Free running
Free running is like parkour except that the former is more expressive than the latter. Whereas parkour is the efficient movement through space, free running adds acrobatic flair for aesthetic purposes. One of the more talented practictioners of free running is Levi Meeuwenberg; here's a demo reel he made of his stunts.
Popular Science recently examined the physics of the jumps involved in both sports.
However, by bending and rolling, the time of impact can be increased to as much as 0.3 or 0.4 seconds. By decreasing his velocity over this extended period of time, the force is substantially reduced. Applying the above calculation with an acceleration time of 0.4 seconds we now get Fground = 2000 N (460 pounds). It's still a significant force but as you can see in the video quite manageable for someone with the proper skill, strength and technique.
I'm behind on my Ninja Warrior, but Meeuwenberg did quite well on a recent appearance, advancing further on the show than any other contestant. (via justin blanton)