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November 8, 2009
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Hamstring Injuries

Medical Author: William C. Shiel Jr., MD, FACR, FACR
Medical Editor: Charles Davis, MD, PhD

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 hamstrings
Picture of the hamstring muscles


Next: How can the hamstrings be injured? »

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Hamstring Injury

What are muscle cramps?

When we use the muscles that can voluntarily be controlled, such as those of our arms and legs, they alternately contract and relax as we move our limbs. Muscles that support our head, neck, and trunk contract similarly in a synchronized fashion to maintain our posture. A muscle (or even a few fibers of a muscle) that involuntarily (without consciously willing it) contracts is called a "spasm." If the spasm is forceful and sustained, it becomes a cramp. A muscle cramp is thus defined as an involuntarily and forcibly contracted muscle that does not relax. This causes a visible or palpable hardening of the involved muscle.

Muscle cramps can last anywhere from a few seconds to a quarter of an hour or occasionally longer. It is not uncommon for a cramp to recur multiple times until it finally goes away. The cramp may involve a part of a muscle, the entire muscle, or several muscles that usually act together, s...

Read the Muscle Cramps article »










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