For most of us who start out practicing yoga for the physical benefits, it’s weird to think about restrictions from practicing due to a full or new moon or your period. One feels superstitious and the other seems a bit sexist. But I’ll lay out what the deal is with moon days and menstrual days, and then you can make a judgment call on how you want to observe those days.
In the Ashtanga tradition, you’re not supposed to practice on Moon Days, which are the days when the moon is at its fullest or when there is a new moon. This happens twice a month and has nothing to do with Jacob or Twilight or werewolves.
Just as the moon’s gravitational pull has an effect on tides, the idea is that your body is mostly water and is thus affected by the moon’s pull. You can read more about the specifics of the moons here.
“Observing moon days is one way to recognize and honor the rhythms of nature so we can live in greater harmony with it.”
Women can certainly practice yoga during their periods – many postures can help with cramps and aches. However, we are advised not to do inversions (headstand, shoulderstand and the like) as the upside-down gravitational pull goes against the natural flow of… aunt flow.
“Hindu philosophy teaches that during menses the direction of energy is down and out of the body. This flow should not be obstructed or reversed as it is in inversions.”
Other postures to avoid are ones that require a lot of energy and balance. The idea is that your energy is already low due to your period, and you don’t want to overexert yourself during this time.
“Physical strength may be somewhat diminished at this time, causing one to be shaky or off balance; therefore, standing poses in the center of the room and strenuous backbends may be difficult and exhausting.”
So take both these points as you will. I think the bottom line is if your body doesn’t feel up for the task, back off the practice. Only you can determine how you’re feeling and what the best way is to honor your body.
FYI: May 5 is the next full moon. Maybe take the day off and celebrate Cinco de Mayo instead!