At 6 ft 5 in (1.96 m), he is the tallest man to have played Jason Voorhees. Freddy vs. Jason Director Ronny Yu tried to limit Kirzinger's stunts on the film as much as possible. Stuntman Glenn Ennis was called in to perform a series of stunts, including a stunt showing Jason walking through a field killing teenagers while on fire.
Long before Kirzinger took over the role of Jason Voorhees from Kane Hodder, he had ties to Friday the 13th. He appeared in 1989's Friday the 13th Part VIII: Jason Takes Manhattan as a New York cook who gets in Jason's way while pursuing Rennie Wickham (Jensen Daggett) and Sean Robertson (Scott Reeves). Jason, played by Kane Hodder, threw Kirzinger over the counter. In addition to his role as the cook, Kirzinger also served as a stunt coordinator for the film. Kirzinger is only the second person besides Hodder to play Jason more than once as he doubled for the latter in the same movie in a few short scenes.
According to Kirzinger, the hardest thing he went through while performing as Jason in Freddy vs. Jason (2003) was sinking into the lake. They shot the scene in a tank which was highly chlorinated and had debris to make it look like lake water. Director Ronny Yu wanted the close-up of Ken's eye and wanted him to sink into the water keeping his eye open. He also could not breathe because it would be visible on film. He was lying on top of the water and had to let himself sink down to the bottom of the tank without breathing and keeping his eye open. Kirzinger really held his breath, and the chlorine in the water burned his eyes.