What are the hamstrings?

The hamstrings are the tendons that attach the large muscles at the back of the thigh to bone. The hamstring muscles are the large muscles that pull on these tendons. It has become common in layman's terminology (and by some medical personnel) to refer to the long muscles at the back of the thigh as the "hamstrings" or "hamstring muscles." Academic anatomists refer to them as the posterior thigh muscles, and more specifically as the semimembranosis, the semitendinosis, and the biceps femoris muscles. These muscles span the thigh, crossing both the hip and the knee. They originate or begin at just below the buttocks, arising from the bone on which we sit (the ischium). They connect by means of their tendons onto the upper parts of the lower leg bones (the tibia and the fibula).

The origin of the word hamstring comes from the old English hamm, meaning thigh. String refers to the characteristic appearance and feel of the tendons just above the back of the knee. Although the tendons are sometimes involved in injuries, this article will refer to the "hamstrings" as the large muscle group at the back of the thigh because the most frequent problems involve the muscle groups. The second Web site listed below has a diagram of the hamstrings attached to the lower leg.

What is the function of the hamstrings?

The hamstring muscles actively bend (flex) the knee. They also act to straighten or (extend) the hip (as in the motion of moving the thigh backward). Surprisingly, these large muscles are not very active with normal walking or standing. However, they are extremely important in power activities such as running, jumping, and climbing. Thus, sedentary individuals can get by with quite weak or deconditioned hamstrings, whereas athletes and very physically active individuals absolutely depend on healthy, well-conditioned hamstrings.

The power advantages of strong hamstrings have been known for a long time. In times past, a sword-wielding knight would disable an opponent by a slice across the back of the thigh. Cruel masters were known to have severed the hamstrings of domestic slaves or prisoners in order to make escape less likely. The origin of the term hamstrung, meaning to have been crippled or held back, is derived from these practices.

Picture of the hamstring muscles

How can the hamstrings be injured?

Injuries to the hamstring group of muscles can range from a minor strain to a major rupture. A minor strain is classified as a grade I tear, whereas a complete rupture, or tear, is classified as a grade III tear. Grade II tears are partial ruptures. Given the function of these muscles, it should not be surprising that grade III injuries most frequently occur in the athletically active. Severely torn muscle causes impaired function. Grade I injuries tend to be mild in that they tend to heal fully with only minor aggravation to the injured, especially in the sedentary individual. On the other hand, in power athletes, hamstring injuries can be severe and debilitating. Many a promising or successful athletic career has been limited or ended by such injuries. One such memorable image is that of Yankee baseball star Mickey Mantle sprawled in agony at first base, having sustained a massive grade III tear while lunging to beat out a throw. Even common exercises, such as jumping rope, tennis, and elliptical machine walking can lead to injury of the hamstring muscles.

What are symptoms of injury to the hamstring muscles?

Hamstring injuries usually occur with sudden lunging, running, or jumping, resulting in muscle injury. The sudden jerking pulls on the tissues of the hamstring muscle. In fact, it is commonly referred to as a "pulled hamstring." Oftentimes, a "pop" is heard or felt by the injured athlete. A variable amount of pain is experienced immediately. The athlete is usually unable to continue and oftentimes cannot even stand.

Examination of the individual with a hamstring injury reveals spasm, tightness, and tenderness. With more severe injury, swelling and a black and blue or bruised appearance will follow. In some cases, a palpable defect (detectable by touching) will be present in the muscle. Tears and strains most often occur at the middle of the back of the thigh where the muscle joins its tendon or at the origin of the hamstring at the base of the buttocks (at the ischium).

How are hamstring injuries treated?

Most hamstring injuries heal without surgery. In rare cases, where there is a complete rupture at the ischium, or where significant piece of ischial bone is jerked away, surgery is necessary. Essentially, all other grade I-III tears are best treated without surgery.

The goal of treatment is to restore muscle function and prevent scar formation. Initially, treatment consists of rest, ice, compression, and elevation (RICE). Rest refers to avoidance of offending activities and oftentimes includes immobilization. In severe cases, crutches or splinting may be necessary. Ice, compression, and elevation all assist in controlling pain and swelling. A short course of nonsteroidal antiinflammatory medication such as aspirin, ibuprofen (Advil, Children's Advil/Motrin, Medipren, Motrin, Nuprin, PediaCare Fever, and others), or naproxen (Anaprox, Naprelan, Naprosyn, Aleve) may be helpful.

As soon as pain permits, it is important to begin a program of stretching and range-of-motion exercises because prolonged immobilization and inactivity results in muscle shrinkage (atrophy) and scar tissue (fibrosis). Excessive scar tissue is incompatible with healthy muscle function. Atrophy and fibrosis are best avoided or reduced by a program of motion and stretching implemented early in the rehabilitation process.

It should be emphasized that an early rehabilitation program does not mean a quick return to the desired usual activity. Given the type of individual that usually sustains a significant hamstring injury, it is usually difficult task to keep athletic patients off the playing field. Reinjury is extremely common and is often due to avoidable premature return to sport. Reinjury not only prolongs recovery, it also increases the risk of permanent damage. People with these injuries should be informed early in the rehabilitation program about the risks of reinjury.

After pain and swelling have been controlled and acceptable range of motion and flexibility has been attained, a gradual strengthening program should follow. After adequate strength has returned, then a gradual return to the desired activity is attempted. Full return is usually possible only after maximal flexibility and optimal strength have been obtained. Depending on the severity of injury, the entire rehabilitative process may take several months. Physical therapists can assist in guiding the exercise program.

Can hamstring injuries be prevented?

There is no foolproof way to completely avoid hamstring injuries. However, the risks can be minimized by paying attention to the principles of muscle strength and flexibility. Individual flexibility should be maximized by a regular stretching program as well as a period of warm-up and stretching before the intended athletic activity.

Optimal individual hamstring strength is at least half of the strength of the quadriceps muscle (muscle of the front of the thigh). Also, there should be minimal imbalance in strength between right and left legs (the injured hamstrings should be about 90% as strong as the uninjured hamstrings). If necessary, a weight-training program should be instituted to optimally achieve these goals.

A well-balanced diet and appropriate fluid intake are essential to avoid electrolyte imbalance and dehydration. Dehydration can lead to muscle cramping, thereby increasing the chance of muscle injury. Excessive body weight increases the risk of muscle injuries in the lower extremities. Some experts have also advocated the use of nutritional supplements, such as antioxidants. Unfortunately, despite the best efforts at prevention and treatment, hamstring injuries will continue to be a common bane of the high-performance athlete as well as the "weekend warrior."

Where can one find more information about hamstring injuries?

http://emedicine.medscape.com/article/90881-overview

http://emedicine.medscape.com/article/307765-overview

Hamstring Injuries At A Glance

• Hamstrings are tendons of the muscles of the back of the thigh.
• Hamstring muscles bend the knee and straighten the hip.
• Hamstring muscle injury is a common athletic injury.
• Most hamstring muscle and tendon injuries heal without surgery.
• The risk of hamstring injury can be reduced with a regular stretching program and exercises.

sourceLast Editorial Review: 7/20/2009

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