Want to win a barroom debate? Start a discussion thread about the "Great Athlete of All Time" and throw out Herschel Walker's name. The 1982 Heisman Trophy winner, Walker played in the USFL and NFL for more than a decade. He ranks second in the NFL in total yardage. He has a sixth degree black belt in tae kwon do. His sprint times -- 10.22 in the 100 -- nearly earned him a spot on the Olympic track team. He competed instead in the Olympic bobsled event in 1992. He won the Superstars competition as a matter of ritual, and even survived a few rounds on Celebrity Apprentice.

And he's not done. A few weeks removed from his 48th birthday, Walker could pass for a good 15 years younger. His muscles bulge; his heart rate rests; he has four percent body fat. And his appetite for competition isn't sated. On Jan. 30, Walker will make his debut as mixed-martial-arts fighter, appearing on a Strikeforce card in Miami that will air on Showtime.

Yes, the mainstream-athlete-tries-MMA trope is getting old. We've seen Jose Canseco embarrass himself and Johnnie Morton, the former NFL receiver, get carried out on a stretcher. Shaquille O'Neal is the latest jock to threaten to get in the cage. Except that Walker is no dilettante and this is no trivial pursuit. He's moved to San Jose to train under at AKA, American Kickboxing Academy, under Crazy Bob Cook. While Walker has no cauliflower ear, he's taken his licks sparring against Jon Fitch, Josh Koscheck and Cain Velasquez, the UFC's brightest heavyweight prospect.

Walker recently sat down with SI.com to discuss his latest sports passion.

SI.com: Why are you doing this?

Herschel Walker: It's a little, "Why not" I've done so any other things. Honestly, if MMA was at the point it is now when I was younger, I might have done that and not football. I wish I had the opportunity before I was 47, but it wasn't meant to be. I'm serious, though. This isn't Jose Canseco insulting the sport, jumping in, thinking it's easy. I'm in a training camp, getting better. I love athletics and I love competition. This is the most fierce athletic competition. I don't how long I can do this. But I can do it now. So, like I say, why not?

SI.com: How's this compare to football in terms of beating up your body?

Walker: I tell people after my football practices, my mom used to say, "Herschel, take a nap." I'd say, "Take a nap? Naps are for babies." After this? I take naps. It's every muscle of the body that gets worked.

SI.com: Do you know the history of the sport, the Shamrocks--

Walker: Oh yeah, the Gracies, the whole story. I've followed MMA for a long time. Always loved this sport. The opportunity for me to get into it just didn't come around until late.

SI.com: How do you feel about hurting people?

Walker: If you're not focused, can you get your head knocked off? Can you submitted? Absolutely. But I don't want to hurt anyone. I like the chess game of it. The competition is what's driving me. I'm not thinking I'm gonna hurt anyone.

SI.com: Aside from overall athleticism, what's your strength as a fighter?

Walker: When I first did my matchmaker [sparring] they were impressed with my standup. Then they saw me again and said they were impressed with my ground game. So I'm trying to do like everyone and be a well-rounded fighter.

SI.com: Are you in this for--

Not for a belt or anything like that. But let's take this fight and see on Jan. 30 whether it's good. If so, let's keep doing it and trying to get better.

SI.com: What's it like training with Cain Velasquez?

Walker: He's a monster. Just a monster. He's so big and strong. He puts you in a Muay Thai clinch and you're thinking, "What am I doing?" But I think I'm most impressed with his cardio. It's a joke. Honestly the Latin community especially should be really proud of him. Great guy, great fighter.

SI.com: A few years a go you wrote a book that surprised people, discussing your multiple personality disorder. What's the latest?

Walker: The book was to help people. You look at the stigma of multiple personalities. But I think we all suffer from multiple personalities in a sense. ... I wanted to get that stigma off. There's nothing wrong with Herschel Walker. I had a trying time but I'm not Sybil, some crazy person. I'm not ashamed though. If you get knocked down, get up. You leave home with the wrong hat on. I want the to leave home with the right hat on.

SI.com: Have you finally started lifting weights? Or are you sticking with the push-ups and sit-ups routine?

Walker: I don't know how to lift. I don't have the proper technique and when that happens, you get injured. I still say no one under 18 should lift weights. I'm healthy as a horse and I sure feel good. I know that.

SI.com: You could still play in the NFL?

Walker: Right now. No doubt. And if I could do that, maybe I could fight MMA.

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