The deepest flat abdominal muscle with transverse fibres. It is the primary spinal stabiliser, contracting prior to limb movement in healthy individuals, and the first muscle targeted in lumbar rehabilitation.
| Origin | Thoracolumbar fascia, inner iliac crest, lateral inguinal ligament, inner surfaces of lower 6 costal cartilages |
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| Insertion | Linea alba, pubic crest, pectineal line via conjoint tendon |
| Nerve Supply | Ventral rami of T7-T12, iliohypogastric and ilioinguinal nerves (L1) |
| Blood Supply | Lower posterior intercostal arteries |
| Actions | Increases intra-abdominal pressure — primary abdominal compression muscle; Thoracolumbar fascial tension for lumbar stabilisation; Main muscle of forced expiration and coughing |
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Delayed transversus abdominis activation is a key feature of chronic LBP. Ultrasound biofeedback is used in physiotherapy for TA activation training. The TAP block targets the TA-internal oblique plane for post-operative abdominal analgesia.
Not directly palpable individually — assessed by real-time ultrasound.
Absent anticipatory TA contraction before limb movement, producing lumbar instability, targeted by motor control rehabilitation with ultrasound biofeedback.
