Endurance Training Decreases Serum Testosterone Levels in Men without Change in Luteinizing Hormone Pulsatile Release*

Abstract

Cross-sectional studies have suggested that total and bioavailable testosterone levels are reduced in some male athletes. Such changes may be related to loss of body weight, increased serum cortisol, and/or alterations in LH pulsatile release. To determine how endurance training may affect androgen levels, we measured serum total testosterone, sex hormone-binding globulin, free androgen index, LH, FSH, PRL, cortisol, and weight in 15 previously sedentary males. We also examined pulsatile LH release in a subset of 5 subjects. Over 6 months of training, the men increased weekly running mileage to an average of 56 km/week. Total testosterone and free androgen index levels decreased significantly. PRL and cortisol also decreased, while single sample LH and FSH remained unchanged. There was a significant reduction in weight, which did not correlate with changes in serum testosterone levels. LH pulsatile release was not altered by training in the subset of 5 runners. These data confirm previous findings of physiological reduction in serum testosterone and PRL levels and suggest that the testosterone decrease is not related to changes in LH pulsatile release, weight, or increased serum cortisol levels.

Testosterone Is Significantly Reduced in Endurance Athletes without Impact on Bone Mineral Density

“…This alteration was associated with a decrease in the FAI, which represents the biologically active form of the hormone. Neither of the hormonal changes was induced by modification of the SHBG level, as previously demonstrated by various authors [20, 24]. …”

“…Alterations in androgens have often been described in the literature on endurance athletes, particularly in marathon runners. However, although low, the values of TT and FT have always been within the normal range [18, 19, 20, 21, 22, 31]. Other authors [23, 24, 27], and Lucia et al [25]especially, have found normal T levels in male endurance athlete groups composed of marathon runners, professional CY and elite TR.…”

“…Although the increase in T during short-term resistance or endurance exercise seems to be unequivocal [15, 16, 17], studies on the effect of endurance exercise training on the hypothalamic-pituitary-gonadal (HPG) axis, as evaluated in subjects at rest, have shown conflicting results [18, 19, 20, 21, 22, 23, 24, 25]. The major subclinical alterations in the male reproductive endocrine system reported in endurance athletes include a reduction in circulating levels of TT and FT [18, 19, 20, 21, 22]. It has been suggested that decreases in TT concentration due to exhaustive endurance training may produce muscular atrophy [26], but the incidence of low TT in association with low BMD in male athletes has rarely been documented [22, 27].…”

Relationship of chronic endurance exercise to the somatotropic and sex hormone status of older men

“…Some evidence indicates a role for aerobic physical activity in SHBG production, at least in men. SHBG concentrations have been observed to increase acutely with such exercises as cycle ergometry, and with longer-term endurance training (38)(39)(40)(41), although some reports involving endurance-trained younger men have not confirmed this effect (18,21,37,42). As SHBG concentrations vary inversely with circulating insulin (43), a plausible explanation for greater SHBG values in trained older men could be attenuation of agerelated insulin-resistance.…”

“…Several authors have reported lower concentrations of both total testosterone (17,18) and free testosterone (19,20) in young endurance-trained men compared with age-matched 'sedentary' controls, whereas others have observed no effect of endurance exercise on total testosterone concentrations (21,22). Even if habitual endurance activity were to improve IGF-I production, an exercise-dependent attenuation of gonadal function might negate any potential benefits of the former on body composition.…”