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Structure
Beginner
9 min read

Hamstrings

The hamstrings occupy the back of the thigh. They extend the hip and flex the knee, and their length depends on the combined position of these two joints.
3D scene
The hamstrings during a hip hinge
The scene shows the back of the thigh as the pelvis travels backward. The three muscles lengthen progressively, one lateral and two medial, then shorten to bring the pelvis back under the trunk. Without the 3D, the idea is that these muscles link the lower pelvis to the leg, and that they come under tension as soon as the pelvis moves back.
Open in the explorer

Where the hamstrings are located

The hamstrings form the muscular mass at the back of the thigh. Three muscles make up this group, and almost all of them start from the same bony point on the pelvis to end on either side of the knee. Their course can be described in a few words: from the ischium, the lower part of the pelvis, down to the leg.

Origin

The three muscles arise from the ischial tuberosity, the bony prominence we sit on. One important exception: the short head of the biceps femoris arises directly from the femur, on the outer lip of the linea aspera and the lateral supracondylar line. It therefore does not cross the hip.

Insertions

  • The biceps femoris, lateral, ends on the head of the fibula and the lateral condyle of the tibia.
  • The semitendinosus, medial and superficial, ends on the inner surface of the tibia by a long tendon.
  • The semimembranosus, medial and deep, ends on the back part of the medial condyle of the tibia.

Innervation and palpable landmarks

Innervation comes from the sciatic nerve, through its tibial division for most of the bundles and through its common fibular division for the short head of the biceps femoris, from roots L5 to S2. The ischial tuberosity is found in a seated position; the tendons can be felt clearly on each side of the popliteal fossa, at the back of the knee, when the leg is flexed.

What the hamstrings do

  • Hip extension: they draw the thigh backward, or straighten the pelvis over the thigh.
  • Knee flexion: they bring the heel toward the buttock.
  • Rotation of the flexed knee: the biceps femoris turns the leg outward, the two medial muscles turn it inward.
  • Control of the lower limb: during walking and running, they slow the forward swing of the leg before the foot lands.
Active insufficiency
A situation in which a muscle crossing two joints is too shortened to produce substantial force, because both joints are flexed or extended in the same direction at the same time.
active shortening
Certainty level · Established
The force the hamstrings can produce depends on the combined position of the hip and the knee.
Like any biarticular muscle, they are stretched when the hip is flexed and the knee straight, and shortened when the hip is extended and the knee bent. The underlying principle is the length–tension relationship, demonstrated on isolated preparations and then confirmed on intact muscle. In practice, the same movement therefore does not load these muscles in the same way depending on the angle of the hip. How large the effect is depends on segment lengths and differs from person to person.
Neumann DA (2016)

Seeing the hamstrings in motion

The hamstrings during a hip hinge

The scene shows the back of the thigh as the pelvis travels backward. The three muscles lengthen progressively, one lateral and two medial, then shorten to bring the pelvis back under the trunk. Without the 3D, the idea is that these muscles link the lower pelvis to the leg, and that they come under tension as soon as the pelvis moves back.
Current step
A single pivot
The hip hinge plays out between three parts: the pelvis, the lumbar spine resting on it, and the femur articulating beneath. The only useful pivot is the hip, where the femoral head turns in the acetabulum. The lumbar spine is not built to supply the range.
Scene description
A three-dimensional diagram of the lower half of the body seen from behind, standing with the legs straight. The pelvis, both femurs, both tibias and a simplified lumbar spine — five vertebral bodies with their spinous processes — are shown in bone tones, while the feet and a reference trunk stay in a neutral paper shade. In terracotta, gluteus maximus caps the back of the pelvis, the hamstrings run down behind each thigh in two bundles — biceps femoris outside, semitendinosus inside — and two columns of erector spinae flank the spine up to the mid back. A three-second animation tips the pelvis forwards around the hips: the buttocks travel back, the trunk leans over, the knees bend only slightly and the hamstrings lengthen, before the movement returns to standing. The volumes are stylised: this is a teaching diagram, not an exact anatomical reconstruction.
Visible structures
  • Gluteus maximus
    The bulkiest muscle in the body, arising from the back of the iliac wing, the sacrum and the sacrotuberous ligament, and inserting on the gluteal tuberosity of the femur and the iliotibial tract. It extends the hip powerfully, above all at the end of the lockout.
  • Hamstrings
    Biceps femoris on the outside, semitendinosus and semimembranosus on the inside, all arising from the ischial tuberosity and inserting on the fibula and tibia. They extend the hip and flex the knee: in the hinge they lengthen while braking the descent.
  • Erector spinae
    Muscular columns — iliocostalis, longissimus and spinalis — running from the sacrum and iliac crest to the ribs and vertebrae. In the hinge they do not produce the movement: they keep the lumbar spine from rounding while the hip flexes.
  • Lumbar spine
    Five vertebrae stacked between the sacrum and the ribs, shown here as their bodies and spinous processes. A sound hinge rotates the pelvis on the hips while these five levels stay almost still relative to one another.
  • The hip joint
    The femoral head turns inside the acetabulum of the pelvis: this is the only pivot of the movement. The whole point of the hinge is to rotate the pelvis around this axis rather than to bend the back.
Guided steps
  • 1/5
    The hip hinge plays out between three parts: the pelvis, the lumbar spine resting on it, and the femur articulating beneath. The only useful pivot is the hip, where the femoral head turns in the acetabulum. The lumbar spine is not built to supply the range.
  • 2/5
    It arises behind the iliac wing, from the sacrum and the sacrotuberous ligament, and reaches the femur and the iliotibial tract. Its bulk and lever arm make it the main hip extensor, especially through the last part of standing back up.
  • 3/5
    All three set off from the ischial tuberosity and run down behind the thigh to the tibia and fibula. Because they cross both hip and knee, they lengthen further the more the pelvis tips forward with the knees nearly straight.
  • 4/5
    The pelvis rotates forwards around the hips, the buttocks travel backwards, and the knees bend only slightly. The hamstrings lengthen while braking the descent, then the glutes bring the pelvis back upright. The trunk follows the pelvis without the back changing shape.
  • 5/5
    Throughout the tip, the erector spinae work without shortening: they stop the spine from rounding. That is how a hinge is judged — the range comes from the hip, the spine keeps its shape, and force travels from the legs to the trunk without leaking.
Model licence · Z-Anatomy et BodyParts3D — CC-BY-SA 4.0

The movements they take part in

The hamstrings are the direct partners of the glutes in the hip hinge, where hip extension comes with a barely bent knee that keeps them long. It is the movement that loads them most clearly.
In the squat, their role is different: hip and knee flex at the same time, which limits how much their length changes. There they contribute mainly to knee stability and to hip extension on the way up.

Synergists

  • The glutes produce most of the hip extension, especially when the hip starts from a flexed position.
  • The adductor magnus, through its posterior fibres, completes that extension.
  • The gastrocnemius, the superficial head of the calves, takes part in knee flexion.
  • The erector spinae hold the trunk while the hip opens.

Antagonists

  • The quadriceps extends the knee, the opposite action to flexion.
  • The psoas and the iliacus flex the hip.

What the 3D model simplifies

Limit
One group, two behaviours
The model displays the hamstrings as a uniform whole. In reality, the short head of the biceps femoris does not cross the hip: it does not undergo the same length changes as the three other bundles and is not supplied by the same division of the sciatic nerve.
The scene does not show the path of the sciatic nerve, nor the close relationship between the tendons and the capsule of the knee. The relative length of the tendons and of the muscle belly varies from person to person, which influences the range reached in hip flexion without that reflecting a quality or a shortcoming.

Sources

Key sources

  • Standring S (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice, 42nd edition. Elsevier.
  • Neumann DA (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 3rd edition. Elsevier.
Put it into practice in Shapier

See the sliding hamstring curl

Open in Shapier the sliding hamstring curl page, a knee-flexion exercise that targets the hamstrings.
See the sliding hamstring curl
Body Lab explains; Shapier lets you act and track.

Check my understanding

Where does the short head of the biceps femoris arise from?
In which movement are the hamstrings loaded most clearly?
What role do the hamstrings play during walking and running?
Choose an answer

Read next

  • Glutes
    The three gluteal muscles cover the back and the side of the pelvis. The gluteus maximus extends the hip, while the gluteus medius and minimus steady the pelvis as soon as the body is supported on one leg.
    With a 3D scene
  • Quadriceps
    The quadriceps brings together four muscles on the front of the thigh that share a common tendon. It extends the knee, and one of its heads also crosses the hip.
    With a 3D scene
  • Calves
    The calf brings together the gastrocnemius and the soleus, which share the calcaneal tendon. They push the foot downward, and one of the two also depends on the position of the knee.
    With a 3D scene

Where to go next

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Trust and method

Author
equipe-editoriale-shapier
Editorial review
Thanh Chau
Scientific review
Pending
Published on
August 2, 2026
Reviewed on August 2, 2026
Next review due August 2, 2027
Limits of this page
  • The short head of the biceps femoris does not cross the hip and therefore does not behave like the three other bundles, a distinction that is hard to read on the model.
  • The path of the sciatic nerve through the back compartment of the thigh is not drawn in the scene.
  • The page describes anatomy and function; it covers neither muscle injury nor its management.
Sources
  • Standring S (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice, 42nd edition. Elsevier.
  • Neumann DA (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 3rd edition. Elsevier.
Educational content. Body Lab does not diagnose and does not replace professional advice.
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