You would never pick South Perton Farm, near Wolverhampton, as the birthplace of a global phenomenon. A vast, rambling farmhouse, the building appears to have been extended, over and over again, by someone whose enthusiasm for the task isn't entirely matched by their aptitude. The farm is home to both a horse sanctuary and an open-sided Dutch barn, entirely filled with the rusting skeletons of Citroën 2CVs. The exterior walls of the main building are decorated with hand-painted murals of biblical scenes. HELP US GET THE KIDS OFF THE STREETS SUFFER LITTLE CHILDREN offers one. JESUS THE ORIGINAL TOUGH GUY HERO suggests another.

Nor would you pick South Perton Farm's proprietor, Billy Wilson, as the progenitor of a global phenomenon. A former Grenadier Guard, hairdresser, nightclub owner and marathon organiser who won't reveal his age, he sports an Edwardian moustache and, in public, usually affects a Windsor Davies-ish sergeant major persona going by the name of Mr Mouse. If anything, Mr Mouse seems marginally less eccentric than the man behind the character. Over the course of a day with him, Wilson will tell me that "in the not-too-distant future" scientists are going to prove that telepathy exists; claim that he has unearthed magical powers while digging a lake in the farmhouse grounds; and, at one diverting juncture, announce that he can attach a rope to his penis and pull a car tyre along with it.

Wilson is the father of what one US magazine, Outside, has called "America's fastest-growing sport": endurance obstacle racing. He started the Tough Guy race here in 1986, after he tired of organising the Wolverhampton Marathon. Initially, it was just a cross-country run with 108 competitors; but every year, Wilson added more obstacles. At first they were just hay bales, and "a couple of boards leaning together to make a jump". Then, Wilson says, his imagination went into overdrive: he started building huge permanent structures, obstacles that involved scrambling under and over barbed wire, running through fire or wires that deliver electric shocks. "That became the challenge to the competitors: I'm going to beat you," he says. "You've come this year and you've conquered the Tough Guy, but next year I'm going to build an obstacle and it's going to defeat you. They loved it."

The race slowly grew, becoming biannual: Tough Guy takes place in January, Nettle Warrior at the end of July. Local news crews started turning up, as local news crews are wont to do when grown men start paying good money to fling themselves into barbed wire and run through fire. Their interest was further piqued following the deaths of two participants, one in 2007, the other in 2000 – the same year Wilson decided to introduce the concept of "Jesus Warriors" (elite competitors who run the course carrying 40kg wooden crucifixes).

Then, about three years ago, something strange happened: companies such as Tough Mudder and Warrior Dash began aggressively marketing endurance obstacle racing across Europe and America. It caught on with a speed that seems to have startled even them: "This is 100 times bigger than we ever thought," Tough Mudder's CEO Will Dean said last year. In 2012, 1.5 million people competed in endurance obstacle races in the US alone; the combined revenue of the three biggest race organisers was estimated at $150m. The sport is also taking off in Australia, South Africa, South Korea, Japan, the Philippines, Hong Kong and Singapore. People around the globe – well, men, mostly – developed an insatiable desire to wade through mud pits and fling themselves into ice-cold water, and chivvied along by the kind of relentlessly macho goading you find on the race organisers' website. (Sample encouragement: "Road running will give you about as much upper body strength as Keira Knightley"; "It ain't about how hard you hit but how hard you can get hit.")

There are those who would argue that there is something faintly embarrassing about the whole business. Are we looking at a physical demonstration of masculinity in crisis, a terrible sporting equivalent of a Chuck Norris DVD marathon – or, else, not really a sport at all? "I think what I class as running purists would probably be a little sniffy about it," says Andy Dixon, the editor of Runner's World, a magazine that covers Tough Guy nonetheless. "They would probably think these are like adult school sports day-style events, for people who want to go 'Raarh!' and feel like they're Rambo."

But in April, a 28-year-old man drowned during a Tough Mudder event in West Virginia, just over a month after another man collapsed and died while competing in an Extreme Rampage race in Kentucky. In 2011, two men died after running in a Warrior Dash event in Kansas City. Even those who master the races tend not to emerge unscathed. "The first time I won Tough Guy, I was hypothermic by the end," says James Appleton, a photographer from Cambridge, who has now won the race three times. "I was out of action for three hours afterwards," he says of that first win, "in the first-aid station being warmed up, completely useless. I had no strength, no energy, I was barely able to get myself warm with the help of paramedics. I've felt my leg bone nearly break, I've had things dislocated, been shredded by the ice and the barbed wire. You get to the end broken."

In January, there was another near-fatality during Tough Guy: a competitor was knocked out and nearly drowned before stewards rescued him. "The Lord was with me, the Lord was with us," Wilson tells me, driving us out on to the course to see where it happened: an underground obstacle filled with mud called the Vietcong Torture Chamber Tunnels. Even so, Wilson is bullish on the subject of safety. "I have perfected it inasmuch as, if somebody is going to get seriously injured or killed, they've got to be suicidal – they're going to have to use our obstacles for suicide. It's impossible." The deaths in America, he says angrily, are down to "neglect and greed" on the part of organisers: "Greed causes serious accidents and serious deaths."

Wilson is not as delighted about the surge in popularity of his idea as you might expect. Two years ago he and Tough Mudder's Will Dean reached a settlement after years of legal wrangling. This is a long and depressing saga that takes in much mutual public mud-slinging, but at its root is the accusation that Dean ripped off Wilson's idea, his obstacles and his slogans after visiting South Perton Farm in 2008; Tough Mudder's launch website featured photographs and video taken at a Tough Guy event. The legal settlement was confidential but, according to court documents, Tough Mudder paid out $725,000.

Wilson says he has no plans to create Tough Guy franchises outside the UK, although he has other expansion plans. He talks about setting up a Tough Guy competition for children, and about involving disabled contestants. He wants to attract more women, who currently make up only 10% of the entrants, "because women are much more capable than men. They smile all the way. The men pull their faces, they scream, they shout, they're cowards, they're self-pitying. Women just enjoy it." He also wants more over-70s: he claims to have developed a series of what he describes as "magnificent exercises" for pensioners, which among their manifold benefits include an effect on wrinkles he compares to Botox. "They could look like me," he enthuses. "I don't look like someone's been chopping wood on my face, do I?"

The question of why endurance obstacle racing has developed such a huge appeal is an intriguing one. One theory is that it appeals to those who are no longer satisfied by road running or marathons, but winner James Appleton isn't sure. Only about 20% of the 5,000 entrants, he estimates, have even seriously trained. It's mostly "guys who might occasionally play five-a-side football with their mates. They're just there for an experience. You see a group of them dressed up like cavemen, carrying clubs, or wearing suits. They've got this 'Let's have a fun day out' attitude to them."

He agrees with another competitor, who told him that he thought the races' popularity had something to do with "the Facebook generation". "These days, people have a real desire to express themselves over the internet. They create a character for themselves online, almost like a PR campaign: they do things, stick the photos online, they're saying, 'This is who I am.' The photos from Tough Guy are visually exciting: people covered in mud, running through fire, spitting mud out of their mouths. They can put them online and go, 'Look at me doing this, aren't I a sportsman?' People are always thinking about how they appear, and this is a very good way of making themselves look like hardcore soldier-type athletes, when at the end of the day, with a couple of weeks' running just to break their legs in, anyone could do it."

There are other theories. Robert Twigger, author of Being A Man (In The Lousy Modern World), talks about men who are desperate to prove they're men in "a culture that constantly tells us the differences between men and women are less important than the similarities". "You might feel you have to define your difference and go out and do something hyper-masculine, a bit ridiculously masculine, really," he says. Twigger thinks the apparent wildness of the race is another part of the appeal. "Even if you do something like rugby, which is perceived to be a tough sport, there are all these rules and regulations. And we've got enough of those in our lives. We've created a culture where we think everything is rule-bound, where you don't do things because you imagine all the red tape involved. Here's a chance to do something that appears to be without all those rules."

"At the very basic biological level, races like this do release neurotransmitters and hormones that give a natural high," says George Karseras, a chartered occupational and sports therapist at consultancy the Leap Partnership. "It's about feeling alive. You don't get the sense of feeling alive so much as when you confront something life-threatening. You're out of your thought processes, you're out of your mind. It's a switch-off mechanism, an extreme one. People doing these races aren't thinking, 'Oh, how's my job going?' These days, because of mobile phones and the internet, we're never really away from work. We need something extreme to overcome this extreme stimulation we're used to."

The latter is a theory with which Billy Wilson would agree, albeit in his own inimitable style. "We take you to the very edge of your endurance, we strip you of all your energy, you go into delirium," he says. "And when you go into delirium, you reach that space between life and death. And in that space, your whole life passes before you in seconds, and the future comes to you. A million thoughts hit you – you don't know what's happening. You're in such a state, so terrible that you don't ever want to come to Tough Guy again. Then, a week or two later, everybody comes back with the same words. 'It was a life-changing experience. I'm now a new person. I'm now looking at life in a different way. I'm now going to start doing something for everyone else instead of being so selfish. I'm now going to be better at my job. I'm now going to be not so snappy and nasty to the secretary or my wife or whatever.' They want to come back and do it again, because they've had such a fantastic experience!"

Enthused, he starts telling me about another of his plans. He wants the government to set up 100 Tough Guy-style "forest gyms" within inner-city boundaries, as a way both of commemorating the centenary of the first world war and "resolving the obesity crisis". He fixes me with a stare and lowers his voice. "Now you understand," he says, "why I believe I can change the world."