Running and/or high intensity training lowers testosterone

Basal reproductive hormonal profiles are altered in endurance trained men.
Hackney AC, Fahrner CL, Gulledge TP.
Source
Endocrine Section, University of North Carolina, Chapel Hill 27599-8700, USA.
Abstract
OBJECTIVE:
The purpose was to examine the basal reproductive hormonal profiles in age-matched groups of endurance trained (ET) and sedentary (SED) men under controlled conditions.
EXPERIMENTAL DESIGN:
Resting basal blood samples were obtained from groups of ET and SED men after a 24-hr control period. Blood specimens were analyzed for testosterone (T), free-testosterone (fT), sex-hormone binding globulin (SHBG), luteinizing hormone (LH), cortisol, and prolactin. The design of the study was retrospective and cross-sectional in nature.
SETTING:
Laboratory setting at the University of North Carolina, North Carolina USA.
PARTICIPANTS:
ET men (n = 53) who had been involved with chronic endurance exercise training for > or = 5 years. SED men (n = 35) were selected of comparable ages and the fact that they had done no formal exercise training.
RESULTS:
Results indicated that the basal T and fT of the ET men were significantly (p < 0.01) lower than that of the SED men. The levels of these hormones in the ET men where in the normal clinical range, but represented only 55% to 85% of those seen in the SED men. For SHBG, LH, cortisol, and prolactin, no significant differences (p > 0.05) were found between the ET and SED men.
CONCLUSIONS:
ET men have lowered basal T and fT levels and this suppression may be related to an alteration in the hypothalamic-pituitary-testicular regulatory axis since the LH of the ET was not elevated. Whether these hormonal changes have any significant beneficial (i.e., protective cardiovascular) or negative (i.e., decrease anabolic-androgenic processes) physiologic consequences remains to be determined.

http://www.ncbi.nlm.nih.gov/pubmed/9763799

Reproducibility of low resting testosterone concentrations in endurance trained men.
Gulledge TP, Hackney AC.
Source
Applied Physiology Laboratory, University of North Carolina, Chapel Hill 27599-8700, USA.
Abstract
Previous reports indicate endurance trained (ET) men have low resting testosterone concentrations without any significant increases in their luteinizing hormone (LH) concentrations. The purpose of this study was to examine the reproducibility of these resting hormonal findings in ET men. Resting blood samples were collected at three separate trials (2 weeks apart) in groups of ET men (n = 15) and age-matched, untrained (UT, n = 13) men. Blood specimens were analyzed for total testosterone, LH, cortisol and prolactin. Results indicated that testosterone was significantly (p < 0.01) lower in ET than UT at each of the three trials. LH, cortisol, and prolactin were not different (p > 0.05) between the groups at any trial. These results confirm earlier findings reported for ET men. Furthermore, the results indicate the resting reproductive hormonal status (i.e., low testosterone) of ET men is reproducible and does not appear to be an artifact of the timing of the blood sampling methodology used.

http://www.ncbi.nlm.nih.gov/pubmed/8817130

Reproductive hormonal profiles of endurance-trained and untrained males.
Hackney AC, Sinning WE, Bruot BC.
Source
Applied Physiology Research Laboratory, Kent State University, Ohio 44242.
Abstract
This study compares the resting reproductive hormonal profiles of untrained (N = 11) and endurance-trained (N = 11) males. Testosterone, free testosterone, estradiol, luteinizing hormone (LH), prolactin, and cortisol were measured by radioimmunoassay in resting blood samples (8 h fast) collected every 60 min for 4 h. The endurance-trained group had been active for (mean +/- SE) 12.4 +/- 6.7 yr, 6.6 +/- 0.2 d.wk-1, 68.5 +/- 4.4 min.d-1, while the untrained group was sedentary. Neither group had histories of hypothalamic-pituitary-testicular disorders. The overall 4 h mean testosterone and free testosterone levels were significantly (P less than 0.05) lower in the trained group (4.99 +/- 0.46 vs 7.25 +/- 0.67 ng.ml-1, and 17.2 +/- 1.4 vs 23.6 +/- 0.6 pg.ml-1, for the trained and untrained groups, respectively). The LH of the endurance-trained group was higher (15.3 +/- 1.9 vs 11.7 +/- 1.2 mIU.ml-1, P = 0.06); however, LH pulse frequency and amplitude did not differ between groups. An enhanced estradiol feedback to the hypothalamus-pituitary could not account for the elevated LH, as estradiol levels were similar in the groups. Prolactin and cortisol levels were normal and did not differ between groups. The results suggested normal hypothalamic-pituitary function existed in the trained subjects, and prolactin and cortisol were not causative factors in the lowered resting testosterone and free testosterone levels. The findings indicate that chronic endurance training lowers testosterone and free testosterone in males possibly by impairing testicular function.

http://www.ncbi.nlm.nih.gov/pubmed/3343919

Relationship between stress hormones and testosterone with prolonged endurance exercise.
Daly W, Seegers CA, Rubin DA, Dobridge JD, Hackney AC.
Source
Endocrine Section, Applied Physiology Laboratory, Department of Exercise and Sport Science, University of North Carolina, Chapel Hill, North Carolina, USA.
Abstract
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.

http://www.ncbi.nlm.nih.gov/pubmed/15618989

Effect of endurance exercise on resting testosterone levels in sedentary subjects.
Hiruntrakul A, Nanagara R, Emasithi A, Borer KT.
Source
Department of Physiotherapy, Faculty of Associated Medical Science, Khon Kaen University, Thailand. hashir@kku.ac.th
Abstract
OBJECTIVE:
To investigate the effects of moderate-intensity and low frequency exercise on resting serum testosterone and cortisol levels, resting heart rate, and isokinetic strength among healthy sedentary young men.
DESIGN:
A randomized controlled study. Forty sedentary young men aged 18 to 25 years old, pedaled 50 minutes on a bicycle ergometry at 60% of maximal effort once a week for 12 weeks in an exercise group.
OUTCOME MEASURES:
Resting total and free serum testosterone, serum cortisol, anthropometric data, resting heart rate, and isokinetic strength during shoulder and knee extensions.
RESULTS:
Resting serum total and free testosterone, as well as cortisol did not differ significantly between groups. Neither group showed any significant changes in anthropometric data and isokinetic strength at the end of study. However, the resting heart rate of the exercise group reduced significantly after the training (p < 0.05). Also, the isokinetic strength of shoulder and knee significantly increased (p < 0.05).
CONCLUSIONS:
Twelve weeks of moderate-intensity and low frequency training had no effect on resting serum testosterone, but were sufficient to increase aerobic fitness among sedentary young men. The type of exercise training may encourage sedentary individuals to participate regularly in the program on physical activity.

http://www.ncbi.nlm.nih.gov/pubmed/21033613