“Let’s come into Shoulder Stand. If you’re on your cycle, just take Happy Baby pose instead.”
This seems to be the standard advice from yoga teachers in regards to inversions, which are often defined as poses where your head is inverted to your head and include poses like Shoulder Stand, Plow, Hand Stand, and Headstand. But is it really the case that women should avoid inversions during the menstrual cycle?
Safety concerns around inversions
The book I co-authored, The Physiology of Yoga, covers this very topic, examining specifically the idea of reversing blood flow during inversions and its effects. Here’s an excerpt:
There is widespread belief among yoga teachers and practitioners that women should not practice inversions including Shoulder Stand (Salamba Sarvangasana) and Headstand (Sirsasana) during their period. The reasoning behind this often has to do with the perceived flow of energy throughout the body. On an energetic level, menstruation is intrinsically linked with apana (the contracting, downward moving force), and therefore it is believed that inverting the body will reverse the direction of this force. Another part of the reasoning comes from the retrograde menstruation theory, which was promoted by Doctor John Sampson (1927). In 1927, Sampson suggested that menstrual tissue can flow backward through the fallopian tubes and deposit on the pelvic organs, causing endometriosis (the abnormal growth of endometrial cells outside the uterus). However, there is little evidence that endometrial cells behave in this way. More recently, researchers have found that up to 90 percent of women have retrograde flow anyway (Sasson and Taylor 2008), but since only 10 percent of women of reproductive age develop endometriosis (Olive and Schwartz 1993), it has been concluded that the cause of endometriosis is much more complicated than this. Sampson’s theory has also been disputed, because it cannot explain the occasional occurrence of endometriosis in prepubertal girls, newborns, women who have had a hysterectomy (surgical removal of the uterus), and men who have received long-term hormonal treatment. Writing about female astronauts in space, Wotring (2012) reported that the myth that zero gravity would cause retrograde menstrual flow, causing blood to accumulate in the abdomen and cause infections, has been shown to be baseless. It is understood that uterine contractions, rather than one’s orientation to the ground, are responsible for the flow of menstrual blood (Bulletti et al. 2000).
It is also important to recognize that the uterus is inverted many times throughout a typical yoga practice—for example, in Standing Forward Fold (Uttanasana), Downward Facing Dog (Adho Mukha Svanasana), Bridge Pose (Setu Bandha Sarvangasana), and others—yet these poses are rarely classed as inversions. Thus, there is little logic to the idea that inverting the uterus in these poses is appropriate but not appropriate during a Shoulder Stand. There is rarely, if ever, a single directive that works for every student. It is important for yoga practitioners to tune into what feels right for them in each moment and for yoga teachers to give options and permission for students to do so.
Menstruation and exercise performance
So, it seems like the safety concerns around inversions and menstruation are not science-based but what about the menstrual cycle phases affecting a woman’s ability to perform these asanas? Well, a 2020 systematic review and meta analysis on the effects of menstrual cycles on exercise performance in women found that exercise performance might be trivially reduced during the early follicular phase of the menstrual cycle compared to all other phases. In other words, the 73 studies included in this analysis found a very small (“trivial”) reduction in how women could perform in both strength- and endurance-related outcome measures. However, the authors also found highly varying results and poor study quality which suggests that no firm conclusions can be drawn. They concluded by stating that “general guidelines on exercise performance across the menstrual cycle cannot be formed.” This science-informed statement stands in stark contrast to a black-or-white stance that all yoga practice must cease during a woman’s cycle.
Social context around menstruation
There’s another thing I need to mention. Within the Iyengar tradition, inversions are strictly forbidden during menstruation and the Ashtanga Vinyasa School created by Pattabhi Jois encourages a “ladies’ holiday” during the first three days of one’s period (as in, refraining from practice altogether during this time). Notice anything about those two advice givers? They were both dudes! Doesn’t it seem a bit strange that our current practice-during-menstruation guidelines were created by men? I am keenly aware that I too am a man writing about the same topic, but my intent is simply to share the latest science from information about retrograde blood flow to studies on exercise performance during menstruation.
Lastly, cultural and religious beliefs have also probably played a role in shaping the notion that women should avoid inversions during menstruation. In many cultures, menstruation has been surrounded by taboos and restrictions, often rooted in the idea of menstrual impurity. These cultural norms have historically discouraged women from engaging in certain activities during their periods, including physical exercise and yoga practices. While these taboos have been challenged and debunked in many modern contexts, their influence on traditional yoga practices has persisted, contributing to the idea that inversions should be avoided during menstruation.
So, what’s the verdict?
The science suggests that safety concerns around retrograde blood flow and endometriosis as a result of practicing inversions during the menstrual cycle are unfounded. We must also examine whether social taboos are playing a role in our beliefs.
As for whether it’s a good idea for you individually, the conclusion of the 2020 systematic review mentioned above sounds pretty darn reasonable. They wrote, “It is recommended that a personalised approach should be taken based on each individual's response to exercise performance across the menstrual cycle.” Mic drop.
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