When you tell friends you're going on a Wild Fitness break, there's a sharp intake of breath. 'Scary,' they say with a knowing look. You're not quite sure if the 'scary' refers to the wild (will there be wild animals lurking about?) or the fitness (does that mean press-ups at dawn?).

With any luck there won't be wild animals (this is the company's first course in the French Alps, the rest having been in Kenya until now) but there will be press-ups, cycling, swimming, running, Swiss ball exercising and stretching - all in the natural wilds of the Alps. Swimming in lakes and running up mountains is mentioned on the phone when I book.

But that isn't the most scary bit. Arriving at Geneva airport, I'm met by Miss Wild Fitness founder herself - Tara Wood, tall, tanned, Amazonian.

'How many people on the course this week?' I venture.

'Just you.'

'You mean, I'm the only journalist?'

'No, the only person. This is our very first week in the Alps,' she says with a big sunshine smile, starting up the car.

I realise there will be no straggling. Plenty of places to run (we're in the mountains aren't we?) but nowhere to hide. Katie Budd (a heptathlete and former Gladiator quarter-finalist for god's sake) will be co-coaching the course. All one of me. I am the guinea pig.

The course is based at eight-room Ferme de Montagne, a luxury chalet run by architect/management consultant couple Henry and Suzanne in Les Gets, an hour from Geneva. Katie leads me into a small room. A piece of string is hanging from the ceiling and a row of measuring instruments, reminiscent of O-level maths, awaits me. I lie, sit, stand and curl semi-clad for an hour while Katie performs her posture assess ment which involves measuring joint angles with a goniometer and examining me with a plumb line (that's the string) for symmetry. I feel like a car undergoing an AA inspection.

As suspected, I am an office animal. My posture is a barometer of my life. Eight hours glued to a computer and two hours on a commuter train each day equal curled shoulders, caved-in chest and a neck and upper back which are out of range. I am Wild Fitness's latest project.

Minutes later we're walking up a hill (flattened frogs everywhere). Just a quick walk before dinner they had told me. We're so high up that clouds waft around us like smoke from a bonfire. A torrential thunderstorm breaks out. Great. Back to the cosy chalet and that nice sauna I spotted earlier. But no. Katie and Tara start yelping how fantastic it is to swim in a lake in the rain, in your clothes, and start running up the hill. Next I find myself sploshing away in the lake in my fleece and jeans (we were so wet anyway) and the athletes are diving off a raft in the middle. 'Awesome, innit?' says Katie. The water is bath temperature and warmer than outside. I skip down the hill like a new woman.

I am no athlete. I swim and gym on a good week and stretch to a bit of capoeira if I'm lucky. I don't generally do lakes and I get out of breath easily. I'm a weak swimmer. And the excuse 'I just had a baby' is beginning to run thin (that was nine months ago). But it is time to get fit. Eat healthily. Make progress. My four days here will be challenging.

'OK, we're going to run up that mountain,' says Katie pointing opposite the chalet. It's 7am, misty and cold. I'm scrabbling up in my new trainers (they say bring two pairs as they get very wet), dodging cowpats and electric fences (which Katie, owner of six pairs of trainers, just limbos under of course) and unsure if I'll even make it to the top.

Tara is waiting in the mist in a clearing having already hauled up all the gym equipment for this session. She's set out a whole circuit and Katie talks me through it. A few star jumps here, a few squats there, a sprint here, weights and a bit of boxing there, Fat Boy Slim music and the tinkle of cow bells all around us. An hour flashes by and in no time we're back at breakfast via the aromatherapy sauna, feeling great. I'm impressed at how Katie and Tara made me do that.

In the afternoon Katie talks me through a 90-minute Swiss ball session in the dojo (a kind of outdoor canopy) with Heidi scenery behind us. There are lots of stretches and shoulder-presses to help my upper back.

We soon get into a pattern. Start at 7am with lakes and mountains. Afternoons feature dojo , stretches and weights with lots of time in between for recovery, and sessions in the sauna or the outdoor hot tub, with time to eat organic gourmet food (not the contradiction it might sound) and receive the odd lecture on nutrition. Although you're encouraged to cut out alcohol and caffeine, nothing is forced and the exercise programme (which takes a maximum of eight) is flexible with the trainers revving things up and down to the group or sub-group's abilities.

The Kenya programme has been running for three years, but when the Foreign Office issued a warning against visiting the country earlier this year, Tara decided to try out the Alps for the summer before restarting in Kenya later on. How you eat is a key part of the course. Revitalising burnt-out professionals is her mission. In Kenya some people stay up to six weeks. In the Alps the course will be a week long.

One day we hire mountain bikes and ride to the top of a mountain range in the chair lifts before bombing down in the sunshine admiring magnificent views of snow-capped Mont Blanc (that was an easier day). Back at the lake there is more coaching. Katie shouts from the sideline: 'Front crawl to the middle, put your face fully in the water, for breaststroke put your feet right together!' Another day we climb along the Praz de Lys to reach the Pic de Marcelly. It takes me five hours (two hours longer than expected). Wild rabbits scurry, eagles glide, cow bells ring like wind chimes. There are Johnson's blue geraniums everywhere. Families huddle on the hillsides gathering wild raspberries in empty ice-cream containers. Eventually I reach the top. I am so knackered I don't think I'll ever make it down again.

Somehow we reconvene by a lake at the bottom in the dazzling sunshine and a couple from the chalet appear with a picnic basket which they lay on the grass - roasted marinated chicken, mozzarella and tomato salad, cold rice salad, freshly squeezed cherry juice with ice in real glasses. Civilised. But maybe a bit too civilised for Tara who dives into the lake (despite a big notice saying, 'Danger, vipers') while we all shiver in horror and debate whether you can be bitten by a viper in water, and, if you can't get bitten in the water, why bother putting a sign up. We drive back to the chalet, my back and limbs aching, my shoulders throbbing with sunburn. I collapse into the sauna then enjoy a massage.

I wake on the final day determined not to get up. I can't take any more. I ache all over. I really want to sleep. I don't want to go to the lake. I don't want to ride a bike. I don't want to run anywhere.

A radiant Katie is tapping on my window. I beg her to change the programme. Somehow she coaxes me into the car. The air is cold and biting. The last place on earth I want to be at 7am is in this people carrier huddled in my fleece with a bikini underneath.

Before I know it I'm on a bike, chasing her and Tara around Lac de Montriond (a little two-lap warm-up) and then wading out into the cold steaming lake. Only a kilometre to the other side they say. I really cannot believe I am doing this.

Then there's a turning point. The sun which has been rising behind the pine trees suddenly hits the lake and the whole land scape turns from menacing grey to orange and there's nowhere I'd rather be right now. I astonish myself and reach the other side (OK, very slowly). While I'm sliding around on the mossy stones trying to claw my way out, Tara and Katie are diving back in... for more!

I'm never going to be an athlete, but I've come a tremendous way in four days. I'm off the booze, I'm on the organic and back into a fitness regime. I've taken on the strange habit of lying down each morning (watched by my stunned children) on my front with my arms behind me lifting each vertebra of my upper spine to help posture with Katie's 'awesome work!' mentoring in my ears. She calls it awesome. I call it a complete miracle.

Factfile

Wild Fitness (020 7368 1632). A one-week course costs £1,380 in a shared twin room or £1,480 in a single room (excluding flights) full-board including coaching, activities and one massage. Courses run from 10-17 August; 17-24 August; 24-31 August; 31 August-7 September

Ferme de Montagne (00 33 450 753679)

EasyJet and British Airways (0870 850 9850) both fly to Geneva, a one-hour transfer away.