Jennifer Garner may love to pretend cook, but there's no faking when it comes to her fitness.

For next year's Deadpool 3, the 51-year-old is set to reprise her role as Elektra—the chiseled Marvel assassin antiheroine she first played in 2003's Daredevil before its eponymous standalone in 2005. And picking up the character's iconic twin sais was light work for Garner, who has only gotten stronger in the two decades that have passed, according to her longtime trainer Beth Nicely. 

"She's doing harder and more difficult things than she did 20 years ago," Nicely told E! News in an exclusive interview. "It's cool to train her in this part of her life and to see how someone who is 51 is so badass and stronger than she's ever been. That's really inspiring as a trainer, as a woman. She's the real deal." 

Perhaps unsurprisingly, the woman who kicked literal butt for five seasons as CIA agent Sydney Bristow "just loves to work out," added Nicely, the founder of The Limit Fit. "She is so consistent and that's why she's so strong."

Among the Alias alum's preferred exercises: Arm moves with two-pound wrist weights, dance cardio and box-jumping. Yes, really.

And Nicely credited the plyo-box for taking Garner's fitness to the next level in recent years.

"We started with an 18-inch box and she was like, 'Whoa, okay, my heart rate is up, this is a new thing!' Nicely recalled. "And now she's jumped on a 36-inch box. We think of it as an adult jungle gym in a way, we do a lot of box jumping and agility and coordination training while holding heavy weights on boxes."

While the Broadway performer and NASM-certified trainer admitted "Jennifer Garner's version of hard is definitely an extreme version of hard," Nicely encouraged everyone to choose their own level of difficulty to aspire to if they are short on time during their sessions, which often occur on Zoom. 

"She's so consistent with her workouts and sometimes it doesn't equal an hour," Nicely explained. "She's a mom of three, she runs businesses, she's an actress and she has a very busy schedule. So whatever amount of time I've got with her, we go hard." 

For Garner—who shares kids Violet, 17, Seraphina, 13, and Samuel, 10, with ex-husband Ben Affleck—that means a mix of dance cardio, high intensity interval training (HIIT), strength training and plyometrics, with an additional 45 minutes of cardio as "homework" if she's training for a project, like Deadpool 3. 

But what if, by chance, you're not prepping to play a superhero?

"Depending on your level of condition, I always think go as hard as you can in the amount of time that you've got," encouraged Nicely. "Everyone's level of hard is different, so whatever that means to you."

The key, Nicely stressed, is just moving your body, whether it's a 10-minute video on The Limit Fit's on-demand platform, which Garner uses, or a 30-minute walk, something Nicely is committed to after welcoming her first child, Ella, in August. 

"Don't feel bad if you can't get a full hour or full anything," she said. "Even if you don't have props, it doesn't matter, just do what you can. And then on the days you can take a class, that's wonderful. It's like, 'Yes, luxury! I can go somewhere and take a class for myself.'"

Aside from moving your body every day, Nicely has two other non-negotiables. "Hydrate," she offered first. "Your muscles and everything else will function better when you hydrate."

Nicely's other tip? "Remember to recover," she advised, suggesting foam rolling, massages, stretching and physical therapy as "important" aspects of a well-rounded fitness routine.

"It's one of those things you will notice later," she promised. "If you do it consistently, just a little bit on a daily basis, your body will thank you for it."