Every year thousands of athletes from across the globe flock to Boston to run the city's marathon, a 26.2-mile test of stamina and endurance. But what drives a normal person to take part, and how does the body – and mind – cope with the strain?

In an intriguing programme that is part reality show, part medical science documentary, NOVA follows the dogged footsteps of six novice runners as they gear themselves up for the Marathon Challenge.

Over a year of training, coaches, doctors and nutritionists must turn these amateurs into fit, focused competitors. Vivid CGI illustrates the enormous changes inside the runners' bodies, swinging between high energy and exhaustion to depression and euphoria.

How does their gruelling schedule conflict with the demands of work and home life, and what really is the right kind of diet? As the race looms, the runners express their mounting hopes, frustrations and fears, until they finally face the lonely battle in the mass of runners.