Hamstring muscles include three muscles in the back of the thigh: semitendinosus, semimembranosus, and biceps femoris. They work to bend the knees, pull back the legs, and extend the hips.
Hamstring strains are often called "pulled muscles," meaning that muscles are stretched and torn. There are three grades of severity, which are based on the number of muscle fibers injured. Grade 1 means there are stretched muscles and minor, very tiny tears. Grade 2 means there are partial muscle tears. Grade 3 is severe and means muscles are completely torn and may need surgery. Hamstring strains are fairly common in activities that involve running, jumping, and kicking. They can also occur with stretching too much (as in yoga) and in other activities needing quick starts and stops.
It’s unclear what the exact causes of hamstring strains are, but decreased flexibility, strength, and endurance of the muscles are often considered. Injury most often occurs when the muscles are contracted forcefully and at their longest. Other factors that increase risks of having a pulled hamstring include increasing age, previous injury, nerve pinches in the low-back area, fatigue, and poor fitness. High-risk activities for hamstring strains are soccer, football, baseball, basketball, water skiing, weightlifting, tae kwon do, ice skating, dancing, and track and field events.
Symptoms are pain in the back of the leg during exercise, muscle spasm, swelling, bruising, and tenderness. With a significant injury, an individual can feel the muscle "tighten" or "pop" and sometimes feel as if they have been struck in the back of the leg. Pain can occur when passively extending the knee with the hip flexed at 90 degrees and with resisted knee flexion. With severe injury, there may be a palpable defect, bruising can occur, and people may have trouble contracting the muscle.
The health care provider makes a diagnosis by the medical history and physical examination. Imaging studies, such as x-rays, may be helpful in the younger athlete, especially to make sure that the muscle hasn’t pulled off a small piece of bone where it connects. Other imaging studies, such as ultrasonography and magnetic resonance imaging (MRI), are rarely needed for simple muscle strains, but may be helpful in more severe injuries and/or if the diagnosis is unclear.
The goal of treatment is to return to activities as soon as it is safely possible. Returning too soon may worsen the injury and lead to permanent damage. The first 48 hours after injury are the most important. Use RICE (rest, ice, compression, and elevation). Rest and avoiding activities that may have started the problem are critical. Using ice packs and special stretching and strengthening exercises often help. Wrapping an elastic bandage around the leg for compression may keep swelling from getting worse. Put a pillow under the thigh for elevation. It is important to avoid rigorous excessive stretching early on, because this may increase the damage to the muscle and impair recovery. Rehabilitation often includes restoring range of motion, then advancing strengthening as well as running and sprinting activities as tolerated. Strengthening of the muscles and returning to sport-specific activities is the final goal of treatment.
Nonsteroidal anti-inflammatory drugs (NSAIDs) (ibuprofen) and acetaminophen, may be useful in relieving pain. Recovery time depends on the person, the extent of the injury, and also the sport that they participate in, and may take 6 to 18 weeks.
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