These muscles stabilise the association between the appendicular and axial skeletons. There are six pairs of large muscles in the back, in addition to those forming the posterior abdominal wall. These six pairs of muscles are arranged the same on either side of the back. These are the shown in the table below:
| Muscle | Origin | Insertion | Action |
| Trapezius | Medial third of the superior nuchal line External occipital protuberance Ligamentum nuchae Spinous processes of vertebrae C7-T12 | Lateral third of the clavicle Medial side of the acromion and the upper crest of the scapular spine Tubercle of the scapular spine | Elevates and depresses the scapula (depending on which part of the muscle contracts) Rotates the scapula superiorly; retracts scapula |
| Muscle | Origin | Insertion | Action |
| Latissimus Dorsi | Vertebral spines from T7 to the sacrum Posterior third of the iliac crest Lower 3 or 4 ribs, sometimes from the inferior angle of the scapula | iliac crest Lower 3 or 4 ribs, sometimes from the inferior angle of the scapula Floor of the intertubercular groove | Extends the arm Rotates the arm medially |
| Muscle | Origin | Insertion | Action |
| Quadratus Lumborum | Posterior part of the iliac crest Iliolumbar ligament | Transverse processes of lumbar vertebrae 1-4 12th rib | Laterally bends the trunk Fixes the 12th rib |
| Muscle | Origin | Insertion | Action |
| Psoas Major | Bodies and transverse processes of lumbar vertebrae | Lesser trochanter of femur via iliopsoas tendon | Flexes the thigh Flexes & laterally bends the lumbar vertebral column |
| Muscle | Origin | Insertion | Action |
| Erector Spinae | Iliac crest Sacrum Transverse and spinous processes of vertebrae Supraspinal ligament | Angles of the ribs Transverse and spinous processes of vertebrae Posterior aspect of the skull | Extends and laterally bends the trunk, neck and head |
