Stress fractures are tiny cracks in your bones that occur when overly tired muscles can no longer absorb the shock of repeated impact. When this happens, the forces are transferred to your bones, causing stress fractures. Stress fractures are most common in weight-bearing bones in the foot, shin and ankle. The major cause of stress fractures is overuse. They are especially common in athletes that participate in high-impact activities, such as basketball, gymnastics, tennis, and long-distance running. Stress fractures are associated with gradual pain that increases during weight-bearing activity.