The traditional ab plank is one of the all-around best ab exercises for developing a svelte midsection, a strong core, and superior posture. Unlike crunches, sit-ups, cable woodchoppers, ab v holds, hanging leg raises and the like, which primarily work the rectus abdominis (the vertical “six-pack” muscles) and obliques, planks blast the transverse abdominis.
The transverse abdominis (TA), aka the “inner abs,” is the deepest abdominal layer and runs as a belt horizontally around the midsection in between the hip bone and ribs. Unlike the biceps, chest, rectus abdominis, etc., the TA muscle is invisible from the outside.
Aesthetically, a strong TA won’t produce the abdominal crevices, caverns, and undulations characteristic of a six-pack, per se, but rather it sucks the midsection into a tight, compact, slender package. It’s essentially the body’s corset — a strong TA naturally compresses the girth of the stomach.
This is critically important. In isolation, a well-developed RA and obliques create six-pack striations and definition, but they’ll also appear bloated, loose, and bulging; strengthening the TA compresses the region and completes the holistic look. Ab planks are the most effective, most direct way to tear up the TA.
If you’re someone who DOESN’T like the “six-pack” look and the block-esque abs that go with it, and simply want a flat, defined stomach (like the one on the right), the TA absolutely should be your primary point of emphasis.