Previous pharmacological and pathological studies have reported negative relationships between circulating testosterone and certain stress hormones (i.e., cortisol and prolactin) in humans. These relationships have subsequently been used in hypotheses explaining the subclinical resting testosterone levels often found in some endurance-trained males, but as of yet no one has specifically examined these relationships as they relate to exercise. Thus, we examined the relationship between total and free testosterone levels and cortisol, and between total and free testosterone and prolactin following prolonged endurance exercise in trained males. Twenty-two endurance-trained males volunteered to run at 100% of their ventilatory threshold (VT) on a treadmill until volitional fatigue. Blood samples were taken at pre-exercise baseline (B0); volitional fatigue (F0); 30 min (F30), 60 min (F60), and 90 min (F90) into recovery; and at 24 h post-baseline (P24 h). At F0 [mean running time = 84.8 (3.8) min], exercise induced significant changes (P<0.05) from B0 in total testosterone, cortisol and prolactin. All three of these hormones were still significantly elevated at F30; but at F60 only cortisol and prolactin were greater than their respective B0 values. Free testosterone displayed no significant changes from B0 at F0, F30, or the F60 time point. At F90, neither cortisol nor prolactin was significantly different from their B0 values, but total and free testosterone were reduced significantly from B0. Cortisol, total testosterone and free testosterone at P24 h were significantly lower than their respective B0 levels. Negative relationships existed between peak cortisol response (at time F30) versus total testosterone (at F90, r=-0.53, P<0.05; and at P24 h, r=-0.60, P<0.01). There were no significant relationships between prolactin and total or free testosterone. In conclusion, the present findings give credence to the hypothesis suggesting a linkage between the low resting testosterone found in endurance-trained runners and stress hormones, with respect to cortisol.

Aim of the study: This study examined the response of the free testosterone and cortisol ratio (fTC) to prolonged endurance exercise. Methods:A trained sportsman performed treadmill exercise at 70% of maximal oxygen uptake to volitional fatigue. Frequent blood samples were collected over 24 hours and analyzed to determine changes in the fTC ratio. Results:Exercise caused an initial increase in the ratio followed by a rapid decline in the immediate recovery from exercise. Approximately 8 hours into recovery from exercise, there was a pronounced and persistent (~6 hours) secondary increase in the ratio. Conclusions:Results suggest that the fTC ratio responds to intensive exercise, but that aspects of the response can be of a delayed nature occurring many hours into recovery. Exercise scientists who wish to monitor this parameter should be aware that the time course by which they choose to conduct their blood sampling could impact upon the interpretation of their data.

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