Hamstring strain is characterized by inflammation and pain in the back of the thigh along the hamstring muscles. There are three muscles that comprise the hamstring muscle group (the biceps femoris, the semimembranousus, and the semitendinosus), going from the hip or upper thigh across the back of the knee to the leg. This structure is important for bending the knee, straightening the hip, and helping stabilize the knee. It is also important for running and jumping. These tendons feel like ropes in the back of the knee. This is the most common injury of the thigh. Hamstring strains are usually grade one or two strains. A Grade 1 Strain is a mild strain. There is a slight pull without obvious tearing (it is microscopic tearing). There is no loss of strength, and the muscle-tendon unit is the correct length. A Grade 2 Strain is a moderate strain. There is tearing of fibers within the substance of the muscle or tendon or where the tendon meets the bone or muscle. The length of the muscle-tendon unit may be increased, and there is usually decreased strength. A Grade 3 Strain is a complete rupture.
Frequent Signs and Symptoms
- Pain, tenderness, swelling, warmth, or redness over the hamstring muscles at the back of the thigh
- Pain that worsens during and after strenuous activity
- “Pop” often heard in the area at the time of injury
- Muscle spasm in the back of the thigh
- Pain or weakness with running, jumping, or bending the knee against resistance
- Crepitation (a crackling sound) when the tendon is moved or touched
- Bruising in the thigh 48 hours following the injury
- Loss of fullness of the muscle or area of muscle bulging with complete rupture