What does it take for the average person to run one of the world’s toughest races? NOVA finds out in a program that's both a human story and an intriguing scientific exploration of the way our bodies respond to intense exercise demands. Filmed in cooperation with the Boston Athletic Association, NOVA has been granted unprecedented access to the Boston Marathon course and will take viewers on a unique adventure inside the human body. Every year thousands of athletes from across the globe flock to Boston to run the city's marathon, known worldwide as the ultimate test of stamina and endurance. In the summer of 2006, NOVA began following 13 novices as they took the first step toward completing the 26.2-mile race in April 2007. The group of participants includes a variety of people from diverse backgrounds - a young woman running in memory of her mother, who died in a tragic car accident; a working single mom; even a former NFL linebacker - the unifying element is that not one of them is c