Hamstring strain

A hamstring strain is a sudden, sharp pain at the back of the thigh, usually when sprinting or accelerating. Stop at once: do not run through it.

• Signs: a sharp pain or a pop, sometimes bruising days later, pain when stretching or bending the knee against resistance. A slow ache high under the buttock, worse sitting, is more often the tendon.
• What usually helps: walking as pain allows, then progressive strengthening (bridges, later Nordic curls). Mild strains often allow running in 1 to 3 weeks, bigger ones in 4 to 8; sprinting returns last.
• A previous strain is the main risk factor: keep strengthening afterwards.
• See a doctor quickly after a pop with large bruising or if you cannot walk normally; a physiotherapist if no better after 2 weeks.