Rachel McAdams is packing a punch ringside

Rachel McAdams enjoyed playing Billy's hardened wife Maureen in Southpaw. Photo / Supplied

Rachel McAdams shines as a boxer’s wife, writes Leena Tailor.

Jake Gyllenhaal's transformation may have everyone talking and Oscar buzz building, but his co-star Rachel McAdams was perhaps most blown away by the actor's rapid reinvention as fighter Billy Hope for boxing drama Southpaw.

The Canadian actor plays Maureen, wife of reigning boxing champ Billy, and was completely taken aback when she witnessed Gyllenhaal after his brutally intensive training programme.

"I saw him when he first started training and he had long hair, a big bushy beard and didn't look like a boxer, then three months later I showed up on set and there he was, a completely transformed person - it caught me off-guard," recalls McAdams, 36.

"He was giving everything he had every day and I just didn't know how long he could last. I didn't know how a person could keep that up.

"A boxer trains however many months - years sometimes - to maybe go 12 rounds, and he was going 35/40 rounds every time because we'd have to do it over and over again, five days a week. I don't know how Jake got as proficient as he did. He's a wildly talented guy, but it just doesn't happen overnight and he did it somehow. It's miraculous and I marvel at it."

The role was initially written for hip-hop artist Eminem, but after he decided to focus on his music, director Antoine Fuqua approached Gyllenhaal.

He trained with three-time Golden Glove champion Terry Claybon for six hours daily in the months leading up to the film, which follows Billy as he takes on the biggest match of his life after a family tragedy.

When the time came to call "action", hits were taken and blood was shed but Gyllenhaal and on-screen opponent Victor Ortiz knew that to reach a level of authenticity which would make Southpaw a boxing film unlike any other, they would have to get hurt.

"We had to give each other the permission to do that," says Gyllenhaal, 34. "When fighters walk into a ring - and ironically when two actors playing fighters walk into a ring - you have to remember that you decided to be there and that means you're going to get hit. We both said, 'Things are going to happen and you've got to keep going. If you knock me out, stay in character because it'll be great for the movie'!"

Rachel McAdams and Jake Gyllenhaal in Southpaw. Photo / Supplied

Gyllenhaal was able to train at Floyd Mayweather's gym and spent countless hours hanging out with fighters but McAdams found little to draw on when it came to the lives of boxers' families.

Wanting a full understanding of the sport, she too spent time with Claybon.

"There's not a lot out there about the wives and families of boxers - it's more focused on the boxers themselves, so it was amazing education learning what sacrifices they make and the fear and anxiety underneath," she tells Living.

"I've gained an incredible respect for the sport. I had no idea how difficult it was - especially when I tried boxing myself. I loved it, still do it and it's such a great workout, but incredibly difficult."

Adds Claybon: "Rachel wanted to feel and understand what a fighter goes through. She was taking boxing with me, so she could get gutted out, per se, and get a real feel of what it takes to be a fighter.

"When she says, 'You're taking too many punches,' she actually understands that because she was around it so much."

The fight scenes were shot in the same style and by the same cameramen as real HBO boxing fights and the cast also attended a Cotto vs Martinez match at Madison Square Garden.

Although her character barely flinches as her husband gets bloody and beaten, McAdams had white knuckles witnessing that first match but enjoyed the challenge of playing such a hardened woman.

"I reacted very differently than Maureen would have, so it was interesting to get into that part where she doesn't even flinch. I had to put away my feelings and the fact that I would have been cringing like I was at the first fight I went to.

"She's been watching him fight for 20-odd years, so it was fun to play that toughness - you have to have a thick skin to be married to a boxer."

Rachel McAdams in Southpaw. Photo / Supplied

Playing the role of Billy's friend and manager Jordan is Curtis Jackson (aka 50 Cent). The hip-hop artist's real-life involvement in boxing promotion became a great asset on-set.

"This is the second time I've worked with 50 which is surreal, but he's lovely," says McAdams. "He's very playful, so brings levity to the set. He had a really good understanding of the world, so he became a good resource.

"And he was recording while we were working, so it was great to watch him bring all his worlds together."

McAdams' own worlds have expanded of late, as the actress transitioned to the small screen in acclaimed television series True Detective.

McAdams was somewhat daunted joining a show which had such high expectations going into its second season but she relished the role of Detective Ani Bezzerides.

"You have to turn the noise off a bit. I fortunately am not on social media so I've been able to live in a black hole, but you still know you're up against something that has an incredible following.

"It's exciting to be part of that and know that people watch and care. And the two seasons are so different, it's almost like starting over and pressing the reset button.

"I felt weirdly comfortable playing her. It's very different for me, but so creatively stimulating and satisfying. Characters like that don't come along every day - we don't see women like that often, which is unfortunate, but I feel very blessed I got to play her."