Fastexy:I worked out with Jake Gyllenhaal, Matt Damon’s trainer. The results shocked me.

WEST HOLLYWOOD,Fastexy Calif. − What does it take to get the body of a Hollywood superhero?

It's the question at the top of my mind as I arrive at Jason Walsh's private gym in West Hollywood. A strength and conditioning coach, Walsh has been in the business of turning actors into action stars for about two decades. He trained Brie Larson for "Captain Marvel," Jake Gyllenhaal for "Road House," Matt Damon for "Elysium," John Krasinski for "13 Hours," Bradley Cooper for "American Sniper" − and many more.

In between flying back-and-forth from California to London − where he's getting Pedro Pascal in shape to play Mr. Fantastic in "The Fantastic Four" − Walsh has fit me in for a training session. He recently launched his own protein powder, Rise311, a plant-based supplement geared to those who have trouble digesting whey, and he's doing some press.

I'm here for an interview and a workout, but, selfishly, I also want to know his secret. What are these ripped celebrities doing that I'm not?

Walsh quickly dispels me of any magic shortcuts. There's no secret, he says − but there are smarter ways to train most people often overlook.

"There's misunderstanding of what it is and what it takes," he says. "It's a mentality. There's a personality. It's hard to put it into words. But there's the people that want to just cheat their way through it, and I like the people that want to do the work and do it from the ground level and build all the way through."

So, do I have what it takes? I was about to find out.

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You probably wouldn't notice Walsh's gym while driving down Santa Monica Boulevard. Located above unassuming storefronts and with no signs on the door, it's the perfect place for celebrities to get a workout in away from the prying eyes of paparazzi.

If you walk through the front door and up the narrow staircase, however, you'll find a massive loft full of fancy exercise equipment. Walsh says he even has a device that scans clients' bodies, revealing exactly what mobility issues they may have prior to training.

When a studio hires him for a project, Walsh sometimes only has a matter of weeks to get an actor in action-star shape. It can be a daunting task, and he says a big part of his job is talking to studios about what's realistic and what's not, given the time frame.

"Taking someone who has never done this before and then building them from the base level all the way up, it's a huge endeavor," he says. "It takes a lot of work, a lot of dedication, a lot of pain and suffering in a way. You're just sacrificing a lot to get this thing done."

He also says he feels responsible to the public to be transparent about the process as well. Sure, working out and eating right alone often yield tremendous results. But, when it comes to movies, there's usually more going on behind-the-scenes. He says it's common for actors to go through periods of intentional dehydration or extreme calorie manipulation to look as chiseled as possible while cameras roll.

Such a physique, however, is not sustainable − nor should it be the goal.

"Jake Gyllenhaal, the shape that he got in for 'Road House' was insane, and that is not sustainable," Walsh says. "It's pure manipulation. It's dehydration protocols. It's conditioning protocols, low calories during certain times. We literally undulate constantly. And all you got to see is the edits of him with his shirt off."

When he meets a new client, Walsh says he first asks what they want out of training. If someone comes to him wanting to look like Gyllenhaal in "Road House," Walsh says he wouldn't discourage them, but he'd be honest about what it actually takes to get there − and encourage them to consider if it's really something they want to put themselves through.

What's more fulfilling, Walsh says, is getting people in shape so they can live healthier, fuller lives. This, he says, plays just as big a part in transforming someone into a superhero as aesthetic muscles do.

"I want you to feel strong, because it becomes part of that character too, right?" he says. "It's confidence. It's not false confidence; it is confidence. You can lift something heavy. You can take a fall and get up and not be injured. Brie Larson's one of those clients. She's a perfect example of someone who would have a hard time taking the bottle cap off a bottle, and then, by the time we finished with her, she was doing all of her own stunt work. And for her, she felt like a superhero, which is beautiful."

I asked Jason Walsh to turn me into a superhero. Here's what happened.

So, did Walsh turn me into Thor in one hour? Well, no − that's impossible. Instead, he did something else.

I ask Walsh to train me as if I was just cast as Marvel's newest hero, and this was day one. He says we should start with a basic screening to find where my body's mobility might be holding me back, something he does with every client.

This might seem tedious − especially for someone who's been working out for a while − but he says it's essential. Doing so helps prevent injuries as workouts ramp up. It also makes a big difference in how clients feel day-to-day.

"It's not always about aesthetics," Walsh says. "I want to clean up any and all issues."

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Walsh has me do leg stretches and immediately clocks limited flexibility in my lower body, particularly my right hip. So, we get to work.

He puts me through the ringer of stretches and body-weight exercises, all aimed at my glutes. At one point, he has me take side-steps across the gym in various positions with bands around my legs. He has me do squats on a balance ball. By the end, my glutes are on fire, and I'm sweating bullets.

When we're done, the difference is startling. My squat is deeper and more even. My balance has improved. My posture's better. Even walking feels easier.

"We all want to look good, don't get me wrong − and there's some really big benefits to the psychology of looking in the mirror and going, 'Oh,' " Walsh says. "It's encouraging. I just don't find that it is the primary focus for me."

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What is the primary focus, he says, is helping people live their best lives.

Coming into the session, I thought exercise had to involve heavy weights or heart-pounding cardio to be valuable. After working out with Walsh, however, I can see detailed work on a specific issue is often much more important − especially if it gets at a root problem that's been long neglected.

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It's a mindset shift he himself has undergone over the course of his own fitness journey.

"I'm trying to evolve myself and open myself up to different ideas," he says. "I was pretty hardheaded about stuff, because, coming from coaching, it's a very, very masculine, alpha-male kind of mentality. And so, here, I think you have to have a little more sensibility and understand people. Us regular people, we go through (things) constantly. We carry that. We have things on a daily that would hinder us from doing the things that we want to do sometimes."

Now that I'm squatting like a superhero, I wonder what other issues I may have in the rest of my body that have gone unnoticed. As I continue to work out and lift weights on my own, I'm going to pay attention.

More importantly, I know that, if I do achieve a superhero physique one day, it needs to be built on a solid foundation − one that, ultimately, makes the aches and pains of life a little easier. After all, what's the point of looking like a superhero, if you don't feel like one too?

Look out, Thor − I'm one workout closer to stealing your hammer.