"Then they sprint until they can't move anymore," he adds. This is about when the puking begins. Jackson's goal with all this is simple: to expand a fighter's threshold for pain and suering. "We always want to out-suffer our opponents in training, so that when other people are sucking wind and dying in the fight, we're used to it," he says. "I always ask my guys, 'Would you rather be on the mountain or in the cage?' I've never gotten 'the mountain' once."

Matt Hughes, a former two-time UFC welterweight champion, thinks of MMA training as "running a marathon while riding a bull." Fighters need to be explosive, strong, technically sound, and mentally impenetrable—and above all else, resilient. "My saying is, 'Cardio is confidence,'" says Hughes, who's come back from near defeat to win fights in the later rounds. "I don't enjoy running, but I might run five miles in one day. If I can do that, it shows me that I can do anything."

Like most of his colleagues in the sport, Hughes' only fear is showing up to the fight out of shape—not defeat, injury, or embarrassment. "I think I've got the tools, so I just have to sharpen them up. Being in the fight is like clockwork. Everything just seems to happen—and if you have to think about things, it's too late."

Hughes' opponent in UFC's upcoming pay-per-view battle Dec. 29 is Matt Serra, the 33-year-old current welterweight champ. Once a journeyman mid-card fighter, Serra has risen to MMA star status with his participation in Spike TV's hit reality show, The Ultimate Fighter (TUF). In season four, when former UFC talents were pitted against each other for a once-in-a-lifetime title shot, Serra emerged as the winner. A heavy underdog, he went on to obliterate thenwelterweight champ Georges St-Pierre in the first round of their bout last April.

St-Pierre had won the title by knocking Hughes silly a few months before, so a Serra-Hughes bout became an instant big-bucks matchup. But the two men had more reasons to clash than just a big payday (six figures for both fighters).Serra began developing a dislike for his opponent during TUF season two, in which Hughes coached the competitors, including a student of one of Serra's two Brazilian jiu-jitsu schools near his home on Long Island, N.Y. Serra claims the student fighter was bullied by Hughes during a rough training session.

Later, when Serra himself competed in season four and Hughes made a guest appearance, he says Hughes played mental games with the fighters and tried to instigate an argument between Serra and the show's Brazilian jiu-jitsu coach. After that, Serra vs. Hughes was on: They have criticized each other in interviews, and to add to the momentum of their nasty feud (which they agreed to settle in the Octagon), they were chosen to serve as opposing team coaches in TUF's sixth season.

Says Serra, "I think Matt is genuinely confused as to why I have a problem with him. He never really did anything to me, but I don't like the way he treats people." Serra often calls Hughes a bully and likens him to a stuck-up high school jock— not to mention "a big furry chipmunk."

Hughes, 34, seems more diplomatic. "I wouldn't call myself a trash-talker," he says. "I just speak my mind. I don't think Serra is one of the top-10 welterweights in the world." Though he admits to sometimes trying to "get into people's heads," Hughes maintains that it's only gamesmanship and not personal.

Hughes does have an issue with how Serra carries himself as champion. A devoted Christian and classic middle American (he's from rural Illinois), he has accused Serra of being a bad role model for younger fans of the sport due to his tendency to "cuss" in interviews. "I try and lead my life like I'm in front of a class of fifth graders," says Hughes, a father of one young boy and a teenage girl. "He doesn't do that. He's being seen as a thug, and I think it hurts the sport." Serra, arguably more a sharp-tongued New Yorker than a potty mouth, retorts that he encourages his nephews and niece to watch Hughes on TV so he can point out to them Hughes' arrogant behavior. "I say, 'Look, kids, see how he's acting? Don't grow up to be an asshole.'"

Having one of the most recognizable names in the sport and a long trail of beaten foes behind him, Hughes is the favorite over Serra. But he's not taking his opponent lightly. Though he won't be preparing with his usual team (he left Iowa-based Miletich Fighting Systems, which has backed him his whole career, so he could stay closer to his family), Hughes says he's as hungry as ever and will be fit for battle.

He's about to open his own training center, HIT (Hughes Intensive Training), near his home in Granite City, Ill., and he vows that "every day, I will train with guys who want to hurt me." When not in the gym, he's rolling a tractor tire along the acres of his family's farm to build up shoulder strength, or smacking it with a sledgehammer until his hands blister to develop his core. Though he claims he's never done neck training, the 170-pounder's collar measures a massive 18 inches.

Serra continues to train on Long Island with the crew that helped him win the title. He performs a heartbursting circuit routine (described at right) to build his conditioning. "There's a dierent wind for each thing," he says, "the kickboxing, the wrestling, and the jiu-jitsu. You can have the heart, but if you don't have the lungs, you're screwed." Just as he did for his fight with GSP, Serra anticipates doing upwards of 80 rounds of sparring, focusing particularly on his stand-up striking.

"Hughes is a better wrestler than me," says Serra, "so I'm not going to bust my ass trying to get him to the floor. If anything, he'll have to try to take me down, because I'll be beating him standing." Undoubtedly, Serra's kickboxing skills shocked the world when he outpunched GSP to win the title. "Hughes is an egomaniac, so he might think he's going to stand up with me. But the second he gets hit, he's going to go right back to trying to wrestle. Hughes is good at being the hammer; he's not when he's the nail."

Hughes doesn't deny that Serra's power is a threat, but if he gets Serra to the ground, Hughes believes he can finish the fight. "If things aren't going my way, then I think back to what got me into this sport and what got me good," he says. "And that's taking people down and beating them up." As for Serra's devastating jiu-jitsu skills, Hughes thinks his wrestling is the perfect counter for that, too. "I think I'm going to pick where the fight goes. And the longer it goes, the better off I am. I'll be in better shape."