Hamstring muscles anatomy

Reading File

Finding Sources

Reading File

Loading Image

Reading File

Loading Image

Reading File

Finding Sources

Loading Image

I now have comprehensive content and two excellent images. Let me compose the full answer.

Hamstring Muscles - Anatomy

The hamstrings are three long muscles occupying the posterior compartment of the thigh: biceps femoris, semitendinosus, and semimembranosus. All three cross both the hip and knee joints (except the short head of biceps femoris, which only crosses the knee). As a group they flex the leg at the knee and extend the thigh at the hip, with rotatory roles at both joints.

Gray's Anatomy for Students, p. 700

Posterior Compartment - Overview

Muscles of the Posterior Compartment of the Thigh - posterior view showing all three hamstrings, adductor magnus, and distal insertions

Fig. 6.63 - Posterior view of the hamstring muscles (Gray's Anatomy for Students)

Individual Muscles

1. Biceps Femoris

Two heads - the only hamstring with a dual origin.
Long head: originates from the inferomedial part of the upper ischial tuberosity (shared with semitendinosus). Innervated by the tibial division of the sciatic nerve.
Short head: originates from the lateral lip of the linea aspera of the femur. Innervated by the common fibular (peroneal) division of the sciatic nerve. - This is the only hamstring NOT arising from the ischium and NOT crossing the hip joint.
Insertion: both heads unite into a common tendon that inserts onto the lateral surface of the head of the fibula. Extensions blend with the fibular collateral ligament and lateral knee capsule.
Function: flexes knee; long head extends and laterally rotates the hip; with knee partly flexed, laterally rotates the leg.
Nerve supply: sciatic nerve (L5, S1, S2) - two divisions.

2. Semitendinosus

Origin: inferomedial part of the upper ischial tuberosity, with the long head of biceps femoris (conjoined tendon). The conjoined tendon with biceps femoris long head divides at ~9-10 cm from the ischial tuberosity.
Muscle belly: spindle-shaped, ends in the lower half of the thigh, becoming a long cord-like tendon that lies superficial to semimembranosus.
Insertion: medial surface of the proximal tibia, just posterior to gracilis and sartorius tendons - all three form the pes anserinus ("goose's foot").
Function: flexes knee, extends hip, medially rotates thigh (at hip) and leg (at knee).
Nerve supply: tibial division of the sciatic nerve (L5, S1, S2).

3. Semimembranosus

Origin: superolateral impression on the ischial tuberosity (separate from the conjoined tendon of the other two). Has the longest proximal tendon (~9 cm). The semimembranosus tendon runs anterior and medial to the other hamstring tendons.
Location: lies deepest - beneath the semitendinosus.
Insertion: groove and adjacent bone on the medial and posterior surfaces of the medial tibial condyle. Expansions from its tendon form and reinforce multiple structures around the knee (posterior capsule, oblique popliteal ligament).
Function: flexes knee, extends hip, medially rotates thigh and leg (same as semitendinosus).
Nerve supply: tibial division of the sciatic nerve (L5, S1, S2).

Summary Table

Muscle	Origin	Insertion	Nerve	Key Function
Biceps femoris (long head)	Inferomedial ischial tuberosity (conjoined)	Head of fibula	Sciatic - tibial division (L5, S1, S2)	Knee flexion; hip extension + lateral rotation
Biceps femoris (short head)	Lateral lip of linea aspera	Head of fibula	Sciatic - common fibular division (L5, S1, S2)	Knee flexion; lateral rotation of leg
Semitendinosus	Inferomedial ischial tuberosity (conjoined)	Medial proximal tibia (pes anserinus)	Sciatic - tibial division (L5, S1, S2)	Knee flexion; hip extension; medial rotation
Semimembranosus	Superolateral ischial tuberosity	Medial tibial condyle (posteromedial groove)	Sciatic - tibial division (L5, S1, S2)	Knee flexion; hip extension; medial rotation

Gray's Anatomy for Students, Table 6.5, p. 701

Proximal Attachment Details (3D Illustration)

3D CT reconstruction showing all three hamstring muscle attachments: ischial tuberosity origin, course through the thigh, and distal insertions with sciatic nerve relationship

Fig. 9.49 - Color-coded 3D CT reconstruction of hamstring muscle attachments and relationship to the sciatic nerve (Imaging Anatomy: Bones, Joints, Vessels and Nerves)

Key points from this image:

Pink = Semitendinosus: wide medial course, inserts on medial tibial condyle
Red = Biceps femoris long head: crosses obliquely from medial to lateral
Green = Biceps femoris short head: arises from linea aspera/lateral supracondylar line
Blue = Semimembranosus: deepest and most medial, largest proximal tendon
Yellow = Sciatic nerve: lies posterior to adductor magnus, between biceps femoris and semimembranosus distally, dividing into tibial and common peroneal nerves

The "Hamstring Part" of Adductor Magnus

The medial (hamstring) part of adductor magnus also shares ischial tuberosity origin and descends to insert at the adductor tubercle on the medial condyle of the femur. It is functionally similar to the hamstrings (hip extension) and is sometimes considered a functional fourth hamstring, though it does not cross the knee.

Gray's Anatomy for Students, p. 699

Nerve Supply Summary

All hamstrings are supplied by the sciatic nerve (L5, S1, S2), with one important exception:

The short head of biceps femoris is the only hamstring innervated by the common fibular (peroneal) division rather than the tibial division. This distinction is clinically important in localizing sciatic nerve lesions.

Blood Supply

The hamstrings are primarily supplied by perforating branches of the profunda femoris (deep femoral) artery, with additional contributions from the inferior gluteal artery proximally and genicular branches distally.

Clinical Relevance

Hamstring strains: most common in athletes requiring explosive speed (sprinting, football). The muscle-tendon junction is the most vulnerable site in adults.
Proximal hamstring avulsion: more common in adolescents, occurring at the ischial apophysis (the weakest link in skeletally immature individuals). Both ultrasound and MRI are used to assess - MRI also provides prognostic information.
Pes anserinus: semitendinosus + gracilis + sartorius tendons converge on the medial tibia; this complex can become inflamed (pes anserine bursitis).
Semimembranosus distal expansion contributes to the oblique popliteal ligament, relevant in posterior knee instability.

Coronal MRI of the posterior pelvis showing hamstring avulsion injury at the ischial tuberosity

Fig. 6.64 - Coronal MRI showing hamstring avulsion injury (Gray's Anatomy for Students)

Gray's Anatomy for Students, pp. 700-702
Imaging Anatomy: Bones, Joints, Vessels and Nerves, pp. 283-284

This is a shared conversation. Sign in to Orris to start your own chat.