---
title: "Latissimus Dorsi | Anatomy and Physiology I"
description: "Latissimus dorsi is the large back muscle that extends, adducts, and medially rotates the shoulder in Anatomy and Physiology I."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/latissimus-dorsi"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 11"
---

# Latissimus Dorsi | Anatomy and Physiology I

## Definition

The latissimus dorsi is the large flat muscle of the lower back that powerfully moves the shoulder. In Anatomy and Physiology I, you study it as a prime mover for extension, adduction, and medial rotation of the upper limb.

## What It Is

The latissimus dorsi is the broad, superficial muscle that covers much of the lower back and helps move the arm at the shoulder joint. It is the largest muscle of the back and one of the strongest muscles acting on the upper limb, which is why it shows up often in upper-body movement and muscle anatomy.

Its actions are easy to remember if you think about pulling your arm down and back. The latissimus dorsi extends the shoulder, adducts the arm, and medially rotates it. That means it helps you bring the humerus behind your body, pull it toward the trunk, and turn it inward. These actions matter together during movements like climbing, rowing, swimming, and pull-ups.

This muscle does not act alone. It works with other pectoral girdle and upper limb muscles to produce smooth motion at the shoulder. Because the shoulder joint is so mobile, large muscles like the latissimus dorsi provide much of the power, while smaller muscles help refine the movement and stabilize the joint.

Anatomically, the latissimus dorsi has a wide origin from the lower thoracic and lumbar vertebrae, the iliac crest, and nearby back structures. Its fibers run upward and laterally to attach on the humerus, so when the muscle shortens, it pulls the arm toward the trunk and posteriorly. That long fiber direction is part of why it can generate such forceful movements.

It is innervated by the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus. If you are tracing nerve supply in A&P I, that innervation helps connect the muscle to the nervous system, since a muscle only contracts when its motor nerve signals it.

## Why It Matters

The latissimus dorsi comes up anytime you need to explain how the shoulder produces strong pulling motions. In Anatomy and Physiology I, that makes it useful for connecting muscle origin, insertion, action, and innervation into one functional picture.

It also helps you see the difference between movement at the shoulder joint and movement of the whole arm as a limb. When the latissimus dorsi contracts, the humerus moves relative to the scapula and trunk, so this muscle is a good example of how skeletal muscles create joint motion rather than just moving one visible body part.

This term also matters because it sits inside a larger chapter on the pectoral girdle and upper limb. If you can place the latissimus dorsi on a diagram and match it to extension, adduction, and medial rotation, you are already using the same reasoning that shows up across the rest of upper-limb muscle anatomy.

It also gives you a realistic clinical and exercise link. A strain or tear can limit pulling, lifting, and overhead control, while exercises like rows, lat pulldowns, and pull-ups target the muscle because they mimic its main actions.

## Connections

### Pectoral Girdle

The latissimus dorsi works with muscles that position and stabilize the pectoral girdle, especially during powerful upper-body movement. Even though it is not a scapular muscle in the narrow sense, it affects how the shoulder complex functions during pulling actions. That is why it is often taught alongside other muscles that move the upper limb as a coordinated system.

### Upper Limb

This muscle controls the humerus, so its actions show up as movements of the upper limb rather than the back alone. When you raise, pull, or rotate your arm, the latissimus dorsi may be contributing along with other muscles. In lab or exam questions, that makes it a good example of how a muscle’s location predicts its function.

### Shoulder Joint

The latissimus dorsi acts on the shoulder joint by extending, adducting, and medially rotating the arm. That makes it one of the major muscles to know when you are tracing motion at the glenohumeral joint. If a question asks which muscle powers a downward pulling movement, the shoulder joint is the joint you should focus on first.

## On the AP Exam

A quiz question may show you a posterior muscle diagram and ask you to identify the structure that powers shoulder extension or adduction. A lab practical can also ask you to locate the latissimus dorsi on a torso model and name its nerve supply. When you see a movement scenario, think about the action first, then match it to the muscle that creates it. If the prompt describes pull-ups, climbing, swimming, or rowing, the latissimus dorsi is a strong candidate because those motions require forceful shoulder extension and adduction. You may also need to distinguish it from muscles that move the scapula, since the latissimus dorsi mainly acts on the humerus at the shoulder joint.

## latissimus dorsi vs Teres Major

These two muscles can be confused because both help extend, adduct, and medially rotate the shoulder. The latissimus dorsi is much larger, broader, and part of the lower back, while teres major is a smaller scapular muscle. If the question asks for the big pulling muscle of the back, the latissimus dorsi is usually the better answer.

## Key Takeaways

- The latissimus dorsi is the largest muscle of the back and a major mover of the shoulder joint.
- Its main actions are shoulder extension, adduction, and medial rotation, which fit pulling motions.
- The muscle is innervated by the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus.
- It is easy to spot in upper-limb anatomy because it connects the back to strong arm movements like rowing and climbing.
- If you can match its action to a movement, you can usually identify it on a diagram or in a case question.

## FAQs

### What is latissimus dorsi in Anatomy and Physiology I?

The latissimus dorsi is the large, flat muscle on the back that moves the arm at the shoulder. In A&P I, you learn it as a powerful muscle for extension, adduction, and medial rotation of the humerus.

### What does the latissimus dorsi do?

It pulls the arm backward, toward the body, and inward. That makes it useful in motions like pull-ups, swimming, climbing, and rowing. Those are all good examples of the muscle working as a strong prime mover.

### What nerve innervates the latissimus dorsi?

The thoracodorsal nerve innervates the latissimus dorsi. This is a branch of the posterior cord of the brachial plexus, so if a question asks for nerve supply, that is the connection to remember.

### Is the latissimus dorsi the same as teres major?

No. They can do similar shoulder actions, but they are different muscles. The latissimus dorsi is much larger and comes from the lower back, while teres major is smaller and sits on the scapula.

## Related Study Guides

- [11.5 Muscles of the Pectoral Girdle and Upper Limbs ](/anatomy-physiology/unit-11/5-muscles-pectoral-girdle-upper-limbs/study-guide/vmMeyxnPvtI7ludS)

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