Arguably, Kyokushin Karate is the most physically demanding of all of the Karate styles, Japanese or Okinawan.
They stress strong offense, and fight full contact, and after the beginner ranks are finished, no pads, either. No punches to the face, but anywhere else that is considered sporting (no groin shots, no attacks to the knee, etc) are fair game.
Basically, folks who want to do full contact sparring on a regular basis, are probably going to find this style to be the one for them. I don't agree with the methods used by Kyokushin, but I won't argue with the results, since those who do get their black belt in Kyokushin are usually some tough SOB's.
Even though I don't agree with their methods, I have the utmost of respect for them. Masutatsu Oyama demanded that his students be honorable folks, and that tradition still continues to this day. The Kyokushinkai aren't a bunch of thughish individuals, and if anything, would probably trounce such people if they tried to invade their schools. They aren't out to cause serious injury to each other, either.
Dean of the Darth Vader School of Personnel Management