest, baseline (BL), at exhaustion (EXH), 30-60-90-minutes into recovery (30 mR, 60 mR, 90 mR), and 24-hours into recovery from exercise (24 hR). Blood was analyzed for free T₃ (fT₃), free T₄ (fT₄), thyroid-stimulating hormone (TSH), cortisol and prolactin.
Results: ANOVA analysis revealed that at EXH all hormones were increased (p < 0.01) from BL levels. At 30 mR and 60 mR the thyroid hormones had decreased and returned to BL levels; however, cortisol and prolactin remained significantly increased (p < 0.05). At 90 mR all hormones were not different from BL levels. By 24 hR, cortisol, fT₃ and TSH were decreased from BL (p < 0.05). Correlations revealed EXH cortisol responses were related to the 24 hR TSH responses (rs = -0.69, p < 0.01). In addition, EXH cortisol and 24 hR fT₃ responses were related (rs = -0.51, p < 0.02). Furthermore, the EXH prolactin and TSH responses were related (rs = +0.56, p < 0.01), and the 30 mR prolactin responses were related to the EXH TSH responses (rs = +0.43, p < 0.05).
Conclusions: Exhaustive exercise; (1) decreases select thyroid hormones by 24 hours into recovery, (2) cortisol responses are inversely related to these thyroid reductions, and (3) prolactin responses (increases) are directly related to TSH changes.