FOX Sports writers Damon Martin and Elias Cepeda answer your questions in our all-new mailbag. This week, they tackle UFC Japan stars Roy Nelson and Gegard Mousasi, the heavyweight title and five must-watch fights for new fans.

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Roy Nelson looks extremely out of shape. Why doesn't he lose like 100 pounds and fight at welterweight?

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-- Austin, Facebook

ELIAS CEPEDA: Nelson's got the height of many welterweights, but I think the ship has sailed on the idea of his dropping pounds to compete at a more natural and healthy weight. Nelson is 39 years old and nearing the end of what has been a very successful career.

He was much lighter 10 years ago, but he's only gotten bigger as time has passed. What makes it even more amazing is that he almost always has the wind necessary to fight hard to the end of a fight, which means he must work hard as hell in the training room. The amount of calories he must consume to still not lose weight is difficult to even fathom. The best we can hope for at this point is that "Big Country" will address his issues and get healthier after he retires.

DAMON MARTIN: Roy Nelson was never going to be the guy you put on the cover of fitness magazines and tell subscribers how he got his rock hard abs, but that doesn't mean the guy is extremely out of shape. There have been plenty of fights throughout his career where he showed good conditioning and endurance regardless of his weight or how he looked going into the cage on that particular night.

Where Nelson struggles is that as he got into the deepest parts of the heavyweight division in the UFC, he wasn't nearly tall enough or strong enough to deal with the biggest fighters at that weight class. He routinely gives up several inches in reach and larger fighters have been able to muscle him around the Octagon when they engage in the clinch.

Nelson probably would have been best served to drop down to light heavyweight at some point during his career, but as he closes in on 40 years of age, that time has probably already passed. Nelson has still managed to put on some of the most entertaining fights in the division, knock out fighters who looked like fitness models and earned the most post-fight bonuses in UFC heavyweight history (six). For a guy that's supposedly out of shape, he's still carrying his weight inside the Octagon.

Who wins the UFC Japan main event?

-- @geargolem75 (Jacob)

DAMON: It's hard not to pick Josh Barnett in this fight when you look at the overall skill set possessed by both fighters. Unless he decides to just stand and trade with Roy Nelson, he has a lot of different ways to win.

Barnett, along with Fabricio Werdum and Frank Mir, has the best grappling credentials in the heavyweight division and he's definitely a better wrestler than both of them. Barnett has a phenomenal ability to bully fighters into the cage and dump them on the ground before applying a nasty submission game, and there's no reason to believe he can't do the same to Nelson.

Nelson just hasn't looked great his last couple of fights, and if he can't stave off Barnett's grappling attacks he's going to get stuck on the ground either eating shots or fending off submission attempts. Either way it looks like a win for Barnett.

ELIAS: I never know who will win a fight before it happens. I just play a man who knows who will win fights before they happen on the Internet.

With that said, I think Josh Barnett is the better-rounded fighter. If he's healthy and at his best, he stands a good chance at taking Roy Nelson down.

Barnett may or may not be able to submit Nelson on the ground, but he can grind away with elbows and punches for a while, that's for sure. For his part, Nelson has the punching power to hurt Barnett if he can keep the catch wrestler off of him. If Nelson manages to get on top of Barnett on the mat, he's got the submission skills to be a threat, but Barnett can probably scramble up safely.

Do you see Mousasi getting cut with another high profile loss? Dude isn't cheap, if can't contend why keep him?

-- @BelowtheBe1t

DAMON: Here's the thing -- Mousasi may not be an elite middleweight, but he's still really good and there are plenty of high-profile matchups for him to take. You could easily argue that he's in the same boat as Michael Bisping, who has fallen short of the gold on a few occasions, but still ultra-talented and puts on good fights.

Mousasi has flashes of brilliance and while losing another high-profile fight like he did against Lyoto Machida or Ronaldo "Jacare" Souza would certainly be damaging to his chances of ever fighting for a title, that doesn't mean you let the guy go.

If Mousasi ever gives up on middleweight, he's the kind of guy who would still take fights at light heavyweight or even heavyweight if that's what the UFC wanted. Don't forget he submitted Mark Hunt once upon a time while he was fighting in PRIDE. Mousasi is still a valuable guy even if he doesn't win every fight he takes against the best fighters in the world at 185 pounds.

ELIAS: Goodness, did Gegard slap your mama, or what, man? There's zero reason to talk about cutting a guy on a two-fight win streak, and who has won three out of his last four fights.

Since when is it a rule that anyone who isn't the champ or No. 1 contender shouldn't have a job? Mousasi is surging, and he's been in the top 15 of two different weight classes for about half a decade. Suffice to say, he's a good value for the UFC roster.

Who is next in line for a heavyweight title shot, after Cain?

-- @PeoplesChamp575 (Jay)

ELIAS: Who freaking knows anymore? Dana White said this summer that it was going to be either Stipe Miocic or Andrei Arlovski next for Fabricio Werdum, then changed his mind and awarded Velasquez an immediate rematch.

Now, Miocic has a fight in front of him against fellow contender Ben Rothwell, and Arlovski may very well fight again before Werdum and Cain lock up. My pick would be either Miocic (I count his fight against Junior Dos Santos as a win for the fireman), Rothwell, or Arlovski.

Then again, a fighter coming off a knockout loss or Holly Holm could end up getting the call. At this point I'm done pretending that the UFC's rankings or title shots make much sense other than marketing sense.

DAMON: It all depends on how things play out in these next few months. On paper, you could easily slot Andrei Arlovski in the top spot based on his four-fight win streak in the UFC, but his last bout against Frank Mir failed to impress and whether it's fair or not, fighters are routinely judged on their most recent performance. His wasn't great.

The two more obvious choices would be either Stipe Miocic or Junior Dos Santos depending their performances in upcoming fights, as well as the outcome of the rematch between Cain Velasquez and Fabricio Werdum.

Miocic has been champing at the bit for a title shot and he would inject some much needed new blood into the title picture while Dos Santos might arguably be the second best heavyweight in the world who just can't get past Velasquez in his prime.

Which 5 fights would you say are an absolute must to watch for a new UFC fan?

-- @Ryledale (Dale)

DAMON: Frank Shamrock vs. Tito Ortiz from UFC 22

Wanderlei Silva vs. Quinton 'Rampage' Jackson 2 from PRIDE 28

Fedor Emelianenko vs. Mirko Cro Cop from PRIDE Final Conflict 2005

Mauricio 'Shogun' Rua vs. Dan Henderson from UFC 139

Anthony Pettis vs. Benson Henderson from WEC 53

ELIAS: Royce Gracie vs. Ken Shamrock/Kimo Leopold/Dan Severn (take your pick)

Antonio Rodrigo "Minotauro" Nogueira vs. Bob Sapp

Any (preferably all) of Mark Coleman's UFC 10 tournament fights

Anderson Silva vs. Forrest Griffin

Mauricio "Shogun" Rua vs. Dan Henderson I

The first three fights show some of what makes MMA different from any other combat sport -- the complete groundwork, the ability to overcome size and strength with grappling technique, and seismic developments in what we know works in real fights. The fourth is an example of incredible striking mastery over a larger opponent, and the fifth is one of countless inspiring and heartbreaking displays of courage and gameness that we've had in our sport, from both fighters.