Deltoid

Musculus deltoideus

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The deltoid is the large triangular muscle capping the shoulder, with three functionally distinct heads. The anterior head flexes and internally rotates the arm (pressing), the lateral head is the prime mover of arm abduction (lateral raises), and the posterior head extends and externally rotates (rear-delt work, rowing). Balanced training across all three heads builds shoulder width and protects the joint during pressing and pulling.

Actions

Shoulder abduction, Shoulder flexion, Shoulder extension, Shoulder internal rotation, Shoulder external rotation, Transverse (horizontal) abduction

Origin

Anterior head: lateral third of the clavicle; Lateral head: acromion of the scapula; Posterior head: spine of the scapula

Insertion

Deltoid tuberosity of the humerus

Innervation

Axillary nerve (C5, C6)

Blood supply

Thoracoacromial artery (deltoid and acromial branches), anterior and posterior circumflex humeral arteries, deltoid branch of the deep brachial (profunda brachii) artery

Heads

Anterior (clavicular) head, Lateral (acromial) head, Posterior (spinal) head

Wikipedia ↗

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