What causes a stress fracture?

Running, jumping, marching, or other repetitive impact creates tiny areas of bone damage. With enough rest, the body normally remodels and repairs them. A rapid change in training, harder surfaces, worn footwear, or altered movement can increase the load before repair catches up. Low bone density, osteoporosis, and vitamin D deficiency may make bone less able to tolerate ordinary activity. Stress fractures often affect weight-bearing bones in the foot or lower leg, but they can occur elsewhere. Pain is typically focused in one area and becomes more noticeable with loading; it may later persist during ordinary activity.

Stop the activity that brings on pain and arrange a clinical assessment rather than testing the area repeatedly. Keep weight off the painful limb if walking hurts, using support if advised. A clinician may examine the tender spot and decide whether imaging or repeat imaging is needed. Do not return to impact exercise simply because pain settles for a short time. A gradual return should follow healing and address training load, footwear, technique, and any bone-health concerns. Further information is available in [Stress Fracture](/conditions/stress-fracture/) and [Vitamin D Deficiency](/conditions/vitamin-d-deficiency/).

Seek prompt care if you cannot bear weight, pain is severe or rapidly worsening, the limb looks deformed, or swelling and bruising follow an injury. Urgent assessment is also sensible when pain occurs at rest or at night, because this can indicate a more advanced bone problem or another diagnosis.

Could this be a stress fracture or another injury? Should I limit weight-bearing? When can I resume impact activity? Do I need assessment of bone density, nutrition, or vitamin D?