The latissimus dorsi originates from a broad sweep of attachment points across the lower and mid-back: the spinous processes of the lower six thoracic vertebrae (T7 through T12), all five lumbar vertebrae (L1 through L5), the sacrum, the iliac crest of the pelvis, and the lower three or four ribs. This makes it the widest muscle in the human body, spanning from the low back and pelvis all the way up to the upper arm. Its name literally translates from Latin as “broadest muscle of the back.”
Where the Muscle Attaches
Most muscles have a single, compact origin. The latissimus dorsi is different. It fans out across multiple structures, connecting to the spine through a broad sheet of connective tissue called the thoracolumbar fascia rather than attaching directly to each vertebra with individual tendons. This fascia anchors the muscle to the spinous processes of the thoracic and lumbar spine and to the back of the sacrum at the base of the spine.
Beyond the spine, the muscle also originates from the posterior iliac crest (the top rim of the pelvis you can feel at your hip) and from the lower three or four ribs, where its fibers interdigitate with the external oblique muscle. Some people also have fibers originating from the inferior angle of the scapula, the bottom tip of the shoulder blade.
From all of these origin points, the muscle fibers converge and twist as they travel upward and laterally, narrowing into a flat tendon that inserts into the front of the humerus, your upper arm bone. Specifically, it attaches to the floor of the intertubercular groove, a small channel near the top of the humerus. This anterior insertion is key to understanding why a back muscle controls arm movement.
What the Latissimus Dorsi Does
Because the muscle connects the lower spine and pelvis to the upper arm, it produces powerful movements at the shoulder. It extends the arm (pulling it backward), adducts the arm (pulling it toward the body), and internally rotates the arm. These three actions combine in movements like pull-ups, swimming strokes, rowing, and climbing. Extension and adduction are strongest when the arm starts from a partially raised or outstretched position, which is why the muscle fires hardest during the pulling phase of a lat pulldown or the catch phase of a swim stroke.
The latissimus dorsi works closely with two other muscles. It teams with the teres major (a small muscle on the back of the shoulder blade) and the pectoralis major (the large chest muscle) to adduct and internally rotate the arm. It also plays a role in forced breathing, such as coughing or sneezing, by compressing the rib cage through its rib attachments. And because it connects the arm to the pelvis, it helps stabilize the trunk during heavy lifting or overhead reaching.
Nerve and Blood Supply
The entire muscle is controlled by a single nerve, the thoracodorsal nerve, which branches from spinal nerve roots at the C6, C7, and C8 levels in the neck. C7 is the dominant root. The thoracodorsal artery, a branch of the subscapular artery, provides the primary blood supply. The nerve and artery travel together as a bundle into the muscle, which becomes important in surgical contexts.
Anatomical Variations
Not everyone’s latissimus dorsi looks the same. The most well-known variation is the axillary arch, sometimes called Langer’s arch. This is a muscular or fibrous slip that detaches from the front edge of the latissimus dorsi and crosses over the armpit, sometimes connecting to the pectoralis major, the coracoid process of the scapula, or the biceps tendon. The arch passes over the blood vessels and nerves of the armpit, which can occasionally cause compression symptoms or complicate axillary surgery. Axillary arches come in two broad forms: a muscular type and a tendinous type, each with different subtypes depending on where the slip inserts and which nerve supplies it.
Why Surgeons Use This Muscle
The latissimus dorsi’s large surface area, reliable blood supply from a single artery, and relative expendability make it one of the most commonly used muscles in reconstructive surgery. Surgeons harvest a section of the muscle, along with overlying skin and fat, as a flap to rebuild tissue elsewhere in the body. The most common application is breast reconstruction after mastectomy, where the flap can fill tissue deficits from lumpectomy, quadrantectomy, or full mastectomy.
The flap is especially valuable for patients who aren’t candidates for abdominal tissue transfer due to previous abdominal surgery, insufficient abdominal fat, or higher-risk conditions like diabetes or obesity. In patients whose chest tissue has been damaged by radiation therapy, the latissimus dorsi flap brings well-vascularized tissue to an area with compromised blood flow. Newer techniques include muscle-sparing approaches that harvest skin and fat while leaving most of the muscle intact, preserving more shoulder function after surgery.
Losing the latissimus dorsi on one side does reduce pulling strength and internal rotation power, but most people compensate well because the teres major and other shoulder muscles share overlapping functions. Athletes and people who rely heavily on overhead pulling motions notice the deficit more than the general population.