Three of the world’s finest distance runners are about to attempt one of the greatest feats of athleticism in history: a sub two-hour marathon. To do it, the athletes will need to maintain an average pace of at least 13.1 miles per hour. So, we timed how long WIRED staffers could run at that speed. Needless to say, we didn’t last long. Here’s why only a handful of people in the world could ever come close to a two-hour marathon.