Thyroid hormones may influence the slow component of Vo2 in professional cyclists

We analyzed the relationship between the plasma concentrations of several hormones (testosterone [T], follicle-stimulating [FSH] and luteinizing hormone [LH], cortisol [C], 3,5,3 ' -triiodothyronine [T-3], thyroxine [T-4], and thyrotrophin [TSH]) and the magnitude of the (V) over dotO(2) slow component (Delta (V) over dotO(2)) in a group of nine professional road cyclists (26 +/-2 years). The resting levels of the aforementioned hormones were determined before the subjects performed a 20-min cycle ergometer test at similar to 80% of (V) over dotO(2max) (or similar to 400 W). Plasma concentrations of T-3 and T-4 were inversely correlated (p <0.05) with Delta (V) over dotO(2) (r=-0.72 and r=-0.66, respectively), suggesting, at least partly, and association between thyroid basal function and the (V) over dotO(2) slow component of euthyroid elite endurance athletes during constant-load intense exercise.