But then this is John Irving, a man who, despite being best known for publishing The World According To Garp and The Cider House Rules – having sold more than 12 million books in 35 languages – is also a former wrestler and inductee into the US National Wrestling Hall of Fame.
So when Irving lies on a mat to do stomach crunches, while I bounce next to him on a gym ball to a soundtrack of J.Lo in the background, I can see he's as comfortable talking here, in the fitness suite of Edinburgh's Balmoral Hotel, as he would be at his desk back home in Vermont. I, on the other hand, am facing a challenge in dexterity, though Irving is keen to make sure I'm comfortable.
Irving, at 70 and dressed in an Adidas tracksuit, is in good shape. Not once during the course of our workout/chat – about his latest novel, In One Person – does he break a sweat. It's only later when we discuss politics that Irving's heart rate seems to creep above calm.
But this, his 13th novel to date, is unavoidably political. A story of sexual identity spanning over 50 years, it follows the life and loves of Billy Abbott, the novel's bisexual narrator, and features a wider cast of characters that defy convention. Its publication comes during an election year in America, when gay rights issues remain a hot topic; when Mitt Romney, the Republican candidate – one of the "dinosaurs," as Irving calls them – has changed his stance on the issue more times than the cross-dressing grandfather in the new novel has changed his frocks.
But the novel is timely in a way that is pure coincidence, says Irving, who had the plot fleshed out over a decade ago. He was also unaware at that time that his youngest son, Everett, now 20, would come out as gay. But when he finally put pen to paper – in June 2009 – he knew.
"I thought he was already handling it exceedingly well, but I can't tell you how lucky I felt for having the knowledge that I had a gay son as I was beginning to write this book. It was a gift. I was proud of him. You can't plan coincidences like that. I thought, 'I don't know who's going to like this book – but I know one person that will.' And that was a great thing to know," he smiles.
It was important to Irving that Everett read this story while he was still young. But in true Irving fashion, he couldn't rush the writing process; he had to wait for just the right ending to come to him. Luckily, it did. "I thought, if there's anything in this book that is positive and gives Everett some confidence to be who he is, wouldn't it be great if he could read it while it might possibly be of some use."
Everett read the book almost a year before publication and loved it. Irving recalls how he would read parts out loud to him when he was home from university. Irving is clearly a devoted father. "I think my kids like me," he says sheepishly. "They said very nice things about me on my 70th birthday."
Is he a protective father? He stops mid stomach crunch (he's gone back to the mat), turns to me, raises his eyebrows and says, "What do you think?" I nod. "Neurotically so," he admits, smiling. "If you had any one of my kids here and asked me that, they'd kick the ball out from under you and laugh."
Irving was only 22 when he had his first son, Colin. His second son is Brendan. Both are in their 40s, with children of their own. "The fear of something happening to someone you love is a big part of most of my books. I certainly got that more from being a father."
It's been reported that Irving and his second wife, Janet, won't fly on the same plane if they're not travelling with Everett.
In many ways, the "what ifs" from Irving's own past allow him to not only empathise with Everett's sexuality, but to relate to the novel's main character, Billy Abbot.
"I don't think I was unique among boys of my generation – especially who grew up in a small town and went to an all boys school – for the fact that in my pre and early teens, I was sexually attracted to just about everyone – my friends' mothers, some girls, frighteningly, the occasional older boy on the wrestling team. I never acted upon most of those attractions but I've not forgotten that period when I was ashamed of my sexual fantasies."
In writing, all Irving had to do was imagine those fantasies had come to fruition. "Frankly it's less of a stretch for me to think of a guy who wants to have sex with men, women and transgender women, than it is for me to get my imagination around someone who doesn't have sex at all," he laughs, referring to some of his previous characters.
Irving turns serious when we talk politics. Regarding Barack Obama's recent announcement in favour of gay marriage, he says, the president had to do it. "It would've looked very cynical to the LGBT [lesbian, gay, bisexual, transgender] community if he hadn't had the courage to come out until after the election. He needed to hear some really horrible comments from all those republican candidates – and he did."
It's not a coincidence, says Irving, that the people who are most against abortion rights are the same people who stand entrenched against gay rights issues.
"It's the same attitude that said during the AIDS crisis that these young men had brought it on themselves; that they had somehow deserved it because of their incorrect behaviour."
Nevertheless, Irving believes these people are a minority. "I hope that isn't false optimism. They are of a desperate mindset – they see their 'family values' being traduced, although they have a very narrow definition of family. It irritates me that they use the family word as if they own it."
Perhaps the most challenging part of In One Person covers the AIDS epidemic of the Eighties. The details are acute. Irving himself watched friends die of the disease, including his close friend, the English director Tony Richardson, who passed away in LA in 1991. "Along with Everett, Tony would've loved this book. It's dedicated to him," says Irving.
Among the support for the novel, there have also been negative reactions – but none that's surprised him. "My political novels have all had among my best reviews and among my worst. When you pick a side, when you are an advocate for someone or something, you're going to alienate people who oppose that. They say, 'This book is a platform, a soapbox.'"
There's another "small minority complaint," explains Irving. "I always expected that there would be some gay men among my negative reviewers, who basically take a territorial ownership of the AIDS epidemic. I say, 'Are my friends who died of AIDS any less dead than yours? Or any less dead because I'm straight?' No. I get testy at that. Too many people died to make that subject anybody's one possession. Do we think Sophocles had to pass a test that he came from an incestuous family to write the Oedipus cycle of plays? I don't think so." And with that, the workout is over.
In One Person is out now in hardback by Doubleday, priced at £18.99.