Runners take steps to reduce stress fractures

Athletes and soldiers are among those who might benefit most from research on stress fractures and biofeedback that is being conducted at UD’s Running Injury Laboratory.

Stress fractures—tiny cracks in bones brought about by repetitive shocks and overuse—have more than likely plagued human beings since our forebears began walking upright. Yet until fairly recently, with the advent of sports medicine and high-tech shoe design, individuals prone to the hairline fissures for the most part suffered in silence.

Stress fractures, which can lead to more serious fractures if left untreated, are so common in the military, in fact, that they’re known as “march fractures” and cost the Department of Defense and other agencies huge monetary losses each year.

With an eye toward prevention, Irene Davis recently was awarded $1.3 million in grants from the National Institutes of Health and the Department of Defense for her ongoing work on reducing the risk of stress fractures. Davis, professor of physical therapy, is director of the University’s Running Injury Laboratory and director of research for Drayer Physical Therapy Institute.

“Preliminary studies have yielded positive evidence,” Davis says. “Stress fractures develop when there is repeated and extreme loading on bones weakened by an imbalance between new bone formation and bone loss, and my intent has always been that, once we were able to understand the running mechanics associated with these types of fractures, we would work to find methods to alter these mechanics and, it is hoped, prevent them.”

The fractures, she adds, most often occur in the tibia, the larger of the two bones in the leg below the knee, and are likely to affect runners who experience high-shock loads or land harder as they run.

“If someone happens to have a relatively high load when they run, they put themselves at greater risk for stress fractures,” Davis says. “When you hit harder, you naturally have a greater load to dissipate.” The rate of reinjury, she notes, is a dismayingly high 36 percent.

If results from preliminary biofeedback studies conducted at the Running Injury Laboratory hold true, gait retraining addresses this. Results for altering mechanics for the better are so promising, in fact, that runners who participated in initial studies were able to change their faulty gaits in eight half-hour sessions, Davis says.

“The preliminary data we’ve developed show that runners, when provided with feedback on their gait, can indeed reduce their loads by about 50 percent, compared with cushioning shoes that might result in a reduction of 10 percent,” says Davis, who presented her research at the Experimental Biology 2007 meeting in April. “This leads me to believe that we have a greater ability to alter mechanics through biofeedback than through external devices such as shoes.”

She says research funded by the grants will involve screening study participants for faulty gaits, retraining them with an accelerometer and a biofeedback monitor and testing them at the end of the study and at follow-up intervals.

Individuals will run on a force treadmill with an accelerometer attached to their lower legs that measures their impact and then translates that g-force—the measurable force of gravity—into a spike that’s shown on a monitor in front of them. The runner must therefore constantly adjust the force of each foot strike to reduce high spikes.

When runners are able to see the immediate data on the impact of each stride, they learn how to make a softer landing, she says.

Following a treadmill accommodation period, research participants will undergo the retraining. Run time will be gradually increased and feedback gradually decreased over eight sessions. Subjects will then have their gaits analyzed for tibial impact and ground reaction forces immediately following clinical testing and again one, six and 12 months later.

As part of the Defense Department grant, Davis and her colleagues will be investigating how running more softly affects loads in the tibia itself. Mathematical modeling will be used to estimate reductions in bone strain.

Runners from ages 16-40 are being sought for the study. To be considered, participants must run at least 10 miles a week and demonstrate (through a treadmill test conducted at UD) high-shock impact when they run. To learn more, call Michael Pohl at (302) 831-4646.

—Becca Hutchinson and Barbara Garrison