Hamstring Muscle Injuries

Hamstring muscle injuries — such as a "pulled hamstring" — occur frequently in athletes. They are especially common in athletes who participate in sports that require sprinting, such as track, soccer, and basketball.

A pulled hamstring or strain is an injury to one or more of the muscles at the back of the thigh. Most hamstring injuries respond well to simple, nonsurgical treatments.

Anatomy

The hamstring muscles run down the back of the thigh. There are three hamstring muscles:

• Semitendinosus
• Semimembranosus
• Biceps femoris

They start at the bottom of the pelvis at a place called the ischial tuberosity. They cross the knee joint and end 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.

The hamstring muscle group helps you extend your leg straight back and bend your knee.

Description

A hamstring injury can be a pull, a partial tear, or a complete tear.

Muscle strains are graded according to their severity. A grade 1 strain is mild and usually heals readily; a grade 3 strain is a complete tear of the muscle that may take months to heal.

Most hamstring injuries occur in the thick part of the muscle or where the muscle fibers join tendon fibers.

In the most severe hamstring injuries, the tendon tears completely away from the bone. It may even pull a piece of bone away with it. This is called an avulsion injury.

Cause

Muscle Overload
Muscle overload is the main cause of hamstring muscle strain. This can happen when the muscle is stretched beyond its capacity or challenged with a sudden load.

Hamstring muscle strains often occur when the muscle lengthens as it contracts, or shortens. Although it sounds contradictory, this happens when you extend a muscle while it is weighted, or loaded. This is called an "eccentric contraction."

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, but they are also 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.

Risk Factors
Several factors can make it more likely you will have a muscle strain, including:

Muscle tightness. Tight muscles are vulnerable to strain. Athletes should follow a year-round program of daily stretching exercises.

Muscle imbalance. When one muscle group is much stronger than its opposing muscle group, the imbalance can lead to a strain. This frequently happens with the hamstring muscles. The quadriceps muscles at the front of the thigh are usually more powerful. During high-speed activities, the hamstring may become fatigued faster than the quadriceps. This fatigue can lead to a strain.

Poor conditioning. If your muscles are weak, they are less able to cope with the stress of exercise and are more likely to be injured.

Muscle fatigue. Fatigue reduces the energy-absorbing capabilities of muscle, making them more susceptible to injury.

Choice of activity. Anyone can experience hamstring strain, but those especially at risk are:

• Athletes who participate in sports like football, soccer, basketball
• Runners or sprinters
• Dancers
• Older athletes whose exercise program is primarily walking
• Adolescent athletes who are still growing

Hamstring strains occur more often in adolescents because bones and muscles do not grow at the same rate. During a growth spurt, a child's bones may grow faster than the muscles. The growing bone pulls the muscle tight. A sudden jump, stretch, or impact can tear the muscle away from its connection to the bone.

Symptoms

If you strain your hamstring while sprinting in full stride, you will notice a sudden, sharp pain in the back of your thigh. It will cause you to come to a quick stop, and either hop on your good leg or fall.

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
• Weakness in your hamstring that can persist for weeks

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