Answer
Of the four abdominal muscles three can act to effect or help to cause rotation of the spine ( trunk). These are the rectus abdominis, the external obliques and the internal obliques. Contraction of the transversus abdominis plays no part in rotation or flexing of the spine or trunk.
Work Step by Step
External obliques: Unilateral contraction of these muscles cause contralateral rotation at the lumbar
region of the spine.
Internal abdominis oblique: Unilateral contraction of these muscles cause ipsilateral rotation at the
lumbar region of the spine.
Rectus abdominis: Contraction of the rectus abdominis flexes the lumbar spine.
Note: Contraction of the transversus abdominis compresses abdominal contents but does not
cause movements of the spine.
