Hamstring

Ahamstring(/ˈhæmstrɪŋ/) is any one of the three posterior thigh muscles in human anatomy between the hip and the knee: frommedialtolateral, thesemimembranosus,semitendinosusandbiceps femoris.
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 the15th century.Stringrefers to tendons, and thus the hamstrings' string-like tendons felt on either side of the back of the knee.
The common criteria of any hamstring muscles are:
Those muscles which fulfill all of the four criteria are called true hamstrings.Theadductor magnusreaches only up to the adductor tubercle of the femur, but it is included amongst the hamstrings because the tibial collateral ligament of the knee joint morphologically is the degenerated tendon of this muscle. The ligament is attached to the medialepicondyle, two millimeters from the adductor tubercle.
The three muscles of the posterior thigh (semitendinosus, semimembranosus, biceps femoris)flex(bend) the knee, while all but the biceps femorisextend(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.
A portion of theadductor magnusis sometimes considered a part of the hamstrings.
The hamstrings cross and act upon two joints – the hip and the knee – and as such they are termedbiarticular muscles.
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) rotate 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 thegluteus. In walking, they are most important as anantagonistto thequadricepsin the deceleration of knee extension.
A common running injury in several sports, excessive stretch of a hamstring results from extensivehip flexionwhile the knee is extended.Duringsprinting, a hamstring injury may occur from excessive muscle strain duringeccentric contractionlate in the leg swing phase.The overall incidence of a hamstring injury in sports and professional dancers is about two per 1000 hours of performance.In some sports, a hamstring injury occurs at the incidence of 19% of all sports injuries, and results in an average time loss from competition of 24  days.
Imaging the hamstring muscles is usually performed with anultrasoundand/orMRI.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 60 mm (2.4 in) in length have a greater risk of recurrence.
Thedistalsemitendinosus tendon is one of the tendons that can be used in thesurgical procedureACL reconstruction. In this procedure, a piece of it is used to replace theanterior cruciate ligament(ACL). The ACL is one of the four major ligaments in the knee, which also include theposterior cruciate ligament(PCL),medial collateral ligament(MCL), andlateral collateral ligament(LCL).