Look around the Vikings’ practice fields in late July and you’ll notice quite the number of muscle-bound billboards for personal trainers from Knoxville to Houston, Maryland to Minnesota and other corners of the country.

Chiseled defensive end Danielle Hunter swears by James Cooper of Houston’s O Athletik Club. Receiver Stefon Diggs salutes his guy, Myron Flowers of Washington, D.C., by saying, “You see what I do in the offseason. You got my Instagram.”

Meanwhile, receiver Adam Thielen’s rags-to-riches story heads into its seventh NFL season and seventh year with personal trainer and now business partner Ryan Englebert, founder and president of ETS Sports Performance Gyms in the Twin Cities.

“It’s really hard” picking a personal trainer, Thielen said. “There are so many guys out there … getting creative and doing a lot of different things. [Englebert] was the guy I felt was a good fit. And once I started working out with him, I knew it was the perfect fit.”

Picking a trainer wasn’t hard for safety Harrison Smith coming out of Notre Dame as a first-round draft pick in 2012.

“I’ve had the same trainer since eighth grade — Charles Petrone in Knoxville,” said Smith, who went to Knoxville Catholic High School.

Former Vikings offensive lineman Tim Irwin was Smith’s eighth-grade football coach. And a believer in Petrone’s Wood Gym.

“Tim knew I was like a decent little football player,” Smith said. “So he sent me to Petrone.”

Coming out of college, Smith gave all prospective agents one nonnegotiable deal-breaker.

“The ones who said they had a trainer they’d send me to, I told them things just wouldn’t work out,” Smith said. “I told them I’m training with Petrone. Period.”

So how do the Vikings and their strength coach, Mark Uyeyama, monitor all the different personal trainers and encourage players not to stray too far from the team’s training principles while working out on their own time?

“That’s a good question,” coach Mike Zimmer said. “It is hard with the way CBA rules are now and guys being away and everyone having their own gurus to do what they want to do.

“Obviously, we prefer to have them [working out] here, but Mark Uyeyama does a great job with them. He communicates with their guys all the time.”

Players overtraining on their own is Zimmer’s biggest concern during the offseason and on off days during the season.

“And we’ve had that before,” Zimmer said. “Guys think they need to have 15 modalities going on here during the week and it really hurts them more than helps them.”

That’s where trust in a personal trainer is vital, Thielen said. Even as Englebert changes Thielen’s workouts, Thielen knows he’s not being overtrained because, well, the on-field results always speak for themselves.

“I just go out there and do the things he says,” Thielen said. “When I get to the field, I can see those things translate.”

Smith said Uyeyama knows his personal training routines and “makes sure I’m not doing anything stupid.” Still, there are some “Olympic-type lifts” Smith said he does in Knoxville that the Vikings don’t want him doing at team headquarters.

“I do more crazy stuff when I’m at Petrone’s,” Smith said. “It kind of keeps my edge a little bit. But if the Vikings don’t want me doing it when I’m here, I won’t do it.”

Asked if he has total freedom to do whatever workout he wanted on his own time, Smith said, “within reason.”

Several players stand out as guys who came to camp in ideal condition. None more so than Hunter (duh!), Diggs, Smith and the ever-evolving Thielen, who’s looking even more explosive and quick into and out of his cuts as his 29th birthday (Aug. 22) closes in.

“Ryan does a great job of switching things up,” building on what has worked and eliminating what hasn’t, Thielen said. “I have the same routine, the same mind-set. But I leave [the details] up to him as to how he wants to train me for the season.”


Mark Craig is an NFL and Vikings Insider. Twitter: @markcraigNFL. E-mail: mcraig@startribune.com