Stress fractures, small cracks on the surface of the bones, usually start out as a minor discomfort in the foot or leg that occurs near the end of a long run. Usually the pain goes away as soon as the athlete stops running. On the next day, the pain returns earlier in the run. If she notices that it hurts to touch just one spot on a bone and then stops running for a week, she can return to running quickly, but usually she ignores the pain and develops a full- blown stress fracture that hurts all the time. She now has to avoid the hard pounding of running, but can ride a bike or swim for exercise until the fracture heals in 6 to 12 weeks. The most common sites for stress fractures are the bones in the front of the feet or the long bone of the lower leg, but running can cause stress fractures anywhere, even in the pelvic bones.
Forty-five percent of competitive female runners develop stress fractures. The women most likely to suffer these injuries are those who restrict food and those who have irregular periods. Restricting food can stop a woman from menstruating regularly, which can stop her body from producing the female hormone, estrogen. Lack of estrogen weakens bones. Exercise does not cause irregular periods, but not taking in enough calories can. Women who stop menstruating when they exercise heavily will usually start to menstruate regularly when they eat more food. I often prescribe bone strengthening medications such as Fosamax or Evista to women with stress fractures that do not heal in six months.