Jennifer Garner "wasn't Marvel fit" when she signed up for 'Deadpool and Wolverine'.

© Jennifer Garner/Instagram

© Jennifer Garner/Instagram

The 52-year-old actress - who ahs Violet, 18, Seraphina, 15 and Samuel, 12, with her ex-husband Ben Affleck - played Elektra in the superhero films 'Daredevil' and 'Elektra' in the early 2000s but when Ryan Renolds asked her to return to the role for the new film, she admitted that she had a lot of work to do physically before she could play the role.

She wrote on Instagram: "We were on the set of ‘The Adam Project,’ and they gave each other this look they have that can communicate an idea, 20 pages of dialogue, nuclear codes — there is a crazy artistic kismet between those two.

"Other than trying to convince my kids’ preschool buddies that I was secretly a ninja, I hadn’t picked up Elektra’s sais since 2004; I was fit, but not Marvel fit."

The '13 Going On 30' star then undertook a series of intense exercise regimes to be at the top of her game for making the movie and detailed the routine further in her caption.

She said: "As this impossible dream became reality, my bestie and OG stunt double @shaunaduggins and I amped up our training, led by @bethjnicely at @thelimitfit: 1x/day, plus whatever homework she assigned for a second workout. Boxing 3x/ week with @flvcothefuture from @matchroomxchurchillgym. And lots and lots of @onepeloton’s @becsgentry. We had #SuperHeroSummer over here, twirling sais in the backyard and laughing at our sore old bodies.

"I didn’t know that Elektra and I needed an ending, but Shawn and Ryan did. They are gifted in many ways, but seeing and elevating people around them is at the top of the list. "