Strenuous, Fatiguing Exercise: Relationship of Cortisol to Circulating Thyroid Hormones

he purposes of this study were to determine how strenuous, fatiguing running exercise affects: 1) selective thyroid hormones, and 2) the relationship of glucocorticoid responses to such exercise with  thyroid hormones.
Materials and Methods: Well-trained subjects (n=12) performed a treadmill run at individual ventilatory threshold (74±8% of maximal aerobic capacity) until volitional fatigue (68.3±12.3 min).Blood samples were taken before exercise as a resting baseline (BO), at fatigue (FG), 90-minutes into recovery (90mR), and 24-hours into recovery (24hR). Blood was analyzed for free T3 (fT3), free T4 (fT4), thyroid-stimulating hormone (TSH),and cortisol.
Results: Significant increases in fT3 and TSH concentrations between BO and FG (fT3= 1.70 pglmL vs. 2.08 pglmL; TSH=1.69 pIU/mL vs. 2.43 pIU/mL, p tively; p<0.05). FG fT4 demonstrated a non significant increase from BO (FG fT4=1.84 ngldL)but by 24hR fT4 was significantly lower than FG (24hR fT4=1.67 ngldL, p (892.2 nmoljL) but returned to baseline by 24hR. Spearman correlation analysis yielded a significant negative correlation between FG cortisol and 24hR TSH (r= -0.65, p<0.05). A strong trend was also noted between FG cortisol and 24hR ft3 (r = -0.55, p<0.07).
Conclusion:? These findings suggest that exhaustive exercise decreases the level of selective thyroid hormones by 24 hours into recovery, and that cortisol levels after fatiguing exercise are negatively related to circulating TSH at this point into recovery.