The latissimus dorsi is the broadest muscle in the human body, spanning from the lower back and pelvis all the way to the upper arm, giving the back its characteristic V-shape. Despite originating far from the shoulder, it converges into a narrow tendon that attaches to the humerus, allowing it to powerfully draw the arm downward and backward from any elevated position. It is the prime mover in pulling exercises such as pull-ups, rows, and lat pulldowns.
| Origin | Spinous processes of T7–T12 vertebrae via the thoracolumbar fascia; Posterior third of the iliac crest; Inferior three or four ribs; Inferior angle of the scapula (variable) |
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| Insertion | Floor of the intertubercular groove of the humerus (bicipital groove) |
| Nerve Supply | Thoracodorsal nerve (C6, C7, C8) |
| Blood Supply | Thoracodorsal artery |
| Actions | Extension of the arm at the shoulder; Adduction of the arm; Internal rotation of the arm; Depression and retraction of the scapula (indirect) |
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It is the dominant muscle for bringing the arm from an overhead or elevated position back down to the body, working maximally during swimming freestyle, climbing, and rowing, and playing a crucial role in maintaining trunk stability by connecting the pelvis to the upper arm.
Isolated latissimus dorsi strains are relatively uncommon given the muscle's broad origin, but acute tears can occur during explosive throwing or heavy pulling movements, producing posterior axillary or lateral thoracic pain. In reconstructive surgery, the latissimus dorsi flap is widely used for breast reconstruction and covering large soft tissue defects because of its reliable and extensive blood supply via the thoracodorsal vessels.
The posterior axillary fold, the rounded cord felt at the back of the armpit, is the distal tendon and muscle belly of the latissimus dorsi. Asking the subject to cough or to press their elbow downward against resistance makes it contract visibly and palpably.
A tear within the muscle belly or at the musculotendinous junction, typically from an explosive pulling or throwing action, causing acute posterior axillary or lateral chest pain that worsens with shoulder elevation and internal rotation.
Injury to the thoracodorsal nerve from axillary dissection or trauma results in weakness of arm adduction and extension, most noticeable during pulling exercises, and may also cause atrophy of the posterior axillary fold over time.
