View source for Hamstring

{{Short description|Any of the three muscles in the thigh}}
{{Infobox muscle
| Name        = Hamstring
| Image       = Hamstrings.gif
| Caption     = Rotating view of the hamstring muscles
| Origin      = [[tuberosity of the ischium]], [[linea aspera]]
| Insertion   = [[tibia]], [[fibula]]
| Blood       = [[inferior gluteal artery]], [[profunda femoris artery]]
| Nerve       = [[sciatic nerve]] ([[tibial nerve]] and [[common fibular nerve]])<ref>{{cite web|url=http://www.gla.ac.uk/ibls/fab/tutorial/anatomy/knee1.html|title=University of Glasgow - Schools - School of Life Sciences|website=www.gla.ac.uk}}</ref><ref>{{cite web|url=http://www.rad.washington.edu/academics/academic-sections/msk/muscle-atlas/lower-body/biceps-femoris-short-head |title=Biceps Femoris - Short Head — Musculoskeletal Radiology — UW Radiology |publisher=Rad.washington.edu |access-date=2012-11-02}}</ref>
| Action      = [[flexion]] of knee, [[Extension (kinesiology)|extension]] of hip
| Antagonist  = [[Rectus femoris muscle]]
}}

A '''hamstring''' ({{IPAc-en|ˈ|h|æ|m|s|t|r|ɪ|ŋ}}) is any one of the three posterior thigh muscles in human anatomy between the hip and the knee: from [[anatomical_terms_of_location#Medial_and_lateral|medial]] to [[anatomical_terms_of_location#Medial_and_lateral|lateral]], the [[semimembranosus]], [[semitendinosus]] and [[biceps femoris]].<ref>{{cite web | url=http://www.mayoclinic.org/diseases-conditions/hamstring-injury/basics/definition/con-20035144 | title=Hamstring injury | publisher=Mayo clinic | date=3 Oct 2015 | access-date=6 July 2016 | author=Mayo Clinic Staff}}</ref><ref name="daniel">{{cite journal | last1=Danielsson | first1=Adam | last2=Horvath | first2=Alexandra | last3=Senorski | first3=Carl | last4=Alentorn-Geli | first4=Eduard | last5=Garrett | first5=William E. | last6=Cugat | first6=Ramón | last7=Samuelsson | first7=Kristian | last8=Hamrin Senorski | first8=Eric | title=The mechanism of hamstring injuries – a systematic review | journal=BMC Musculoskeletal Disorders | volume=21 | issue=1 | date=2020-09-29 | page=641 | issn=1471-2474 | pmid=32993700 | pmc=7526261 | doi=10.1186/s12891-020-03658-8 | doi-access=free }}</ref>

==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]].<ref>Brown, Lesley, ed. (2007). Shorter Oxford English Dictionary II (Sixth ed.). Oxford: Oxford University press. p. 3611.</ref> ''String'' refers to tendons, and thus the hamstrings' string-like tendons felt on either side of the back of the knee.<ref>{{cite web|url=http://www.etymonline.com/index.php?search=hamstring |title=Online Etymology Dictionary |publisher=Etymonline.com |access-date=2012-11-02}}</ref>

==Criteria==
The common criteria of any hamstring muscles are: 
# Muscles should originate from [[ischial tuberosity]].
# Muscles should be inserted over the knee joint, in the [[tibia]] or in the [[fibula]].
# Muscles will be innervated by the [[tibial nerve|tibial branch of the sciatic nerve]].
# Muscle will participate in flexion of the [[knee joint]] and extension of the [[hip joint]].

Those muscles which fulfill all of the four criteria are called true hamstrings.
<br /> The [[adductor magnus]] reaches 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 medial [[epicondyle]], two millimeters from the adductor tubercle.

==Structure==
The three muscles of the posterior thigh (semitendinosus, semimembranosus, biceps femoris) [[Flexion|flex]] (bend) the knee, while all but the biceps femoris [[Extension (kinesiology)|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.<ref name="norman">{{NormanAnatomy|postthigh}}</ref>

{| class="wikitable"
|-
| '''Muscle''' || '''Origin''' || '''Insertion''' || '''Nerve'''
|-
| [[semitendinosus]] || [[ischial tuberosity]] || medial surface of [[tibia]] || tibial part of [[sciatic nerve|sciatic]]
|-
| [[semimembranosus]] || ischial tuberosity || [[medial tibial condyle]] || tibial part of [[sciatic nerve|sciatic]]
|- 	
| [[biceps femoris]] - long head || ischial tuberosity || lateral side of the [[head of the fibula]] || tibial part of [[sciatic nerve|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 nerve|common peroneal]]
|}

A portion of the [[adductor magnus]] is sometimes considered a part of the hamstrings.<ref name="norman" />
[[File:Gray434.png|thumb|150px|Biceps femoris, semitendinosus and semimembranosus muscles of the right leg]]

==Function==
The hamstrings cross and act upon two joints – the hip and the knee – and as such they are termed [[biarticular muscle]]s. The hamstrings contract when the knee is bent, and lengthen when the knee is extended, and when the hips are extended.

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 the [[Gluteal muscles|gluteus]]. In walking, they are most important as an [[antagonist (muscle)|antagonist]] to the [[quadriceps]] in the deceleration of knee extension.

==Clinical significance==
===Sports running injuries===
A common running injury in several sports, excessive stretch of a hamstring results from extensive [[hip flexion]] while the knee is extended.<ref name=daniel/><ref name="Kenn">{{cite journal | last1=Kenneally-Dabrowski | first1=Claire J. B. | last2=Brown | first2=Nicholas A. T. | last3=Lai | first3=Adrian K. M. | last4=Perriman | first4=Diana | last5=Spratford | first5=Wayne | last6=Serpell | first6=Benjamin G. | title=Late swing or early stance? A narrative review of hamstring injury mechanisms during high-speed running | journal=Scandinavian Journal of Medicine and Science in Sports | volume=29 | issue=8 | date=2019-05-22 | issn=0905-7188 | pmid=31033024 | doi=10.1111/sms.13437 | pages=1083–1091| s2cid=139106410 }}</ref> During [[sprinting]], a hamstring injury may occur from excessive muscle strain during [[eccentric contraction]] late in the leg swing phase.<ref name=daniel/><ref name=Kenn/> The overall incidence of a hamstring injury in sports and professional dancers is about two per 1000 hours of performance.<ref name=daniel/> 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.<ref name=daniel/>

===Imaging===
[[File:Hamstring tear STIR cor annotatios.jpg|thumb|Tear of the hamstrings muscles at the ischial tuberosity seen on MRI (visible on a coronal [[Short tau inversion recovery|STIR]] MRI sequence). The arrowheads indicate the tuber{{which|reason=Upper or lower arrowhead?|date=November 2024}} and the retracted tendon stump.{{which|reason=Upper or lower arrowhead?|date=November 2024}} Significant bleeding around and into the muscles.]]
[[File:Pulled Hamstring.png|thumb|Picture of pulled hamstring showing location of hamstring]]

Imaging the hamstring muscles is usually performed with an [[ultrasound]] and/or [[MRI]].<ref name="pmid12942206">{{cite journal |vauthors=Koulouris G, Connell D |title=Evaluation of the hamstring muscle complex following acute injury|journal=Skeletal Radiol.|volume=32 |issue=10 |pages=582–9 |year=2003 |pmid=12942206 |doi=10.1007/s00256-003-0674-5|s2cid=23597752}}</ref> &nbsp;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.<ref name="pmid18360748">{{cite journal |vauthors=Schache AG, Koulouris G, Kofoed W, Morris HG, Pandy MG |title=Rupture of the conjoint tendon at the proximal musculotendinous junction of the biceps femoris long head: a case report.|journal=Knee Surg Sports Traumatol Arthrosc|volume=16 |issue=8 |pages=797–802 |year=2008 |pmid=18360748 |doi=10.1007/s00167-008-0517-y|s2cid=23953024}}</ref> 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 {{cvt|60|mm|in}} in length have a greater risk of recurrence.<ref name="pmid17426283">{{cite journal |vauthors=Koulouris G, Connell DA, Brukner P, Schneider-Kolsky M |title=Magnetic resonance imaging parameters for assessing risk of recurrent hamstring injuries in elite athletes.|journal=Am J Sports Med|volume=35 |issue=9 |pages=1500–6 |year=2007 |pmid=17426283 |doi=10.1177/0363546507301258|s2cid=174755}}</ref>

===Use in surgery===
The [[Anatomical terms of location#Proximal and distal|distal]] semitendinosus tendon is one of the tendons that can be used in the [[surgery|surgical procedure]] [[anterior cruciate ligament reconstruction|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, which also include the [[posterior cruciate ligament]] (PCL), [[medial collateral ligament]] (MCL), and [[fibular collateral ligament|lateral collateral ligament]] (LCL).

==See also==
{{Anatomy-terms}}
*[[Hamstringing]]
*[[Hamstring curl]]
*[[Lombard's paradox]]
*[[Popliteal fossa]]
*[[Pulled hamstring]]

== References ==
{{reflist}}

== External links ==
*[http://www.melbourneradiology.com.au/mri-gallery/mri-hamstring.html MRI Images demonstrating avulsion fracture of the hamstring muscle origin] {{Webarchive|url=https://web.archive.org/web/20200327015515/http://melbourneradiology.com.au/mri-gallery/mri-hamstring.html |date=2020-03-27 }}

{{Muscles of lower limb}}

[[Category:Hip extensors]]
[[Category:Knee flexors]]
[[Category:Muscles of the lower limb]]
[[Category:Posterior compartment of thigh]]
[[Category:Hamstring]]