Japan is the most running-obsessed country on earth, and the 135-mile relay race "ekiden," is the country's biggest annual sporting event. This aspect of Japan remains a mystery to the outside world, and so Guardian journalist Adharanand Finn spent six months immersed in this one-of-a-kind running culture to discover what it might reveal about the sport and about Japan. As an amateur runner about to turn 40, he also hoped to find out whether a new approach to training might help him run faster. What he learns—about competition, teamwork, form, chasing personal bests, and about himself—offers fascinating insight into why we run and how we might do it better.