Transversus abdominis muscle

Transverse abdominal muscle
Muscles of the trunk.
The Transversus abdominis, Rectus abdominis, and Pyramidalis.
Latin	Musculus transversus abdominis
Gray's	subject #118 414
Origin	Iliac crest, inguinal ligament, thoracolumbar fascia, and costal cartilages 7-12
Insertion	Xiphoid process, linea alba, pubic crest and pecten pubis via conjoint tendon
Artery	subcostal arteries.
Nerve	Thoracoabdominal nn. (T6-T11), Subcostal n. (T12), iliohypogastric nerve (L1), and ilioinguinal nerve (L1).
Actions	Compresses abdominal contents

The transversus abdominis muscle, also known as the transverse abdominus, transversalis muscle and transverse abdominal muscle, is a muscle layer of the anterior and lateral (front and side) abdominal wall which is deep to (layered below) the internal oblique muscle. It is thought to be a significant component of the core.

Structure

The transversus abdominis, so called for the direction of its fibers, is the innermost of the flat muscles of the abdomen, being placed immediately beneath the internal oblique muscle.

Origin

It arises, as fleshy fibers, from the lateral third of the inguinal ligament, from the anterior three-fourths of the inner lip of the iliac crest, from the inner surfaces of the cartilages of the lower six ribs, interdigitating with the diaphragm, and from the lumbodorsal fascia.

Insertion

The muscle ends anteriorly in a broad aponeurosis, the lower fibers of which curve inferomedially (medially and downward), and are inserted, together with those of the internal oblique muscle, into the crest of the pubis and pectineal line, forming the inguinal aponeurotic falx, also called the conjoint tendon. In layman's terms, the muscle ends in the middle line of a person's abdomen.

Throughout the rest of its extent the aponeurosis passes horizontally to the middle line, and is inserted into the linea alba; its upper three-fourths lie behind the rectus muscle and blend with the posterior lamella of the aponeurosis of the internal oblique; its lower fourth is in front of the rectus abdominis.

Innervation

The transversus abdominis is innervated by the lower intercostal nerves (thoracoabdominal, nerve root T7-T11), as well as the iliohypogastric nerve and the ilioinguinal nerve.

Actions

The transversus abdominis (TVA) helps to compress the ribs and viscera, providing thoracic and pelvic stability. This is explained further here. The transversus abdominis also helps pregnant women deliver their child.

Variations

It may be more or less fused with the Obliquus internus or absent. The spermatic cord may pierce its lower border. Slender muscle slips from the ileopectineal line to transversalis fascia, the aponeurosis of the Transversus abdominis or the outer end of the linea semicircularis and other slender slips are occasionally found. The nerves associated with the transverse abdominus are the intercostal, iliohypogastric, and the ilioinguinal.

Exercise

The most well known method of strengthening the TVA is the vacuum exercise. The TVA also (involuntarily) contracts during many lifts; it is the body's natural weight-lifting belt, stabilizing the spine and pelvis during lifting movements. It has been estimated that the contraction of the TVA and other muscles reduces the vertical pressure on the intervertebral discs by as much as 40%. Failure to engage the TVA during higher intensity lifts is dangerous and encourages injury to the spine. The TVA acts as a girdle or corset by creating hoop tension around the midsection.

Without a stable spine, one aided by proper contraction of the TVA, the nervous system fails to recruit the muscles in the extremities efficiently, and functional movements cannot be properly performed. The transversus abdominis and the segmental stabilizers (e.g. the multifidi) of the spine are designed to work in tandem.

While it is true that the TVA is vital to back and core health, the muscle also has the effect of pulling in what would otherwise be a protruding abdomen (hence its nickname, the “corset muscle”). Training the rectus abdominis muscles alone will not and can not give one a "flat" belly; this effect is achieved only through training the TVA. Thus to the extent that traditional abdominal exercises (e.g. crunches) or more advanced abdominal exercises tend to "flatten" the belly, this is owed to the tangential training of the TVA inherent in such exercises. Recently the transversus abdominis has become the subject of debate between kinesiologists, strength trainers, and physical therapists. The two positions on the muscle are (1) that the muscle is effective and capable of bracing the human core during extremely heavy lifts and (2) that it is not.

Additional images

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  Diagram of a transverse section of the posterior abdominal wall, to show the disposition of the lumbodorsal fascia.

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  Posterior surface of sternum and costal cartilages, showing Transversus thoracis.

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  The interfoveolar ligament, seen from in front.

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  Diagram of sheath of Rectus.

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  Diagram of a transverse section through the anterior abdomina wall, below the linea semicircularis.

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  The abdominal inguinal ring.

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  The abdominal aorta and its branches.

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  Transversus abdominis muscle

References

This article incorporates text from a public domain edition of Gray's Anatomy.

External links

• 718274638 at GPnotebook
• LUC trab
• SUNY Figs 35:07-04 - "Incision and reflection of the internal abdominal oblique muscle."
• SUNY Labs 35:17-0100 - "Anterior Abdominal Wall: The Transversus Abdominis Muscle"
• SUNY Figs 40:07-06 - "Muscles and nerves of the posterior abdominal wall."
• SUNY Anatomy Image 7183
• SUNY Anatomy Image 7194
• SUNY Anatomy Image 7209
• SUNY Anatomy Image 7311
• Exercising the Transversus Abdominis
• TVA vs. Weight Belt Debate