James McArdle skips into the National Theatre's interview room looking like an athlete. He is slim, lithe and focused. On the table between us, he sets out his lunch. There's a tub of pasta with Bolognese sauce, fruit porridge desert, and a glass of water. 'I get this same lunch every day, and the same dinner as well,' says the Glasgow-born 30-year-old. 'I'm making sure it's carbs and it's healthy and I'm in bed by a certain time.'

The job he has before him requires a sportsman's stamina. To play the title role in Peer Gynt (rechristened Peter Gynt in a new David Hare translation) takes marathon-levels of energy. He's on stage for most of the four-hour running time and will be clocking up eight performances a week. 'Starting with the very first scene and knowing where I end up, I have to take a deep breath,' he says, seemingly galvanised by the prospect. 'It takes a tenacity to make sure I get there.'

Written by Henrik Ibsen in 1867, the unwieldy 40-scene verse drama is about a fantasist who flees his family home after kidnapping a bride on her wedding day. On his folkloric journey, he meets trolls, crosses mountains and hangs around with the moneyed set, before ending up back where he started, 50 years older and little the wiser.

It's such an undertaking that when Dundee Rep staged it with the National Theatre of Scotland in 2007, it took two fine actors – Keith Fleming and Gerry Mulgrew – to share the role between them. For this version, it felt right for McArdle to tackle it singlehandedly. 'It's an adventure as big as life,' he says. 'He goes through sex, marriage, love, hatred, ambition, feuds, death – you name it – and by the end of it you feel you've lived a life. There's a catharsis because the audience has gone through it with the one person.'

credit: Manuel Harlan

Like any good athlete, he's been building up strength bout by bout. Peter Gynt follows such premier-league roles as King James I of Scotland in the first of Rona Munro's trilogy of James Plays; Louis Ironson in Tony Kushner's epic Angels in America (for which he was nominated for an Olivier Award); and the title part in Chekhov's Platonov in Chichester. 'Those roles trained me up for this one,' he agrees. 'It's realistic and emotionally engaged, it gets really sad, it also has to be really funny, and it has a showman quality to it. I'm like the host of the evening because there's so much direct address.'

It was in 2015's Platonov that the seeds of Peter Gynt were sown. Bringing together McArdle with playwright Hare and director Jonathan Kent, it set the template for the collaboration to come. 'Platonov is a difficult, unyielding play that required a real collaboration between actor, writer and director,' he says. 'After it finished, the three of us felt that if we wanted to continue to take on these beasts, then the natural progression was Peer Gynt. Because we'd done Platonov together, David knew my rhythms. It was eerie when I read the first draft because he can hear me. David's sentences are long and there is often an A track and a B track within the one sentence, and it requires a real muscularity to get through them.'

Coaching him through this theatrical workout is Kent, for the fifth time they have collaborated. 'I would walk the earth to work for Jonathan,' he says. 'I get better working with him and learn more about the craft of acting. He's building me up to play bigger parts and to learn how to lead an evening. I feel very lucky to have access to such experience.'

But there's more to McArdle's ambition than a vainglorious bid to take on formidable roles. He's had his sights on Peer Gynt for years, but he's a political animal and hates the idea of doing classics for the sake of it. 'There has to be a reason to do a play. Recently, people have been asking me if I'd like to play these big parts that actors are supposed to do and the reason I've said no to some of them is "why? Why are you doing it?" Peter Gynt has such a reason: it's about fooling yourself, fake news, identity and being obsessed with the self.'

credit: Manuel Harlan

Resonating with the era of social media and #MeToo, Hare's modernised version is performed by a predominantly Scottish cast and set in Dunoon. They reckon this decent-sized town with convenient access to the Highlands and the big city is not a bad match for Ibsen's Norway. It also happens to be where McArdle's uncle has a pub, so a cast reccy is on the cards.

He reckons Peer Gynt adapts well to a self-regarding age where the line between fact and fiction is fuzzy. 'The play was extremely satirical, political and modern in its time. Now the narcissism and chauvinism of Peter feels so vital. You see that destructive force undo him and undo the world around him. That is so relevant, as is the idea of creating narratives about ourselves, creating ourselves as icons. It's embarrassing and it's how Peter lives his life. David is bringing Ibsen out of the dust and into high-def. It's brimming with wit, humour, fun and life. It's a play for how we live now.'

So is Peter Gynt his bid for Olympic gold or merely a staging post on his way to some even greater triathlon triumph? 'It'll be interesting to see what parts I get offered after this,' he says, admitting to having a sizeable role on the cards in two years' time. 'There are two big classical parts that keep coming back and I think if one of them is meant to be, it'll come with full force and a distinct sense of why I should do it. I don't have a checklist. It's got to come with a reason to do it.'

Peter Gynt, Festival Theatre, Nicolson Street, 3–9 Aug (not 5), 7pm, 4, 7, 9 & 10 Aug, 12.30pm, £15–£38. Previews 1 & 2 Aug, 7pm, £10–£35.