Transversus abdominis
Musculus transversus abdominis
Also known as: transverse abdominal, TrA, corset muscle
The deepest flat abdominal muscle. Its fibres run horizontally like a corset, compressing the abdomen and stiffening the lumbar spine.
Overview
Transversus abdominis arises from the internal surfaces of the costal cartilages 7–12 (interdigitating with the diaphragm), the thoracolumbar fascia, the anterior two-thirds of the iliac crest and the lateral third of the inguinal ligament. Its fibres run transversely to an aponeurosis that joins the posterior rectus sheath above the arcuate line and the anterior sheath below it. It inserts on the linea alba, the pubic crest and the pecten pubis via the conjoint tendon.
Deep to it lies the transversalis fascia, in which the deep inguinal ring is a defect midway between the ASIS and the pubic tubercle, just above the inguinal ligament. Transversus works like a corset. It compresses the abdominal contents and raises intra-abdominal pressure, and through its attachment to the thoracolumbar fascia it stiffens the lumbar spine. It is activated in a feedforward manner just before limb movements. This anticipatory activation is delayed in some people with chronic low back pain, which is why it is a target of "core stability" training.
Anatomy
- Origin
Internal surfaces of costal cartilages 7–12, thoracolumbar fascia, anterior two-thirds of the iliac crest and the lateral third of the inguinal ligament.
- Insertion
Linea alba (via the aponeurosis), pubic crest and pecten pubis (via the conjoint tendon).
- Action
Compresses and supports the abdominal viscera; stabilises the trunk.
- Innervation
Thoraco-abdominal nerves (T7–T11), subcostal nerve (T12), iliohypogastric and ilioinguinal nerves (L1).
- Nerve roots
T7–L1
- Arterial supply
Lower posterior intercostal and subcostal arteries; deep circumflex iliac and inferior epigastric arteries.
- Relations
The neurovascular plane (T7–L1 nerves, with deep circumflex iliac and intercostal vessels) lies between it and the internal oblique. The transversalis fascia and extraperitoneal fat lie deep to it.
Function
- Compresses the abdominal contents (raises intra-abdominal pressure)
- Stabilises the lumbopelvic region via the thoracolumbar fascia
- Assists forced expiration
Clinical significance
Direct inguinal hernia
Weakness of the transversalis fascia in Hesselbach's triangle, where the posterior wall of the canal is not reinforced by the conjoint tendon, allows a direct hernia medial to the inferior epigastric vessels.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.