A new study reveals female runners who are underweight have a higher risk for tibial stress fractures and take longer to heal. This is the first study to focus specifically on one bone and one group of athletes, according to Dr. Timothy Miller, assistant professor of clinical orthopaedic surgery and sports medicine, and lead author.
There is a strong correlation between lower Body Mass Index, or BMI, and a stress fracture taking place, he says.
Also, lighter women who suffered stress fractures took longer to recover from them than other runners. It usually takes between four and six weeks for such injury to heal. But, among the women in the study, “some took longer than three months, six months in one case,” Dr. Miller adds.
The study, conducted at The Ohio State University Wexner Medical Center and recently published in Current Orthopaedic Practice, concludes that female runners who have a BMI of less than 19 are at a higher risk than women with a BMI of 19 or higher.
BMI is a person’s weight in kilograms divided by the square of height in meters. It’s important to remember that the number does not measure body fat directly, but it is still strongly correlated with various metabolic illnesses, according to the Centers for Disease Control and Prevention.
Most people, including athletes, use BMI as an inexpensive and easy-to-perform method of screening for weight category, for example underweight, normal or healthy weight, overweight, and obesity.
However, BMI doesn’t account for muscle. The logic of the problem is simple: Runners endure repetitive pounding on hard surfaces and, without enough lean muscle mass for dissipation of impact forces, the bones of the legs are vulnerable.
You have to consider the reaction force that comes back from the ground when people are running, Dr. Miller says. The lack of muscle means the shock has nowhere to go; it is not absorbed other than directly back into the bone, he adds. “You always want a little fat in the body, never less than 5 percent body fat.”
Elite athletes at college level are pushing themselves too hard to achieve the best possible results. It is common to mistakenly think that losing weight will make them faster because they are lighter, Dr. Miller says. “It works with beginner runners because the result of getting in running shape.” Losing more is not healthy. “You have to have lean muscle to propel the body forward,” he adds.
A total of 18 college athletes with 24 diagnosed fractures were observed for the research over the period of three years. It is actually part of a much bigger study on stress fractures, which are some of the most common injuries in the sport, in all runners, Dr. Miller says.
Between 20 and 25 percent of athletes will develop a stress fracture. This is a very high number, Dr. Miller says. “One person can have multiple stress fractures.” The injury can occur throughout the body – in front of the tibia, inside the hip, outside the foot and on top of the foot.