For most of sports science’s history, women were studied as ‘small men,’ their hormonal variation treated as confounding noise. The field is finally correcting that oversight, with significant implications for how women train.
A research gap with consequences
Sports science has a long-standing problem with women. Until relatively recently, and the change is still incomplete, the vast majority of exercise physiology research was conducted exclusively on male subjects, or on women only in the follicular phase of their cycle (the first two weeks, post-menstruation), when oestrogen levels are lower and hormonal variation is less pronounced. The rationale was methodological tidiness: excluding hormonal variation reduced confounding variables. The consequence was a body of knowledge that applied poorly, or not at all, to half the population.
The assumption that findings from male physiology could simply be translated to female physiology has proven, repeatedly, to be incorrect. Women are not hormonally stable across a month. Oestrogen and progesterone fluctuate significantly across the four phases of the menstrual cycle (menstruation, follicular, ovulation, and luteal) and those fluctuations have measurable effects on everything from aerobic capacity and muscle recovery to injury risk and perceived exertion.
The four phases and what they mean for training
The menstrual phase (days 1–5 approximately) is characterised by shedding of the uterine lining and typically a low-hormone environment. Energy may be lower, and for women who experience dysmenorrhoea, painful periods affecting up to 80% of reproductive-age women, this phase can be genuinely difficult. Research suggests that moderate exercise can reduce cramping via endorphin release and anti-inflammatory pathways, but that this is highly individual. Forcing high-intensity training through significant pain is not evidence-based; it is cultural performance.
The follicular phase (days 6–14) sees rising oestrogen, which appears to support muscle protein synthesis, glycogen storage, and neuromuscular efficiency. Multiple studies have found that women achieve greater strength gains and tolerate higher training loads in this phase. If your schedule allows any flexibility, this is the time to attempt personal records, increase training volume, or introduce new challenges.
Ovulation (around day 14) brings peak oestrogen alongside a surge in luteinising hormone. This is often a period of high energy and mood, but also, crucially, elevated injury risk. Oestrogen in high concentrations reduces ligament stiffness, which increases the risk of ACL injury. The well-documented female-to-male disparity in ACL injury rates (women tear their ACLs at rates two to eight times higher than men in equivalent sports) is at least partially explained by this hormonal mechanism.
The luteal phase (days 15–28) sees rising progesterone alongside declining oestrogen. This phase is associated with higher core temperature, elevated perceived exertion at equivalent workloads, reduced glycogen availability, increased protein catabolism, and, for many women, the psychological and physical symptoms of premenstrual syndrome. Training in the luteal phase is not impossible, but it genuinely requires more effort for equivalent output, which is not weakness but basic endocrinology.
“When women are told their harder days are mental, the problem is often the science, not the woman.”
The injury story nobody told us
The ACL injury disparity between men and women is one of the most significant and least publicised gender gaps in sport. Female athletes at elite level are subject to intensive biomechanical analysis and targeted prevention programmes. Recreational female athletes, who make up the vast majority of active women, typically receive none of this. They are simply told to play, train, and hope for the best.
Cycle-aware training approaches that reduce high-impact pivoting, jumping, and cutting movements in the days around ovulation have shown promising results in reducing injury incidence in pilot studies. More broadly, neuromuscular training programmes, teaching athletes to land with better knee alignment and controlled deceleration, reduce ACL injury risk by up to 50% according to some systematic reviews. These programmes should be standard, particularly for young female athletes. That they are not is a function of a sports science system that spent decades not asking the right questions about women.
Practical implications, without the pseudoscience
A note of caution is warranted here, because the menstrual cycle and exercise conversation has attracted significant pseudoscience alongside the legitimate research. The claim that women should not exercise at all during menstruation has no evidence base. The idea that all women experience the same hormonal fluctuations on the same timeline is anatomically incorrect, cycle length, symptom experience, and hormonal profiles vary significantly between individuals and across the lifespan.
What the evidence does support is this: tracking your cycle and noticing how it correlates with training performance, energy, and mood is genuinely useful self-knowledge. Apps and wearables that attempt to predict ‘optimal’ training windows based on cycle data are becoming more sophisticated, but remain imprecise because they cannot account for individual hormonal variation without actual hormone testing. The most evidence-based approach is honest self-observation combined with the permission, still radical in many fitness cultures, to adjust training intensity based on how you actually feel.
A field catching up
The Lionesses’ use of cycle-aware training protocols in their historic 2022 Euros campaign brought this science into mainstream sports coverage for perhaps the first time. Several Premier League clubs now work with female sports scientists to monitor hormonal cycles in their women’s teams. Research funding for female-specific exercise physiology has increased markedly; though it remains a fraction of what is invested in male sport.
For the millions of women who exercise outside elite sport, the message is both validating and practical: your hormonal cycle affects your training. That variability is not a design flaw. It is simply biology that was ignored for too long, and that deserves, at last, to be taken seriously.