Author: Dr Peter de Souza
Last modified: 17 December 2020

The major muscles of the back, from superficial to deep are divided in three groups: extrinsic, intermediate and intrinsic muscles. The general action of the back muscles allows movement in the head, shoulders, arms, and the spine they are also involved in movement of the ribs which allows for respiratory function. These groups are:

  • Extrinsic muscles (superficial)
    • Trapezius - actions: Elevates and depresses the scapula; Retract scapula.
    • Latissimus dorsi - Biggest muscle of the back. Inserts on to the humerus. Actions: Adducts, extends and internally rotates the humerus.
      • Rhomboids- Both attach to the scapula. Actions: keep scapula pressed against the thoracic wall; also can retract the scapula.
        • Rhomboid major
        • Rhomboid minor
      • Levator scapulae - attaches to the top of the scapula. Action: Elevates scapula
  • Intermediate Muscles- Attached to ribs; involved in respiratory function.
    • Serratus posterior superior: elevates ribs
    • Serratus posterior inferior: depresses ribs
  • Intrinsic Muscles (deep)
    • Spinotransversales:
      • Splenius capitus: contraction of both muscles extends the neck; contraction of one rotates head.
      • Splenius cervicus
    • Erector spinae: three groups (“I long for spinach”), lateral to medial:
      • illiocostalis: lateral
      • longissimus: in the middle
      • spinalis: medial
    • Transversospinales: three groups, from superficial to deep:
      • semispinalis
      • multifidus
      • rotares