Effects of exercise on serum cortisol and thyroid hormones

Serum levels of hydrocortisone, T4, T3 and rT3 were estimated before and after exercise. In group A, untrained young subjects had to cope with a submaximal, fractionated load on a bicycle ergometer. T3 increased, rT3 and cortisol decreased, T4 remained unchanged. Sportsmen in group B accomplished a 10 or 15 km run as a part of their regular training. A rise of cortisol and rT3 was observed, T3 remained unchanged and T4 decreased. In better trained sportsmen the initial level of serum T3 exceeded the upper border of normal values (3.3 nmol/l) and the terminal values of cortisol reached a higher value than in the less trained subjects. It is suggested that the mobilization of fuel from energy stores and the oxidative processes are better regulated in trained sportsmen than in untrained subjects. A sign of the best adjustment to a long run was accompanied by an initial serum T3 above the normal borderline and by a great increase of cortisol after the run.