Hamstrings Muscle Anatomy

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Semitendinosus	Origin: Ischial tuberosity Insertion: Medial surface of the superior tibia Action: Knee flexion, hip extension, and medial tibial rotation when the knee is flexed Innervation: Tibial division of the sciatic nerve (L5, S1, S2) Blood Supply: Inferior gluteal artery and perforating arteries
Semimembranosus	Origin: Ischial tuberosity Insertion: Medial condyle of the tibia Action: Knee flexion, hip extension, and medial tibial rotation when the knee is flexed Innervation: Tibial division of the sciatic nerve (L5, S1, S2) Blood Supply: Profunda femoris artery and gluteal arteries
Biceps femoris	Origin (long head): Ischial tuberosity Origin (short head): Linea aspera and lateral supracondylar line of the femur Insertion: Lateral head of the fibula Action: Knee flexion and lateral tibial rotation when the knee is flexed; the long head also assists hip extension Innervation (long head): Tibial division of the sciatic nerve (L5, S1, S2) Innervation (short head): Common fibular division of the sciatic nerve (L5, S1, S2) Blood Supply: Deep femoral (profunda femoris) artery and perforating branches

Last updated: 8 June 2026 Estimated Reading Time: 12 min

Location & Overview

The hamstrings are a group of posterior thigh muscles. They are commonly described as semitendinosus, semimembranosus, and biceps femoris.^[1] These muscles sit in the posterior compartment of the thigh, which is also called the flexor compartment of the thigh.^[2]

Stricter anatomical definitions treat semitendinosus, semimembranosus, and the long head of biceps femoris as the true hamstrings. These muscles arise from the ischial tuberosity, cross both the hip and knee joints, and receive motor supply from the tibial division of the sciatic nerve.^[3] The short head of biceps femoris is still part of the posterior thigh group, but it is different from the true hamstrings because it begins on the femur, crosses only the knee, and is supplied by the common fibular division of the sciatic nerve.^[3]

Semitendinosus and semimembranosus form the medial hamstrings. Semitendinosus is the more superficial of the two, while semimembranosus lies deeper and has a broader, flatter shape. Biceps femoris lies on the lateral side of the posterior thigh and has a long head and a short head.^[1]

The hamstrings are important because they act across the hip and knee. As a group, they flex the knee. The true hamstring portions also extend the hip, meaning they move the thigh backward at the hip joint.^[3]

Hamstring muscles labeled from a posterior view — Here, we can see the hamstring muscles from a posterior view. The long and short heads of biceps femoris, semitendinosus, and semimembranosus are labeled.

semitendinosus muscle posterior view — Here, we can see the semitendinosus muscle from a posterior view.

Here, we can see the semimembranosus muscle from a posterior view.

biceps femoris muscle long head and short head, posterior view — Here, we can see the long head and short head of the biceps femoris muscle from a posterior view. The short head is deep to the long head, meaning the long head would cover or obscure most of the short head if they were viewed together.

Compartments of the thigh — Here, we can see the compartments of the thigh. The hamstrings are located in the posterior compartment, which is marked in red in this image.

Origin & Insertion

Semitendinosus, semimembranosus, and the long head of biceps femoris all originate from the ischial tuberosity.^[1,3] The ischial tuberosity is the strong bony prominence at the lower part of the pelvis. This shared pelvic origin is one of the major features that separates the true hamstrings from the short head of biceps femoris.

Semitendinosus and the long head of biceps femoris share a common origin tendon. Farfan et al. (2020) dissected 35 fixed human lower limbs and reported a musculotendinous type of common origin in 91.4% of their sample, and a more tendinous type in 8.6%.^[4] These figures describe the studied cadaveric sample, but they show why the proximal hamstring origin can vary in appearance.

Semitendinosus Origin & Insertion

Semitendinosus originates from the ischial tuberosity. From there, it travels down the posterior and medial side of the thigh before forming a long distal tendon. This tendon inserts on the medial surface of the superior tibia as part of the pes anserinus, the shared medial tibial insertion region for sartorius, gracilis, and semitendinosus.^[1,3]

Origin of the semitendinosus muscle marked in red — Here, we can see the origin of the semitendinosus muscle marked in red on the ischial tuberosity.

Insertion of the semitendinosus muscle marked in blue — Here, we can see the insertion of the semitendinosus muscle marked in blue on the medial surface of the superior tibia.

Semimembranosus Origin & Insertion

Semimembranosus also originates from the ischial tuberosity, but it lies deeper and more medially than semitendinosus. It inserts mainly on the medial condyle of the tibia. Detailed anatomical descriptions also include distal expansions around the posteromedial knee region, including attachments related to the oblique popliteal ligament and nearby fascial tissue.^[1,3]

Origin of the semimembranosus muscle marked in red — Here, we can see the origin of the semimembranosus muscle marked in red on the ischial tuberosity.

Insertion of the semimembranosus muscle marked in blue — Here, we can see the insertion of the semimembranosus muscle marked in blue on the medial condyle of the tibia.

Biceps Femoris Origin & Insertion

Biceps femoris has two heads with different origins. The long head originates from the ischial tuberosity and is part of the true hamstring group. The short head does not originate from the pelvis. Instead, it originates from the linea aspera and lateral supracondylar line of the femur.^[1,3]

The long and short heads join distally and insert mainly onto the lateral head of the fibula.^[1,3] This lateral insertion helps explain why biceps femoris laterally rotates the tibia when the knee is flexed.

Origin of the long head of biceps femoris marked in red — Here, we can see the origin of the **long head** of biceps femoris marked in red on the ischial tuberosity.

Origin of the short head of biceps femoris marked in red — Here, we can see the origin of the **short head** of biceps femoris marked in red on the femur.

Insertion of biceps femoris marked in blue — Here, we can see the insertion of the long and short heads of biceps femoris marked in blue on the lateral head of the fibula.

Action & Function

The main shared action of the hamstrings is knee flexion. Knee flexion is the movement of bending the knee.^[1,3] Semitendinosus, semimembranosus, and both heads of biceps femoris can contribute to this movement.

Person demonstrating knee flexion — This image shows an example of knee flexion, which is the action of bending the knee. The opposite movement of knee flexion is knee extension. The **hamstrings** contribute to knee flexion.

Hip extension is another major action of the true hamstring muscles. Semitendinosus, semimembranosus, and the long head of biceps femoris cross behind the hip joint, so they can help move the thigh backward at the hip.^[3] The short head of biceps femoris does not cross the hip joint, so it does not extend the hip.

Person demonstrating hip extension — This image shows an example of hip extension. Hip extension is the movement of the thigh or upper leg backward, away from the body. **Semitendinosus, semimembranosus, and the long head of biceps femoris** contribute to hip extension.

The hamstrings also rotate the tibia when the knee is flexed. Semitendinosus and semimembranosus medially rotate the tibia, meaning they turn the shin inward. Biceps femoris laterally rotates the tibia, meaning it turns the shin outward.^[1,3]

Person demonstrating medial rotation of the tibia — This image shows an example of medial rotation of the tibia. Medial rotation of the tibia involves inward rotation of the shinbone toward the midline of the body. **Semitendinosus and semimembranosus** contribute to this action when the knee is flexed.

Person demonstrating lateral rotation of the tibia — This image shows an example of lateral rotation of the tibia. Lateral rotation of the tibia involves outward rotation of the shinbone away from the midline of the body. **Biceps femoris** contributes to this action when the knee is flexed.

When the stricter definition of the hamstrings is used, the biceps femoris short head is excluded and the hamstrings are biarticular muscles, meaning they cross two joints. Because the same muscle fibers are shortened by hip extension and by knee flexion, the group cannot produce maximal hip extension and maximal knee flexion at the same time. This principle is known as active insufficiency.^[3] During walking, the hamstrings are especially important near the end of the swing phase, where they act eccentrically to resist hip flexion and knee extension before the foot contacts the ground.^[3]

Innervation

The hamstrings are supplied through the sciatic nerve pathway, but the tibial and common fibular divisions supply different parts of the group. Semitendinosus, semimembranosus, and the long head of biceps femoris are supplied by the tibial division of the sciatic nerve, with roots listed as L5, S1, and S2.^[1,3]

The short head of biceps femoris is the important exception. It is supplied by the common fibular division of the sciatic nerve, also with roots listed as L5, S1, and S2.^[1,3] This split nerve supply is one reason biceps femoris is useful to discuss carefully: the long and short heads share a distal tendon, but they do not share the same motor division.

Sciatic nerve highlighted in red — Here, we can see the sciatic nerve highlighted in red. The sciatic nerve pathway supplies the hamstring muscles through its tibial and common fibular divisions.

Tibial nerve highlighted in red — Here, we can see the tibial nerve branching from the sciatic nerve. The tibial division supplies semitendinosus, semimembranosus, and the long head of biceps femoris.

The course of the sciatic nerve can vary. The tibial and common fibular divisions usually separate in the distal thigh, but separation can occur as the nerve leaves the pelvis in a minority of people.^[3] These course variations do not change the standard motor pattern: the true hamstring portions receive tibial-division branches, while the short head of biceps femoris receives common-fibular-division branches.^[1,3]

Blood Supply

The hamstrings receive blood from posterior thigh and gluteal-region arterial supply patterns. The profunda femoris artery, also called the deep artery of the thigh, supplies the posterior compartment through perforating branches.^[1,3]

Semitendinosus is supplied by the inferior gluteal artery and perforating arteries. Semimembranosus is supplied by the profunda femoris artery and gluteal arteries. Biceps femoris is supplied by the deep femoral/profunda femoris artery and perforating branches.^[1,3]

Additional regional contributors can include inferior gluteal supply near the proximal hamstrings and genicular or popliteal-region supply near the knee.^[1] Overall, hamstring blood supply is not from a single isolated artery. It is built from profunda femoris perforating branches plus nearby gluteal and knee-region vessels.

Arteries of the lower limb — This image shows the arteries of the lower limb. The hamstrings receive blood from posterior thigh and gluteal-region supply patterns, including perforating branches from the profunda femoris artery.

References

[1] Standring S, editor. Gray’s anatomy: the anatomical basis of clinical practice. 42nd ed. Amsterdam: Elsevier; 2021.
[2] FIPAT. Terminologia Anatomica: International Anatomical Terminology. 2nd ed. Halifax: Dalhousie University Libraries; 2019.
[3] Dalley AF 2nd, Agur AMR. Moore’s clinically oriented anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
[4] Farfan CE, Gaete CM, Olive VR, Rodriguez-Baeza A. Common Origin Tendon of the Biceps Femoris and Semitendinosus Muscles, Functional and Clinical Relevance. Int J Morphol. 2020;38(5):1341-1349.

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Hamstrings Muscle Anatomy

Location & Overview