Oh Oh God.

With powder-white sands, azure seas and lofty palms, Zanzibar is all of the tropical-island clichés rolled into one. But I was not in paradise to bask in its beauty. I was here to check out Wildfitness, a transformative retreat (the phrase "boot camp" is strictly forbidden) based on the principles of "wild living".

Guests here are encouraged to throw off the shackles of a restrictive urban lifestyle and reconnect with nature, drawing on a paleo approach to holistic fitness and clean eating to achieve a balanced body and mind. This isn't a "drop a dress size in a week" sort of place. Weight is never mentioned, and the goal isn't to lose it (although it's often a side effect). I was here to mix things up, move differently and think differently. In short, to go wild.

I'd be lying if I said that I wasn't nervous. I'm averagely fit - I go to the gym three times a week, and I eat pretty well. However, the course isn't cheap (it costs from £2,840) and I had nightmares about turning up to a group of high-achieving, triathlon-running CEOs, who'd no doubt be bashing out emails while breastfeeding and nonchalantly swinging kettlebells around.

Glancing around on that first afternoon, though, I was relieved to see how "normal" everyone looked, and the five coaches were quick to get us bonding with liberatingly childish beach games such as It. Play and group mentality is central to the Wildfitness philosophy and, using the analogy of geese who fly in a V-formation so that weaklings can glide in the wake of those at the front, we were solemnly informed that we would carry each other through whatever was thrown at us that week. The proclamation brought comfort and trepidation (and led to encouraging cries of "honk honk" becoming the soundtrack to the week).

Day two: 6AM. My alarm rudely reverberates around my room at Zanzibar White Sand Luxury Villas & Spa, disturbing a deep slumber induced by the lull of the waves and the rustle of palm trees (rather than the usual East London sirens). I automatically reach to hit snooze, then remember where I am and scramble to get dressed, grabbing mismatched items from a suitcase stuffed with Lycra and quick-dry items - no kaftans and bejewelled sandals here.

I'm greeted by the head trainer, Uju. Strong, lean and positively glowing, she couldn't be a better advertisement for wild living. She hands us each a long stick, instructing us to hold it in two hands and lift it forward and backwards over our heads, coming as far down our backs as we can. It's surprisingly painful and I hear the crunch of desk-induced gristle between my shoulder blades. We then roll golf balls underfoot - it's strangely satisfying and I feel a peculiar twinge in my back. This class is named "structural hygiene and animal movement". We're waking up our captive city bodies, moving like our cave(wo)men ancestors would have done and how we haven't since we were small children. It is to form the basis of everything that we do that week.

The next two hours are spent contorting ourselves into various shapes, as unfamiliar as they are undignified. We squat, stretch, lunge, chase and climb over each other. We balance in awkward positions and hang out of trees, mimicking the monkeys who seem to be laughing at us overhead. Finally, we crawl like crabs a good 200m down to the sea. It's exhausting. I ache in places where I didn't know it was possible to ache, and blisters are already forming on my hands and feet (you're encouraged to go barefoot throughout). My high-intensity gym workout back home pales in comparison, and I start to do panicky maths in my head. Two more workouts today, then three a day for six more days - that's 21 sessions in a week! I couldn't be more grateful when we stretch and it's time for breakfast.

It's a lavish spread reflecting a "wild-eating ethos" in which calories are not counted. You're encouraged to eat when you're hungry and until you're full, avoiding processed foods, sugar, alcohol, carbs and caffeine in order to listen to your body's natural needs, which are often muted by contemporary quick- fixes. Over the next week we gorge on platters of mango, passion fruit and rambutan (a lychee-like fruit) and get to know each other over feasts of freshly caught lobster, exotic salads and calamari cooked up by our French-trained chef.

We're a mixed bag of professional women (although the split is usually 70:30 women to men) including a barrister, a UN worker and a doctor hailing from everywhere from Austria to Saudi Arabia, and bringing stories as varied as our fitness levels. There's nothing like sweat, sand and pain to break down barriers, and any time between sessions is spent sunbathing on the idyllic Paje beach, discussing everything from humidity-induced hair frizz to being a woman in the Middle East, ghastly exes - including one who took a chainsaw to a sofa - clean eating-induced bowel movements and what it's like to live under armed guard in Kabul. They are some of the smartest women I've ever met, and although it might sound trite, I learn as much from them that week as I do about fitness.

Day three is the worst. While some are struggling with the lack of carbs, I've fairly easily adapted, but my caffeine-craving headache is chronic. I just want to lie down and fall asleep. When my head finally hits the pillow at 9.30PM I am dead to the world. I dig seriously deep to get my energy levels up three times a day - although probably not quite as deep as the person who catastrophically thought that the workout schedule was for us to pick and choose from as we liked. If only.

It turns out that boxing is not my forte. I discover that I like hitting things a disturbing amount, but I'm right-handed, and can't seem to compute that in boxing "one" is left and "two" is right, so I systematically take out the trainers when I throw the wrong punch, leading to feebly masked winces when they're partnered with me again. The variety of the course, however, means that we soon discover our different strengths and weaknesses. We're filmed running to assess our technique, and I'm disgustingly smug when they say that mine is pretty good. I come in second in the 5km beach/village run, while the "lactic" sprints are terrible, but not terminal. The playing field is quickly levelled when I come second-last in the 2km open-water swim, having breast-stroked, granny-style, the entire way and therefore spent nearly an hour being baptised by the relentless salty waves, getting so infuriated by my constant choking and spluttering that I actually start to swear at the sea. Hearing cries of "honk honk!" from the shore, I finally make it.

We are starting to see changes. On day four I'm awake before my alarm, and look around as we gather for a beach obstacle course - involving delights such as deadlifting palm trees and slogging sandbags up the beach before sprinting to dip our heads into the sea - and see an alert tribe of stronger, fitter bodies and developing tans. Most noticeably we're standing straight and proud, thanks to our achievements, as well as our improved posture. We have a day off (after a 6AM workout, of course) and wander around historic Stone Town, go for clandestine cocktails away from the watchful eyes of our trainers and soothe aching limbs with full-body massages. My skin is clearer, my eyes are brighter and my headaches have gone.

The last couple of days slip by much more quickly, and I'm soon bikini-clad again, reluctantly squinting at my "before" and "after" pictures. There's a perceptible difference. It's difficult to pinpoint exactly - although Uju charitably points out some improved muscle tone - but my whole body seems to have woken up. My wonky shoulders (which I never realised that I had, but which explain the constant pain) have levelled out somewhat. I'm standing taller, stronger, leaner. I undeniably just look a hell of a lot healthier - and certainly wilder, thanks to the catalogue of war wounds decorating my body.

We end the week with an extravagant poolside barbecue for which we all brush our hair and change out of our workout gear. Prizes are handed out to everyone, and I win the "wild" prize, which I'm not entirely sure how to interpret, but am immeasurably chuffed about. When I get home I take up waving a broom handle over my head every morning in an attempt to stay loose, look up boxing classes and try to steer clear of wine. I feel lighter and brighter both physically and mentally, and people generously tell me that I'm glowing. However, this is all spectacularly outshone a few days later by the wonderful news that one of our party completed the course while unknowingly being three months pregnant. Honk honk all around.