You zip up a nylon suit, your heart rate maxes out, you rock forward past the point of no return, and then you have about 4 seconds to perform at your absolute peak or you die. At full speed you're moving at 120 mph with your face, sometimes 6 feet above the ground, weaving through trees. The suit pressurizes like an air mattress when slow, but pitch it over and it feels like licking the world's biggest 9-volt battery.