Transcript for Bear Grylls talks about his vigorous training for survival, ‘Running Wild’
man who turned an obstacle into the obstacle course of a lifetime. Okay. One leg over. Reporter: I know what you're I am concerned about the crocodile situation. It would be ridiculous to not be concerned about the crocodile situation. Reporter: I'm thinking it, too. Chest low to the rope. Use your legs to balance. It will get easier. Keep going, well done. Ah! Reporter: Is this guy about to get captain marvel eaten by a crocodile? Now you got to go, now you got to go. One, two, three. Ah! Reporter: Mott today. Ah. Good job. Reporter: This guy, of course, is bear grylls, famed Hollywood adventurer and survival expert. Who's forced fans to watch through their fingers. He's taken them on adventures in running wild with bear grylls. If you think back on everything you've eaten over the years, is there something that really sticks out to you? There's a long list of bad things, from raw goat's testicles. I think the lesson for me is survival food's not going to be pretty. It's fuel. Nobody ever comes around for dinner anymore. We're not coming if you're Reporter: Now on nat geo, running wild with bear grylls is entering its fifth season, pushing the limits of what we think our favorite Hollywood stars can and can't do. Can I just stay here? Ah, it's a long way down. I want to see what I just caught. Did you see that? Reporter: For those like me, who prefer the practice of the art of armchair survival, all of this -- What was that? I don't know, but that Boulder definitely moved under your feet. Reporter: Might seem a bit extreme, but for bear grylls, it's in his DNA. Where did you get the nickname bear from? I was teddy. Everybody was like, did you wrestle a bear when you were it's more that I had an older, bossy sister who said Ted is such a boring name, we're going to call you bear. Reporter: Growing up in England, his love for the outdoors first came from bonding trips with his dad Michael. I've got three young boys. It's a great privilege to show them how to manage themselves in situations in the outdoors. Reporter: Those survival skills sharpened to a point by the military. Did you want to go in because of your dad? Yeah, of course. He was a marine, how can I do one better? I got to join the British special forces. To me, it was a great outlook to live an adventurous life. Reporter: But a tragic parachuting accident cut his service short. Broke my back in three different places. Had to leave the army after that because I couldn't do the job in the way I had before, and just slowly trying to rebuild my life. Reporter: Down but not out, bear attacked his injury head on. Just 18 months after a skydiving accident, he became one of the youngest people ever to summit Everest, really a symbolic thing for me. I'm going to get strong again, I'm going to learn to walk again, climb again, and stand on the top of the world. And on the back of that, the TV door opened. My name is bear grylls. I'm about to undertake my toughest challenge yet. Reporter: His first show escape the legion appeared in 2005. I never knew anything about TV. And I just wanted to keep climbing and doing the expeditions and try and raise money and get sponsors and keep going on that road, and I might never make any money, but it's going to be an adventure. Reporter: His first major U.S. Show, man versus wild, ran for five seasons and launched bear as the go-to television adventurer for the millennial generation. I'd meet them in the streets and they'd say when I said in that jungle, smile when it's raining. I understood that as a single mum, bringing up kids or doing four jobs. The wild is a great mirror on life of how to have kind of drive and survive and dig deep in big moment. And I'm always trying to keep it on that. It's the wild built here, it can empower you and test you. And that really was the beating heart to running wild. These people had never done anything like this outside their Hollywood bubble. Look, the wild won't judge you, but till test you. Come for the adventure. Reporter: Adventure mixed with those moments that make you oh, so gloriously uncomfortable. Bear's gut-wrenching feats gas tron any became legend. Many times I've got it wrong and things, I've ended up sick and, you know, I've looked back over the years on the many, you know, the episodes that we've done all over the place, and after it's gone wrong and I've hung offer the rock face with diarrhea, and the camera's still rolling, it's fine. I've never minded the mistakes. You squeezed its heart out. That's many things, but that's not a heart. I've got smarter, you know stay agray that one. And never get complacent. It's always the little things that come and trip you up. Sorry, mom. We're not looking down. Oh, no. We would never look down. Reporter: Now, after more than a decade on television. I can't. One, two. Reporter: Bear is back to his usual ways once again. For "Nightline," I'm will Karr. You're alive. I'm alive. You can watch running wild with bear grylls every Tuesday night on the nat geochannel at 10:00/9:00 central.
This transcript has been automatically generated and may not be 100% accurate.