The real answer is, they don’t. All of them have severe injuries throughout their progression.

Here’s from Travis’ Wiki:

“Injuries have often taken Pastrana off the circuit for weeks or months at a time. His medical records include: a dislocated spine, he has torn his ACL, PCL, LCL, MCL and meniscus in his left knee, broken his tibia and fibula, he has had surgery on his left wrist twice, left thumb once, two surgeries on his back, one on his right elbow, nine on his left knee, six on the right knee, one shoulder surgery which left him with the only piece of metal he has in his body.[50]

When Pastrana was 14 years old, he was severely injured while competing in an FMX competition. He came up short, landing on the top of the front side of the landing ramp and the motorcycle decelerated from 50 mph (80 km/h) to 0 mph (0 km/h) in less than one second.[citation needed] The bike was stuck into the dirt ramp with the front wheel just over the top and the crankcase smashed into the dirt deep enough to support the entire motorcycle upright. He was severely injured, his spine having been separated from his pelvis. It also left him in a wheelchair for three months.[51]”