This mindset lasts until we get back on dry land and I'm shown snaps taken during the session.
To my horror, I seem to have been photoshopped out and replaced by some contorted, grimacing imposter performing a pale imitation of the poses perfected by my four flexible female yoga buddies.
Oh wait, it's me.
And I'm rubbish.
As my SUP yoga instructor Charlotte Piho explains, I'm not the first male participant to underestimate just how difficult the activity can be.
"Women tend to be better at stand-up paddleboard yoga as they're naturally more balanced," she reassures me.
Although my pride is dented, Charlotte is quick to offer a positive spin.
"It's a good sport for guys to do because it helps to lower your ego and appreciate that women have this strength and balance," she says.
Stand-up paddleboarding and yoga are not obvious bedfellows.
In fact, to somebody who's never attempted either of the activities, the thought of attempting strange stretches while balancing on a wobbly platform on the ocean seems slightly ridiculous.
But the truth is the two dovetail perfectly, offering an adrenaline rush when paddling and a challenging yet peaceful satisfaction while striking poses on the board.
All this set to the sound of the sea.
Charlotte has taught SUP yoga in Sydney for the past three years and says being out on the harbour offers respite from the busy city and helps her appreciate life.
But this year she decided to offer week-long retreats in her picturesque homeland of the Cook Islands, where relaxation is taken to a whole new level.
"I love that feeling of having totally glassy water, and having the fish swimming under you, and the sight of the mountains," she says.
"It's just such an amazing feeling."
And the amazing feelings in the Cook Islands aren't confined to the water during the retreat.
Despite an urge to coin a more original word to describe the place, it's impossible to go beyond "paradise".
The scenery on Rarotonga, the most populous island of the 15 making up the archipelago, is breathtaking.
The island is ringed by crystal waters and framed by a volcanic, mountainous backdrop which entices even the laziest of tourists to lace up their hiking boots.
It's warm and sunny year round, with a hotter, wetter season between December and February.
The SUP yoga retreats take place during the peak winter months, when temperatures average about 26 degrees C.
There's a wealth of activities for the energetic, including fishing, diving and trekking. But for those who just want to kick back with a coffee or cocktail, there are scores of cafes and restaurants scattered around the island's 32km circumference.
And the best ingredient in the Cooks' recipe?
The people, no question.
Always smiling and joking, they're keen to say "kia orana" but won't bother you if you're busy.
Going on a boat cruise or attending an "island night" offers an interactive celebration of their heritage, and countless colourful stalls at the weekly Saturday market provide an insight into Cooks' culture.
It was on Rarotonga in 2010 that Charlotte discovered she could perform her yoga routine to even greater effect on the water.
"I started doing shoulder stands on the board and it developed from there. You can be a little bit lazy in your yoga if you're doing it on a flat surface ... whereas on a paddleboard it's going to start tipping over if you're not perfectly balanced.
"So it makes you really suck in your core, and you work much harder than in a studio."
She'll return to the Cook Islands next winter for another batch of SUP yoga retreats.
Charlotte says her Sydney classes appeal to all sorts of men, from corporate types to water sport enthusiasts, although they remain dominated by women.
"We probably get one male to every three or four females ... generally a lot of girls come with their partners, and then the guy continues to come along."
Lots of men giggle at first, but they stop as the class progresses when they realise that people take it very seriously, she says.
And when they commit they can achieve great things.
"Guys are actually quite flexible and they're a lot stronger than a female.
"They may be bad at some poses, but then they'll have more strength for other things. I find guys like to push themselves."
And by pushing yourself you discover that, aside from the general sense of wellbeing it engenders, the beauty of SUP yoga is its steep improvement curve. By the end of my week on Rarotonga, I've rediscovered some of my childhood flexibility, and I'm nailing warrior poses and shoulder stands on the board.
It may not be perfect profile picture material, but at least it looks like yoga.
CHECKLIST
Getting there: Air New Zealand flies direct to Rarotonga from Auckland.
Accommodation: The Sanctuary offers 48 adults-only suites on the beachfront, from $395 per night.
Details: Find out about SUP yoga at workoutonwater.com. Their next Aitutaki retreat runs from August 23-29.
The writer travelled as a guest of Cook Islands Tourism.
- AAP
