Running, jumping, lifting, pushing, stretching - our bodies are naturally built to move and work, strengthen and adapt. Yet the gym is a 20th century phenomenon and 'working out'a concept that has produced one of the world's biggest industries: fitness. An industry whose changing ideals reflect society's cultural shifts on what it means to be fit, and how to have the perfect physique.Why the Pain? What's the Gain? takes you on a guided tour of humankind's 3000-year wayward search for the perfect workout; from the dirt courtyards of the ancient Greek gymnasium to the birth of the modern gym in 19th-century Paris; to the weekend, beachside Olympic-caliber gymnasts of Santa Monica and Sydney. Daniel Kunitz seeks the answer to a simple yet profound question: Why do we work out?We will listen in on the innovators and charlatans who lifted the multibillion-dollar business of gym-fitness into being. We will learn how the women's movement sparked an enormous exercise boom and tell the story not only of how we arrived at the big-box gym era but also of the last decade's acceleration into a new fitness frontier.Daniel Kunitz puts himself through the grit and pain of the cross fit, parkour and tough mudder regimes, searching not just for new-found physique, but on a quest to understand the pain and more precisely the gain of working out.