Cordarrelle Patterson spent four long weeks of the biggest offseason of his young career at the beach. But it’s definitely not what you have in mind.

The third-year wide receiver traveled to San Francisco this winter to work out with the mystery man “Men’s Health” magazine once dubbed “Hell’s trainer.” Patterson believes he returned to Minnesota last month much stronger, and not just physically.

Patterson wasn’t thinking about the sun, sand or mild California weather on that first day on the beach back in late February. Out of breath and his hamstrings burning after just 14 minutes of running hills and doing sprints in the sand, Patterson was completely gassed when the trainer, Frank Matrisciano, told him his first workout was already done.

“It was only 14 minutes, but it felt like an hour and a half,” Patterson said last week. “The first time I got there, it was the hardest thing I ever went through — not in life, but working out-wise. It was hard mentally. You’ve got to set your mind aside, because you’re going there to the good weather and hills.”

Many have bailed after that initial trial run, Matrisciano says. But Patterson stuck around. He participated in the grueling two-a-day workouts for a week, running over sand dunes with a weighted vest strapped to his chest, sprinting up steep staircases on the cliffs, doing pullups on a jungle gym at a playground until his arms ached.

Patterson then worked out in Los Angeles with quarterback Teddy Bridgewater and other Vikings teammates. He returned to San Francisco for three more weeks of workouts with Matrisciano, gradually ramping up what his body could handle.

“When he first got here, like anyone else, he was taken aback by it a little bit. But he adapted to it and gradually worked into it,” Matrisciano said. “He did a great job.”

‘It will make me or break me’

Patterson, an All-Pro kickoff returner as a rookie who scored nine touchdowns as a receiver, runner and returner that season, decided he needed to do something drastic after his lost second season. Patterson was hyped as a breakout candidate in 2014, but he struggled in coordinator Norv Turner’s offense and was benched in November.

Humbled and hungry, Patterson wanted to do his own thing this offseason instead of training with his teammates. After getting a recommendation from Timberwolves forward Shabazz Muhammad, who survived Matrisciano’s program last summer and then thrived this past season, Patterson reached out to Matrisciano.

“I feel like this year is going to be the year. It will make me or break me,” Patterson said. “This whole offseason, I spent a lot of time just thinking to myself, ‘How can I get better?’”

Making a name in conditioning

Matrisciano, the one-time University of Memphis basketball team’s strength and conditioning coach, is a rogue figure in the billion-dollar fitness industry. He doesn’t own a gym. He doesn’t recruit, so no website, either. Getting his phone number isn’t easy. And if you actually come out to San Francisco, he isn’t going to beg you to stay.

He has been profiled by many publications, but he has refused to be photographed, either turning his back on the camera or wearing what looks like a ninja mask.

Matrisciano has trained everyone from boxers and triathletes to SWAT teams and special ops military personnel. But he is probably best known for his work with NBA All-Stars Blake Griffin and Zach Randolph, helping to take those two to the next level on the hard court by breaking them down and then building them back up in the soft sand.

A tough taskmaster, and he knows it

The New Jersey native uses unprintable words when talking about the bench press and popular weight machines. His unique program, which he calls “Chameleon Training,” is centered on the great outdoors, hard work and his imagination. Every day is different, with Matrisciano presenting athletes new obstacles on a whim.

“My easy stuff is someone else’s hard stuff,” he said. “That’s not me saying it. It’s the guys saying it. They are like, ‘What the hell?’ And I’m being nice about the language.”

Sprint there! Climb that! Now go jump rope! As Patterson put it, “You’re never stopping.”

But over his four weeks with Matrisciano, Patterson toughened up while stacking workout on top of workout. By the time he left San Francisco to arrive early for the Vikings’ voluntary offseason workout program in April, his sessions with Matrisciano lasted upward of 50 minutes.

“Night and day,” Matrisciano said. “For him to come back after what he did here in the beginning, it shows me a lot. He wants to get better and better.”

Hoping for more production

The Vikings are cautiously optimistic about the work that Patterson has put in, which includes football-oriented workouts with a former NFL wide receiver whose identity neither the Vikings or Patterson will reveal. They are pleased the 24-year-old took the initiative to hook up with Matrisciano.

“Rick Spielman said he was going to try to go out there. I don’t know how long that’s going to last,” Patterson said, finally flashing his grin again. “I think he’ll be done in two minutes.”

While other players might be making plans to chill out on a beach somewhere this summer, Patterson intends to spend another four weeks in San Francisco with Matrisciano between the end of the team’s workout program in June and the start of training camp in late July.

“I feel like everything he is doing is going to help me with my game,” Patterson said. “Working out with him helped me mentally and physically. I can’t wait to get back.”