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Structure
Beginner
8 min read

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.
3D scene
The deltoid on the body map
The body map isolates the shoulder and rotates the model to show the three heads one after another. Seen from the front, the anterior head dominates; from the side, the middle head; from behind, the posterior head. Without the 3D, the idea to remember is that these three portions surround the joint and pull the arm bone in three different directions.
Open in the explorer

Where the deltoid is located

The deltoid is the thick muscle that covers the shoulder like a shoulder pad and gives it its rounded shape. It starts at the shoulder girdle, wraps around the shoulder joint on three sides, and narrows toward a single point on the outer surface of the arm. This inverted-triangle geometry, which gives the muscle its name, is the key to how it works: one muscle can produce opposing actions depending on which head contracts.

Origins

The origin of the deltoid follows a continuous line that starts at the clavicle, passes over the acromion and ends on the spine of the shoulder blade. It is described in three segments.
  • The anterior, or clavicular, head arises from the outer third of the front border of the clavicle.
  • The middle, or acromial, head arises from the outer border of the acromion.
  • The posterior, or spinal, head arises from the lower border of the spine of the shoulder blade.

Insertion

The three heads converge on the deltoid tuberosity, a rough prominence on the outer surface of the humerus, about halfway down the arm. The fibres of the middle head are multipennate: they attach obliquely to internal tendinous septa, an arrangement that increases available force at the cost of shortening range.

Innervation and palpable landmarks

The deltoid is supplied by the axillary nerve, from roots C5 and C6. The acromion is found as the highest and most lateral bony point of the shoulder; the deltoid tuberosity can be traced by following the relief of the muscle downward to its tip.

What the deltoid does

Each head pulls the humerus in a different direction, and the result depends on where the arm starts.
  • The middle head takes the arm away from the body, which is abduction. It is the main driver once the movement is under way.
  • The anterior head carries the arm forward, and contributes to internal rotation and horizontal adduction.
  • The posterior head draws the arm backward, and contributes to external rotation and horizontal abduction.
Abduction
Movement that takes a segment away from the midline of the body. At the shoulder, it is the arm moving out to the side, from the body toward the horizontal and then upward.
lateral raise
The deltoid never works alone. As the arm rises, the shoulder blade rotates on the rib cage: without that rotation, the humerus runs into the acromion before reaching vertical. At the same time, the rotator cuff, lying beneath the deltoid, keeps the head of the humerus centred in its socket.
Certainty level · Established
Full elevation of the arm combines movement of the humerus and rotation of the shoulder blade.
This coupling, described as the scapulohumeral rhythm, is observed by radiography and by motion analysis. Both joints contribute together to the total range, and the share of each changes over the course of elevation. The measured values vary between people, with the load carried and with the measurement method: this rhythm describes a general coordination, not a fixed ratio that applies to an individual.
Neumann DA (2016)

Seeing the deltoid in motion

The deltoid on the body map

The body map isolates the shoulder and rotates the model to show the three heads one after another. Seen from the front, the anterior head dominates; from the side, the middle head; from behind, the posterior head. Without the 3D, the idea to remember is that these three portions surround the joint and pull the arm bone in three different directions.
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 deltoid is the central muscle of the vertical push: overhead press, single-arm press, carrying a load above the head. The anterior head also contributes to the horizontal push, alongside the pectoralis major.
The posterior head, for its part, works during the horizontal pull, as the elbows travel backward. It is the only head that accompanies pulling movements rather than pushing ones.

Synergists

  • The supraspinatus, a rotator cuff muscle, starts the arm moving away from the body before the middle head takes over.
  • The trapezius and the serratus anterior rotate the shoulder blade upward and make full elevation possible.
  • The triceps brachii extends the elbow in every push above the head.

Antagonists

  • The latissimus dorsi brings the arm back toward the body and opposes abduction.
  • The pectoralis major opposes the posterior head when it carries the arm forward.

What the 3D model simplifies

Limit
Three heads, a continuous reality
Splitting the muscle into three heads is a teaching convention. Anatomical studies describe a muscle made of several sub-units whose boundaries are not visible to the naked eye, and the nervous system can activate these portions partly independently.
The model shows the deltoid without the deep muscles it covers. The rotator cuff, the subacromial bursa and the joint capsule are not represented, even though they govern how arm elevation normally unfolds.

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

Train with the shoulder press

Open in Shapier the shoulder press page, the vertical push in which the deltoid is the central muscle.
Train with the shoulder press
Body Lab explains; Shapier lets you act and track.

Check my understanding

What should be remembered about the deltoid's division into three heads?
Which muscle starts the abduction of the arm?
What should be remembered about the scapulohumeral rhythm during arm elevation?
Choose an answer

Read next

  • 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
  • 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
  • Triceps brachii
    The triceps brachii fills the whole back of the upper arm and extends the elbow. Its long head also crosses the shoulder, which changes its length depending on the position of the arm.
    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 deltoid is presented as three heads, whereas dissection distinguishes several multipennate sub-units whose boundaries are not clear-cut.
  • The 3D model does not show the rotator cuff lying beneath the deltoid, without which arm elevation does not unfold normally.
  • How the work is shared between heads depends on the load and on the path of the movement; this page does not quantify it.
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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