The group of three muscles at the back of the thigh that flex the knee and extend the hip
Hamstrings — semitendinosus, semimembranosus and biceps femoris.
Anatomy · Muscles
Hamstrings
Three muscles of the back of the thigh
Lower limb · thigh, posterior compartment
The hamstrings are the group of three muscles at the back of the thigh: biceps femoris, semitendinosus and semimembranosus. They arise from the ischial tuberosity, extend the hip and flex the knee, and are supplied by the tibial part of the sciatic nerve. Their tendons form the palpable cords on either side behind the knee.
How to spot them
- ▸Three muscles: semitendinosus and semimembranosus on the inner side, biceps femoris on the outer
- ▸All arise from the ischial tuberosity (the sitting bone)
- ▸Cross both hip and knee, extending one and flexing the other
- ▸Tendons make two cords behind the knee: one lateral and two medial
What to know
The tendons felt as cords on both sides behind the knee, with the lateral one single and the medial ones paired
Hamstrings.
Muscles that arise from the ischial tuberosity and are often strained in sprinting and kicking
Hamstrings.
The name comes from butchers hanging hams by these long tendons
Hamstrings — the ham is the back of the thigh.
A muscle group supplied by the tibial part of the sciatic nerve
Hamstrings.
The antagonists of the muscle group on the front of the thigh, extending the hip while bending the knee
Hamstrings.
Key ideas
- They oppose the quadriceps: the quadriceps extend the knee, the hamstrings flex it, and they also extend the hip.
- Adductor magnus has a 'hamstring part', arising from the ischial tuberosity and supplied by the tibial nerve, sometimes counted as a fourth.
Quick-fire facts
- •The three hamstrings: biceps femoris, semitendinosus and semimembranosus.
- •All arise from the ischial tuberosity (biceps femoris also has a short head from the femur).
- •Nerve supply: tibial part of the sciatic nerve (L5–S2); the short head of biceps femoris uses the common fibular part.
- •Actions: extend the hip, flex the knee.
- •Behind the knee the lateral tendon is biceps femoris; the medial tendons are semitendinosus (cord-like, more superficial) and semimembranosus.
- •Semitendinosus joins sartorius and gracilis at the pes anserinus; semimembranosus inserts behind the medial tibial condyle.
- •Hamstring strains are among the commonest injuries in sprinting and football.
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