The short answer
- Across 78 studies, the effect of menstrual cycle phase on exercise performance was trivial, and the authors concluded that general guidelines cannot be formed.
- For oral contraceptives the picture is the same: any group-level effect is most likely trivial, and performance was consistent across the pill cycle.
- A trivial average across a population is entirely compatible with a large effect in one person. The average hides you rather than describing you.
- Symptoms are a separate question from lab performance, and they are well documented: pain, mood, and reduced motivation to train.
- Three cycles of your own notes will tell you more about you than any study can. Periods stopping is the one finding that is never a convenient side effect.
There is a whole industry built on training your cycle in phases, with apps to tell you which week to lift heavy and which week to go easy. There is also a large body of evidence saying the effect on performance is close to nothing. Both of those statements can be true at once, and the way they fit together is the useful part.
What the research found
The same research group did the equivalent work on the pill.
Why that does not mean it is in your head
An average across a population is a statement about the population. It is not a statement about you, and a trivial mean effect can sit on top of enormous variation between individuals. Both reviews say so explicitly, which is why both end with the word individualised rather than with a recommendation.
There is also a second thing going on. Those studies measured performance in controlled conditions, usually a single effort on a single day. That is a different question from how training feels across a week, whether you sleep, and whether you get out of the door at all.
Reduced motivation to train is not a performance decrement in a laboratory sense. Over a twelve-week block it is a far bigger deal than a two percent difference in a time trial, because it decides how many sessions actually happened.
What to do instead of following a phase plan
Three cycles of notes will give you better information than the whole literature, because it will be about you.
Keep it small enough that you will actually do it. Cycle day, how the session felt on a scale you invent, sleep, and any symptoms that mattered. That is four fields and about fifteen seconds a day. After three cycles, look for a pattern that repeats. If one is there, you can plan around it. If nothing repeats, you have learnt something worth knowing too, and you can stop wondering.
The one finding that is never convenient
Periods becoming irregular or stopping is not an acceptable consequence of training hard, and it is not a sign that the training is working.
It is one of the clearest signals that energy intake is not covering training, which is the condition the IOC describes as Relative Energy Deficiency in Sport4. It carries consequences for bone and for long-term health that arrive quietly and take years to reverse.
Hormonal contraception complicates this, because a withdrawal bleed on the pill is not the same as a natural period and can mask the signal entirely. That is worth knowing if you are using it and training heavily.
When to get it looked at
The last two are medical decisions rather than training ones, and they are worth having with a doctor rather than a physiotherapist or a coach.