Junyong Pak, 2 time Toughest Mudder World Champ smashes Guinness Book World Record by  running the fastest marathon (3:12:47) carrying a 40lb. weight.  Pak says: “it's an addictive rush when you're so good at tolerating pain—and you come out the other side”.  

Richard Diaz catches up with him to find out how he does it.  We’ll talk nutrition, training and grit and plans for future competitions, obstacle racing and marathon running.