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Structure
Intermediate
8 min read

Serratus anterior

Serratus anterior links the ribs to the inner border of the shoulder blade and holds it flat against the ribcage. Without it the blade wings out and the arm cannot fully rise.
3D scene
Serratus anterior beneath the shoulder blade
The scene removes the surface muscles to show the sheet stretched between the ribs and the edge of the shoulder blade. Without the 3D, the picture stays simple: serratus is a strap that passes around the ribcage and holds the shoulder blade against it, like a hand pressed flat on your back.
Open in the explorer

Where serratus anterior is

Serratus anterior lines the side of the chest, between the ribs and the shoulder blade. Its name comes from its attachment: a row of triangular slips, each hooked onto one rib, drawing a saw-toothed line along the flank.
It is a broad, flat muscle, almost entirely hidden. The lower part of its slips sometimes shows under the skin, above the external oblique; everything else passes beneath the shoulder blade and beneath pectoralis major.

Origin

It arises by fleshy slips from the outer surface of the first nine or ten ribs, on the side of the chest. The exact number of slips varies from person to person.

Insertion

All the fibres converge backwards, slide under the shoulder blade and attach along the whole length of its medial border — the inner edge, the one running alongside the spine. The lowest fibres concentrate on the inferior angle, which gives them the most effective leverage.

Nerve supply and palpable landmarks

The nerve supply comes from the long thoracic nerve, from the C5 to C7 roots. This nerve runs superficially down the chest wall, a position that makes it vulnerable. The lower slips can be palpated on the side of the ribs, below the armpit, when pushing against a wall.

What serratus anterior does

Its work is entirely on the shoulder blade, never directly on the arm.
  • Holding the blade flat: it keeps the medial border of the shoulder blade applied against the ribs.
  • Upward rotation: it turns the blade so that its socket faces upwards, which lets the arm go above horizontal.
  • Protraction: it draws the blade forward around the chest, which extends the reach of a push.
Upward rotation
Rotation of the shoulder blade in which its lower angle swings outwards and its socket turns to face upwards. This is what allows the arm to be raised overhead: the shoulder joint alone does not offer that range.
scapular upward rotation
Full arm elevation is therefore not the shoulder's doing alone. Roughly a third of the range comes from rotation of the shoulder blade, produced by serratus anterior working with the trapezius. That is why a failing serratus shows up as an arm that no longer rises fully, and as a shoulder blade that wings out from the back.
Certainty level · Established
Serratus anterior produces upward rotation of the shoulder blade, which is required for full arm elevation.
Descriptive anatomy and kinesiology describe the mechanism in matching terms: the lower fibres pull the angle of the blade forwards and outwards, which rotates the bone. The exact share of arm movement attributable to the shoulder blade varies with the measurement method and the range considered.
Standring S (2020) · Neumann DA (2016)

Seeing serratus in movement

Serratus anterior beneath the shoulder blade

The scene removes the surface muscles to show the sheet stretched between the ribs and the edge of the shoulder blade. Without the 3D, the picture stays simple: serratus is a strap that passes around the ribcage and holds the shoulder blade against it, like a hand pressed flat on your back.
Current step
Deep and medial muscles
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.
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

Serratus works in every push. In the vertical push, it rotates the shoulder blade so the arm can reach overhead. In the horizontal push, it draws the blade forward at the end of the movement, extending the reach beyond what the shoulder alone would allow.
It also stabilises in positions supported on the hands, where it stops the chest from sinking between the shoulder blades.

Synergists

  • The upper and lower trapezius complete the upward rotation: serratus and trapezius form a force couple around the shoulder blade.
  • The rotator cuff centres the humerus while serratus orients the socket that receives it.
  • Pectoralis major and pectoralis minor act on the same region, the latter in the opposite direction.

Antagonists

  • The rhomboids and middle trapezius draw the shoulder blade towards the spine, the reverse of protraction.
  • Pectoralis minor produces downward rotation, exactly contrary to the action of serratus.

What the 3D model simplifies

Limit
A muscle you only see by lifting the bone
The scene shows serratus exposed, as if laid on the ribs. In a body it is caught between two surfaces: the ribcage on one side, the deep face of the shoulder blade on the other. No dissection presents it that way without lifting the blade.
The number of slips and their extent vary noticeably between people. The model shows a common arrangement, not an individual anatomy. Winging of the shoulder blade, often linked to this muscle in general discussion, can have several origins and calls for examination by a professional.

Sources

Main 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

Train the serratus with push-ups

Follow the push-up technique sheet in Shapier: the push finishes by drawing the shoulder blade forward, the phase where the serratus comes in.
Train the serratus with push-ups
Body Lab explains; Shapier lets you act and track.

Check my understanding

What does serratus anterior act on directly?
Where does the full range come from when the arm rises overhead?
Does a shoulder blade that wings out prove a failing serratus?
Choose an answer

Read next

  • 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.
    With a 3D scene
  • Rotator cuff
    Four short muscles link the shoulder blade to the upper arm and hold the head of the humerus against its socket. They orient the shoulder more than they move it.
    With a 3D scene
  • Pectoralis major
    The pectoralis major covers the front of the chest and draws the arm toward the midline. It is the main driver of horizontal pushing and contributes to internal rotation of the shoulder.
    With a 3D scene

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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 muscle is sandwiched between the shoulder blade and the ribs: the scene shows it isolated, a position no dissection presents without lifting the blade away.
  • Its lower slips are visible under the skin in some people, but the upper ones are covered by pectoralis major and never are.
  • A winging shoulder blade has several possible causes. This page describes an anatomy and supports no self-diagnosis.
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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