We’ve seen people on skateboards and motorcycles loop the loop many times. Damian Walter is the first human to do it on foot. To run it without falling, you need to reach the right speed; then, centrifugal forces
will keep you locked on the track. Note how his shoulder line stays
dead center of the loop. For this particular one, Damian needed to
accelerate up to 8.65 mph in the highest point to be able to gain enough
inertia as to rotate his body and legs around his head fast enough, so
when gravity finally wins, he’s already feet down on the track. The full video is part of a Pepsi promotional campaign. (Source)