If the actor Craig Bierko looks slightly nervous, it’s perhaps understandable. Right now, the PA system in the cavernous Maple Leaf Gardens in Toronto is blasting out Elvis Costello’s I Can’t Stand Up for Falling Down and that can only mean one thing: Russell Crowe is on his way into the boxing ring. For the next eight or nine hours, Bierko will exchange blows with Crowe as they recreate, as faithfully as possible, the bruising 15-round battle between world heavyweight champion Max Baer and rank outsider James J. Braddock – who was nicknamed Cinderella Man by the great New York writer and sports reporter Damon Runyon. Mostly those blows are meant to miss. Often they don’t.

“You are aiming to miss, you are aiming for it to be a stunt, but because of the speed you work, now and then you will connect, and with some angles you can’t get away with not connecting,” says Crowe. “It’s all about making it look real. And sometimes it is real.” Each morning, after Crowe has warmed up in his changing room deep in the bowels of this former hockey venue (doubling as Madison Square Garden) and listened to stories from Muhammad Ali’s entertaining former trainer, on-set adviser Angelo Dundee, he selects a song to put on the sound system and get him in the mood. And then he heads off down the corridors and into the auditorium.

So far, his hit list has included Under Pressure by David Bowie and Queen, Frankie Goes to Hollywood’s version of Born to Run and Cold Hard Bitch by Jet, revealing not only catholic tastes but also a mischievous sense of humour. And perhaps some mind games, too.

Crowe and Bierko have not exactly become bosom buddies during this long shoot, and maybe that’s what Crowe wants. The Baer/Braddock fight is the climax of Cinderella Man and the authenticity of the sequence is crucial to the success of the film, which tells the remarkable true story of Braddock’s Depression-era comeback against all the odds. If there’s a whiff of genuine animosity in the air, it might hurt the players now and again, but certainly not the film.

“Russell has a very intense way of working, so by design he kind of separated us,” says Bierko. “I didn’t deal with him at all until we stepped into the ring together. It’s as close to a real fight as possible, given that we are not really trying to kill each other. When we started on the first round, we were pasting each other pretty good.”

Boxing movies have made reputations in the past – from Rocky, which turned Sylvester Stallone into a star, to Raging Bull, which confirmed Martin Scorsese as one of the very best directors, and more recently, Clint Eastwood’s Oscar-winning Million Dollar Baby. Cinderella Man’s director, Ron Howard, has a lot to live up to.

The 250 or so extras gathered at ringside, all dressed as mid-Thirties New Yorkers, sense the fun is about to start. For the past half-hour they have lounged around amid thousands of plastic dummies dotted throughout the arena (a rather spooky but surprisingly convincing rent-a-crowd), drinking coffee and reading the papers. Now that Crowe has arrived there’s an expectant buzz: it’s fight time.

Crowe disrobes to reveal a body that, once again, he has radically altered for a role. For his last film, playing the beefy Captain Jack Aubrey in the Napoleonic sea saga Master and Commander, he was 228lb. Now he’s down to a chiselled 178lb. “The basic principle is energy in and energy out, count the calories and do the miles,” he says, which hardly captures the months of painful training he endured. At its peak, he would start the day with a 3km walk, followed by a 1km run on the sand of Sydney’s beautiful beaches, then into a skipping and stretching “warm-up”, followed by 15 minutes of shadow-boxing, on to the speed bag, pad work and then a further session of stretching and stomach work. That would be followed by another walk, this time 6km. This was supplemented by burning up endless miles on the bicycle, swimming and, of course, countless rounds of sparring in the ring. Plus the extra games he invented, just to keep things interesting – like a wood-chopping contest.

“Not just any old wood chopping,” he protests. “It was the double-handed saw world championship. And do you know who won? Yep, that’s right. Me and a mate. And we beat two Olympic boxers at the highest level of fitness into second place.”

There must have been one or two nervous film studio executives who worried that Crowe wouldn’t make fighting weight. Crowe says he knew that everything was riding on him being in shape.

“I said to Ron at the beginning, ‘There’s only one thing that could screw this up and that’s if I don’t achieve it physically.’” But the fact that there were those who doubted he’d do it would have spurred him on even more. No one should underestimate his competitive nature. “I need a high level of motivation,” he smiles. “I’m a very old combustion engine – you need to give me a good kick to get me going. But once I’m going, I’ll go for ever.”

He relishes the physical transformation, which he has done plenty of times before, piling on the pounds to play a paunchy tobacco executive 15 years his senior in The Insider, then turning it into muscle for Gladiator, dropping down again for A Beautiful Mind and going up for Master and Commander.

The cost of pushing himself to the physical limits has been a high one. He’s suffered numerous injuries on film sets over the years, and Cinderella Man had to be postponed after he dislocated his shoulder sparring in a Sydney gym.

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