Adventure junkies Simon Donato and Paul "Turbo" Trebilcock try to prove that boundaries are meant to be broken as they test their limits in some of the world's toughest endurance races. Donato, who holds a doctorate in geology, is the brains of the duo and a self-proclaimed nomad. Trebilcock, a dedicated athlete with a background in running, is considered the heart of the team. Together, they participate in competitions that include a seven-day race through volcanic terrain in Iceland, a 46-mile foot race with obstacles, and a 142-mile run through Cambodian jungles. From running, biking, skiing, swimming and climbing, their love for the rush coupled with their undeniable stamina makes it a wild ride with a few cuts and bruised egos along the way. Endurance athletes Rory Bosio and Hunter McIntyre join the team beginning in Season 3.