Erector Spinae (EE-reotor SPEE-neh)
This group has three sets of muscles running parallel to the vertebral column. The spinalis runs up the center of the back from one vertebral spinous process to the next. The longissimus are more lateral and run from one vertebral transverse process to the next. The iliocostals are the most lateral and run from one rib to the next. Contracting these muscles straightens the spine, as in tadanasa. Contracting the laterally placed longissimus and iliocostal produces lateral bending as in utthita trikonasana. Contracting one side or the other produces a rotational effect in twisting postures.
Forward bends such as utthanasana and kurmasana stretch these muscles. When they reach full length they tilt the pelvis forward by pulling on the back of the ilium. This tilt draws the ischial tuberosity upward and stretches the hamstrings. Backbends such as urdhvadhanurasana strengthen these muscles.
Quadratus Lumborum (quad-RA-tus lum-BOR-um)
Deep to the erector spinae Lies the quadratus Lumborum, a combination of five heads that form a square-shaped muscle. They have a common origin from the posterior iliac crest, dividing into four parts, inserting on the transverse processes of the lumbar vertebrae and the posterior section of rib twelve. Contracting the quadratus lumborum unilaterally flexes the trunk to the side in utthita trikonasana. Contracting both sides extends the lumbar spine in urdhvadhanurasana.
When the pelvis is fixed, contracting the quadratus lumborum draws the ribcage downward. This action can be used to deepen respiration.
1) Quadratus Lumborum
2) Psoas major
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