The short version: Arthur Boorman was a paratrooper in the Gulf War. Eventually, the cumulative toll of repeated jumps took a devastating toll on his knees and back, and he was no longer able to walk unassisted, with no expectation that that would ever change. Unable to move easily, and depressed about it, his heath suffered, and his weight ballooned, which didn't do his knees, back, mobility, health, or depression any favors. . .
Then, eventually, he started trying to see if he couldn't go in the other direction.