Fitness Tracker

S1, E5: With around a third of the population now owning fitness trackers, many have become obsessed with tracking every move in the name of their future well-being. In this compelling science documentary, Hannah Fry finds out how 1970s car crashes helped us to count our steps, why high-altitude WWII dogfights led to crucial health technology and how fitness trackers are even being used to catch killers.