Thyroid hormones may influence the slow component of VO(2) 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 VO(2) slow component (Delta VO(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 approximately 80% of VO(2 max) (or approximately 400 W). Plasma concentrations of T(3) and T(4) were inversely correlated (p<0.05) with Delta VO(2) (r=-0.72 and rr=-0.66, respectively), suggesting, at least partly, and association between thyroid basal function and the VO(2) slow component of euthyroid elite endurance athletes during constant-load intense exercise.