An informative piece that clearly explains why back pain is a very real side effect of menstruation and the mechanism of how it happens. When the uterus sheds it’s lining it contacts, much like during child birth, but much milder. These contractions cause a constriction of nearby blood vessels which limits the amount of oxygen reaching nearby muscles. This lack of available oxygen causes cramps. While moderate back pain is normal, the article also warns that intense back pain may be a sign of endometriosis. It also offers that light exercise and stretching, like yoga, may relieve some symptoms.