'We'd just like to check your target weights,' says Rita Pring, 28, a little sternly. She is one of the partners in Aventura Holidays, which has been operating in Andalucia for more than 20 years. A communal frisson of guilt hits us, but no one admits deceit.
Then there is the riding experience. Susan, a tall insurance administrator from Perth, used to have a horse; Janine, who runs a marketing company in London, has mustered cattle out in Australia; Maura, a Central TV contracts manager, used to hunt regularly; Jackie, a research assistant in Edinburgh, simply loves horses; Fiona, a sales manager with a London design company, rides regularly.
I confess to my inadequacy. I ride maybe once a year, and the last time I went on a day trek I was unable to walk for two days. Will I be relegated to the mule?
Orgiva is a market town in the fertile but arid Alpujarra, the southern foothills of the Sierra Nevada. Aventura's farm (set up by a Welshman, Jeff Judd, who is still there but keeps a low profile) is all whitewashed walls, orange trees, jasmine fragrance and lots of photographs of horses. Anneka Rice beams dazzlingly out of one. 'She was really nice,' says Rita, 'nothing like her image.'
At breakfast - we share comfortable twin-bedded rooms and two bathrooms - footwear is examined. 'Those boots really are not suitable,' says Rita about Maura's leather ankle boots. Mine are deemed OK but lacking in ankle support for the walking part of the trip. We carry on regardless.
My horse is a gorgeous chestnut Andalucian 13-year-old called Maracena. She turns out to be a real sweetheart, although I am warned by Gillian Smith, the older, thinner, quieter partner, that she is easily frightened by flapping plastic and is endlessly greedy.
The others rapidly find out their horses' foibles. Tequila likes biting ankles, Flamenco is one for the women, Gitana is excitable, while Sahib, the beautiful stallion ridden by Rita, constantly dances up and down as though he is about to gallop off.
Having all managed to get into the saddles without a leg up - a major triumph in my case - Rita leads us in single file past olive trees and farmers harvesting almonds, through stone-filled river beds and up into the Sierra de Lujar, where we look down into the Guadalfeo valley below and up at the stunning peaks of the Sierra Nevada ahead. The horses are frisky because they have had a day off and Rita is constantly anticipating danger in the form of yapping farm dogs or oncoming lorries.
This was the initial three-hour test ride. We all passed with flying colours. We did not, for instance, allow our horses to canter, trot or gallop. And there was one occasion where they all nearly broke into a gallop. 'We keep the horses at walking pace for trekking as a safety measure,' says Rita. 'The climbs are often very steep.' I could not help feeling dismayed as I recalled the exhilaration of cantering on my last ride in the South of France.
By that evening, we are learning to groom and tack up the horses. 'Be firm with those body brushes, girls,' shouts Gillian, like a horsey version of Miss Jean Brodie. Girths, throat lashes, breastplates - it is a whole new linguistic genre. Not to mention the practical application. There are rules about which side of the blanket to use, how to put the bridle on and how high up to put the saddle.
Tuesday is the first day of the trek. Initially, there is the saddlebag test. We have to get all the luggage we need down to 9lb. I fail. It is a hot September day and we make our way through bamboo-covered trails, along the considerably dried-up Guadalfeo river - 'There's been no rain since April,' says Gillian - up and down ancient mule tracks surrounded by rosemary bushes, and finally into a shady conifer wood for lunch.
'We're having a picnic,' Gillian had said enthusiastically at 7am; it turns out to be a bit of a euphemism. We try to eat tuna sandwiches while holding the horses and preventing them invading our precious lunch bags. It is hell. Flamenco slobbers all over Janine, Khalif refuses to stand still for Susan, and Tequila insists on trying to steal Maura's apple.
Five hours later, we arrive at the little village of Almegijar where we are staying at a local posada or, in this case, inn. We are exhausted but, after liquid refreshment, make our way down to the stables for some extensive body rubbing. Many of the village houses still have stables underneath where they keep mules or pigs. This is one of them.
A large Bacardi does not do much for my grooming skills but Maracena seems to love it, anyway. Some of the other women are not so keen at the end of a long, dusty, hot day. 'Didn't we use to pay people to do this?' says Janine half-jokingly. 'Now we pay to do it. We could do with some chilled champagne.'
The rooms at the inn are more basic than simple and now for a true test of our female team spirit: there is one bathroom between seven of us. 'It reminds me of being a student,' comments Fiona tartly. Fortunately, the annual fiesta is still taking place in Almegijar, so we cheer up. There is a brass band, children throwing eggs at each other and lots of older, rotund ladies dancing together in the square. As we go to bed, the whole village is just beginning to party.
Unfortunately, there is a youth disco in our posada which keeps Susan awake all night. So she is in a terrible mood the next day. As is her horse, Khalif. It is chilly at 7am and we groom in semi-silence amid a rainshower. Gillian, our leader, is at her best with the horses, she is devoted to them. 'Maracena looks lovely,' she says and I glow appropriately from the praise.
We ride out of Almegijar past fields of fig, pomegranate and unripe oranges. We are climbing right into the Sierra Nevada. 'Be very careful here,' warns Gillian. 'No going fast at the back or one of the horses could fall to its death.' First, we have to descend the spectacular Carriguelas gorge, which we do by leading our horses on foot. It is an arduous and dangerous route. Walking in front of your horse, you are always in fear of it falling or treading on you. It is a relief to get on again.
The other side of the gorge sees mellower woodland and little whitewashed villages with geraniums in pots and red peppers drying in lines. Pitres, our stopover village, is at 4,000ft and we stay in a family-run guest house. The food is nourishing: bean soup, deep-fried calamares, and marinated pork with delicious home-made chips cooked in olive oil.
By Thursday afternoon and our arrival at the Morena posada at Torvizcon, the trek has divided up into two camps. On one side are Gillian and Jackie, the horse-lovers, and on the other are Susan, Janine, Maura, Fiona and me, the career women on 'holiday'. Moans about accommodation, inflexibility, breakfasts and grooming are increasing from the latter. The problem is that Aventura looks after its horses fantastically well, but not its guests. And for pounds 545 plus airfare, clients expect a caring service.
Getting there: Flights to Malaga range between pounds 120 and pounds 180. Aventura picks you up at the airport as long as you arrive before 8.30pm on the Sunday.
Accommodation is at Aventura's comfortable farmhouse in Orgiva for four nights and three nights at basic posadas along the way. Shared bedrooms.
Further information: Aventura Holidays, 42 Greenlands Road, Staines, Middlesex TW18 4LR (0784 459018). The summer price for a week's trekking is pounds 545, including all meals, and pounds 393 for winter.