Latissimus Dorsi

1. Overview

The latissimus dorsi is a large, flat, triangular muscle located in the lower back. Commonly referred to as the "lats," it is one of the broadest muscles in the human body. This powerful muscle plays a central role in upper limb movement, particularly in actions involving pulling, extension, and internal rotation of the shoulder. It also contributes to posture and trunk stabilization.

2. Location

The latissimus dorsi is located in the posterior thoracic and lumbar regions of the body:

• Origin:

  • Spinous processes of T7–T12 vertebrae

  • Thoracolumbar fascia

  • Iliac crest (posterior part)

  • Inferior 3 to 4 ribs

  • (Sometimes) the inferior angle of the scapula

• Insertion:

  • Floor of the intertubercular sulcus (bicipital groove) of the humerus

• Superficial to: Deeper muscles of the back such as the erector spinae

3. Structure

The latissimus dorsi is a broad, fan-shaped muscle with a wide origin and a narrow tendon of insertion:

• Shape: Triangular and sheet-like

• Fibers: Run superolaterally from the spine and lower back to converge into a tendon that passes anterior to the shoulder joint

• Innervation: Thoracodorsal nerve (C6, C7, C8), a branch of the posterior cord of the brachial plexus

• Blood supply: Thoracodorsal artery (a branch of the subscapular artery)

4. Function

The latissimus dorsi is involved in several key movements of the upper limb:

• Extension of the shoulder: Moves the arm backward

• Adduction of the arm: Brings the arm toward the body's midline

• Internal (medial) rotation of the humerus: Rotates the arm inward

• Assists in respiration: Acts as an accessory muscle in forceful expiration (e.g., coughing or heavy breathing)

5. Physiological role(s)

In addition to movement, the latissimus dorsi supports various physiological functions:

• Postural support: Helps stabilize the spine and pelvis during dynamic upper limb movements

• Trunk motion: Assists in lateral flexion and rotation of the trunk when the arm is fixed

• Force generation: Critical for pulling motions such as climbing, swimming, and rowing

• Muscle synergy: Works with the teres major, pectoralis major, and rotator cuff muscles to coordinate shoulder movements

6. Clinical Significance

The latissimus dorsi is clinically relevant in musculoskeletal health, injury, and reconstructive surgery:

• Muscle strain or tear:

  • Can occur during sports involving sudden pulling motions (e.g., gymnastics, rock climbing); leads to pain and weakness in shoulder extension

• Thoracodorsal nerve injury:

  • May occur during axillary surgery or trauma, resulting in weakness of shoulder adduction and extension

• Myofascial pain syndrome:

  • Trigger points in the latissimus can refer pain to the mid-back or posterior shoulder area

• Reconstructive surgery:

  • The muscle is commonly used in flap procedures, such as latissimus dorsi flap for breast reconstruction after mastectomy

• Posture and imbalance:

  • Overactivation or tightness can contribute to shoulder internal rotation and poor posture, often seen in athletes with repetitive pulling tasks