When you're lying on your back in a pool of sweat, looking up at the crotch of a man you've just met as you grip his ankles, local precipitation being a real risk, the last thing you want to be told is to inhale. But you do, because you need to breathe – deeply – because you're knackered and about to be hoisted into an "assisted wheel" by your yoga instructor, a heavyweight bodybuilder and American footballer whose nickname is "Miller the Pillar".
Matt Miller is the very large man behind Broga UK, a new network of classes infiltrating gyms to cater for a growing national demand for yoga that appeals to, well, bros (aka dudes, aka men). His target audience is me, a physically active man who understands very well the benefits of the downward dog but would sooner cultivate his horribly stiff hamstrings than walk into a room full of girls spouting mystical Sanskrit (om, no thanks).
My only previous brush with yoga came in a beachside gazebo in Brazil, in a class during a surfing holiday. As my terribly earnest instructor struggled with English while I sat with crossed legs – "feel the energy from the Earth. Feeeeel it come through the floor and touch your c***s [he meant coccyx] and travel up your colon [column, spinal]" – it took all my energy and focus not to break the awkward silence with a fit of giggles. I did not go back.
Sure, not all yoga classes are transported straight from a hippy Himalayan hill station, but nor do even the good ones necessarily appeal to men. The British Wheel of Yoga, the governing body for yoga, has 8,000 members, only one in 10 of whom are male. The proportion of men among its network of 4,000 teachers is lower still.
I meet Miller at 7.30am in a basement room with chain-mail curtains at a branch of Gymbox, one of those blue-lit, black-walled gyms with an apparent lightbulb shortage and a nightclub soundtrack. The first thing I notice, after Miller's ridiculous physique, is the women. Girls make up about a third of the class of 17 City types. They, too, come for no-nonsense yoga, with minimal meditating but all of the breathing and positions that make the practice so good for you.
"It's the best bits together," says Clare Ginty, 29. "It's got the hard stuff we like without taking two hours out of the day. You feel like you've had a really good workout every time, even if you're aching like a bitch afterwards."
Miller says that American men, particularly in his native California (he's from Laguna Beach), are bigger on yoga, which is a training staple for top sports teams. In 2011, for example, the US goalkeeper Brad Friedel, then 40, introduced his yoga instructor to team-mates and staff at Tottenham Hotspur Football Club. They convinced their veteran manager, Harry Redknapp, to use yoga to combat a growing injury problem. Elsewhere, the Premier League's oldest outfield player, Ryan Giggs, has also attributed his longevity to the activity. You can even buy Giggs Fitness ("Strength and conditioning, inspiredby yoga") on a 2011 DVD.
The "back and twist" class at Gymbox starts with breathing and some raising of the arms to the sky. Sadly there's no escaping the dreaded down dog, the arched-back position with bum in the air. The pace is high as Miller guides the class between moves, and I'm soon sweating as much as I would be on my bike, but working a lot more muscles.
We attempt the assisted wheel towards the end of the class. It's the arch position you rise up to from a supine position, as if your navel has been attached to a winch. I stopped being able to pull one when I was about six but, with sweaty-ankle man supporting my shoulders as I rise, and Miller pulling up my hips, I make it.
Ankle man is Andrew Dougall. He's 44, works in insurance and has done almost 10 broga classes. Before that his wife had taken him to a regular yoga class. "This is more physical," he says. "I'm a very unsupple person. Even when I was young playing rugby I was the one who had to really stretch his hamstrings. Now I do Thai boxing and I'm physically stronger and don't get any back ache."
There are signs away from Miller's macho marketing – his website is illustrated with Action Man figures and the slogan "Challenge. Sweat. Stretch" – that men at least like the idea of yoga. Babita Bahal is a spokeswoman for the British Wheel of Yoga and an instructor based in North London. She says men still make up 3 per cent of her clients but that demand is shifting. "I teach at a golf club across from the bar and every week these guys come and stick their heads in. They're curious but can't bring themselves to take part because it feels a bit female."
But one of Bahal's keenest customers is now Kevin, a strapping electrician and Sunday footballer in his 40s whose legs were as supple as cured hams. "He can feel the backs of them really opening and lengthening now, and is trying to get all his boys down at the club to come along," she says.
Even Miller admits that he was once a yoga sceptic. "I went to a few classes, from chanting and breathing to hot power flow, but none really appealed to me," he says.
He fell into the sport by accident, after being signed as an ambassador to Lululemon, the Canadian yoga clothing chain, after he moved to London in 2011. "I was like, OK, I'm going to have to start doing yoga, so I hooked up with Rachel and quickly wondered why I hadn't figured this out a long time ago."
Rachel Okimo is a dancer and senior yoga teacher, and now Miller's business partner. They set up Broga UK (not to be confused with its older, American namesake) last year and now offer classes across the capital.
What did he think of his newest customer? "You managed," he says. "You weren't great at it, but you didn't fall behind and as you were doing it you knew exactly where you could make little improvements. You'll be better next time."
Two days later, when it aches to type these words, I am seriously considering my options.