Too Much Too Soon

Running marathons or walking to work, you could be at risk for a stress fracture.

Many of us exercise to reduce stress; sometimes our bones don't get the right message and we end up with a stress fracture instead. Surprisingly, it's not just long-distance runners who get stress fractures. Anyone who increases her weight-bearing activity is at risk.

At the beginning of every school year, students new to the UCLA campus begin walking an additional one to four miles a day to classes. Four to six weeks into the school year, we see students who have sustained stress fractures just from this added activity.

What is a Stress Fracture?

A stress fracture is a microscopic break caused by an overload of forces on a bone that has been unable to adapt to the increased stress. Unlike a broken bone, which occurs with a distinct traumatic event, a stress fracture is the result of cumulative overload that occurs over many days or weeks.

Bone is a living tissue that constantly adjusts to the demands placed upon it. As force is applied, the bone will remodel itself to better handle the force. In a runner, for instance, the bones of the lower legs and feet strengthen to handle the impact of landing.

The body makes bone stronger by increasing blood flow to the area and by reabsorbing minerals to form new bone. If too much force is applied, the bone may fracture before it can successfully remodel.

In sports medicine, we often say that stress fractures can be caused by doing too much too soon: Too much impact or force is applied to the bone before it can successfully remodel itself to handle the load.

The bones most commonly fractured are those of the lower leg, the tibia and fibula, followed by the metatarsal bones of the feet. Athletes who use their upper arms, such as baseball pitchers and gymnasts, can experience stress fractures in their wrists and upper arms.

What causes stress fractures?

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