Hamstring

Hamstring

[ham-string]
In human anatomy, a hamstring refers to one of the tendons that make up the borders of the space behind the knee. In modern anatomical contexts, however, they usually refer to the tendons of the semitendinosus, the semimembranosus, and the biceps femoris. In quadrupeds, it refers to the single large tendon found behind the knee or comparable area.

As shown in the diagram, the human hamstring occupies the posterior of the body of the femur.

Etymology

The word ham originally referred to the fat and muscle behind the knee. String refers to tendons, and thus, the hamstrings are the string-like tendons felt on either side of the back of the knee, the long muscle.

The three muscles of the posterior thigh (semitendinosus, semimembranosus, biceps femoris) flex (bend) the knee, while three of the four extend (straighten) the hip. The short head of the biceps femoris, with its divergent origin and innervation, is not involved in hip extension, and thus is sometimes excluded from the 'hamstring' characterization.

Muscle Origin Insertion Nerve
semitendinosus ischial tuberosity medial surface of tibia tibial
semimembranosus ischial tuberosity medial tibial condyle tibial
biceps femoris - long head ischial tuberosity lateral side of the head of the fibula tibial
biceps femoris - short head linea aspera near the head of the femur lateral side of the head of the fibula (common tendon with the long head) common fibular

A portion of the adductor magnus is sometimes considered a part of the hamstrings.

Functions

The hamstrings cross and act upon two joints - the hip and the knee.

Semitendinosus and semimembranosus extend the hip when the trunk is fixed or extend the trunk when the hip is fixed; they also flex the knee and medially (inwardly) rotate the lower leg when the knee is bent.

The long head of the biceps femoris extends the hip as when beginning to walk; both short and long heads flex the knee and laterally (outwardly) rotates the lower leg when the knee is bent.

The hamstrings play a crucial role in many daily activities, such as, walking, running, jumping, and controlling some movement in the trunk. In walking, they are most important as an antagonist to the quadriceps in the deceleration of knee extension.

Injuries

Straining of the hamstring, also known as a pulled hamstring, is defined as an excessive stretch or tear of muscle fibers and related tissues.

Use in surgery

The distal semitendinosis tendon is one of the tendons that can be used in the surgical procedure ACL reconstruction. In this procedure, a piece of it is used to replace the anterior cruciate ligament (ACL). The ACL is one of the four major ligaments in the knee.

See also

References

External links

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