The muscles of the posterior aspect of the trunk

Name of muscle

Position

Attachments

Action/s

Key facts

Erector spinae

(ee-rek-tor spee-nee)

Made up of separate bands of muscle that lie in the groove between the vertebral column and the ribs

Attaches to the sacrum and iliac crest at one end to the ribs, transverse and spinous processes of the vertebrae and the occipital bone at the other end of the ribs

Extension, lateral flexion and rotation of the vertebral column

A very important postural muscle as it helps to extend the spine

(Continued )

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The muscles of the posterior aspect of the trunk 137

Name of muscle

Position

Attachments

Action/s

Key facts

Latissimus dorsi

(la-tis-i-mus door-si)

Large sheet of muscle extending across the back of the thorax

Broad muscle that attaches to the posterior of the iliac crest and sacrum, lower six thoracic and five lumbar vertebrae at one end and the humerus at the other end

Extends, adducts and rotates the humerus medially

Often referred top as the 'swimmer's muscle' as it allows extension of the arm in water One of the major muscles implicated in lower back pain due to its pelvis attachments

Quadratus lumborum (quad-dra-tus lum-bor-um)

Deep muscle located medially either side of the lumbar vertebrae

Attaches to the top of the posterior of the iliac crest at one end and to the twelfth rib and transverse processes of the first four lumbar vertebrae at the other end

Lateral flexion (sidebending) of the lumbar vertebrae

Excessive bending to the side can strain and injure the quadratus lumborum muscle

Gluteus maximus

(gloo-tee-us max-i-mus)

Large muscle covering the buttock

Attaches to the back of the ilium along the sacroiliac joint at one end, and into the top of the femur at the other

Extends the hip, abducts and laterally rotates thigh

Sometimes referred to as the 'speedskater's muscle' as it is powerful in extending, abducting and lateralling rotating the thigh

Often implicated in postural defects

Gluteus medius

(gloo-tee-us meed-ee-us)

Muscle is partly covered by the gluteus maximus

Attaches to the outer surface of the ilium at one end and the outer surface of the femur at the other end

Abducts thigh, medially rotates thigh

When this muscle becomes tight it can create postural distortions. It pulls and depresses the pelvis towards the thigh on that side, resulting in a 'functional short leg'

Gluteus mimimus

(gloo-tee-us min-i-mus)

Lies beneath the gluteus medius

Attachments are the same as for gluteus medius: outer surface of the ilium at one end to the outer surface of the femur at the other end

Abducts thigh, medially rotates thigh

See above re gluteus medius

Piriformis

(pi-ri-for-mis)

Deeply seated pelvic girdle muscle

Attaches to the anterior of the sacrum at one end and the top of the femur at the other

Lateral rotation and abduction of the hip

Largest lateral rotator of the hip. If it becomes tight, it can restrict mobility in the hip

Fig 4.14 The muscles of the posterior of the trunk
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