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

Abstract

To investigate putative abrogating effects of habitual endurance exercise on age-related changes in endocrine function and body composition, we compared insulin-like growth factor-I (IGF-I), sex hormonal status and body composition in 15 Masters runners and 15 minimally exercising men (MEM) aged 60-70 years. A higher maximal oxygen uptake (VO 2 max.) in the runners (41.4 Ϯ 1.6 compared with 27.3 Ϯ 1.4 ml/kg/min, P ¼ 0.0001; mean Ϯ S.E.M.) reflected our group allocations. Analysis of body composition and bone mineral density (BMD) by dual energy X-ray absorptiometry showed no group differences in lean tissue mass or in regional or whole body BMD, but MEM were heavier, reflecting greater adiposity. Of nine muscle groups tested, only quadriceps strength differed significantly, being greater in runners (60.3 Ϯ 2.8 compared with 51.1 Ϯ 2.3 kg, P ¼ 0.02). Total IGF-I (129 Ϯ 10 compared with 124 Ϯ 11 ng/ml, P ¼ 0.72) and IGF-binding protein-3 (2854 Ϯ 94 compared with 2623 Ϯ 128 ng/ml, P ¼ 0.16), were similarly depressed compared with young adult norms in both groups. There was no relationship between total or bioavailable IGF-I and any body composition, BMD or muscle strength variable. In the runners, concentrations of total testosterone (19.1 Ϯ 0.8 compared with 15.0 Ϯ 0.9 nmol/l, P ¼ 0.002) and sex hormone binding globulin (SHBG) (124.4 Ϯ 21.6 compared with 67.7 Ϯ 11.6 nmol/l, P ¼ 0.03) were significantly greater, but the free androgen index was significantly lower (20.7 Ϯ 2.7 compared with 31.4 Ϯ 4.1, P ¼ 0.04). Directly measured free testosterone, however, was similar between the runners and MEM (47.9 Ϯ 1.8 compared with 47.1 Ϯ 2.0 nmol/l, P ¼ 0.80). Therefore the group differences in total testosterone and free androgen index were due to their different SHBG concentrations. Although estrone concentration was higher in MEM (85.1 Ϯ 5.2 compared with 108 Ϯ 6.7 pmol/l, P ¼ 0.03), estradiol concentration was similar between groups (73.0 Ϯ 6.3 compared with 81.8 Ϯ 8.0 pmol/l, P ¼ 0.18), indicating that estrogens were not responsible for the increased SHBG in runners. These results indicate that even high levels of regular endurance exercise do not prevent the decline in the somatotropic axis that occurs with aging. Furthermore, the somatic effects of exercise in older men (reduced adiposity and increased regional muscle strength) occurred independently of somatotropic or androgen status. Although habitual exercise does not influence free testosterone concentrations in older men, it appears to enhance the age-associated increase in SHBG synthesis.

The effects of intensive, long-term treadmill running on reproductive hormones, hypothalamus–pituitary–testis axis, and semen quality: a randomized controlled study

“…Low serum FSH, LH, and T values indicate hypothalamo-pituitary disease, i.e., hypogonadotropic hypogonadism. Lower basal levels of Tor fT have also been reported in endurance-trained individuals in previous studies (Cooper et al 1998, Hackney et al 1998. In another study, 20 male marathon athletes were evaluated by hormonal profiles, psychological testing, anthropomorphic indices, and semen evaluations by Ayers et al (1985).…”

“…Despite the strong evidence for the health benefits of exercise, serum markers do not necessarily support this (Cooper et al 1998). The exercise protocol used in this study proved to be an effective means of examining the effects of stress on reproductive function.…”

Effect of Exercise on Serum Sex Hormones in Men

“…In some studies, elevations in free testosterone, bioavailable testosterone, SHBG, and other androgens such as dihydroepiandosterone have also been observed, but the hormone changes are variable and may depend on the exercise paradigm (resistance vs aerobic), the exercise intensity, and/ or the study population (young vs older men) (4,20,53,58). When testosterone levels are compared cross-sectionally between middle-aged and older men who have engaged in longterm exercise versus those who have not, testosterone levels are higher among regular exercisers (3,40), with similar findings for SHBG (10). However, among highly trained endurance athletes, testosterone levels have also been found to be lower than among either resistance-trained or control subjects, introducing the possibility of exercise-related sex hormone dysfunction (17).…”

Jogging and bone mineral density in men: results from NHANES III

“…The mechanism underlying this ceiling effect is probably multifactorial and may include factors such as body weight 14 or sex hormone status. 24 Our study focused on the proximal femur, which is a skeletal site that receives increased loading from jogging. The effect of jogging on other skeletal sites, which may not be as directly loaded, has varied.…”