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. But how do you run 26 miles if you have trouble making it around the block? With good coaching, discipline, and lots of group support, as NOVA shows when it follows 13 sedentary people through a nine-month regimen designed to prepare them for the grueling Boston Marathon.

Filled with personal drama, Marathon Challenge also takes viewers on a scientific adventure inside the human body. What happens to our muscles and hearts when couch potatoes become endurance runners? And what are the hidden risks? NOVA's behind-the-scenes portrait of the trials, tribulations, and joys of marathon training reaches a climax at the 2007 Boston Marathon. Here our 13 rookie athletes put all their hopes and hard work to the final test, experiencing hidden rewards and floods of emotion at the finish line.