LatsLatissimus Dorsi

backMusculus latissimus dorsi

The latissimus dorsi is the largest muscle in your back — a broad sheet from your lower spine and hips up to your upper arm. Its job is pulling your arm down and back, which is what every pull-up and row is asking for.

The lats cover most of the lower and middle back. They start along the spine from the middle of the back down to the pelvis, sweep upward and outward across the ribs, narrow sharply as they pass under the armpit, and attach to the front of the upper arm bone. That last detail surprises people: a back muscle that finishes on the front of the arm. It is what allows the lat to rotate the arm inward as well as pull it down.

The action is straightforward. Reach overhead and pull your arm back down to your side and the lats do it. Reach out to the side and pull your arm in against your ribs and the lats do that too. Anything where your elbow is travelling toward your hip is lat work, whether you are hanging from a bar, sitting at a pulldown machine, or rowing.

Because they attach to the pelvis and the lower spine through a thick sheet of connective tissue, the lats also connect the arm to the hips. This is why they are involved in a deadlift even though nothing about a deadlift looks like an arm movement: they hold the bar in tight against the body and help resist the upper back rounding forward.

The lats are what people mean by a wide back. They are the widest part of the torso when developed, and because they flare outward from a narrow waist, they are most of what produces the V shape that back training is usually aiming at.

Training notes

The lat is the muscle most commonly trained by the biceps. Because every pulling movement bends the elbow at the same time, it is very easy to complete a set of rows or pulldowns with the arms doing the work and the back along for the ride. The fix is thinking about driving the elbow down and back rather than pulling with the hand — the arm is a hook, not a lever.

Vertical and horizontal pulling are not interchangeable. Pull-ups and pulldowns pull the arm down from overhead and train the lat through its longest range; rows pull the arm back from in front and put more of the work into the middle of the back. A back program with only one of the two directions is not a complete back program.

Grip width matters less than most people are told, and where the bar finishes matters more. A pulldown to the collarbone with the elbows tracking down along the ribs trains the lat well at any reasonable grip. Behind-the-neck pulldowns get the arms further back at the cost of a much less comfortable shoulder position, and give up more than they gain.

Full range at the top is where lat work is usually shortened. At the bottom of a hang the muscle is at its longest and the shoulder blade should be allowed to travel up with the arm; stopping short and holding the shoulders permanently pinned down removes the part of the range where the lat is doing the most stretching under load.

Anatomy

Origin
  • Spinous processes of the seventh thoracic to fifth lumbar vertebrae and the median sacral crest, through the thoracolumbar fascia
  • Posterior third of the iliac crest
  • Lower three or four ribs
  • Inferior angle of the scapula, variably
Insertion
  • Floor of the intertubercular sulcus of the humerus
Actions
  • Extends the arm, drawing it backward and downward from overhead
  • Adducts the arm toward the midline
  • Internally rotates the humerus
  • Depresses the shoulder girdle
  • Elevates the trunk toward the arms when the arms are fixed
Innervation
Thoracodorsal nerve (C6–C8)

Latissimus dorsi is a large triangular sheet covering the lower half of the back. Its origin is unusually extensive: the spinous processes of the lower six thoracic and all lumbar vertebrae and the sacrum, reached indirectly through the thoracolumbar fascia; the back third of the iliac crest; the lowest three or four ribs; and, in most but not all people, a slip from the inferior angle of the scapula.

From that broad base the fibres converge sharply as they run upward and laterally, spiral around the teres major, and end in a short flat tendon on the floor of the intertubercular sulcus — the groove on the front of the humerus. The spiral means fibres that began lowest on the back finish highest on the tendon, and it is what allows a muscle attached behind the body to rotate the arm inward.

Its two most distinctive properties both follow from that anatomy. Attaching to the pelvis and lumbar spine makes it a mechanical link between the arm and the trunk, engaged in loaded trunk work such as deadlifting where no arm movement occurs. And its insertion beside teres major, sharing direction and action, makes the two functionally inseparable in almost every movement.

With the arms fixed overhead, its action reverses and it draws the trunk upward toward the arms — the underlying mechanics of a pull-up, and of using the arms to assist forced expiration or a cough.

Under load

Under load its behaviour is dominated by the elbow. Every pulling movement flexes the elbow at the same time as extending or adducting the shoulder, so the biceps and brachialis readily take a larger share than intended. Movements that keep the elbow relatively extended — straight-arm pulldowns, pullovers — remove that competition.

Vertical and horizontal pulling load different parts of its range. Pulling from overhead takes the muscle through its greatest length change; pulling from in front works it in a shorter range while recruiting more of the scapular retractors.

Its length is greatest with the arm fully overhead and externally rotated, and shortest with the arm at the side and internally rotated. Training that lengthened position under load — a full hang, or the top of a pulldown — is the part most often cut short.

Exercises

Antagonists

Synergists