You might want to be extra careful when Aunt Flo makes her monthly visit. Australian researchers found that female athletes are more likely to get injured during their periods than any other time of their cycle. Why? Low estrogen at the beginning of the menstrual cycle (when you're actually bleeding) causes reduced muscle tone and impairs coordination, making you more susceptible to injury, especially in the knees, feet, and ankles.
It's not just our physiology that suffers. Rachel Cosgrove, in her book The Female Body Breakthrough, adds that "more than one study has shown that exercise feels harder the week before and the week of women's periods because of increased levels of progesterone and decreased levels of serotonin." You may find that your workouts feel harder than usual and that you're more tired, but don't beat yourself up if you don't set a personal best this week. Just get in and get it done," Cosgrove says.
If you want to make the most of menstruation, power through those weight routines. According to Cosgrove, your body's fat-burning potential peaks during this time. And there's more good news: Taking birth control can help counter the negative effects. The Aussie scientists say, "there's now quite a global body of research saying that the pill actually is protective of injuries. It protects you from injuries, it improves performance, and improves muscle function." Birth control as a performance enhancer? Double win!