It just wouldn’t be a B.J. Penn fight without weeks’ worth of speculation about his weight, his body-fat percentage, his general shape.

His physique is treated as such a reliable predictor of future performance that he’s become MMA’s version of the groundhog. If Penn emerges from his Hawaiian paradise and sees his own shadow – and if that shadow is even the least bit pudgy – he’s in for 15 more minutes of suffering on fight night. We look for his abs like we’re reading tealeaves. Is that one? Do we have an official ab sighting? Does that mean we’re in for a good harvest this year? Won’t someone tell us what the future will look like before it gets here?

The answer is no, they won’t. That’s as true for Penn (who’ll turn 34 next month but somehow seems like he’s been around forever) as it is for his opponent at next Saturday’s UFC on FOX 5 event at Seattle’s KeyArena, Rory MacDonald.

At the moment, the 23-year-old MacDonald seems to be getting plenty of enjoyment out of life as a successful young pro fighter. When he showed up to a fan Q&A session prior to the UFC 154 weigh-ins in Montreal, dressed like he’d just mugged a Banana Republic mannequin, he casually mentioned both videogames and girls among his two favorite pastimes. He told a story about the few months when he’d worked a regular job as a carpenter before deciding that it was no way to live, so he quit and became a UFC fighter instead. You know, like you do.

That’s life for MacDonald (13-1 MMA, 4-1 UFC) now. He’s young, on his way up, and the future is one great promise, soon to be fulfilled and then fulfilled some more. He just knows it.

For Penn (16-8-2 MMA, 12-7-2 UFC), the future is more like the last few bites of ice cream in the bowl. He wants to savor what he’s got instead of rushing to the end, but if he waits too long, it will all melt right in front of him. He’s close enough to the end that he can’t help but think about what it will be like once it’s over, even though thinking too much about it is the best way to ensure you don’t enjoy the time between now and then.

What will they say about “Baby Jay” once he’s gone? That he was great when he really wanted to be, and merely very good when he didn’t? That he had his moments, here and there? As he explained on Tuesday’s pre-fight media call, that doesn’t sound like such an appealing legacy to “The Prodigy.”

“I don’t want to just be known as, oh, he was good back in the day,” Penn said. “I want to be known as one of the best.”

This is what sometimes happens when a young fighter becomes an old one. He goes from not caring what people say about him to trying to change it at the last minute. When you’re still on your way up, you can afford not to give too much thought to your legacy. They’re just words. Once you spy the finish line, you might start to wonder if those words (along with some highlight videos, ideally) won’t be all that’s left after you call it quits.

MacDonald’s not there yet. Not even close. When I spoke to him after his Q&A in Montreal, he said he intentionally tries to “stay off the Internet” because once he’s on, it’s tough not to read what someone else thinks about him.

“I know people have a lot of negative things to say about me and a lot of positive things,” MacDonald said. “It’s a 50-50 thing, but I’m not in this sport to make people like me.”

Which is, of course, easy to say when you’re a 23-year-old with what everyone seems to agree is a bright future in front of you. When you get to be Penn’s age and you feel like you don’t hear your name mentioned in the conversations about the all-time greats as much as you’d like, that’s when other people’s opinions might feel like they matter more. Then again, by that point it might already be too late.

The irony for a guy such as Penn is that, since the scouting report on him is filled with criticisms of his inconsistency, it’s hard to do much now that doesn’t inadvertently reinforce that narrative. Imagine him showing up in Seattle with a ripped physique and that same muttering, psychotic, crazy-man-at-the-bus-station look he had against Matt Hughes in their third meeting. Imagine him going out and destroying the UFC’s next welterweight golden child on live network TV and then licking MacDonald’s blood off his gloves (hey, at least it’ll have been tested thoroughly by VADA). What would we say about Penn after that?

Honestly, I can’t imagine it would be much different. He’d still be the frighteningly talented fighter capable of blowing our minds when he felt like it. This fight would go down in the “felt like it” column, but his overall legacy probably wouldn’t change much. That’s the problem with being sometimes great: Even if you bounce back from a few mediocre performances with a surprisingly awesome one, it just reminds us of the gulf between the good and the great versions of yourself.

That’s the difference between Penn and a fighter such as Georges St-Pierre. If there’s one thing you’ll never hear GSP criticized for, it’s a lack of consistency. He’s consistent the way a drum machine is consistent. Not a ton of flair, but dependable almost to the point of being mundane. MacDonald seems like he might be headed down the same path, only with more of a nose for the finish (at least against the lower tier of UFC fighters).

Penn’s never been like that, which is part of what has made his career so fascinating. That’s why we scrutinize his training and his body so intensely before a fight. We never feel totally certain who’s going to be standing there when the curtain goes up on Saturday night. Whether you think that’s a sad waste of potential or the one thing that can make a gifted athlete endearingly relatable, at least it’s never boring.

Penn might not like the idea of leaving that particular legacy behind, and I can’t say that I blame him. I’m just not sure there’s much he can do about it now, when he’s so much closer to the end than the beginning.

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