Do the Vikings have a winning formula that features a running back in his 30s?

Oh, I don’t know. They went 6-9 and missed the playoffs without Adrian Peterson last year. This year, they went 11-5 and won the NFC North with Adrian Peterson capturing the league rushing title and All-Pro first-team honors behind an offensive line that lost two starters in August and struggled throughout the season.

You’d think that kind of logic would silence an argument. But Vikings fans are a tormented band of brothers. With good reason, as we saw once again Sunday.

They’re hurting, again, and they want to share their pain. Next to Blair Walsh’s missed 27-yard field-goal attempt with 22 seconds left, Peterson’s fourth-quarter fumble ranks No. 2 on the Purple Pain-O-Meter that runneth over. It was that fumble that handed Seattle a 12-yard drive that produced the go-ahead field goal in the Vikings’ 10-9 NFC wild-card loss.

Speaking for those who have suggested on occasion that Peterson ain’t half bad, it took less than one rising sun for the cyber pitchforks to arrive at the pillow. And away we go with what likely will be a popular offseason story line. Again.

Peterson is bad for the offense and the team, they said. He can’t be trusted with the ball, they said. He’s stunting Teddy Bridgewater’s growth, they said. And, of course, Peterson must be cut or traded because he’s making too much money, they said.

In a strange sort of way, this is good news to Peterson’s teammates.

“I think Adrian has shown that he thrives on doubt,” fullback Zach Line said. “So the more people who doubt him, I think the better off we’ll be next year when he’s 31.”

Peterson won his third rushing title, had six 100-yard games, one 200-yard game, started all 17 games and heads into the offseason healthy and in need of no cleanup surgeries. His track record for preparing his body and staying motivated at the highest level is unchallengeable.

As for the salary cap, there’s room for Peterson’s $11 million hit. Bridgewater is in his rookie contract, so his cap number is only $1.8 million. Plus, clearing space won’t be hard when you consider the team can unload Mike Wallace’s team-high $11.5 million number without any cap hit.

In other words, enjoy what the Vikings have — a standout defense, a young quarterback they can build around and a great running back who defies all age limitations. And hold tight as coach Mike Zimmer and General Manager Rick Spielman presumably shift their focus from defense to an offense in need of fortification on the line and at receiver.

Vikings fans also should appreciate Peterson’s work ethic. He left Winter Park on Monday vowing to return not only as a better player, but a better fit for Norv Turner’s offense.

But first, he vowed to do something about the fumbling. Sunday’s fumble was his ninth of the season and the fourth he’s lost.

“That’s going to be my number one objective going into this offseason,” he said. “Because you take things for granted — I’ve joked around and said, ‘Yeah I done put the ball on the turf, but how many have I lost? There’s guys that have lost more fumbles than me this year.’ But when it comes back and it bites you in this type of way, it’s something I want to put an emphasis on for this offseason.”

As for being a better fit for the offense, Peterson realizes he has to grow in order to play more on third downs.

“Just being more versatile,” he said. “You look at the young guys, Jerick [McKinnon], he comes in a lot on third down and he presents a different piece to our offense, running routes and things like that. I envision myself doing things like that at a different level.”

And, of course, Peterson set goals of winning a fourth rushing title, the NFC’s No. 1 seed and playing in the Super Bowl in his hometown of Houston.

“It’s definitely realistic,” Peterson said. “I feel the sky’s the limit for us. I think our chances are as good as anyone’s.”

The Vikings haven’t been to the Super Bowl since the 1976 season. And only one 31-year-old running back — Curtis Martin in 2004 — ever has won an NFL rushing title.

“But he’s Adrian,” safety Antone Exum said. “He’s one of those guys who has a strong enough will that if he says something is going to happen, you don’t bet against it.”