When it comes to training for Hollywood blockbusters, nothing is off limits.

Just ask Michael Fassbender who revealed he's been using a bikini body challenge program to get in shape for the latest X-Men film, reports news.com.au.

In an interview on The Project, Fassbender, who plays Magneto in X-Men: Dark Phoenix, explained he didn't do many stunts in the film other than the wire work.

"Although I do have to say, I've been using this app which is an Australian woman … Kayla Itsines," he said.

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"It started off as the bikini body app and now it's called the sweat app," he said, turning to co-star James McAvoy.

Fassbender, who plays Magneto in the film, says while he isn't too sure if many men use the app, they should. Photo / Supplied
Fassbender, who plays Magneto in the film, says while he isn't too sure if many men use the app, they should. Photo / Supplied

However, news.com.au can confirm the Sweat app is not in any way affiliated with the Bikini Body Challenge.

The 42-year-old, who stars in the film alongside Jessica Chastain and Sophie Turner, added although he wasn't too sure how many men used the app, he would love to see more blokes download it.

"I do and I'm saying other men should too!" he said.

Itsines, who recently gave birth to her first child Arna Leia Pearce, is the founder of the Bikini Body Guide and co-founded the Sweat app with her fiance Tobi Pearce.

While there's nothing saying men can't be part of the "Kayla Army", their target is mainly woman, particularly those aged between 20 and 35 years of age.

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It's just that time of year when the weather is changing and EVERYONE around me is SICK 😷 (even Tobi so he is on STRICT instruction to stay far away from me and muffin haha). If you have been recently sick or injured, getting back into your routine can feel intimidating. Often after taking time off due to illness, you can lose drive and motivation. It can be hard to even know where to begin! Here are my top tips to help you bounce back to your routine: ⁣ ⁣ ✅Don't beat yourself up - I say this SO often. But if you are unwell or injured it's important to listen to your body and take the time you need to heal before getting back in the gym. Instead of feeling guilty, try to focus on excitement to get back to the gym when you are HEALTHY. ⁣ ⁣ ✅Take it slow - Don't rush. Start off with light or MODIFIED versions of your usual workouts and gradually increase your weights/intensity.⁣ ⁣ ✅Be prepared - Make a plan. Knowing what you need to do will make things SO much easier. Start by writing down how many days a week you want to exercise. I like to write down one or two days extra because if something comes up and I get busy, I can relax in the fact that I’ll still be able to fit all my sessions in. ⁣ ⁣ ✅Start fresh - One of my BIGGEST tips when it comes to motivation is finding something that you actually enjoy doing. If you hate running (like me!), don't run. Finding a type of exercise which you genuinely love, will help you to achieve MAXIMUM results and you will be less likely to quit!⁣ ⁣ ✅Find your motivation - One of the best ways to stay motivated/get motivated is to include fitness as a part of your regular routine. For example, we don't always WANT to wash our hair but we know it needs to be done and we will FEEL better if we do. Try thinking of your exercise regime in the same way. ⁣ ⁣ ✅Light workouts - The best exercises to do when first jumping back into routine are ones that focus on flexibility and light cardio. This will get your blood circulating and help your joints get back into the swing of things. My favourites include stretches, yoga and light walking/jogging depending on your fitness level ✅ www.kaylaitsines.com/app

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In 2014, the Adelaide-based couple created the 12-week Bikini Body Guide fitness program. Itsines, also a personal trainer, published before and after photos of her clients on her Instagram profile, which ended up gathering a huge fanbase that dubbed itself "Kayla's Army" and was a phenomenal success for the couple.

Pearce helped create the company 'Sweat', publishing e-books and an app under the same name on which fitness trainers (including Itsines) host various fitness programs.

Both Kayla and Tobi have a combined wealth of $486 million.

Last year Kayla came fifth in the Financial Review's Young Rich List.