Erector Spinae (Sacrospinalis)

The erector spinae (also called sacrospinalis) consists of 3 major muscle groups: the iliocostalis group (most lateral), the longissimus group, and the spinalis group (most medial). The muscle runs almost the entire length of the back from skull to sacrum — so it is incorrect to call the erector spinae merely the "lower back" muscles. Acting on one side of the body at a time, each of these muscles moves the vertebral column laterally. The iliocostalis is the best rotator of the vertebral column.

Detailed components:

• Iliocostalis Group (most lateral): iliocostalis cervicis, iliocostalis thoracis, iliocostalis lumborum.
• Longissimus Group: longissimus capitis, longissimus cervicis, longissimus thoracis, longissimus lumborum.
• Spinalis Group (most medial): spinalis cervicis, spinalis thoracis.

Functions: (1) extension (hyperextension) — exercise: back extension; (2) lateral flexion (with the quadratus lumborum and obliques) — exercise: side bends; (3) torso rotation (with external and internal obliques) — exercise: rotary torso. Four deeper muscle groups lie under the erector spinae: semispinalis, multifidus, rotatores, and interspinales & intertransversarii.

• 3 columns: iliocostalis (most lateral), longissimus, spinalis (most medial).
• Runs skull to sacrum — NOT just a "lower back" muscle.
• Unilateral action: moves the vertebral column laterally; iliocostalis is the best rotator.
• Functions: extension/hyperextension, lateral flexion, torso rotation.
• 4 deep groups beneath it: semispinalis, multifidus, rotatores, interspinales & intertransversarii.

• spinal-column — the structure it extends.
• quadratus-lumborum — co-produces lateral flexion.
• extension — spinal extension/hyperextension.
• antigravity-musculature — trunk antigravity muscle.
• back-extension / deadlift — training exercises.