The menstrual cycle and athletic performance

The menstrual cycle has moved from a topic sport science largely ignored to one it now studies seriously, and that is overdue progress. But the swing has brought a second problem: confident claims, cycle-phase training apps, and performance promises that run well ahead of the evidence. The honest picture is more measured and, in places, more important than the headlines. This piece sets out what the research currently supports, where it is genuinely uncertain, and which part of this topic carries a real and preventable health risk. It is written for the staff, coaches, performance teams, and medical practitioners, who support female athletes and want to act on evidence rather than assumption.

The cycle in brief

A typical menstrual cycle runs around 21 to 35 days and is governed by the rise and fall of two ovarian hormones, oestrogen and progesterone, alongside the pituitary hormones that drive them. In broad terms the cycle is divided at ovulation. The follicular phase runs from the first day of menstruation up to ovulation; oestrogen rises across it while progesterone stays low. Ovulation occurs around mid-cycle. The luteal phase follows, with progesterone rising and oestrogen at a secondary level, before both fall and the next period begins. These hormones do more than govern reproduction: they have receptors throughout muscle, bone, connective tissue, and the brain, which is the biological reason researchers ask whether cycle phase affects how an athlete trains, performs, and recovers.

What the evidence says about phase and performance

Here the careful answer matters. The most cited synthesis, the 2020 systematic review and meta-analysis by McNulty and colleagues in Sports Medicine, pooled a large body of studies on cycle phase and exercise performance in naturally menstruating women. Its conclusion was deliberately restrained: exercise performance might be trivially reduced during the early follicular phase, the days of menstruation itself, compared with other phases, but the average effect was small and the overlap between phases was considerable.

Two caveats sit on top of that finding and both are important. First, the effect size is trivial, which is to say not the kind of swing that should reshape a training week for a whole squad. Second, the review judged the quality of the underlying studies to be largely low: of the studies analysed, only a small fraction were rated high quality, and the majority were rated low or very low. The authors' own recommendation follows directly from this: because the effects are trivial and the evidence limited, general population-level guidelines on training across the cycle cannot be drawn. Instead, they advocate an individualised approach, tracking how a specific athlete actually responds, rather than applying a generic phase-based template to everyone.

That is the responsible summary of the performance question: the average signal is weak and the data are imperfect, so the evidence does not support confident, one-size phase-based programming. It does support paying attention to the individual.

Why the research is hard, and why that matters

The uncertainty is not a failure of interest; it reflects how genuinely difficult this research is to do well. Defining which phase an athlete is in requires more than counting days from the last period, because cycle length and ovulation timing vary between and within women. The 2021 methodological guidance led by Elliott-Sale, a working standard for research with women as participants, set out why so many earlier findings conflict: phases were estimated rather than confirmed, hormone status was not measured, and terms were used loosely. Verifying a phase properly means confirming ovulation and, ideally, measuring hormone concentrations, which many older studies did not do. When you read a strong claim about cycle phase and performance, the first question is whether the phase was actually verified. Often it was not.

The cycle and injury risk

A specific question that gets attention is whether injury risk, particularly to the anterior cruciate ligament (ACL), varies across the cycle. Women sustain ACL injuries at several times the rate of men, and oestrogen influences collagen and ligament laxity, so the hypothesis is biologically reasonable. Some reviews report greater knee laxity, and a signal toward higher ACL injury occurrence, around the late follicular and ovulatory phase when oestrogen peaks.

But the evidence here is graded weak and is inconsistent. The systematic review and meta-analysis by Herzberg and colleagues found the strength of evidence very low and called for better-designed studies to address bias and confounding, and not all reviews agree that laxity measured in the lab translates into injuries on the pitch. The practical implication is not to bench athletes on particular days, which the evidence does not justify, but to keep doing what reduces ACL risk for everyone regardless of cycle: sound neuromuscular training, landing and change-of-direction mechanics, and load management. The cycle is, at most, one factor among several here, and a weakly evidenced one.

The part that genuinely matters: low energy availability and REDs

If one section of this article changes practice, it should be this one. The most consequential menstrual-cycle signal in sport is not a performance edge to chase across phases; it is the absence of a normal cycle as a warning sign. Menstrual dysfunction, irregular cycles or the loss of menstruation altogether, is one of the clearest indicators that an athlete is chronically under-fuelled.

The 2023 IOC consensus statement on Relative Energy Deficiency in Sport (REDs) is the current authority. When energy availability is too low for too long, the energy left after training is insufficient to support normal physiological function, the body downregulates systems it can defer, including reproductive hormone production. Disrupted or absent menstruation is a downstream effect, and it travels with impaired bone health, raising the risk of stress fractures, alongside effects on immunity, metabolism, cardiovascular health, and performance itself. The statement frames low energy availability on a spectrum from adaptable to problematic, and is explicit that awareness of the syndrome remains low among athletes and the staff around them.

This reframes the whole topic. A missed period in an athlete is not a convenience or a sign of being "in good shape"; it is a clinical signal that warrants attention to energy availability and, where appropriate, medical assessment. The downside of getting the performance question wrong is a slightly mistimed training week. The downside of missing chronic under-fuelling is a stress fracture, lost bone density that may not fully recover, and a career interrupted. Of everything in this article, this is the signal worth building a program's vigilance around.

Hormonal contraception

Many athletes use hormonal contraception, which changes the hormonal picture again: combined oral contraceptives suppress the body's own oestrogen and progesterone and supply synthetic hormones instead, so a user's profile differs from a natural cycle. The 2020 systematic review and meta-analysis by Elliott-Sale and colleagues examined oral contraceptives and exercise performance and reached a conclusion that rhymes with the cycle research: oral contraceptive use might result in slightly inferior performance on average compared with naturally menstruating women, but the effect was small and, again, the body of evidence was largely of low quality.

The takeaway is not that athletes should start or stop contraception for performance reasons. That is a personal and medical decision with many considerations beyond sport, and it belongs with the athlete and their clinician. The relevant points for support staff are narrower: a hormonal contraceptive changes what cycle tracking can and cannot tell you, it does not produce a natural ovulatory cycle, and it should never be used to mask the loss of menstruation that low energy availability would otherwise reveal.

What this means in practice

Read together, the evidence supports a clear and unsensational stance. Individualise rather than generalise: the performance effects of cycle phase are, on average, trivial and uncertain, so track how each athlete actually responds rather than imposing a generic phase template. Hold the injury evidence lightly: it is weak, and the proven prevention work, neuromuscular training and load management, applies regardless of cycle. And treat menstrual health as the real signal it is: a disrupted or absent cycle is a flag for low energy availability and a prompt for proper assessment, not something to train through.

Doing this well at squad scale needs two things that are easy to say and hard to run by hand: a way for athletes to record cycle and symptom data with dignity and appropriate privacy, and a unified record where that information sits beside training load, nutrition, and availability so the patterns that matter, especially the energy-availability picture, become visible to the right people at the right time. Handled with care and grounded in evidence, this is not a gimmick. It is part of taking female athletes' health and performance as seriously as the science now allows.