FSH: What the Test Shows and Why It Matters for Athletes
Follicle-stimulating hormone, or FSH, rarely features in gym conversations, yet it is one of the clearest windows into how well the reproductive axis is working. For athletes it can reveal the hormonal cost of under-fuelling, overtraining or the use of performance-enhancing drugs. Our editors explain what the test measures and how to interpret it sensibly.
What FSH is and where it comes from
FSH is a glycoprotein hormone released by the anterior pituitary gland at the base of the brain. Its release is driven by pulses of gonadotrophin-releasing hormone (GnRH) from the hypothalamus. Together with luteinising hormone (LH), it forms the link between the brain and the gonads.
The system works through negative feedback. When the testes or ovaries produce enough sex hormones and inhibin B, the pituitary reduces FSH output. When gonadal output falls, FSH normally rises in an attempt to stimulate it. This simple principle is the key to interpreting the test.
A raised FSH usually points to a problem in the gonads themselves, which are not responding to the signal. A low or inappropriately normal FSH alongside low sex hormones suggests a problem further up, at the level of the hypothalamus or pituitary.
For athletes, the upper part of the axis is the most vulnerable. Energy deficiency, extreme training loads, psychological stress and exogenous hormones all act mainly on the hypothalamus and pituitary, which is why FSH can be informative.
FSH in men: sperm production and suppression
In men, FSH acts on Sertoli cells in the testes, which support the development of sperm. LH, by contrast, drives testosterone production in Leydig cells. Both are needed for normal fertility.
Exogenous androgens, including anabolic steroids and testosterone taken without medical supervision, strongly suppress both FSH and LH through feedback. Rahnema and colleagues described how this leads to reduced testicular size and impaired or absent sperm production, which may persist for months after stopping.
An Endocrine Society scientific statement by Pope and colleagues lists suppressed gonadotrophins as a hallmark of androgen misuse. A very low FSH and LH in a muscular man with high or erratic testosterone levels is a characteristic laboratory pattern.
Endurance athletes can also show changes. Hackney described an "exercise-hypogonadal male condition", in which men with very high training volumes have lower resting testosterone. Gonadotrophins in this condition are often within the normal range but inappropriately low for the testosterone level, suggesting central adaptation.
| Pattern | FSH | LH | Testosterone / oestradiol | Possible meaning |
|---|---|---|---|---|
| Primary gonadal failure | High | High | Low | Testes or ovaries not responding |
| Central suppression | Low or normal | Low or normal | Low | Energy deficiency, stress, pituitary disease |
| Exogenous androgen use | Very low | Very low | Often high | Feedback suppression from external hormones |
| Isolated raised FSH (men) | High | Normal | Normal | Possible impaired sperm production |
FSH in women: the cycle and energy availability
In women, FSH stimulates the growth of ovarian follicles in the first half of the cycle. Its level varies with cycle phase: it rises early in the follicular phase, surges briefly with LH around ovulation and falls in the luteal phase.
Because of this variation, FSH in a menstruating woman is usually measured on day 2–5 of the cycle. A single random value is hard to interpret without knowing the cycle day.
Female athletes with low energy availability may develop functional hypothalamic amenorrhoea, where periods stop because GnRH pulses slow down. FSH and LH are typically low or low-normal, and oestradiol is low. The IOC consensus statement on relative energy deficiency in sport (RED-S) highlights this as a central feature.
The consequences go well beyond fertility. Low oestrogen impairs bone accrual and increases stress fracture risk, and may affect cardiovascular health. A raised FSH, on the other hand, may suggest reduced ovarian reserve or premature ovarian insufficiency, which needs specialist assessment.
How the test is done and how to read it
FSH is measured from a standard blood sample, usually taken in the morning. Fasting is not strictly necessary, but many clinicians prefer a morning sample alongside other hormones such as testosterone, which do require morning sampling in men.
Results are reported in international units per litre (IU/L). Reference ranges differ between laboratories and depend on sex, age and, for women, cycle phase and menopausal status. The range printed on your report is the one to use.
FSH should rarely be interpreted on its own. A useful panel usually includes:
- LH, to see whether both gonadotrophins move together;
- total testosterone and SHBG in men, or oestradiol in women;
- prolactin and thyroid function, which can disturb the axis;
- in some cases, semen analysis in men or anti-Müllerian hormone in women.
Hormonal contraception suppresses FSH, so results taken while using the pill, implant or hormonal coil do not reflect natural ovarian function. Recent intense training, illness or a very low-calorie diet can also influence the result, so these should be mentioned to the clinician.
When an athlete should ask for the test
For female athletes, missing three or more consecutive periods, or never having started periods by age 15, warrants assessment. FSH is part of the work-up, alongside a careful review of energy intake and training load.
For male athletes, symptoms such as low libido, erectile problems, persistent fatigue, reduced testicular size or difficulty conceiving are reasons to seek testing through the GP.
Men who have used anabolic steroids and wish to understand their recovery or fertility should speak openly with a doctor. NHS services treat such information confidentially, and accurate history is essential for correct interpretation and referral to an endocrinologist or fertility specialist.
Routine FSH checks in healthy athletes without symptoms are not usually needed. The test is most valuable when there is a specific clinical question.
Conclusions of the editorial team
FSH reflects the conversation between brain and gonads. A high value usually points to the testes or ovaries; a low value with low sex hormones points to the hypothalamus or pituitary.
In athletes, the most common reasons for disturbed FSH are low energy availability, very heavy training and the use of exogenous hormones. Each has consequences for fertility and bone health.
Interpretation requires context: sex, age, cycle phase, contraception and other hormone results. Related topics on our site include LH and testosterone testing, preparing for an apolipoprotein B test, and recognising relative energy deficiency in sport.
References
- Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
- Rahnema CD, Lipshultz LI, Crosnoe LE, et al. Anabolic steroid-induced hypogonadism: diagnosis and treatment. Fertil Steril. 2014;101(5):1271–1279.
- Hackney AC. Effects of endurance exercise on the reproductive system of men: the "exercise-hypogonadal male condition". J Endocrinol Invest. 2008;31(10):932–938.
- Mountjoy M, Sundgot-Borgen JK, Burke LM, et al. IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med. 2018;52(11):687–697.
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744.
