Fittingly in this Olympic year, one of the highlights of the Edinburgh International Festival is an extraordinary combination of sport and art. For NVA's Speed of Light, hundreds of people have been climbing Arthur's Seat after dark to watch runners wearing specially commissioned light suits perform choreographed moves. The spectators are part of the work too as they carry staffs that emit sound and light, bringing the hills to life. This ArtWorks Scotland documentary follows the creation of this hugely ambitious project and finds out why people run and what motivates endurance athletes to push their bodies to the limit.