From local Parkruns to grueling 100km mountain races, running is undergoing a massive transformation. Participation is surging, the "marathon age" is getting younger, and the sport is becoming more "sticky" than ever—especially in the world of ultrarunning. Explore the data behind the endurance boom, from the millions of Couch to 5k downloads to the commercially valuable loyalty of long-distance athletes, and discover why this growth is global, digital, and deeply communal.