Ronsen, O., Haug, E., Rasmussen, T., Pedersen, B., K., & Bahr, R. (1998). Hormonal response to single vs repeated bouts of intensive endurance exercise. Medicine and Science in Sports and Exercise, 30(5), Supplement abstract 1551.

The hormonal response of one versus two endurance bouts of exercise on the same day was compared. Elite athletes (triathlon = 4; speed skating = 5) were measured at rest and during exercise (65% VO2max for 65 minutes on a cycle ergometer). A rest period of three hours was provided between the two test trials. Ss rested in bed when not exercising.

The responses of testosterone and human growth hormone (hGH) were different between the rest and exercise trials. Under the rest condition, there was no diurnal change in hGH but testosterone was 33% lower in the early evening. During both exercise trials testosterone and hGH increased similarly and significantly above rest values. During recovery from exercise, testosterone was suppressed but hGH was elevated when compared to the rest condition values. There was a difference between the one and two-bout exercise conditions in hGH but not testosterone. In the two-exercise condition, the level of testosterone in the second bout was significantly lower than in the first.

Previous exercise on the same day suppresses testosterone reactivity in the second exercise bout. There is no affect of previous exercise on hGH values.

Implication. Previous exercise suppresses testosterone but not hGH. Extraneous use of testosterone, as in drug cheating, would increase the quality of responses in a second training session.

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