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Structure
Beginner
8 min read

Trapezius

The trapezius links the skull and the spine to the shoulder girdle. Its three portions orient the shoulder blade, a condition without which the arm cannot rise fully.
3D scene
The trapezius on the body map
The body map shows the trapezius from behind, then isolates each portion. Following the arm as it rises, the shoulder blade can be seen pivoting beneath the muscular sheet. Without the 3D, the essential point fits in one sentence: the trapezius does not act on the arm but on the flat bone that carries it, and it is that orientation which makes the movement possible.
Open in the explorer

Where the trapezius is located

The trapezius is the superficial muscle of the upper back. It forms a wide diamond that starts at the base of the skull, runs down along the spine to the middle of the back, and extends sideways to the shoulder. It never attaches to the arm bone: its outer insertions are on the clavicle and on the shoulder blade. The trapezius is therefore a muscle of the shoulder girdle, not a muscle of the arm.

Origin

The origin follows the whole midline of the back and of the neck.
  • The external occipital protuberance and the inner third of the superior nuchal line, on the occipital bone.
  • The nuchal ligament, which spans the neck from the occiput to the seventh cervical vertebra.
  • The spinous processes of the seventh cervical vertebra and of all the thoracic vertebrae.

Insertions

This is where the organisation into three portions can be read, defined by the direction of their fibres.
  • The upper portion descends toward the outer third of the back border of the clavicle.
  • The middle portion runs horizontally toward the acromion and the upper border of the spine of the shoulder blade.
  • The lower portion rises toward the inner end of that same spine.

Innervation and palpable landmarks

Motor innervation comes from the accessory nerve, the eleventh cranial nerve, supplemented by fibres from the C3 and C4 cervical roots. The spinous process of the seventh cervical vertebra, prominent at the base of the neck when the head tips forward, is the central landmark of the muscle.

What the trapezius does

Each portion moves the shoulder blade in a different direction.
  • The upper portion elevates the shoulder girdle and supports the weight of the upper limb.
  • The middle portion draws the shoulder blade toward the spine, which is retraction.
  • The lower portion depresses the shoulder blade.
  • Together, the upper and lower portions rotate the shoulder blade so that its socket faces upward.
Upward rotation of the shoulder blade
Pivoting of the shoulder blade on the rib cage that turns its socket upward. It is the movement that lets the arm rise above the horizontal without the humerus running into the acromion.
scapular upward rotation
Certainty level · Established
Upward rotation of the shoulder blade results from the combined action of several muscles pulling in different directions.
The upper and lower portions of the trapezius and the serratus anterior form what biomechanics calls a force couple: each pulls the shoulder blade from one side, and the resultant is a rotation. This arrangement is consistently described in anatomy and kinesiology textbooks, and confirmed by electromyography during arm elevation. The relative contribution of each muscle depends on the angle of elevation and varies from person to person.
Standring S (2020) · Neumann DA (2016)

Seeing the trapezius in motion

The trapezius on the body map

The body map shows the trapezius from behind, then isolates each portion. Following the arm as it rises, the shoulder blade can be seen pivoting beneath the muscular sheet. Without the 3D, the essential point fits in one sentence: the trapezius does not act on the arm but on the flat bone that carries it, and it is that orientation which makes the movement possible.
Current step
Anterior view
The front of the body. Pectoralis major covers the upper chest, the deltoid caps the shoulder, the biceps fills the front of the arm, the abdominal wall links the ribs to the pelvis, and the quadriceps fills the front of the thigh. Further out on the limbs, the forearm muscles drive the wrist and hand, and tibialis anterior lifts the foot.
Scene description
A three-dimensional diagram of a standing human body, arms by the sides, built from simplified paper-coloured volumes. Twelve priority muscle groups are laid over this outline in terracotta: at the front, pectoralis major, the deltoid, biceps brachii, the abdominal wall and the quadriceps; at the back, the trapezius, latissimus dorsi, the erector spinae, triceps brachii, the glutes, the hamstrings and the calves. A simplified skeleton — skull, spine, ribcage, pelvis, humerus, femur and tibia — can be shown beneath the outline to reveal the bony levers these muscles pull on. Each group is selectable and opens its own reference page. This is a teaching diagram with stylised volumes, not an exact anatomical reconstruction.
Visible structures
  • Pectoralis major
    A thick sheet running from the clavicle, the sternum and the upper costal cartilages to the lateral lip of the bicipital groove of the humerus. It draws the arm towards the midline and forwards, and drives horizontal pushing.
  • Deltoids
    Three heads — anterior, lateral and posterior — running from the clavicle, the acromion and the spine of the scapula to the deltoid tuberosity of the humerus. Together they raise the arm; separately they carry it forwards, out to the side or backwards.
  • Biceps brachii
    Two heads arising from the scapula — the supraglenoid tubercle and the coracoid process — joining on the radial tuberosity. It flexes the elbow and supinates the forearm, and contributes to every pulling movement.
  • Abdominal wall
    Rectus abdominis, the external and internal obliques and transversus, running from the ribs and sternum to the pubis and iliac crest. They flex and rotate the trunk and, above all, stabilise the spine by regulating intra-abdominal pressure.
  • Quadriceps
    Four heads — rectus femoris, vastus lateralis, vastus medialis and vastus intermedius — joining through the quadriceps tendon onto the patella and then the tibial tuberosity. They extend the knee, and rectus femoris also flexes the hip.
  • Trapezius
    A diamond-shaped muscle spanning from the occiput and the cervical and thoracic spinous processes to the clavicle, the acromion and the spine of the scapula. Its upper, middle and lower portions elevate, retract and depress the scapula.
  • Latissimus dorsi
    A broad fan arising from the lower thoracic vertebrae, the thoracolumbar fascia, the iliac crest and the lowest ribs, converging on the bicipital groove of the humerus. It pulls the arm down and back, and drives vertical pulling.
  • Erector spinae
    Muscular columns — iliocostalis, longissimus and spinalis — running from the sacrum and iliac crest to the ribs, the vertebrae and the skull, on either side of the spinous processes. They extend the spine and control the trunk as it lowers.
  • Triceps brachii
    Three heads — long, lateral and medial — arising from the scapula and the back of the humerus and joining on the olecranon of the ulna. It extends the elbow, and its long head also assists shoulder extension.
  • Glutes
    Gluteus maximus, medius and minimus, arising from the iliac wing and the sacrum and inserting on the femur and the iliotibial tract. They extend, abduct and rotate the hip, and drive the pelvis upright in the hinge and the squat.
  • Hamstrings
    Biceps femoris, semitendinosus and semimembranosus, running from the ischial tuberosity to the tibia and fibula. They extend the hip and flex the knee, and control the trunk as it lowers in the hip hinge.
  • Calves
    The gastrocnemius and soleus, joining through the Achilles tendon onto the calcaneus. They plantarflex the ankle, and the gastrocnemius, which crosses the knee, also assists knee flexion.
  • Rotator cuff
    Four short muscles running from the shoulder blade to the top of the humerus. Their tendons merge into a sheet that holds the head of the bone against its socket while the deltoid moves the arm.
  • Serratus anterior
    A sheet hooked onto the upper ribs by triangular slips, passing under the shoulder blade and attaching to its inner border. It holds the blade against the ribcage and rotates it.
  • Iliopsoas
    The only muscle linking the lumbar spine directly to the femur. It descends from the vertebrae and the iliac fossa, curves around the rim of the pelvis and attaches to the lesser trochanter.
  • Hip adductors
    Five muscles running from the pubis to the back of the femur in overlapping layers. They draw the thigh towards the midline and control the pelvis in single-leg stance.
  • Forearm muscles
    Masses gathered near the elbow, continued by long tendons to the wrist and fingers. They drive the hand from a distance and carry grip strength.
  • Tibialis anterior
    A muscle pressed against the outer surface of the tibia, its tendon swinging towards the inside of the foot. It lifts the toes on every step and brakes the forefoot after heel strike.
  • Diaphragm
    A muscular dome running from the lower border of the ribs, the sternum and the lumbar vertebrae to a central tendon. As it contracts it descends, the chest gains volume and air enters: it is the engine of quiet breathing, and the ceiling of the abdominal cavity.
Guided steps
  • 1/5
    The front of the body. Pectoralis major covers the upper chest, the deltoid caps the shoulder, the biceps fills the front of the arm, the abdominal wall links the ribs to the pelvis, and the quadriceps fills the front of the thigh. Further out on the limbs, the forearm muscles drive the wrist and hand, and tibialis anterior lifts the foot.
  • 2/5
    The back of the body. The trapezius links the neck to the shoulder blades, the latissimus dorsi fans down to the pelvis, the erector spinae flank the spine, and the triceps fills the back of the arm. Glutes, hamstrings and calves form the posterior chain from hip to ankle.
  • 3/5
    Beneath the visible groups work muscles no silhouette shows. The rotator cuff holds the head of the humerus against the shoulder blade, serratus anterior keeps the shoulder blade flat on the ribcage, the iliopsoas links the lumbar spine to the femur, and the adductors fill the inner thigh. Deeper still, the diaphragm closes the trunk as a dome, inside the ribs. They orient and stabilise more than they move.
  • 4/5
    In a push, force starts at the ground, travels through the quadriceps and the abdominal wall, and then pectoralis major, the anterior deltoid and the triceps drive the load away from the trunk. The skeleton acts as the lever: no group works alone, and the quality of the movement comes from their sequencing.
  • 5/5
    In a pull, the latissimus dorsi and trapezius bring the arm and shoulder blade towards the trunk while the biceps flexes the elbow. Glutes, hamstrings and erector spinae hold the pelvis and spine so that force transfers without the trunk collapsing.
Model licence · Z-Anatomy et BodyParts3D — CC-BY-SA 4.0

The movements it takes part in

The middle trapezius is strongly engaged in the horizontal pull, where the shoulder blade travels back as the elbows return behind the body. The lower trapezius is involved in the vertical pull, depressing the shoulder blade at the start of the pull.
The upper and lower portions work together during the vertical push: without their coordinated rotation, the arm cannot finish its travel above the head. The upper trapezius is also active in any carrying task with the arms at the sides, where it supports the shoulder girdle.

Synergists

  • The serratus anterior completes the upward rotation of the shoulder blade and holds it against the rib cage.
  • The rhomboids assist the retraction produced by the middle portion.
  • The levator scapulae assists the upper portion in elevation.
  • The deltoid raises the arm while the trapezius orients the shoulder blade.

Antagonists

  • The pectoralis minor depresses and tilts the shoulder blade forward, the opposite of the lower portion.
  • The latissimus dorsi depresses the shoulder girdle and opposes the upper portion.

What the 3D model simplifies

Limit
Three portions of a continuous sheet
The trapezius is shown with three clearly delimited portions. In a real body, the fibres change orientation gradually and there is no sharp boundary between them; the division serves to describe directions of pull, not separate muscles.
The scene shows the trapezius at the surface, without the muscles it covers. The rhomboids, the levator scapulae and the erector spinae occupy the same territory at different depths. The serratus anterior, essential to the movement described here, stays largely hidden by the rib cage.

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

Practice the dumbbell row

Learning the dumbbell row and tracking your sets happens in Shapier; Body Lab only explains why this horizontal pull strongly engages the middle trapezius.
Practice the dumbbell row
Body Lab explains; Shapier lets you act and track.

Check my understanding

Why is the trapezius a muscle of the shoulder girdle rather than of the arm?
Where does the rotation of the shoulder blade that turns its socket upward come from?
What does the division of the trapezius into three portions mean?
Choose an answer

Read next

  • Deltoids
    The deltoid caps the shoulder with three heads pointing in different directions. It raises the arm in every direction, and its shape explains why the same shoulder changes function depending on the angle of the movement.
    With a 3D scene
  • Latissimus dorsi
    The latissimus dorsi is the broadest muscle of the back. It links the pelvis and the spine to the humerus, and draws the arm down and backward in every pulling movement.
    With a 3D scene
  • Erector spinae
    The erector spinae form three muscular columns running along the spine. They straighten it, control its forward bending and hold the trunk during hip hinge movements.
    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 serratus anterior, an essential partner of the trapezius for rotation of the shoulder blade, lies against the rib cage and stays barely visible in the scene.
  • Dividing the muscle into three portions is a convention; the fibres form a continuous sheet whose orientation changes gradually from top to bottom.
  • The levator scapulae and the rhomboids, lying beneath the trapezius, are not drawn separately.
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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