Generally lasting three to five days, your menstrual period or menstruation is the portion of your menstrual cycle during which your body sheds blood and uterine tissue. The first day of your menstrual period marks the first day of your menstrual cycle, which typically lasts 28 to 32 days for most women. During the first half of your menstrual cycle, your body’s levels of the hormone estrogen increase; this hormone boost causes the uterine lining to thicken in preparation for pregnancy. Additional hormone fluctuations cause one of your ovaries to release an egg, which travels to the uterus for fertilization. If fertilization doesn’t occur, your hormone levels drop, the egg disintegrates and you undergo menstruation.
Moderate physical activity may actually improve various severe side effects of menstruation – including uterine cramping, vomiting, nausea and back pain – that occur in approximately 50 percent of women, according to Dr. Thomas Hyde, sports chiropractic physician and co-author of “Conservative Management of Sports Injuries.” These menstrual symptoms most likely develop when the uterine lining releases prostaglandins, hormones that limit blood flow to your uterus and cause painful uterine contractions. When you exercise, your body increases blood flow to the uterus and boosts its production of endorphins, “feel-good” hormones that may counter the effects of these pain-inducing prostaglandins in some women.
Intense physical activity combined with decreased caloric intake may cause your menstrual period to cease. This condition, called amenorrhea, occurs most frequently in female distance runners, but it also may develop in women who participate in other sports that emphasize slenderness, like ballet, gymnastics and figure skating. Women who develop amenorrhea experience an ongoing energy deficit, which eventually causes the hypothalamus – your brain’s control center – to suppress the release of hormones that regulate ovarian function. The ovaries fail to release an egg for fertilization, which keeps you from experiencing a menstrual period.