A significant amount of research has previously been done on the effects of estrogen throughout the menstrual cycle on ligament laxity with some showing a correlation of increased estrogen levels with increased ligament laxity.

Does estrogen cause ligament laxity?

When estrogen concentration increased during the menstrual cycle, knee laxity increased as well (Shultz et al., 2010, 2011, 2012a). In fact, these authors found that knee laxity increased between 1 and 5 mm between the first day of menstruation and the day following ovulation, depending on estrogen levels.

Does estrogen make you flexible?

Girls can also become tighter during the rapid growth of puberty if they cannot stretch to keep up with their growth. However, the increase in estrogen usually allows girls to maintain or improve their flexibility once they slow down their speed of growth.