Latissimus Dorsi (*Lats)
Back · Trunk
The latissimus dorsi is a broad, fan-shaped muscle that sweeps across the lower back and wraps toward the armpit, forming the posterior fold of the axilla. It arises from a wide aponeurotic origin including the spinous processes of T7 to T12, the thoracolumbar fascia, the iliac crest, and the lower three or four ribs, and its fibres converge into a narrow tendon that inserts into the floor of the intertubercular (bicipital) groove of the humerus. From this arrangement it extends, adducts, and medially rotates the arm, the combination used to pull the body upward in climbing or to drive the arm down and back in a swimming stroke. It is supplied by the thoracodorsal nerve (C6, C7, C8). Its long, mobile reach and reliable blood supply make it a favourite muscle for reconstructive flap surgery.
Origin, Insertion, Action & Nerve
Origin
Spinous processes of T7–T12, thoracolumbar fascia, iliac crest, and lower 3–4 ribs
Insertion
Floor of intertubercular (bicipital) groove of humerus
Action
Extension, adduction, and medial rotation of arm
Nerve
Thoracodorsal nerve (C6, C7, C8)
Attachments explained
The Latissimus Dorsi (*Lats) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Spinous processes of T7–T12, thoracolumbar fascia, iliac crest, and lower 3–4 ribs
Insertion
Floor of intertubercular (bicipital) groove of humerus
Action & function
When the Latissimus Dorsi (*Lats) contracts, it produces the following movement: Extension, adduction, and medial rotation of arm.
As part of the Back group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Latissimus Dorsi (*Lats) receives its nerve supply from the Thoracodorsal nerve (C6, C7, C8). This nerve carries fibres from spinal segment(s) C6, C7, C8.
Because a muscle can only contract when its nerve is intact, injury to the Thoracodorsal nerve or to its spinal roots (C6, C7, C8) can weaken or paralyse the Latissimus Dorsi (*Lats), impairing the movements it normally produces (extension, adduction, and medial rotation of arm). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Latissimus Dorsi (*Lats) (the OIANS method)
Learn the latissimus dorsi through the memory phrase for its actions, adduction, extension, and medial rotation, then connect that to a familiar movement such as pulling yourself up on a bar or bringing a raised arm down and behind you. Its enormous origin over the lower spine, fascia, iliac crest, and ribs explains how such a thin sheet can generate powerful arm movement.
Pair it with teres major, since both insert near the intertubercular groove and share the same three arm actions, but keep their nerves distinct: latissimus dorsi is driven by the thoracodorsal nerve while teres major uses the lower subscapular nerve. Remembering that the tendon reaches the floor of the bicipital groove, deep between the two lips, also helps separate the trio of muscles attaching there.
Frequently asked questions
Where is the Latissimus Dorsi (*Lats) located?
The Latissimus Dorsi (*Lats) is a muscle of the Back group, located in the Trunk.
What is the origin of the Latissimus Dorsi (*Lats)?
Spinous processes of T7–T12, thoracolumbar fascia, iliac crest, and lower 3–4 ribs
What is the insertion of the Latissimus Dorsi (*Lats)?
Floor of intertubercular (bicipital) groove of humerus
What movements does the Latissimus Dorsi (*Lats) produce?
Extension, adduction, and medial rotation of arm
What nerve supplies the Latissimus Dorsi (*Lats)?
Thoracodorsal nerve (C6, C7, C8)
Is the Latissimus Dorsi (*Lats) free to study in OIANS?
The Latissimus Dorsi (*Lats) is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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