We are bombarded with images of fitness and sport, everything from the sculpted torsos of reality TV shows to stories about cycle races and ultra-marathons. But at the same time, four in ten British adults, and 80% of children, are so sedentary they don't meet even the minimum recommended levels for movement. What's going on? The answer is simple: activity became exercise. What for centuries was universal and everyday has become the fetishised pursuit of a minority, whether the superhuman feats of elite athletes, or a chore slotted into busy schedules. This book is a chronicle of this very modern and largely unexplored catastrophe, and the story of the people trying to turn it around. But it also offers readers an empowering individual template for change - as well as, for some, a wake-up call that their lifestyle might not be quite as healthy as they believe.