Thyroid hormones response in simulated laboratory sprint duathlon

Abstract

Increased activity of the pituitary-thyroid axis, plays a role in adaptations to exercise. The aim of this study was to assess changes in thyroid hormones (TH) in a simulated laboratory competition of sprint duathlon. Eight duathletes trained males [mean (SD), age 24.8 (6.8) years, height 174.4 (6.8) cm, body mass 67.12 (8.1) kg] participate in this study. The duathletes performed two graded maximal exercise in random order, one on cycle-ergometer and other on a treadmill, to determine their VO2peak. Simulated laboratory competition was carried out during 20 min Run1, 40 min Bike and 12 min Run2 sectors. A blood sample was drawn to determine serum concentrations of TSH, T4, T3 and were analyzed by chemiluminiscence. A one-way analysis of variance (ANOVA) was used to analyze differences among sectors and Pearson correlation coefficients were calculated between TH and exercise intensity. Athletes perform a high intensity exercise reaching high mean values of aerobic power (89.6 ± 6.1, 85.1 ± 8.7 and 87.1 ± 6.9 of %VO2 in Run1, Bike and Run2 respectively). TSH shown differences between -30 min and Run2 (p< 0.05), and did not found changes in T3 and T4 during exercise (p>0.05). Significant inverse correlations between T3 (r= -0.86) and T4 (r= -0.86) and percent VO2 (p<0.01) were found. The hormones of the hypothalamic-pituitary-thyroid axis show significant changes in TSH. Thus our results suggest, at least partly, an association between both T3 and T4 with intensity of competition as percent of VO2 in athletes with normal thyroid function during intense and submaximal exercise simulating a duathlon competition. The decrease of TH in relation to exercise intensity is due to the use of peripheral tissues. In conclusion our findings suggest that thyroid function might play a role related to exercises performed to high intensity.