Back in January, 40-year-old Woody Thornton couldn’t run on a treadmill for a full minute. He’d wobble. His tiger-striped prosthetic legs couldn’t keep him straight. So Thornton practiced. He walked. He jogged. He made himself go to the gym and do laps around his house. And April 4, it took him only 39 minutes, 6 seconds, to cross the finish…