The transversus abdominis is the deepest abdominal muscle with horizontal fibres wrapping around the trunk like a natural weightlifting belt. It is the cornerstone of the lumbar stabilisation system, contracting tonically before and during limb movements to pre-stiffen the lumbar spine through increased intra-abdominal pressure and thoracolumbar fascia tension. Its preferential inhibition in low back pain and its restoration through specific training is a central concept in spinal rehabilitation.
| Origin | Inner surfaces of the lower six costal cartilages, thoracolumbar fascia, iliac crest, and inguinal ligament |
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| Insertion | Linea alba via the aponeurosis, pubic crest, and pectineal line |
| Nerve Supply | Lower six intercostal nerves (T7 through T11); Subcostal nerve (T12); Iliohypogastric and ilioinguinal nerves (L1) |
| Blood Supply | Superior and inferior epigastric arteries; Lower posterior intercostal arteries |
| Actions | Compression of the abdominal contents (increasing intra-abdominal pressure); Forced expiration; Stabilisation of the lumbar spine and pelvis via intra-abdominal pressure and thoracolumbar fascia tension; Reduces the lumbar lordosis |
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Electromyography studies demonstrate that the transversus abdominis fires before any limb movement regardless of direction, indicating its role in feedforward lumbar stabilisation rather than reactive postural control. This anticipatory activation is lost in chronic low back pain.
Transversus abdominis rehabilitation through abdominal hollowing, dead bugs, and prone planks is a central component of lumbar stabilisation programmes for low back pain. Real-time ultrasound imaging of TrA thickness change during contraction provides biofeedback for patient education. The transversus abdominis forms the posterior wall of the inguinal canal and its weakness is implicated in direct inguinal hernia formation.
The TrA is assessed by placing fingers just medial to the ASIS and asking the patient to gently hollow the lower abdomen without flattening the lumbar spine, feeling for a gentle co-contraction tension deep to the overlying internal oblique.
Selective TrA inhibition in low back pain producing impaired anticipatory lumbar stabilisation and increased spinal injury risk during limb movements, managed with specific motor control retraining.
