Short answer: they can influence how you feel. They do not automatically decide how well you perform.
Oestrogen and progesterone act on several systems at once.
Here’s the nuance nobody puts on a t-shirt: oestrogen and progesterone are genuinely powerful. Oestrogen can boost muscle strength and reactivity while also making ligaments a little more lax. Progesterone can calm your central nervous system, while also nudging your mood around. Two hormones, several systems, sometimes pulling in opposite directions at once. Charming.
The result? The net effect varies enormously from one athlete to the next. Which is precisely why “hormones made me slow today” is a satisfying sentence but not always an accurate one.
Feeling different is not the same as performing worse.
Here’s what the current evidence actually says: there is no solid proof that performance systematically drops during your period or in the days before it. Different sensations? Yes, very possibly. Lower performance? Not automatically. Sensation and capability are not the same thing, even though they love to pretend they are at 6am on a hard interval day.
RED-S: Relative Energy Deficiency in Sport.
So what should get some side-eye? Irregular or missing periods for several months. That’s not “just what happens when you train hard” — we retired that explanation sometime around the 1990s. Irregular or absent cycles can signal Relative Energy Deficiency in Sport (RED-S), basically, your body quietly deciding it doesn’t have enough energy to run training and every other system, so it starts switching things off. Bone health, recovery, metabolism, long-term performance all can take the hit.
Heavy periods? Ask about iron.
Heavy bleeding deserves a mention too: it can contribute to iron deficiency, which absolutely can affect energy and recovery. That’s not drama, that’s blood, literally.
The takeaway: hormones are one variable in a very long list: sleep, stress, nutrition, load, life. Powerful, yes. The sole author of your bad session? Rarely.