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Pathophysiology
A “strain” occurs when muscle fibers cannot handle the demand placed on them, resulting in a tearing of the muscle fibers. Strains can occur as a result of a powerful “eccentric” contraction or “over-stretched” muscle fibers. They commonly occur in “two joint muscles” (muscles that cross over and move two different joints) such as the hamstring, hip adductors, gastrocnemius and erector spinae musculature. For these reasons, non-contact athletes such as sprinters and speed athletes are the most affected.
A hamstring strain can be graded on a 1 to 3 scale.
Grade 1: < 10% muscle fiber disruption
Grade 2: >10% - 15% muscle fiber disruption
Grade 3: 50% - 100% muscle fiber disruption (full thickness tear)
Physical therapy for hamstring strains consists of a thorough evaluation and assessment of the irritability of the injury. Once the acute phase of healing is over, progressive loading of the muscle is KEY to restoring pain free range of motion and muscle length. Weight training including concentric strengthening, eccentric strengthening and eventually plyometric strengthening is required in order to return the patient to their prior level of function.
Due to the nature of strains, physical therapy is often indicated for up to 12 weeks in order to fully eliminate pain and dysfunction.
