Female endurance athletes, especially runners, sometimes stop getting their period, a condition called amenorrhea. (This obviously doesn’t apply to women who are pregnant, breastfeeding or in menopause.) Amenorrhea occurs when your body slows down production of estrogen as a result of exercising a lot, low body fat percentage, stress or some combination of the three.  If you’re not trying to get pregnant, amenorrhea may seem like a good thing, but low estrogen levels can lead to bone loss. In the short term, bone loss — especially for runners — can lead to low bone density, stress fractures, and later, osteoporosis, according to the American Academy of Orthopaedic Surgeons.  If your period stops, see your doctor.  “The only way to reverse menstrual irregularity is to reduce high-impact physical exercise and for women who have very lean body weights and are on a low fat diets to increase their good fat intake,” says Dr. Minkin. Often, Dr. Minkin will refer women to nutritional counseling. She may also recommend they take a low-dose birth control pill because it will give their body enough estrogen to protect their bones.  Don’t ignore the stress component either, says Dr. Jessica B. Spencer, associate professor in the department of gynecology and obstetrics at Emory University School of Medicine and medical director of the Emory Reproductive Center. “Usually these things are additive,” she says. For example, someone may undergo a very stressful event and, because of it, lose 15 pounds. “The two together may cause a period to stop,” she says.  Note: Taking birth control pills can mask amenorrhoea, because they regulate your cycle. So, often, women won’t realize there is a problem with their cycle until they stop taking birth control. If this happens to you, speak with your Ob/Gyn about your options to start your cycle again.
Women really do run the world. For nearly a decade, more women runners have been crossing the finish line than men. In the United States, women make up 57 percent of finishers —  that's about 10.7 million women racing. Globally, female race participation is up 25 percent, compared to 7 percent for men. That’s a lot of girl power, which is why we’ve created this women-only guide to running. Here you’ll find advice about the big and small challenges of running while female, and how women can get faster and stronger in spite of them. So ladies, grab the sports bra, lace up your sneakers and let’s hit the road.