Peter Walker is a political correspondent with the Guardian, and a commentator and frequent broadcaster on issues including politics, active living and health. He has written a previous book about the many benefits of everyday cycling, Bike Nation: How Cycling Can Save the World, which is how he became fascinated by the problem of inactive lifestyles. His new book is The Miracle Pill: Why A Sedentary World Is Getting It All Wrong, published by Simon & Schuster. As a journalist he has reported from countries including North Korea, China and Iraq, and is now based in parliament. @peterwalker99