Etiology — what causes it

Eccentric overload of the hamstring during high-speed running, kicking, or stretching. Most commonly biceps femoris long head. Risk factors include prior hamstring injury, age over 25, reduced eccentric strength, and increased fatigue.

Epidemiology — who gets it

Hamstring strain is the most common muscle injury in football (soccer), AFL, rugby, and sprint athletics. Recurrence is high — up to 30% within one year.

Clinical signs

Acute pain in the posterior thigh, sometimes with palpable defect, tenderness localized to the injury site, weakness on resisted knee flexion or hip extension. Askling H-test reproduces apprehension and pain.

Symptoms

Sudden onset of posterior thigh pain during sprinting or stretching. Pain with walking, climbing stairs, and bending forward. Sometimes ecchymosis appears 24–48 hours later.

Best evidence for chiropractic treatment

The Askling L-protocol (lengthening exercises — extender, diver, glider) reduces recurrence compared to conventional rehab (Askling et al., BJSM). Nordic hamstring exercise reduces hamstring injury rate in football (Petersen et al., AJSM). Return-to-sport decisions follow criteria — strength symmetry, sport-specific testing, and the Askling H-test for apprehension.

Subtypes

  • Grade I (mild). Few muscle fibers torn; mild pain, minimal strength loss.
  • Grade II (moderate). More extensive tearing; clear pain, moderate strength deficit.
  • Grade III (severe). Complete tear or near-complete; significant pain, marked strength loss. May require surgical consultation for proximal avulsions.

When to seek emergency care

Some symptoms need urgent medical attention — not a chiropractic visit. Call 911 or go to the nearest emergency department for: progressive limb weakness, loss of bowel or bladder control, saddle anesthesia (numbness in the groin/inner thighs), severe unrelenting pain unrelieved by position, signs of fracture after significant trauma, chest pain, stroke-like symptoms (face drooping, arm weakness, speech changes), or any rapidly worsening or unusual symptom.

Bottom line

Hamstring strain rehab is criteria-based. The Askling L-protocol and Nordic hamstring exercise reduce recurrence — calendar timelines alone don't.