Bob McCarthy's karate teacher
To perform it, a fighter has to stiffen his body to it's utmost limits on the moment of impact. When fighter uses it at the right moment during a seiken punch, all of his joints will be fixed. It's very difficult to do, but if he succeeds, his fist will strike with the weight of his whole body.
At the first time, Baki used the Gotaijutsu against Kureha Shinogi during their fight at the Tokyo Dome Underground Arena. He almost killed Kureha with this technique. He used it also when he fought Biscuit Oliva during the Prison Battle Saga. Oliva used his Ball technique, then Baki strike him with the Gotaijutsu but did not hurt Oliva. Bob McCarthy, a prison guard from the Arizona State Prizon, stated he had a karate teacher who could do the Gotaijutsu with the edgewise of the hand, being able to break a bowling ball made of plastic with one blow.