Heath Calhoun never thought about cycling across the country—until he lost his legs. The Appalachian native—born in Bristol, Tenn., and raised in Grundy, Va.,—served as squad leader with the 3rd Battalion in Iraq for four months. But on November 7, 2003, a rocket-propelled grenade struck his convoy’s truck. His injuries were so severe that both of his legs had to be amputated...