The 'hamstrings' or 'hamstring muscles' are the muscles at the back of the thigh - semimembranosus, semitendinosus and biceps femoris.

Page updated November 2023 by Dr Sheila Strover (Clinical Editor)



Side view of the tendons on the medial side of the knee - showing the semitendinosus - where it can be harvested for cruciate ligament reconstructions. The semimembranosus lies behind it.

biceps femoris component of the hamstrings muscles


View from the back of the two heads of the biceps femoris component of the hamstrings inserting on the lateral side of the knee.


Why are they called the 'hamstrings'?

They are so called because in pigs they are the muscles used to make ham, and the hams were strung up using hooks through the long string-like tendons.

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What do the hamstrings muscles do?

The hamstrings muscles' main function is to bend the knee but they also work to straighten the hip. One can check hamstrings function and strength by letting the patient lie on their tummy on an examination table with the hips bent and the lower limbs hanging over the end. If the hamstrings are weak then the patient will have difficulty bending the bad knee as much as the opposite side, especially if an observer applies a bit of extension force.

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The hamstrings as a graft material for cruciate ligament reconstruction

During cruciate ligament reconstruction the surgeon may choose to take the tendon of the semitendinosis and that of the gracilis as a graft material.

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Forum discussions

  • weak hamstring??

    ACL reconstruction patients discuss problems with weak hamstrings after surgery.

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Peer-reviewed papers

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Pes anserine tendons

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Dr Sheila Strover (Editor)
BSc (Hons), MB BCh, MBA

See biography...