The deep muscles of the back are muscles located deep within the back. They are intrinsic back muscles as they fuse with the spine. Only these muscles are considered to be the actual back muscles. Therefore, they are also called the true back muscles.

The deep back muscles extend along the entire length of the spine. They stretch between the skull and pelvis and lie on either side of the spine. These muscles can be subdivided into four layers - superficial, intermediate, deep (transversospinales) and deepest. Each layer contains specific muscles listed below.

Superficial layer:

• Splenius capitis
• Splenius cervicis

Intermediate layer:

• Erector spinae, consisting of:
  • Spinalis
    • Spinalis capitis
    • Spinalis cervicis
    • Spinalis thoracis
  • Longissimus
    • Longissimus capitis
    • Longissimus cervicis
    • Longissimus thoracis
  • Iliocostalis
    • Iliocostalis cervicis
    • Iliocostalis thoracis
    • Iliocostalis lumborum

Deep layer (transversospinales):

• Rotatores spinae
• Multifidus
  • Multifidus cervicis
  • Multifidus thoracis
  • Multifidus lumborum
• Semispinalis
  • Semispinalis capitis
  • Semispinalis cervicis
  • Semispinalis thoracis

Deepest layer:

• Interspinales
  • Interspinales cervicis
  • Interspinales thoracis
  • Interspinales lumborum
• Intertransversarii
  • Intertransversarii cervicis
  • Intertransversarii lumborum
• Levatores costarum