A stress fracture is a microscopic crack in a bone that occurs from overuse. Muscles normally absorb the shock of physical activities, but when they become too fatigued to do so, they transfer the stress to the bones which results in a hairline-sized fracture.

Stress fractures usually develop in the weight-bearing bones of the feet and lower legs, often after a rapid increase in the duration or intensity of exercise or from wearing improper or worn-out athletic shoes.