TSH, T3, rT3 and fT4 in maximal and submaximal physical exercise.

The response of various thyroid hormone parameters to maximal physical exercise (MPE) was investigated in 14 medium and long distance runners and 13 divers. The effects of submaximal long time physical exercise (SMPE) was examined in seven divers. The TSH-level decreases significantly during MPE and slightly rises again after the end of the exercise. In SMPE, however, TSH continuously rises until 15 min after the end of the exercise. The T3 level rises significantly in MPE and falls below the initial value 15 min after the exercise finishes, during SMPE it remains practically unchanged and slightly decreases after the finish. In MPE, the rT3 level does not change and slightly decreases after termination, while the fT4 level continuously decreases from the beginning till 15 min after the exercise period. The latter two parameters do not show any change in SMPE. As possible reasons for the changes of TSH levels a decrease (MPE) or an increase (SMPE) of pituitary secretion might play a role. Furthermore, in MPE the rise in T3 level might be related to hemoconcentration, and the decrease in fT4 level to an elevated cellular utilization.