At his heaviest, Mark Rucker weighed 386 pounds. Despite his efforts, he never managed to lose weight and keep it off, instead falling back into old habits. One fateful afternoon, he visited a theme park with his family and found he couldn't fit on the roller coasters--and couldn't share that experience with his daughter. Armed with new motivation, Mark set out to change his life: to lose the weight, regain his health, and earn back the chance to live his fullest life.

What began as a journey back to health became a campaign to complete one of the most grueling athletic feats in the...