A stress fracture is a fatigue-induced fracture of the bone caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated trauma from repeated submaximal loading, such as running or jumping. Because of this mechanism, stress fractures are common overuse injuries in athletes. Stress fractures can be described as very small slivers or cracks in the bone; and are sometimes referred to as "hairline fractures." Stress fractures most frequently occur in weight-bearing bones, such as the tibia (bone of the lower leg), metatarsals, and navicular bones (bones of the foot). Less common are fractures to the femur, pelvis, and sacrum.