but THIS thread was about women.
Men and women are different physiologically and in how training stress affects them. The similarity is that the pituitary axis is affected, and overall reproduction suffers - which in MEN means less testosterone and in WOMEN means less estrogen:
From: Kronenberg: Williams Textbook of Endocrinology, 11th ed.; CHAPTER 25 - HORMONES AND ATHLETIC PERFORMANCE > ... > Hypothalamus-Pituitary-Gonadal Axis
Female Gonadal Axis
Circulating levels of testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulphate, estradiol, growth hormone (GH), and cortisol have been shown to increase in response to an acute bout of endurance exercise in women. However, only GH, estradiol, and cortisol have been reported to increase following resistance exercise.[84]
Hyperandrogenism has been suggested as a possible alternative mechanism underlying oligomenorrhea or amenorrhea in some female athletes with menstrual disturbances.[85] Interestingly, hyperandrogenic female athletes have a more anabolic body composition and higher VO2max and performance values in comparison with female athletes with menstrual disturbances but normal androgen concentrations.[85]
Summary
The endocrine equilibrium that regulates reproductive function in women can be affected by physical and psychological factors. Many female athletes develop oligomenorrhea, amenorrhea, and luteal phase defects. Negative energy balance is the primary cause of the impairment of normal reproductive function commonly observed in female athletes. The link between negative energy balance and reproductive dysfunction is represented by leptin, which serves as a signal to the CNS with information on the critical amount of adipose tissue stores that is necessary for GnRH secretion and pubertal activation of the hypothalamic-pituitary-gonadal axis. Possible alternative mechanisms underlying oligomenorrhea or amenorrhea in some female athletes include the stress-induced activation of the hypothalamic-pituitary-adrenal axis, endogenous opioid peptides, catecholestrogens, and hyperandrogenism.
In MEN testosterone decreases (and sometimes libido):
Male Gonadal Axis
Endurance training induces changes in the function of the reproductive axis in men in a similar manner to the changes in women. There is a subclinical inhibition of normal reproductive function but it is unclear whether clinical expression of reproductive suppression is common in men. Although measures of sperm function are generally normal in runners with very strenuous training regimens even with very low physiologic androgen levels,[56] there is evidence that males with a high level of physical activity have some abnormalities of semen analysis. [57] [58] Libido may also be reduced in some [male]athletes during intense endurance training periods; reduced testosterone levels but also chronic fatigue may play a role. [49] [56]
Summary
Short, intense exercise usually increases while prolonged exercise usually decreases serum testosterone levels. The exercise-associated increment in circulating testosterone does not seem to be mediated by LH. Possible mechanisms such as hemoconcentration, reduced clearance, and/or increased testosterone synthesis may be involved. A variety of systems could influence the testosterone decrease during and subsequent to more prolonged exercise, including decreased gonadotropins, increased cortisol or catecholamine levels, or even an accumulation of metabolic waste materials. The fall in serum testosterone results from decreased production rates, decreased binding, or increased clearance.
Endurance and other forms of training can induce subclinical inhibition of normal reproductive function. Libido may also be reduced in some [male]athletes during intense endurance training periods, due to reduced testosterone levels and to chronic fatigue.
Men and women are different physiologically and in how training stress affects them. The similarity is that the pituitary axis is affected, and overall reproduction suffers - which in MEN means less testosterone and in WOMEN means less estrogen:
From: Kronenberg: Williams Textbook of Endocrinology, 11th ed.; CHAPTER 25 - HORMONES AND ATHLETIC PERFORMANCE > ... > Hypothalamus-Pituitary-Gonadal Axis
Female Gonadal Axis
Circulating levels of testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulphate, estradiol, growth hormone (GH), and cortisol have been shown to increase in response to an acute bout of endurance exercise in women. However, only GH, estradiol, and cortisol have been reported to increase following resistance exercise.[84]
Hyperandrogenism has been suggested as a possible alternative mechanism underlying oligomenorrhea or amenorrhea in some female athletes with menstrual disturbances.[85] Interestingly, hyperandrogenic female athletes have a more anabolic body composition and higher VO2max and performance values in comparison with female athletes with menstrual disturbances but normal androgen concentrations.[85]
Summary
The endocrine equilibrium that regulates reproductive function in women can be affected by physical and psychological factors. Many female athletes develop oligomenorrhea, amenorrhea, and luteal phase defects. Negative energy balance is the primary cause of the impairment of normal reproductive function commonly observed in female athletes. The link between negative energy balance and reproductive dysfunction is represented by leptin, which serves as a signal to the CNS with information on the critical amount of adipose tissue stores that is necessary for GnRH secretion and pubertal activation of the hypothalamic-pituitary-gonadal axis. Possible alternative mechanisms underlying oligomenorrhea or amenorrhea in some female athletes include the stress-induced activation of the hypothalamic-pituitary-adrenal axis, endogenous opioid peptides, catecholestrogens, and hyperandrogenism.
In MEN testosterone decreases (and sometimes libido):
Male Gonadal Axis
Endurance training induces changes in the function of the reproductive axis in men in a similar manner to the changes in women. There is a subclinical inhibition of normal reproductive function but it is unclear whether clinical expression of reproductive suppression is common in men. Although measures of sperm function are generally normal in runners with very strenuous training regimens even with very low physiologic androgen levels,[56] there is evidence that males with a high level of physical activity have some abnormalities of semen analysis. [57] [58] Libido may also be reduced in some [male]athletes during intense endurance training periods; reduced testosterone levels but also chronic fatigue may play a role. [49] [56]
Summary
Short, intense exercise usually increases while prolonged exercise usually decreases serum testosterone levels. The exercise-associated increment in circulating testosterone does not seem to be mediated by LH. Possible mechanisms such as hemoconcentration, reduced clearance, and/or increased testosterone synthesis may be involved. A variety of systems could influence the testosterone decrease during and subsequent to more prolonged exercise, including decreased gonadotropins, increased cortisol or catecholamine levels, or even an accumulation of metabolic waste materials. The fall in serum testosterone results from decreased production rates, decreased binding, or increased clearance.
Endurance and other forms of training can induce subclinical inhibition of normal reproductive function. Libido may also be reduced in some [male]athletes during intense endurance training periods, due to reduced testosterone levels and to chronic fatigue.