What is the name of the deep abdominal muscle that acts like a corset and supports the spine?

The deep abdominal muscle that acts like a corset and supports the spine is the transversus abdominis.

It is the deepest of the three broad muscles forming the anterolateral abdominal wall. Its fibers run mostly horizontally around the trunk, allowing it to tighten the abdominal contents and increase pressure within the abdomen. That bracing action helps stabilize the lumbar spine during lifting, bending, coughing, and other movements.

The muscle is often confused with the rectus abdominis, the vertical “six-pack” muscle, or the internal and external obliques, whose fibers run diagonally. The transversus abdominis is less visible because it lies beneath those more superficial muscles, but it is important to trunk control and load transfer between the torso and limbs.

A neighbouring fact readers often ask about is whether simply drawing the navel inward always trains it effectively. Bracing the trunk while breathing normally is generally more useful for loaded movement than holding the abdomen rigid or sucking it in continuously.