The hamstring muscle group helps you to extend your leg straight back and bend your knee. The three hamstring muscles (semitendinosus, semimembranosus, biceps femoris) begin at the bottom of the pelvis (at the ischial tuberosity) and run down the back of the thigh, crossing the knee joint and ending at the lower leg. Hamstring muscle fibers join with the tough, connective tissue of the hamstring tendons near the points where the tendons attach to bones.
A hamstring muscle injury can be a pull, a partial tear, or a complete tear. Occurring frequently in athletes, these injuries are especially common for participants in sports that require sprinting, such as track, soccer or basketball. Most hamstring injuries occur in the thick part of the muscle or where the muscle fibers join tendon fibers.
Muscle strains are graded according to their severity. Grade 1 is mild and usually responds well to simple, nonsurgical treatments. Grade 3 is a complete tear of the muscle that may take months to heal. In the most severe hamstring injuries, the tendon tears completely away from the bone, possibly even pulling a piece of bone away with it. This is called an avulsion injury.
Straining your hamstring while sprinting in full stride will result in a sudden, sharp pain in the back of your thigh that causes you to quickly come to stop—either hopping on your uninjured leg or falling to the ground. Additional symptoms may include: swelling during the first few hours after injury, bruising or discoloration of the back of your leg below the knee over the first few days, and weakness in your hamstring that can persist for weeks.
Muscle overload, the main cause of hamstring muscle strain, occurs when the muscle is stretched beyond its capacity or challenged with a sudden load.
Hamstring muscle strains often occur during an "eccentric contraction," when the muscle lengthens as it contracts, or shortens. Although this may sound contradictory, it is the result of extending a muscle while it is weighted, or loaded. During sprinting, the hamstring muscles contract eccentrically as the back leg is straightened and the toes are used to push off and move forward. The hamstring muscles are not only lengthened at this point in the stride, they are loaded—with body weight as well as the force required for forward motion.
Like strains, hamstring tendon avulsions are also caused by large, sudden loads.
Common factors that can make it more likely for you to experience a muscle strain include:
During the physical examination, your doctor will examine the injured area for tenderness or bruising, palpating, or pressing, the back of your thigh to check for pain, weakness and swelling, and to determine the severity of the injury. Other tests which may help confirm your diagnosis include magnetic resonance imaging (MRI), and X-rays, which can reveal a hamstring tendon avulsion, where the injured tendon has pulled away a small piece of bone.
Most hamstring strains heal very well with simple, nonsurgical treatment. Rest, ice, compression (using a bandage), and elevation—or R.I.C.E., as the protocol is often referred to—are effective for most sports-related injuries.
Surgery is most often performed for tendon avulsion injuries, where the tendon has pulled completely away from the bone. Tears from the pelvis (proximal tendon avulsions) are more common than tears from the shinbone (distal tendon avulsions). To repair a tendon avulsion, your surgeon must pull the hamstring muscle back into place, remove any scar tissue, and then reattach the tendon to the bone using large stitches or staples.
Following your doctor's treatment plan will allow you return to the activities you enjoy more quickly, and also help you prevent further problems in the future. After surgery, using crutches will allow you to keep weight off your leg, protecting the repair while it heals. You may also need a brace to keep your hamstring in a relaxed position. The length of time you will need these aids will depend on your injury.
Your physical therapy program will begin with gentle stretches to improve flexibility and range of motion. As your healing progresses, strengthening exercises will be gradually added. Rehabilitation for a proximal hamstring reattachment typically takes at least six months, due to the severity of the injury. Distal hamstring reattachments require approximately three months of rehabilitation before returning to athletic activities. Your doctor will advise you when it is safe to return to sports.
Early treatment with a plan that includes the R.I.C.E. protocol and physical therapy has been shown to result in better function and a quicker return to sports. After completing a rehabilitation plan, most people who injure a hamstring recover full function. To prevent reinjuring your hamstring and risking permanent damage, be sure to follow your doctor's treatment plan. Return to sports only after your doctor has given you the go-ahead.