Menstrual Cycle and Performance

A eumenorrhoeic cycle runs roughly 21 to 35 days and divides at ovulation. In the follicular phase, follicle stimulating hormone (FSH) drives follicular growth and oestradiol climbs, peaking late in the phase. A surge in luteinising hormone (LH) triggers ovulation near the midpoint. In the luteal phase the corpus luteum secretes progesterone alongside oestradiol, and if conception does not occur it regresses, both hormones fall, and menstruation follows.

Neither hormone confines itself to the reproductive tract. Oestradiol acts on connective tissue, substrate metabolism and the neuromuscular system, while progesterone raises resting core temperature slightly and stimulates ventilation. These are the mechanisms usually invoked to explain phase-related performance change, and they are plausible. Whether they translate into a measurable effect in a trained athlete is a separate question.

Hormonal contraception changes the picture entirely. Combined preparations suppress the hypothalamic-pituitary-ovarian axis, so there is no true cycle and no ovulation, and the bleed during the hormone-free interval is a withdrawal bleed rather than a period. That matters clinically, because an athlete on the pill who bleeds every month is telling you nothing about her own axis.

The best available synthesis, a network meta-analysis in eumenorrhoeic women, found that performance might be trivially reduced in the early follicular phase compared with all other phases, and was consistent across every other phase. The effect was small, variation between studies was large, most included studies were of poor quality, and overall confidence in the evidence was rated low. The conclusion the authors themselves drew is the one to take into clinic: general guidelines cannot be formed, and the approach should be personalised to how the individual athlete actually responds. A companion analysis of oral contraceptive users found, on average, slightly inferior performance compared with eumenorrhoeic women, again a trivial difference on low-quality evidence.

Blanket phase-based periodisation, of the sort marketed with some enthusiasm, is therefore not supported. What is well supported is simpler: many athletes report symptoms that impair training, and those symptoms matter whether or not oestradiol is doing anything measurable to muscle. Dysmenorrhoea, heavy bleeding, fatigue and low mood are performance problems in their own right, and they are treatable.

The injury question has the same shape. Higher oestradiol in the late follicular phase has been proposed to increase ligament laxity and anterior cruciate ligament (ACL) injury risk, but the studies are inconsistent and methodologically limited, and this should not influence selection or training decisions.

Heavy menstrual bleeding is defined by its impact on quality of life rather than by a measured volume, and it is common and consistently under-reported, partly because an athlete has nothing to compare her own experience against. Dysmenorrhoea and premenstrual symptoms are similarly common and similarly tolerated in silence.

Dysfunction is defined by the cycle interval. Oligomenorrhoea means cycles longer than 35 days, and amenorrhoea their absence, with secondary amenorrhoea diagnosed after three months without periods in someone previously regular, or six months if previously irregular. Primary amenorrhoea, meaning no menarche by 15 years with normal secondary sexual characteristics, or by 13 years without them, needs assessment in its own right. In an athlete, exclude pregnancy first, then assess for low energy availability alongside the other causes, since polycystic ovary syndrome, hyperprolactinaemia, thyroid disease and primary ovarian insufficiency all need considering.

A menstrual history belongs in every female athlete assessment and takes a minute: age at menarche, cycle length and regularity, how heavy the bleeding is, associated symptoms, contraception, and whether any of it affects training.

For heavy bleeding a full blood count is carried out in every case, and ferritin is checked as well, because iron deficiency without anaemia is enough to blunt endurance and training adaptation in an athlete. Current NICE guidance no longer advises against routine serum ferritin testing in women with heavy menstrual bleeding, having removed that recommendation in 2026 on the grounds that it was not justified given the risk of iron deficiency, so checking ferritin now aligns with both general and sports practice. Examine and refer where a structural cause is suspected or a red flag is present.

Treatment follows current NICE guidance on heavy menstrual bleeding. A levonorgestrel-releasing intrauterine system is first choice where the uterine cavity is suitable and there is no significant structural pathology. Where it is declined or unsuitable, tranexamic acid 1 g three times daily for up to four days from the onset of bleeding is effective, as is a non-steroidal anti-inflammatory such as mefenamic acid 500 mg three times daily, which treats the dysmenorrhoea at the same time. Both are taken only during bleeding. Combined hormonal contraception and cyclical oral progestogens are alternatives, and any iron deficiency is corrected in parallel.

Where a withdrawal bleed falls awkwardly, a tailored or extended contraceptive regimen can move it away from competition, trialled well in advance rather than in the week of an event. Amenorrhoea is worked up rather than accepted: a pregnancy test first, then FSH, LH, oestradiol, prolactin and thyroid function, since functional hypothalamic amenorrhoea is a diagnosis of exclusion. Hormonal contraception should not be prescribed solely to induce a withdrawal bleed or to protect bone, since it masks spontaneous recovery and does not reliably improve bone mineral density. Anti-doping is straightforward here, since hormonal contraceptives and tranexamic acid are not prohibited, though every medicine is checked before use.

• •The systematic review and meta-analysis of menstrual cycle phase and exercise performance in eumenorrhoeic women, in Sports Medicine, found a trivial effect on low-quality evidence and recommends a personalised rather than a general approach.
• •Its companion analysis of oral contraceptive users found a similarly trivial difference in performance.
• •Current NICE guidance on heavy menstrual bleeding sets out assessment, the first-choice intrauterine system and the non-hormonal alternatives; a 2026 update removed its earlier advice against routine serum ferritin testing.
• •The 2023 International Olympic Committee consensus on relative energy deficiency in sport covers menstrual dysfunction as a marker of low energy availability.

• •A eumenorrhoeic cycle runs about 21 to 35 days, and amenorrhoea is never a normal training response.
• •Evidence that cycle phase alters performance is trivial and low quality, so avoid blanket phase-based programmes.
• •Symptoms such as dysmenorrhoea and heavy bleeding impair training regardless of any direct hormonal effect.
• •Heavy menstrual bleeding is defined by quality-of-life impact, not by a measured blood volume.
• •Check a full blood count for heavy bleeding, and ferritin as well, since iron deficiency without anaemia can impair endurance in an athlete.
• •Hormonal contraceptives and tranexamic acid are not prohibited in sport.