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Latissimus Dorsi: Anatomy, Actions, Innervation, and Training Applications

The latissimus dorsi ("lats") is the broadest muscle of the back, spanning from thoracolumbar fascia to the humerus. It is a primary mover of the shoulder joint and a key respiratory accessory muscle.

Anatomy

  • Origin: Spinous processes T7–T12, thoracolumbar fascia, iliac crest (posterior 1/3), lower 3–4 ribs, inferior angle of scapula (inconstant).
  • Insertion: Intertubercular groove (bicipital groove) of humerus (medial lip).
  • Innervation: Thoracodorsal nerve (C6, C7, C8) – branch of posterior cord, brachial plexus.
  • Blood Supply: Thoracodorsal artery (subscapular → axillary).

Primary Actions (Glenohumeral Joint)

  1. Extension: Arm posteriorly (from flexed position).
  2. Adduction: Arm toward midline.
  3. Medial (Internal) Rotation: Humerus rotates inward.
  4. Horizontal Abduction (assist): Arm moves posteriorly in transverse plane.

Synergy: Works with teres major, posterior deltoid, long head of triceps.

Scapular and Trunk Actions

  • Depresses shoulder girdle (via humeral fixation).
  • Assists lateral flexion/extension of lumbar spine (when arms fixed).
  • Accessory inspiration: elevates lower ribs (if arms fixed overhead).

Training Applications

ExercisePrimary FocusKey Cue
Pull-up / Chin-upVertical pulling (adduction + extension)Depress scapulae first; drive elbows to pockets
Lat PulldownSame pattern, adjustable loadLean back slightly; pull to upper chest
Seated Cable RowHorizontal pulling (extension + adduction)Squeeze scapulae; elbows close
Single-Arm Dumbbell RowUnilateral, anti-rotation coreSupport on bench; row to hip
Straight-Arm PulldownIsolation (extension dominant)Arms straight; hinge at shoulder only
DeadliftIsometric lat tension (bar proximity)"Put shoulder blades in back pockets"

Clinical Relevance

  • Thoracodorsal nerve injury: Weakness in adduction/extension/IR; winging not typical (serratus anterior).
  • Flap surgery: Latissimus dorsi myocutaneous flap (breast reconstruction, coverage).
  • Tight lats: Limit overhead mobility, contribute to lumbar extension compensation. Stretch: child's pose, foam roller, doorframe.

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