It's designed to be one of the toughest events you can sign up for. But wounded warriors have been through much worse.
"I was in a building in Iraq that was hit by artillery fire and it collapsed on me and buried me alive," says Cpl. John Rego, an Army Ranger.
His right arm and hip were shattered, and internal organs ruptured. But now, even with metal rods and mesh holding them together, he's ready to take on anything.
"I just want to prove that I'm still tough to myself after I got injured, you've got to, you feel as if you lost a step from all the training and everything that you've done in the military," says Rego.
Tough Mudder is the biggest supporter of the Wounded Warrior Project, and it often draws the warriors into its trenches.
"Walking and doing swimming, getting my lungs in order to do this, I got my Ibuterol in my pouch here and my wife's running next to me who's a nurse, so she's going to make sure everything works good," says Christopher Braman, who was injured rescuing people in the Pentagon on 9/11.
They were surrounded by thousands heading for the finish line, but wherever they were on the course, it was this team who lead the way.