Two approaches for developing the abdominals. First is from traditional martial arts, specifically from Goju Ryu's advanced kata (form) called "sanchin". It is performed by no less than Morio Higaonna whose name is revered in the world of Okinawan and Japanese karate-do.
Next is from a modern approach that's a "crunch-free" exercise; the Cat Vomit. You could imagine why it's called as such.
Notice anything similar on both methods? It's the mechanics of slow intense breathing coupled with the focused muscular tension (isometrics).