Stress fractures are micro-cracks in bone that occur when a bone is faced with more load, or "stress,” than it can handle. The most common sites of stress fractures are the bones of the foot and lower leg, but they can occur in virtually any bone, including the femur (thigh bone), pelvis, and back.
Although any runner can suffer a stress fracture, runners who have some underlying bone health weakness, or those who significantly increase their weekly mileage and/or the frequency of their running are especially susceptible. Studies suggest that running more than 35 miles/week; not taking rest days; and having a history of eating inadequate amounts of nutrients (contributing to weak bones), loss of the menstrual cycle in female runners, and prior stress fracture all increase risk of stress fracture.
Recurrent stress fractures deserve special attention, as they may be an indication of osteopenia or osteoporosis (bones that are weaker or thinner than expected for the age and health of the patient). A runner with recurrent stress fractures usually either has inappropriate training habits or an underlying bone health issue and should be evaluated by a physician who is experienced in dealing with bone health issues as well as running injuries.
Dr. Lisa Callahan is a sports medicine physician and co-director of the Women's Sports Medicine Center at Hospital for Special Surgery. Since 2004, Dr. Callahan has been the Director of Player Care for the New York Knicks and New York Liberty basketball teams. She is the author of The Fitness Factor: Every Woman’s Key to a Lifetime of Health and Well-Being (April 2002, Lyons Press).