A "stress" fracture is really a crack within the bone. It is a partial fracture, or micro-fracture, rather than the complete fracture. Stress fractures most often result from overuse and repetitive stress on the bone. They often result from any increased amount or intensity of activity, which occurs too rapidly for the bone to adjust.

Every day bone cells work to strengthen bone, or to allow the bone to become less strong, depending upon the perceived need. Every day the body makes new bone to replace the bone that is broken down by the stresses of every day activity. Ideally, the body produces as much new bone as it breaks down. In many cases, however, bone breakdown comes to exceed new bone formation. This can weaken the bone and lead to micro-factures known as stress fractures.

In many cases, stress fractures occur because an individual increases the activity and stress put upon the bone too quickly for the body to adapt. If the bone is not accustomed to the new loading, and if it is unable to strengthen itself quickly enough, stress fractures develop. About half of all stress fractures occur in association with athletic activity. More than 50% of all stress fractures occur in the lower leg, the most common of these being tibial stress fracture.