Semitendinosus is one of the hamstring muscles that runs down the posteromedial aspect of the thigh.
It is so named due to its long tendon of insertion at the back of the knee.
Semitendinosus works with the other hamstring muscles to bend the knee and plays an important role in stability.
Semitendinosus and biceps femoris share a common tendon origin arising from the lower medial facet of the lateral section of the ischial tuberosity.
After a short distance, the tendons divide and semitendinosus forms a fusiform muscle belly (wide spindle shape like a feather) before quickly giving way to a long tendon.
This tendon passes downwards and slightly medially (inwards). It runs behind the medial femoral condyle, being separated from the medial collateral ligament (MCL) by a bursa (small fluid-filled sac), and attaches to a vertical line on the medial tibial condyle.
It sits just behind the insertion of the Sartorius muscle and just behind and below the attachment of the Gracilis tendon.
These three tendons form the Pes Anserinus, thus named due to the appearance resembling a webbed “goose’s foot”. Underneath these tendons site the Pes Anserine bursa, a small fluid-filled sac which helps to reduce friction which can often get inflamed if the hamstrings are tight.
Semitendinosus works with the other hamstring muscles to help:
The hamstrings also play an important role in stability, working with the abdominal muscles and glutes to control the fine balancing and position of the pelvis when standing such as the anteroposterior tilt of the pelvis and lumbar lordosis.
They also control the forward movement of the tibia during the swing phase of walking and running, working eccentrically to decelerate knee extension.
As with any muscle, semitendinosus can develop problems in either the muscle belly (the main bulk of the muscle) or in the tendon. Common problems that can develop in senitendinosus are:
If you have a problem in your semitendinosus muscle, or indeed any of your hamstrings, check out these articles:
Muscle Group: Semitendinosus is one of the three hamstring muscles
Action: Knee flexion and extension, hip extension
Origin: Lower medial facet of the ischial tuberosity
Insertion: Medial surface of the medial tibial condyle
Nerve Supply: Tibial branch of the sciatic nerve (L5, S1, S2)
Special Features: At its insertion, it forms part of the pes anserinus, along with tendons from the Sartorius and Gracilis muscles
Page Last Updated: 05/07/23
Next Review Due: 05/07/25