Stress fractures occur when bone remodeling can't keep up with mechanical load. Risk factors: rapid mileage increase (>20% per week), low energy availability (eating too little for training load), low vitamin D, low calcium, narrow tibia/metatarsals, prior stress fractures, female athletes during the low-oestrogen phase.
Prevention: ACWR ≤ 1.3 ceiling, RED-S screening (especially for athletes with menstrual dysfunction or low body weight), 25(OH)D blood test, calcium intake 1000–1500 mg/day, gait retraining if you're a heavy heel-striker, periodised rest weeks every 3–4 weeks.
Most recurrences are at the same site or contralateral within 12 months. The fix is fueling and load management, not equipment.