The three phases, in one sentence each
The menstrual cycle is usually divided into three moments. The follicular phase begins on the first day of menstruation and runs to ovulation, with estrogen rising. Ovulation is the hormonal peak, around mid-cycle. The luteal phase comes after, with high progesterone, and ends at the next menstruation. The hypothesis that became popular is simple: if hormones change this much, training should change along. The honest question is: change how much, and for whom?
What the best evidence really says
The central reference is the meta-analysis by McNulty and colleagues, published in 2020 in Sports Medicine, which pooled 78 studies on cycle phase and performance in women with regular cycles. The result surprises those expecting a dramatic answer: the average effect of phase on performance was trivial. Performance was slightly reduced in the early follicular phase (the first days, during menstruation) compared with the other phases, with an effect size of about minus 0.06, so small that in practice it is nearly indistinguishable from zero.
In other words: periodizing training by cycle is a promising idea, but today it rests on weak evidence. The average says little. What may matter is your response, measured over several cycles, not that of a generic spreadsheet.
Symptoms are real, and that is different from performance
There is an important distinction. One thing is the phase changing laboratory-measured performance. Another is the woman feeling worse and training differently because of it. Cramps (dysmenorrhea) and premenstrual symptoms are common and can indeed get in the way. In a survey with 1,086 athletes from 57 sports, about half reported perceived negative impact on performance during menstruation days, and 45% had already skipped a planned workout for cycle-related reasons. Curiously, only 18% adjusted training in an organized way based on the cycle.
The sensible reading: if cramps or premenstrual fatigue take down your week, it makes complete sense to adjust volume and intensity on those days. That is not sophisticated periodization, it is listening to the body and planning around the symptoms you actually have.
Iron, menstruation and a risk that goes unnoticed
Monthly blood loss increases iron needs. Iron deficiency is notably more common in women, and estimates in female athletes usually range from 15% to 35% with low stores, that is, up to about a third in some groups. Low iron drags down oxygen transport and shows up as tiredness and falling performance, especially in endurance sports. That is not solved with a cycle app. If there is persistent fatigue, the path is testing and evaluation, not supplementing on your own.
Why we know so little
Part of the answer is embarrassing: sports science studied mostly men. An audit of more than 5 thousand publications between 2014 and 2020 found that only 6% of studies were done exclusively with women, and that women were only about 34% of all participants. Many protocols avoided women precisely to avoid dealing with the cycle's hormonal variation. The result is that much of what is taught as universal was validated in male bodies. That is why top athletes started publicly demanding more research.
What the elite does (and why not to copy the dose)
Top national teams and clubs started mapping athletes' cycles. The US women's national team, champion of the 2019 World Cup, monitored players' cycles during the tournament to adjust sleep, nutrition and load, work conducted by performance coach Dawn Scott with scientific support. And in 2022, sprinter Dina Asher-Smith did not finish the 100m final at the European Championships due to cramps she attributed to her period, and used the microphone to call for more research investment.
How to act without becoming a hostage of the calendar
- Record for a few cycles. Note symptoms, sleep, energy and how training went. Patterns only appear with your own data, over time.
- Adjust by symptoms, not by theory. If cramps take you down, lighten the load on those days. If you feel fine, train normally. Do not force a performance drop that the average does not even confirm.
- Treat iron and fatigue as a medical matter. Persistent tiredness calls for testing, not self-prescribed supplements.
- Distrust closed promises. No app today proves that training more in phase X yields more. The evidence is weak, and being honest about that is part of the method.
The conclusion fits in one line: the cycle may matter to your training, but in an individual way that only your observation reveals. Science is still building that answer. In the meantime, the best plan is the one that respects how you actually feel, with medical follow-up when the subject is health.
