that's where bob mckinzie watched recruits who hope to join the navy's best of the best in 1993. >> to hang with your elbows up in the air until you feel you may black out, until you are sure you can't stand it another second then to keep on doing it, well that's just how these young men start the day. >> if you can't keep up to a simple speed, that's still way down to do then we're going to pull you to the back and we're going to start our secondary little group of pt for individuals that can't hang with the rest of the men. do you guys understand that? >> sit up, three. >> reporter: in high school or college they were the top jocks, triathletes, here they are just young men. people can do 100 sit ups, but how about hundreds of sit ups in a row. we checked in with them later on in the day. those who can keep going longer than the others in what is acknowledged as the toughest physical training regimen in the world will become navy seal, it's that simple. when the body cries out to quit, you are reminded that navy seals do not quit. if you try to get a second's rest, that's all you wil