This is a prevalent claim in the yoga world. But is it accurate?
The basic idea is that if we invert while menstruating, this change in orientation to gravity can reverse or stop menstrual flow, which can be problematic.
There are also more traditional yogic beliefs about the importance of “apana”, or “downward energy” during menstruation. These beliefs state that inversions disturb that energy.
In fact, in the Astanga tradition, students are instructed to stop their yoga practice altegother during menstruation - a time referred to as “ladies holiday”.
(My Ashtanga teachers taught me that engaging the bandhas (muscular/ energetic “locks” or “lifts”) of the Asthanga system during one’s practice will disrupt the downward flow of menstruation.)
So what does the science say about the physiology involved? Well, contrary to popular blood does not actually reply on gravity(!)
In fact, did you know that astronauts in zero gravity still have normal periods?
This is because the doward flow of menstrual blood is created instead by muscular contractions in the uterus (peristalsis), and these operate independently of the body’s orientation to gravity.
Additionally, even if the claim were true, why does the “no inversions” rule not apply to less obvious inverted poses like halasana, uttanasan, and down dog? Why are these ok to practice while handstand and headstang are not?
In the end, if your only reason for not inveerting while menstruation is concern about reversing menstrual flow, you can be assured in knowing that menstruation operates independently of gravity.
It is a great idea for people to listen to their bodies when menstruating and decide for themselves whether inversions in yoga feel appropriate.