Hamstring

Hams
Posterior view of left lower extremity.
Details
Origin	tuberosity of the ischium, linea aspera
Insertion	tibia, fibula
Artery	inferior gluteal artery, profunda femoris artery
Nerve	sciatic nerve (tibial nerve and common fibular nerve)
Actions	flexion of knee, extension of hip
Antagonist	Rectus femoris muscle
Identifiers
Dorlands /Elsevier	h_02/12407578
TA
TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
Anatomical terms of muscle [[[d:|edit on Wikidata]]]

In human anatomy, a hamstring is any of the three tendons contracted by three posterior thigh muscles (semitendinosus, semimembranosus and biceps femoris), and the term is often also used to refer to the muscles themselves. The hamstring tendons make up the borders of the space behind the knee; the muscles are involved in knee flexion and hip extension.

In quadrupeds, the hamstring is the single large tendon found behind the knee or comparable area.

Structure

The three muscles of the posterior thigh (semitendinosus, semimembranosus, biceps femoris long & short head) flex (bend) the knee, while all but the short head of biceps femoris extend (straighten) the hip. The three 'true' hamstrings cross both the hip and the knee joint and are therefore involved in knee flexion and hip extension. The short head of the biceps femoris crosses only one joint (knee) and is therefore not involved in hip extension. With its divergent origin and innervation it is sometimes excluded from the 'hamstring' characterization.

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

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

Function

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

Semitendinosus and semimembranosus extend the hip when the trunk 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.

Clinical significance

Imaging

Tear of the hamstrings muscles at the ischial tuberosity seen on MRI (coronal STIR). The arrowheads indicate the tuber and the retracted tendon stump. Significant bleeding around and into the muscles.

Imaging the hamstring muscles is usually performed with an ultrasound and/or MRI.  The biceps femoris is most commonly injured, followed by semitendinosus. Semimembranosus injury is rare. Imaging is useful in differentiating the grade of strain, especially if the muscle is completely torn. In this setting, the level and degree of retraction can be determined, serving as a useful roadmap prior to any surgery. Those with a hamstring strain of greater than 60mm in length have a greater risk of recurrence.

Use in surgery

The distal semitendinosus 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.

Society and culture

Training

In strength training, squats, leg curls and the Romanian deadlift are combined with other lower body exercises to develop the hamstrings.

Hamstring extension is key to determining flexibility, assessed by performing a sit and reach test.

History

Etymology

The word "ham" is derived from the Old English ham or hom meaning the hollow or bend of the knee, from a Germanic base where it meant "crooked". It gained the meaning of the leg of an animal around the 15th century. String refers to tendons, and thus, the hamstrings are the string-like tendons felt on either side of the back of the knee.

See also

This article uses anatomical terminology; for an overview, see Anatomical terminology.

• Hamstringing
• Lombard's Paradox
• Popliteal fossa

External links

• MRI Images demonstrating avulsion fracture of the hamstring muscle origin