From Jonathan Cluett, M.D.,
Your Guide to Orthopedics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

The hamstring muscle is a group of large, powerful muscles that span the back of the thigh, from the lower pelvis to the back of the shin bone. The hamstring is the important muscle that functions to extend the hip joint and flex the knee joint.

The hamstring is used in many sporting activities, as well as normal daily activities. Sports that commonly cause a hamstring injury are sprinting sports that involve sudden accelerations. These include track and field, soccer, and basketball.

A hamstring injury can also occur as a result of a direct blow to the muscle, such as being kicked in the back of the thigh, or falling on the back of the thigh. Hamstring contusions are different from pulled hamstrings, although they may cause similar symptoms.

What is a pulled hamstring?
A pulled hamstring, also called a hamstring strain, is a tear of the hamstring muscle fibers. In less severe hamstring strains, Grade I injuries, the tearing is microscopic. The muscle fibers are essentially stretched too far, and some bleeding occurs within the muscle. In very severe hamstring strains, severe Grade III injuries, the hamstring muscle can completely rupture, and may require surgery to repair the torn ends of the muscle.

Muscle strains and tears most commonly occur because of what is called an "eccentric contraction." When this occurs, the muscle is trying to contract while another force (the ground, another player, etc.) is forcing the muscle in the opposite direction. This creates tremendous force on the muscle, and if the force is strong enough, it will tear the muscle fibers.

What are the symptoms of a pulled hamstring?
The symptoms of a pulled hamstring depend on the severity of the injury. The hamstring injury is usually sudden and painful. Other common symptoms include:

• Bruising: Small tears within the muscle cause bleeding and subsequent bruising. The bruise begins in the back of the thigh, and as time passes the bruise will pass down below the knee and often into the foot.
• Swelling: The accumulation of blood from the hamstring injury causes swelling of the thigh. This can make further muscle contraction difficult and painful. Wearing a compressive bandage can help control the swelling.
• Spasm: Muscle spasm is a common and painful symptom of a hamstring injury. Because of the trauma to the muscle, signals of contraction are confused, and the muscle may be stimulated. If severe, muscle relaxants can help with spasms.
• Difficulty Contracting: Flexing the knee is often painful after a pulled hamstring, and can even prevent the patient from walking normally. If you are unable to contract the hamstring, the muscle may be completely ruptured.

What is the treatment of a pulled hamstring?
Treatment of a pulled hamstring is dependent on the severity of the injury. Because of bleeding and swelling, athletes should stop their activity and rest immediately. An ice pack and compressive bandage can be applied to control swelling. Crutches may be necessary if walking is painful or if spasms are severe. If the pain is significant, or if the symptoms do not steadily resolve, medical evaluation should be obtained.

Some steps to take include:

• Ice the injury
• Apply a compressive bandage
• Use crutches
• Gently stretch the hamstrings
• Massage the injured area/Seek physical therapy
• Seek medical attention if:
  • You have difficulty walking
  • The pain is significant and not relieved with rest
  • You think you may have a complete hamstring rupture