I’m riding a bike through a tropical island, then beneath the earth’s crust. It’s mid-morning on a Thursday in Newmarket, central Auckland. The gym world’s new gamble is ‘immersive’ training. A big chunk of the $20m cost of the newest, flashest Les Mills branch was outfitting a new cycle room (in Les Mills speak, the CHAIN studio) with a giant curved screen to accommodate The Trip.

The Trip’s virtual reality bike ride can take you through the streets of San Francisco or across the surface of an alien planet. I’ve never managed to book in, as classes are always over-subscribed. But Phillip Mills - who is departing the next day for the annual Les Mills Europe ‘tribal gathering’ of 600 master trainers and executives in Punto Umbria, southern Spain - rides it with a handful of mates any Thursday he’s in town. He’s told me it’s “mindblowing”, and invites me along to join him and former NZ sprint champion Shane Downey for the ride. Indeed, it’s brilliant fun: like a rollercoaster that makes you forget you’re exercising.

The Trip was co-designed by Phillip’s son, the very private Les Mills Jr (who doesn’t want to talk to me for this story); Les Jr’s sister Diana calls him a “creative genius”.

Ironically, Les Mills Sr isn’t too sure about the concept. “I’m a bit sceptical about how these immersion studios are going to go,” he says, genially. “They are hugely expensive to put together, but what do I know about virtual reality? [Phillip] thinks it will work … and where I do think he is right, he is still trying to be at the cutting edge. If he hits a few losses, it doesn’t matter: you want to be up the front pushing and you have to be prepared to stuff up a few times.”

The Les Mills model is to pick trends, analyse them, and jump in if they think they work. Recently, it’s been high impact intensity training - HiiT - where you basically work as hard as physically possible for 30 seconds. Next on the horizon is more holistic mind-body-spirit type stuff. Group fitness will keep growing: 75 per cent of visits to flashy Newmarket are to classes, against 50 per cent elsewhere.

Phillip’s daughter Diana has ideas about the next big thing after the next big thing. The virtual reality stuff, she says, could lead to gamification. Imagine going for a run, but pursued by a dinosaur?

Phillip Mills talks to BodyCombat trainers after filming; US trainer Marlon Woods is at right. Phillip Mills talks to BodyCombat trainers after filming; US trainer Marlon Woods is at right.

It took Phillip Mills about five years to pay off his debts when he bought the company back. There was the patch where LMI couldn’t pay its way, but for the past decade or so it appears to have been plain sailing. He doesn’t want to talk about what the company, or indeed the family, is worth. “We have enough to be comfortable, we have for a long time,” he says. “We’re not people who want to live a rich person’s lifestyle.” They are more into organic, clean living: Mills is extremely exercised about climate change and green business. There are signs of it everywhere, including above the rubbish bins at HQ, where a diagram shows which types of takeaway coffee cups are recyclable.

The 2017 NBR Rich List puts the family fortune about $210m (68th equal); Mills doesn’t seem to quibble too much with that. Their house, where they’ve lived since 1982, is valued at $11.25m. “Les [Jr] and I have never been poor, never known poverty - I think we have had the remarkable privilege never to have had to worry about it,” says Diana Mills. “So we are not concerned about it: we are not a monetarily-driven family. It was never about accruing wealth for the sake of having things.”

The family trust owns 86 per cent of the New Zealand company and 92 per cent of LMI, the remaining fractions split between long-serving employees and friends. That will all, eventually, pass down to Les Jr and Diana. At 63, Phillip is still lean and athletic, and like all his staff, perpetually clad in gym gear. The second time I interview him, I forget my jacket. He eschews the lift and bounds up and down four flights of stairs to collect it, explaining he’s making up for missing the gym that day. He seems slightly taken aback at the question of succession. He wants to keep going, he says, “for a long while yet”.

But, for the first time, he’s ceded control of gym design, allowing Les Jr to lead an $8m, two-year remodelling of the flagship Auckland gym - a rambling old building which once even had a nightclub, Grapes, co-owned with John Banks and Tony’s Steakhouse owner Tony White. The redesign will include what they claim is the world’s largest ‘immersive’ cycle studio with 100 bikes.

Diana, who first visited the gym at two days old and joined the family business full-time after graduation at 21, says: “I think that now we are both [her and Les Jr] completely dedicated to being the future of this company.” She adds: “[The company] is easily the way we can make the biggest difference to this world in a positive way.”

Marching relentlessly into the future: red marks the countries with gyms that take Les Mills classes. The total stands at 105, with the latest additions including the Congo, Benin and Burkina Faso. Marching relentlessly into the future: red marks the countries with gyms that take Les Mills classes. The total stands at 105, with the latest additions including the Congo, Benin and Burkina Faso.

Les Mills is expanding aggressively, not just in Iraq and Iceland, but here. The goal is one new gym a year; a massive undertaking when they typically buy their sites outright and never close them (Christchurch’s Ferrymead a quake-forced exception). Les Mills NZ chief executive Dione Forbes-Ryrie says the North Shore and Mt Wellington are their next targets. The family ownership and the professed disinterest in money lets them play a very long game. “We have to be commercially astute, but not commercial driven,” Forbes-Ryrie says.

“I’ve got to say they are very, very good at what they do,” independent personal trainer Grant Helleur says.

“They are world class leaders in group exercise, no two ways about that.”

Relentless attention to detail is everywhere. Attendance at every class is counted and used to re-format the timetable every three months. Gym floor time-and-motion studies remove pieces of equipment that don’t get used enough to justify their real estate. There’s even a gym lab at Penn State University led by a professor of kinesiology churning out academic papers on the efficacy of Les Mills programmes.

After six months of membership and three weeks observing how they work, it’s not hard to see the Les Mills brand marching relentlessly forward, growing ever dominant, its legion of “raving fans” behind them. When I ask where she sees them in the future, Diana Mills imagines a second, simpler stream of classes sold direct to instructors to run in parks and community centres; “Everywhere,” she says, with a smile.