The intense exercise program known as crossfit inspires obsessive devotion from its disciples. These athletes strive to laugh in the face of pain. And tonight, we're going to the crossfit games, where... See More
The intense exercise program known as crossfit inspires obsessive devotion from its disciples. These athletes strive to laugh in the face of pain. And tonight, we're going to the crossfit games, where the fittest of the fit fight it out. But when the gospel says to grin and bear it, there can be consequences. Here's ABC's Rachel smith. Reporter: That guy squatting with almost 100 pounds overhead is on a mission to become the fittest man in America. I'm James Hobart, 28 years old. My hometown is Otis, Massachusetts. Reporter: James is here to show his prowess at the crossfit games. One of the athletes competing in the four-day smackdown in southern California. For an event like this, try to think how bad it's going to feel. Reporter: With 10,000 crossfit gyms around the world, the high-intensity strength training program has become an obsession for millions. It's hard to argue with a body of evidence like this. Do you feel like it's become an obsession? Yeah. Reporter: For better or worse? For better. It hasn't done anything unhealthy to my life. Only good things. You know what I mean? Obsessive only in the sense that it takes up a lot of my time. Reporter: The sport has also come under fire. The crossfit fail videos, showcasing the dangers of the court if not done properly. And James is not immune, either. Check out that. I fell in a hand stand, trying to get the last couple steps. It feels good. I'm a little black and blue. Reporter: But that won't slow him down. There's too much at stake. If he wins, $275,000, endorsement deals and fame. Rich Froning. Reporter: What do you consider being a success for you? And what do you consider being a failure? The goal is always to win. So, that would be the success. The failure is anything less than that. You train all year, that's what you're training for. Try to get back on top of that podium. Reporter: James' journey to the super bowl of crossfit, began weeks prior, here in Massachusetts. It doesn't happen overnight. You know, you've got to take years to cultivate a face like this. Reporter: He's been practicing for the big games daily, starting crossfit seven years ago. Even getting his mom in on the act. You are a self-proclaimed momma's boy. You saw that. Reporter: I did. Still a momma's boy. I don't think that goes away. Once you're in that, you're locked in. Squat it down. Reporter: James who works as a crossfit instructor, put me to the test. Drive up. Punch. Not bad. Reporter: It's not just the guys that are here to compete. There's 42 women who will do overhead squats and sprint sleds to prove they are the most fit in the country. Becca Voight. Toluca, California. Reporter: Becca has been training all year long. Every year gets harder and harder. At the event tonight, we have no idea what it is. So, in about three hour, they will unveil it. And then, we'll probably have about an hour and a half to be ready. First heat here. Reporter: And that competition, watch becca's mate, as she makes a run during this sandbag carry, she suffered a knee injury in 20 2008. And now, it's acting up. At the medical tent, becca wincing in pain. Do you feel this is something you're going to be able to push through at this point? Absolutely. It's just one of those things. Mind over matter. I know that, you know, when it comes time to play, I'll be ready to go. Reporter: Will there come a point that you would pull out of the competition? I mean, if I couldn't walk, maybe. It would be extreme measures, I think. If it was permanently damaged, my ability to walk. Reporter: Is competing the best thing for becca? Does the sport end up pushing athletes too far? We went to crossfit games director. It's safe to be honest with you, when you start it on your own with no coaching. And I did that. And I know hundreds, if not thousands of people who got into crossfit on their own without proper coaching. Reporter: Others at the event back up the mantra here, that it's not the safety that people are most concerned with. Do you feel, though, that safety is a priority? In the training, absolutely. Safety is always paramount. We're doing things that are safe. But out here, things are a little more intense because there's something on the line. Out here, safety is not the priority. Winning is the priority. And sometimes safety falls to the side. Reporter: Crossfit trainers only have to go through 16 hours of training. Just one weekend to coach the athletes. Is that enough to keep crossfitters safe? You can get your level one, that lets you know that you've been through the basic elements. It's an affiliate owners' responsibility, to take on the quality of products he wants to deliver to his community, by further training. My staff that's all here have been doing this for years. And they study and read constantly. Reporter: Back on the field, it's two hours before the competition. And becca is back warming up. I feel like a newbie. These workouts are not the same. They never have been. Reporter: Becca and James have the strength to keep going, and move on to the final competition. Becca struggles in pain during this rope climb. But manages to press forward and finish in 24th place. Back in the stadium, with mom cheering from the stands. Go, James. Reporter: James completes an obstacle course of rope climbing and dead lifts. But it's not enough. He ends up in 21st place. James Hobart. Reporter: Why do you do all this? Because I love it. Aside from the physical aspect of it, the community and the people inside of crossfit I've met in the last seven years are amazing. And maybe that's not why I started it. But that's certainly why I'll keep doing it. Reporter: In a battle of endurance like this, merely completing the race is a victory. For "Nightline," I'm Rachel smith, in Los Angeles.
This transcript has been automatically generated and may not be 100% accurate.