Why does my heel hurt when running?

Heel pain in runners has four main causes, and the location tells you which. Bottom of the heel, sharp pain first thing in the morning: plantar fasciitis. Treatment is eccentric calf raises, foot stretching, and rolling the arch over a frozen bottle. Back of the heel, tender on the tendon: Achilles tendonitis. Treatment is heel drops, heel lifts in shoes, and reduced hills. Underneath the heel, dull bruising after long runs on hard surfaces: heel pad contusion or fat pad atrophy. Treatment is cushioned shoes, heel cups, and reduced impact. Deep heel pain that worsens with continued activity and hurts to press the heel bone directly: calcaneal stress fracture (rare but serious). This requires an MRI and 6-8 weeks of non-weight-bearing recovery. Contributing factors across all of these: worn-out shoes past 800 km, sudden mileage increases, tight calves, hard running surfaces, and weak foot intrinsic muscles. General protocol: ice 15 minutes after running, reduce mileage by 30-50% for 2 weeks, strengthen calves, replace shoes if worn, and check for biomechanical issues with a sports physio if pain persists past 4 weeks. Don't run through sharp or worsening heel pain — it commonly progresses and delays return to running by weeks.