If you were Adrian Peterson, you might feel invincible.

After all, you regularly make some of the fiercest athletes in North America crumble to the their knees, and send others flying on their backs. You leave even the swiftest grasping at air. You have an MVP award in your trophy case. You came back from a torn ACL as if it were a torn fingernail. At 29, you are at the height of your powers. You have the body of an action movie hero -- muscular, lean and perfectly proportioned. Your nickname is Purple Jesus.

If you were Adrian Peterson, you might feel invincible. Except for one thing.

Seafood gumbo.

Before we get into why, let's, for a moment, consider the concept of the invincible Peterson as it relates to the world around him.

We are at a point in time when most running backs are more vulnerable than ever. The devaluation of the position has led to many teams minimizing their running back investments. The average salary of the top 10 paid free agent running backs this year was $2.47 million, compared to $4.8 million for the top 10 wide receivers. Some general managers flat out admit the No. 1 skill they look for in a running back is ability to pass protect. 

Chris Johnson long had been Peterson's primary rival for the throne that belongs to football's best back. Johnson, six months younger than Peterson, was cut this offseason by the Titans. Peterson gets it. "It was surprising, but then again it wasn't because it's all about what have you done for me lately in this league," Peterson said. "If he came off a 2,000 yard rushing season, they probably aren't [cutting him] and somebody is paying big money for him. Unfortunately it was a down year for him."

It isn't just veterans who have felt the pinch. No running back has been drafted in the first round in two years. The way Peterson sees it, what has happened in the draft might be reflecting the talent at the position more than the desire for running backs. "We haven't had a good back, a must have guy, come out of college in a couple years," he said. "That's what's missing. You get a guy who comes out who is like Marshawn Lynch … you'll definitely want to bring that guy in."

If there is anyone who can prove that the running back position still can make a difference, it is Peterson. Swimming against the tide isn't enough for him though. He wants to reverse the tide. So as the flag bearer for all who take a handoff and run with a football high and tight, Peterson feels a personal responsibility to bring back the back. His goal, he says, is to "beat down the things they are saying about the running back position."

Peterson believes he is football's best player at any position. He easily is the best running back, despite LeSean McCoy's contrary opinion. Peterson, in fact, said McCoy is not even the second best running back in the league. He rates McCoy third, behind Lynch and ahead of Matt Forte.

Peterson once ran for more yards in a game than any player ever. He has rushed for ten or more touchdowns in each of his seven seasons. His 2,097 rushing yards in 2012 were second most in a season in NFL history.

Eight years into his career, he still runs with a combination of vision, power and speed that the sport rarely has seen. Even anesthesia and scalpels have not diminished him. He has had five surgeries, including three in the last three years for an ACL, sports hernia and adductor muscle. "The ACL was the most severe, and I won an MVP after that," Peterson said.

Of course, things can change quickly at the running back position, as Johnson can attest. Peterson's contract calls for him to earn more than $78 million over the next four years. For him to collect that, his performance will have to justify it, year-by-year, game-by-game, carry-by-carry.

Peterson is resolute in his belief that he can remain the best for many more years, even after he has seen so many other running backs eroded by time and contact. "I like breaking through boundaries, crossing the line, doing what people say is not possible," he said. " I've always been that type of thrill seeker. Always challenging myself. You let someone say you can't do this, or you're not going to be able to do that, or this is not possible based off of what they have seen in history, then you are settling for less. I don't accept it."

Why haven't others been able to go where Peterson plans on going? "Conditioning," he said. "Taking care of your body. Making sure your body is battle proof and able to withstand the punishment a running back goes though. It's doing the small things -- ice tub, cold tub, massages, making sure you help your body rejuvenate."

Peterson isn't doing any more than he ever has done in that regard, or doing anything differently. But one of the most physical runners in the league acknowledges that over time he has made subtle, body-preserving adjustments to the way he plays. He no longer seeks every collision possible as he once did.  

"There comes a point in time when you know the extra yard really doesn't matter if you already have the first down, and you know you aren't going to get it," he said. " Or I'm sprinting to the sideline and two guys are chasing me with an angle. I know I'm not going to get the corner on them. Earlier in my career, I would have dug in and have that contact for two extra yards, but now it depends on the situation. If I'm trying to get the first down, I'm dipping my shoulder and going for it. First down accomplished, I can step out."

That isn't insecurity talking. It's wisdom, a wisdom that comes with time and experience. "You definitely start thinking about making sure you are healthy and avoiding things that cause harm to you, whether it's on the football field or dealing with allergies," Peterson said.

Which leads us back to seafood gumbo. In July of 2012, I visited Vikings training camp in Mankato, Minn. One of the people I had hoped to talk to was Peterson, who was quite a story coming off his ACL injury and feeling much better than he had a right to. But Peterson was not around. 

Peterson loves gumbo and seafood. He ate it all the time. So he was happy to see it on the training camp menu that day. He had two bowls of it in the cafeteria. As he was walking back to his dorm room, he noticed his eyes were itchy. He didn't think much of it. When he got back in his room, his throat was swelling a little. He lay down to rest. By now, he wanted to scratch his eyes out of their sockets, and his throat was worsening. When he stood and looked in the mirror, he saw puffy eyes and lips. Then the symptoms worsened. He could barely breathe or talk, but he managed to phone Eric Sugarman. The Vikings trainer rushed over with an EpiPen, and Peterson had an injection of epinephrine in his thigh before visiting the hospital.

A few weeks later, an allergist confirmed Peterson was allergic to scallops, lobster and shrimp. Since, Peterson has avoided shellfish and anaphylaxis. But he hasn't gone anywhere without an EpiPen. I finally got the chance to talk with Peterson when he was in Chicago over the weekend to speak at the National Food Allergy Conference.

Most kids aren't very much like Adrian Peterson. But a lot of them have severe food allergies like he does. So Peterson has seized an opportunity to help educate others with the Ready2Go campaign.  

"It definitely was my most frightening medical experience," Peterson said. "I could have been gone just like that. What if I had just lain there and went to sleep? Who knows? I probably wouldn't have woken up. When you can't breathe, that's one of the most frightening things anyone can experience. 

The situation showed me I was just normal. Especially that season, I thought I came in the best shape possible. It was the ACL recovery year. It was the last thing I suspected."

If you were Adrian Peterson and you saw a swollen face staring back at you in the mirror, you would realize there are some things that even you cannot dominate.

But not many.