Contraction of the external oblique draws the same side shoulder forward. This action combines with contraction of the contralateral (other side) internal oblique, accentuating twisting poses. Tightness in this muscle limits these postures. Contraction assists in compressing the abdominal contents and contributes to the "air bag" effect, protecting the lumbar spine.
This is also a sheet-like muscle with fibers running opposite to the internal oblique. It is the larger of the two obliques and lies superficial. Its anterior fibers are more superior, originating from the front of the ribs, crossing diagonally forward and downward and inserting on the linea alba. Its lateral fibers are more posterior, originating from the back of the ribs, crossing downward and forward and inserting on the structures atthe front of the pelvis.
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