Directly in front of me a huge, semi-naked man is kneeling on top of another man, smashing him about the head. Over and over again. Sweat flies, blood flows, and the packed crowd watching it with me screams for more. My stomach churns - in a few days it'll be my turn.

This is cage fighting, or Mixed Martial Arts (MMA) as it's more properly known: a combat sport that embraces several different fighting techniques. There is a buzz about MMA - partly down to Alex Reid, the sport's most high-profile figure in the UK, but also to a growing appetite for extreme sports. Venues as big as Birmingham's NEC regularly sell out; cage fighting was the biggest-selling event on pay-per-view TV last year; top fighters command hundreds of thousands of pounds a fight. And it doesn't stop there: ordinary blokes are now descending on boxing gyms and learning how to become fighters themselves.

A man's world

A rude introduction: a UCMMA fight at the Troxy, east London. Photograph: PR

So how would a woman fare in this aggressively macho sport? More to the point, how would I, a 5"2, eight-stone woman, cope? I went along to a training session with the BanDogs at a spit-and-sawdust gym in south London to find out. (By way of explanation, I'm competing in Tough Guy in the summer, a gruelling obstacle course boasting barbed wire, fire and electric fences, and as part of my training I plan to try out all kinds of tough sports - and they don't get much tougher than MMA).

The BanDogs didn't bat an eyelid when I joined in their warm-up, and they were happy to explain any complex moves. Within seconds I was in the 'sprawl' position; in minutes I was pinning a young amateur to the ground; and by the end of the session a semi-professional fighter submitted as I choked his windpipe between my thighs.

It's certainly not for the faint-hearted. The next day I counted seven bruises and one pulled muscle. And then I arranged another session, this time a one-on-one lesson with Ultimate Challenge's cage-fighting supremo Dave O'Donnell. In breaks between slamming him against the cage, hitting him in the face and choking him (all with his express permission, I should add), I grilled him about the glaring lack of female fighters in MMA.

Rachel Dixon practises a submission move. Photograph: Martin Argles

It's not for want of trying, he assured me. "We're trying to arrange more women's fights but because the number of fighters is still small it's hard to find matching weights," he said. Weight classes were introduced to the sport as part of a raft of measures - including bans on biting, eye-gouging and fish-hooking (don't ask) - to improve safety and dispel the dangerous, no-holds-barred image. "Even a 5kg difference in weight makes a massive difference."

But women's interest in the sport is growing. More women are training, and there are a handful of UK professionals, including Rosi Sexton, the world bantamweight No 1. Abroad, female fighters have a higher profile, especially in the US, Japan and Brazil. Pay is lower than for top male fighters, but is rising with their status: last August, a women's fight headlined an MMA event for the first time.

MMA has a reputation for sexism outside the cage. At the sell-out live event I attended in east London, I was uncomfortable with the scantily clad 'ring girls' who led the fighters out. Proponents claim the women attract new fans to the sport, and while they're no doubt a draw for some, these seedy sorts of trappings may well deter female participants.

Reservations aside, could I cut it in the intimidating world of MMA? According to O'Donnell, I possess the necessary aggression, which is rare. "If 100 women walk into my gym, only one of them will have what it takes. If you want me to, I can make you into a cage fighter." Tempting … now, where did I put my gum shield?

Fighting fit

Mark Buchanan takes his fighters through a warm-up. Photograph: Martin Argles

The multi-disciplinary nature of MMA makes it a uniquely difficult sport. The image may be of a fight-to-the-death free-for-all, but it is actually incredibly skilful, and successful fighters need to be extremely disciplined with their training. If you too want to be a MMA hero, or if you just want a body like one, there are no shortcuts. Aspiring fighter Sam Chinque, 19, trains three nights a week, lifts weights on the fourth, and gets up at 4am every day to go running before college. It's not an easy route to fame, fortune or even fitness. "It's made me work harder to get the things I want in life", he said.

Tommy Gunn, an undefeated cage fighter turned trainer, told me where to start. "Three words: cardio, cardio, cardio", he said. Excellent cardiovascular fitness is mandatory - without it, you'll never stay the course. Rounds typically last five minutes with a one-minute break in between. That's two agonising minutes longer than a typical round of boxing, although the fight itself is much shorter - generally three or five rounds in total.

So how do you improve your fitness level? Running is the most straightforward way. Mark Buchanan, a cage fighter and instructor at Rooney's boxing gym in south London, recommends running four miles once a week, as fast as you can. He also recommends a weekly hill sprints session: find a steep 50-60m hill, sprint up it, and jog back down. Repeat to exhaustion. For variety, throw in a circuits session every now and then. Avoid the treadmill - it's seen as the cheat's option. Instead, go swimming or rowing if you can't face another run.

After endurance, strength will be your most important physical attribute inside the cage. Perhaps surprisingly, weightlifting isn't a big part of the MMA scene. The emphasis is very much on 'real-world' training and controlling your own body. So to build strength, perform lots of squats, sit-ups and press-ups. More dynamic exercises include throwing yourself to the ground (sprawling) then springing up into a star jump; leap-frogging a partner then turning and going through their legs; and dragging yourself along the ground with your arms.

Don't try this sport if you have intimacy issues ... Photograph: Martin Argles

While complex machines may be out, basic equipment does feature in MMA training. Rooney's gym boasts a hardcore conditioning room that even the fighters are a little afraid of: the ropes, pulleys and heavy objects are more torture chamber than fitness centre. There are kettle bells that can be used in a variety of ways: Turkish get-ups, clean-and-jerk, tossing. Rope climbing, tyre flipping and pounding a tyre with a sledgehammer (seriously) are also common practices. While, as mentioned above, bulking up with heavy weights is frowned upon (it's for posers), fatiguing your muscles by performing lots of reps with a light dumbbell is acceptable.

Ultimately, the best way to get fighting fit is to, well, fight. Punchbag and pad work is necessary for honing technique and building fitness, but sparring is essential for fighting experience. Cage fighters focus on a different discipline each day, so Monday might be boxing, Tuesday Brazilian jiu-jitsu, Wednesday vale tudo, and so on. In the run-up to a fight, they will train six days a week.

Diet doesn't seem to be a key consideration in MMA training - unlike, say, football, with its army of nutritionists. No doubt this will be addressed as the sport continues to professionalise. However, food does become a preoccupation when a fighter needs to lose or gain a few kilograms for a fight. Welterweight Jamaine Facey needed to transform himself into a middleweight at short notice for a recent bout. "Normally I have to slim down before a fight, but for my last fight I had to put weight on," he said. "It was great; I ate whatever I liked for five weeks. I stuffed myself with steak - some days I had three steaks on my plate at once." Not recommended for those who only manage a weekly boxercise class …

It's all in the mind

A grand entrance: Jamaine Facey walks out to the cage. Photograph: PR

Mental preparation is just as important as physical training. Fighters need to be calm and focused, but able to turn on their aggression as soon as they get in the cage. O'Donnell said: "Your aggression levels go up in the run-up to the fight. You can't sleep. You're distracted. You argue. 50-60% of the battle is mental attitude. You can lose the fight before you get in the cage."

Facey agrees. Two weeks before his first fight, he was partying in Thailand with his friends. He felt no fear about his forthcoming fight. On the night, he made a grand entrance with his entourage - "my boys" - and swaggered into the cage. Twenty seconds later, he woke up on his back. He had been knocked out by his opponent's first blow.

"It was a good but a hard lesson for me to learn," he said. "I was physically fit and ready, but mentally I was nowhere near. I'm glad I lost - it changed my mentality. You need to sweat blood and tears."

Even after months of mental and physical preparation, the hours before a fight must be incredibly nerve-wracking. How do the fighters stay calm? Everyone's different, Buchanan told me. "Some people listen to music, some get grumpy, some go to sleep." Many practice visualisation techniques. Are there any no-nos? "No one reads."

These days, Facey is fully prepared for his fights. When I watched him at the live event, the swagger was still there, but there was a steely focus, too. Again, the contest was over almost before it had begun, but this time, it was Facey who delivered the knockout blow: a trademark high kick to the head. The ringside paramedics rushed to the scene, but his opponent was unharmed. Dazed and a little embarrassed, perhaps, but otherwise fine.

A change of attitudes

Do violent sports help to channel pent-up aggression? Photograph: PR

Cage fighting has a reputation of a dangerous, bloodthirsty spectacle, and while clearly risky - there have been three confirmed fatalities - the sport is now considered by many to be no more dangerous than boxing. And like boxing, its advocates argue that it promotes discipline and is a good way for young people to channel their aggression.

"Too many young men are walking around full of aggression and anger," said O'Donnell. "The whole world is pressurised, and this is a release. If you had a gym like this [the Diesel gym in east London] on every estate, there'd be a lot less crime."

Facey has had first-hand experience both of youth crime and the transformative powers of sport. "I've known people who have died from gunshots and stabbings," he said. Now he devotes three hours a week to running an after-school MMA class for children, under the slogan, 'hands up, guns down'. "What you learn here, you leave here", he said. "You understand discipline."

Gunn agrees. "Our fighters don't want to go out and fight on the street," he said, quickly adding: "But if they have to, they can" - just in case you thought MMA was for pussycats.

It isn't. I've tried it, and it definitely isn't.