Claude T. Moorman III, director of sports medicine at Duke University Medical Center, explains.

The simple answer to this question is that "shin splints" is a laymans wastebasket term to describe pain felt between the knee and the ankle after athletic activity. Although there are different reasons why pain is felt in this area, shin splints are considered a cumulative stress disorder as opposed to an acute injury. They occur when the constant pounding and stresses placed on the bones, muscles and joints overwhelm the bodys natural ability to repair the damage and restore itself.

The root causes of the pain of shin splints can be divided into two areas: muscle and bone. The muscles that connect to the ankle are covered by a "sausage skin" known as fascia. This fascia holds the muscles together, and it is quite tough and inelastic. When the muscles naturally expand as a result of exertion, the resulting pressure causes the pain. We see this form of shin splints, known as exertional compartment syndrome, in athletes who play field sports like soccer or run a lot on hard surfaces.

The second major source of shin splint pain stems from the bones and ranges from stress reactions to full-blown fractures. The constant pounding the skeleton endures during running, for example, can cause many microscopic cracks to appear on the bones of the leg. Normally, with rest, the body easily repairs these cracks. Over time, however, these tiny cracks can coalesce into a complete stress fracture, or even a complete fracture.

Shin splints are commonly seen in athletes, military recruits and even middle-aged weekend warriors, especially at the beginning of the season. Treating them can be as simple as adding extra arch support to shoes to redistribute the stresses or changing to softer running surfaces. Doctors also recommend active rest, which means that a runner, for instance, should take up swimming or biking for a while, which gives the affected areas time to heal but maintains the cardiovascular benefits of exercise.

Warming up before exercise is controversial, with smart people on both sides arguing for and against it as a preventive measure for injuries such as shin splints. We at Duke, based on research at the Michael W. Krzyzewski Human Performance Laboratory (K Lab), recommend a slow warm-up period before beginning the activity. We believe that about 10 minutes of graduated activity is the best way to prepare the body for exertion. In general, like most things in life, moderation appears to be the best medicine for shin splints.

Answer originally published May 17, 2004.