For decades, sports science had a remarkably consistent research participant.
The default subject
Young. Healthy. Usually in his twenties. He trained regularly, had no menstrual cycle to complicate the protocol, and could be asked to come back to the lab next Tuesday without checking where he was in his cycle. Convenient.
Women, on the other hand, came with hormones, menstrual cycles, pregnancy, contraception, family schedules, historically restricted access to sport, and a bit more biological variability. From a researcher’s perspective, this could look like a statistical nuisance. From an athlete’s perspective, it’s simply called having a body.
This history matters because much of what we know about exercise physiology was built from research where women were underrepresented or with poor scientific design. That doesn’t mean everything we’ve learned about training is wrong for women, far from it. The fundamentals of adaptation, overload, recovery and performance remain remarkably similar across sexes.
But it does mean we should be careful assuming that evidence generated mostly from male athletes automatically tells the whole story for female ones.
This is where female physiology becomes relevant, not because women need an entirely different rulebook, but because sometimes an athlete holds information the generic rulebook simply doesn’t contain.
The female body is not a special edition of the male body
Women and men share the same basic physiological machinery for producing movement and adapting to training. Muscles still need fuel. The cardiovascular system still has to deliver oxygen. Training still creates a stimulus, and the body still has to recover before it can adapt. But the starting conditions aren’t identical.
Differences on average — not rules for any individual athlete.
- 1 A wider, shallower pelvis relative to shoulder width.
- 2 A rounder pelvic opening.
- 3 Thigh bones that angle more steeply toward the knee, a larger Q-angle.
On average, women and men differ in body composition, muscle mass, haemoglobin concentration, hormonal environment and other physiological traits, differences that can shape exercise responses and performance.
Then there’s the menstrual cycle, for those who have one. Across a natural cycle, ovarian hormones like oestrogen and progesterone rise and fall. These hormones do far more than regulate reproduction, they interact with bone, connective tissue, metabolism, thermoregulation, the nervous system and more.
So yes, hormones matter.
But here’s the important caveat: their presence doesn’t make the athlete predictable.
There is no universal “female response.” Female physiology can’t be reduced to a single menstrual-cycle model. And unfortunately, physiology didn’t come with a colour-coded training calendar.
The same hormonal environment can be experienced very differently by different women, and even the same woman may experience different cycles differently. Not every female athlete shares the same hormonal or reproductive context, either. Some use hormonal contraception, some have irregular or absent cycles, some are pregnant or postpartum, others move through different stages of reproductive life.
The menstrual cycle: relevant, but not the whole story
21–35 days is the typical range. Only a minority land on 28.
A menstrual cycle is often described as a perfectly predictable 28-day loop. It isn’t.
A typical cycle can run anywhere from 21 to 35 days, and only a minority of women have one that lands exactly on 28. Ovulation timing varies too, in fact, ovulation is a far more useful landmark for understanding where someone actually is in her cycle than simply counting days since the last period.
How hormones move across one cycle
3–7 days
10–22 days, from day one
10–16 days
- 1 Who am I during my period?
- 2 How do I feel after my period?
- 3 Can I identify my ovulatory window?
- 4 How do I feel after ovulation?
- 5 What characterizes my premenstrual phase?
And even when we know exactly where someone is in the cycle, we still can’t reliably predict how she’ll feel or perform.
Some women notice little to no meaningful change across the month. Others experience real shifts in energy, mood, sleep, appetite, motivation, coordination, recovery or pain. Premenstrual symptoms alone take many forms, and their combination can affect both physical and mental wellbeing.
The tidy version of the story — and the reason it falls apart.
This is why “cycle-based training” is an attractive idea with a slightly problematic execution. The temptation is to say: Follicular phase? Train hard. Ovulation? Explosive work. Luteal phase? Recover. Period? Take it easy.
It sounds wonderfully organised. It’s also far too simple.
The body doesn’t read the training plan. The useful question isn’t “What should women do on day 21–28?” It’s “What actually happens to this athlete on day 21–28?”
That distinction changes everything. The menstrual cycle can influence energy, motivation, recovery, temperature regulation and mood, but these effects are highly individual, and the overall experience of a session is also shaped by sleep, nutrition, stress, training load, illness, travel and life circumstances.
Picture two athletes arriving at training on the exact same day of their cycle. One feels fantastic, energetic, motivated, ready. The other slept badly, has significant premenstrual symptoms, and feels unusually fatigued.
Two athletes, one calendar.
Same sex. Same phase. Same programme. Very different athletes.
And even when an athlete is menstruating, that doesn’t automatically mean performance is impaired. An athlete can absolutely train hard, and perform, on day one of her period. What matters is how she’s actually feeling and responding, not what the calendar says she should be capable of.
This is why individualisation is about gathering enough information to make better decisions, and letting the age-old method of trial and error do its job.
Sometimes the most important signal isn’t performance
Female physiology matters in sport for another reason: performance isn’t the only outcome worth monitoring.
RED-S — Relative Energy Deficiency in Sport.
A regular menstrual cycle can be a sign the body has sufficient resources to maintain its physiological functions. Conversely, irregular or absent menstruation in an athlete shouldn’t be dismissed as simply “what happens when you train a lot.” We used to say that in the 1980s. It’s 2026. We know better now.
It can be associated with chronic low energy availability and may form part of Relative Energy Deficiency in Sport (RED-S), with potential consequences for hormonal, bone and metabolic health. A missed period isn’t necessarily a problem with the period, sometimes it’s a message from the wider system. And that system is remarkably good at prioritising survival over your race calendar.
Female physiology matters in sport for another reason: performance isn’t the only outcome worth monitoring.
The same broader perspective applies to heavy or painful periods. Significant menstrual blood loss can contribute to iron deficiency, which in turn can affect energy and recovery. Severe menstrual pain isn’t something an athlete should simply learn to tolerate, some symptoms warrant assessment by a healthcare professional.
In other words, understanding female physiology isn’t only about squeezing out another 0.5% of performance. Sometimes it’s about noticing when the body is telling you something needs attention.
Fuel, training and recovery still follow the same basic rules
None of this means female athletes need a completely different physiological rulebook. They still need enough energy. Adequate carbohydrate and protein. Sleep. Appropriate training loads and recovery. Strength training, cardiovascular development, sport-specific practice. But female physiology can add another layer of context.
An athlete experiencing fatigue during menstruation may need to look at symptoms, sleep, nutrition and, depending on the situation, iron status. An athlete with pronounced premenstrual symptoms may benefit from anticipating them rather than discovering them halfway through an important session. An athlete whose cycle becomes irregular may need to look beyond that single session and ask whether her overall balance of training demands, energy intake and recovery is sustainable.
Not every hard day needs a physiological explanation.
The intervention isn’t always “change the workout.” Sometimes it’s “eat more.” Sometimes it’s “recover better.” Sometimes it’s “talk to someone.” And sometimes it’s simply not assuming that every hard training day needs a physiological explanation.
“The assumption has been that ‘lighter is faster’ but our findings underscore the message that ‘fueling is faster’.”
Kristin Whitney
The danger of turning female physiology into another set of rules
There’s an irony here. For decades, female physiology was largely ignored. Now that we’re finally paying attention to it, there’s a risk of swinging too far the other way.
Suddenly every dip in performance gets blamed on oestrogen. Every poor session becomes “luteal phase.” Every injury becomes “ovulation.” Every craving becomes “hormones.”
Hormones are powerful. They’re also not responsible for everything. A difficult session may have more to do with three hours of sleep, a stressful week or inadequate fuelling than with the exact concentration of progesterone in the blood at that moment.
Neither ignored nor worshipped.
The menstrual cycle should be treated as one variable among many, neither ignored nor worshipped. That’s the most useful position, somewhere between “women are just small men” and “women need a completely different training system.”
Individualisation starts with curiosity
Start with simple observations. How’s your energy? Your sleep? How motivated do you feel to train? Do you notice pain or other symptoms? Do you notice recurring changes at a particular point in your cycle? And, perhaps most importantly: does any of this actually affect you?
Tracking these observations over several cycles helps distinguish a one-off bad day from a genuine pattern. The goal isn’t to label a phase “good” or “bad” it’s to understand how you, specifically, respond, and whether that information is actually useful for training and recovery.
Over time, this builds an athlete’s own cyclical profile: recognising recurring patterns, and more importantly identifying the strategies that help her train, fuel and recover well.
For some athletes, the answer is: “Yes, I see a clear pattern, and knowing it helps me plan.” For others: “Not really.” And for others, the pattern is clear, but the solution isn’t to train less, it’s to put the right nutritional, mental or recovery strategies in place so they can keep training hard.
There is no correct answer here.
All of these answers are perfectly valid.
The future isn’t female-only sport science. It’s better sport science.
Female physiology matters because women are athletes, and because their physiology can hold information relevant to how they train, recover and stay healthy.
Progress isn’t about writing a separate rulebook for women. It’s about building a sporting environment where relevant physiological information can be noticed, discussed and put to use.
That means research that properly includes women. Coaches and athletes who are comfortable discussing female physiology out loud. Tools that help track, understand and act on individual data. Athletes who know their own bodies without becoming obsessed with them. And practitioners who can tell the difference between a real physiological signal, normal individual variation, and a problem that deserves a closer look.
The goal was never to train women differently just because they’re women. It’s to know enough about the individual athlete to make better decisions.
Because good sports science doesn’t give every athlete the same answer. It gives us better questions.