Cute glutes: how to get a celebrity bottom

As I sink down low into the undignified stance of "platypus walk", the tiny roof terrace by The Berkeley hotel's gym seems a large space to cover. 

As exercises go, this is very hard indeed. It's tweaking muscles that normal bottom-toners — lunges, squats et al — don't touch. But then this is what gives David Kirsch his edge.

New York-based Kirsch is exercise royalty, and the chance of working out with him is a rare treat. For 20 years he has run the Madison Square Club where he has perfected his techniques for sculpting the backsides and bodies of the famous and beautiful. Heidi Klum, Karolina Kurkova and Liv Tyler are among his many fans and clients.

He is in the UK to promote his new range of high-class vitamin supplements (of which more later) and his Butt Book, and I get to interview him before we hit the gym. So how much can he improve the look of someone's backside?

"I've never met a butt I can't lift, tone and tighten," he says solemnly, "though one needs to be realistic. I can't change the basic shape but I can make sure that what you have is firm."
I'd expected a big blast of ego, or whoop-it-up enthusiasm, but Kirsch has a still, slightly wary presence, with the sort of thoughtful gaze that speaks of regular meditation and which suggests that he doesn't suffer fools.

I proceed with caution. I've read the details of his celeb-transforming 14-day New York Body Plan and it sounds gruelling, all egg-white omelettes and ferocious workouts. He has a reputation,
I venture, for being extremely tough.

"Am I so scary?" he asks, looking genuinely pained. "I'd rather be thought serious than not."
He himself gets up at 5am and works out before anything else gets in the way. "I wear many hats," he says. "I have a lot to get through." As well as running the club, writing the books, filming DVDs and developing the supplements, he spends five hours a day training clients. "It's what I love," he says simply. I tell him that I'm getting up at 5am, too, but it's killing me. He reaches for a sachet of his new energy powder, shakes it in a bottle of water and hands it over.

When we get to the gym, what with the combined effects of the energy drink and sheer fear, I'm feeling lively. Kirsch is not one for platitudes. His gaze trails down my sides and stops pointedly at the saggy overhand of my backside. I flinch, and catch his eye. "Yeah," he says. "Let's do that bit."

We get to work, with squats ending in high kicks, deep pliés with heels lifted that you hold until it really hurts, lunges forwards and backwards and that platypus walk (you sink into a deep plié, then, keeping your bum at that height, you stagger forwards, then backwards, lifting your feet as high as you can at each step). They're all moves I've never tried before, they all hit home and they're all in his book, should you wish to try them, along with his rules for eating to maximise the effects of your exercise.

"What about cardio?" I ask. "Running? Swimming? What do your clients do?" Kirsch pulls a face. "I loathe cardio," he says. "It bores me to tears, though I love rowing. Anyway, you do this session, then tell me if you think you need cardio."