I'm a personal trainer for stars like Harry Styles and Britney Spears. Here's how I found my niche and built my A-list client base from scratch.

© Magnus Lygdbäck Magnus Lygdbäck, right, and Lygdbäck with Gal Gadot training in London for "Wonder Woman 1984." Magnus Lygdbäck

Magnus Lygdbäck, a personal trainer, found a niche in training entertainers such as pro athletes.

Lygdbäck was introduced to Alexander Skarsgård, his first Hollywood client, by a friend in Sweden.

While he loves working with stars like Gal Gadot and Harry Styles, the long months on set are hard.

I've been in the sporting world from as early as I can remember. When I was just 3, my dad would take me to the gym. I played for an elite hockey team as a teenager in Sweden. Becoming a personal trainer felt like a natural progression.

At 21, I became a certified personal trainer and slowly built up my client base in Stockholm.

Now, I train Hollywood actors such as James McAvoy, Gal Gadot, and Alexander Skarsgård and singers including Harry Styles and Britney Spears. 

I worked for free a lot in the beginning 

I started as a young, unknown trainer working many free hours and saying yes to everything. Unfortunately, that's the nature of the industry.

I slowly built up my client list with successful athletes, entrepreneurs, actors, and artists in Sweden. 

My first high-profile client was Sweden's answer to Jane Fonda – a trainer known for her fitness videos. 

While it was luck that we connected, I made my luck in a way. I was very aware certain gyms had more-high-profile clientele, so I would work out in those gyms where I would meet these kinds of people.

I naturally gravitated toward very ambitious, successful people because I was ambitious myself. 

I found a niche in helping celebrities prepare for tours

When I started working with performers in Sweden, I realized that no one saw them as athletes.

I created a program to help performers focus on tailored movements and breathing. I would analyze everything involved in a performer's show — song lengths, dance moves — and created a perfect training plan so they'd be able to execute it.

My first musician client was E-Type, a European pop star. I happened to be working the day he walked into the gym, and the owner thought we'd be a good fit.

Working in this niche, I scaled my offering from trainer to celebrity life coach 

I specialized in this kind of training in Sweden in the early 2000s. I would travel with the artists and realized I trained them for only an hour a day in the gym. The rest of their lives were chaotic and could be unhealthy.

As a result, I became a "lifestyle" coach in 2008 to help artists with structure and healthy habits.

I give advice on things such as their performances at night. I suggest when they should wake up, what they should eat for breakfast, that they do mental and physical preshow warm-ups, and how to decompress afterward.

Being an entertainer is an extremely challenging job. I couldn't do it, and I'm a structured, stable man who lives a healthy lifestyle.

Networking and luck got me my first gig in Hollywood

I'd worked with only small Swedish actors until I was connected with Skarsgård for "The Legend of Tarzan" in 2014.

We had a couple of mutual friends in Sweden, and I'd worked with some artists he knew. It was pure luck that I got to sit down with him to discuss the film. He introduced me to the director, David Yates. We hit it off and I got the gig. 

When Ben Affleck saw "Tarzan," he wanted to hire me as his trainer for playing Batman in "Justice League." My Hollywood career snowballed from there.

A big part of my success in Hollywood is reputation and networking. I've now worked with some of the biggest names in music, from Styles to Spears.

  What my schedule is like working with superstars

Sometimes I work with multiple clients at a time — in one day, I've worked with Eric Prydz, Kendrick Lamar, and Baby Keem. But for intense film training, I can spend months training one client six days a week.

I'm involved in a film really early in production, before most of the other characters are cast. It's just me and the main character I'm training.

The average actor takes three to six months to train for a movie; then shooting takes four to six months. I travel out with them and help out on set for the shooting period.

Unfortunately, when you go full time with an actor, you will lose some of the clients you have back home. I have a small team who trains my clients while I'm away, but some clients leave.

It can be difficult to be away from your life, your family, your house, and your bed for such a long time. You put everything on hold to go with one person to a location.

What I do on set 

During filming, I'm in charge of the whole physicality of that person.

Once filming starts, I travel with the actor, hire them a chef, create their daily menu, and ensure they're eating right. I help with movement coaching. I'll teach an actor how to look like a boxer, how to highlight certain muscles, or how to express a certain physical emotion.

When I trained McAvoy as The Beast in "Glass," I'd stand off-screen and give feedback like: "Your traps are popping," or, "You look really animalistic when you do this thing."

With Skarsgård in "The Northman," his character had to swing a sword and an ax, so we worked on ensuring he had flexibility and mobility in his shoulders for those stunts.

Diversifying my fitness business 

I have so many plans. I'm starting a nutrition-coach app and launching my own line of supplements, and I continue to work with musicians and actors.

I've been working on the new Michael Jackson movie, helping Michael Jackson's nephew Jaafar Jackson. I'm also going on a summer festival tour with Lamar. There's plenty to do.

I've been blessed to be around successful people who are the best at what they do. I love training people with so much ambition — whether they're a CEO or rap star.