In an era of superbrands and mega-marketing, trainers have kept their place as a feisty front-runner. They're not just a pair of shoes, but a triumph of the image-makers. They are sports shoes for people who don't play sport, symbols of affluence for people who don't have much money, and urban shoes for suburban kids. They might be packaged with plenty of talk about shoe technology, but it's their attitude, not practicality, that sells them.
And their image of hip streetwear has a global appeal, with people from Chicago to Shanghai ready to lace up the latest brands. These huge international markets have turned the leading trainer companies into commercial giants. In 2004, Nike reported record revenues exceeding $1 billion per month, and young people are paying almost pound;100 for a pair of the latest Nike Shox.
How did these brands become global superstars? Only a few decades ago, sports shoes were still a niche market. Now, the trainer companies are about fashion and lifestyle, selling a whole range of clothes and accessories. If you click on the Reebok website, it's Jamelia - a pop star, not a sports player - who is there to pitch you the advertising message.
Athletes have been wearing shoes to play sport for thousands of years, with the ancient Greeks and Etruscans having varieties of sandals that were strong enough to protect the foot, but light enough not to impede running.
And throughout history, shoes have been adapted for sports or purpose-made for leisure activities. Researchers at the University of Southampton found inventories of clothing from the household of Henry VIII showing he owned a pair of leather football boots.
The idea of companies making customised sports shoes began to develop alongside the great surge in interest in athletics and sports in the late 19th century. In Lancashire in the 1890s, Joseph Foster's company emerged as a specialist sports shoe manufacturer, producing hand-made running shoes for competitors in the modern Olympic Games, inaugurated in Athens in 1896.
This Bolton-based business eventually became the firm that is now known as Reebok.
But the types of shoe made by JW Foster and Sons were designed to help athletes run faster, and spiked running shoes were never likely to become a fashion statement. Instead, to find the ancestry of the trainer with street-appeal, you have to look at another humbler type of sports shoe - the plimsoll. This simple canvas and rubber shoe appeared in the second half of the 19th century, following the development of vulcanisation, which allowed rubber to be bonded more effectively with other materials. And, like trainers, the plimsoll appealed to a wide range of social classes and blurred the boundary between sport and fashion.
For the working classes, the mass-produced plimsoll was an affordable leisure shoe. Day-trippers or Sunday strollers didn't want to be stuck in their heavy working boots, and plimsolls were an attractive summery alternative. They also had the advantage of being easy to make new-looking again, with whiteners to restore the canvas uppers.
For the Victorian middle classes, plimsolls could be worn for any of the summer sports that were becoming popular, whether it was tennis, badminton, cycling or boating, or just for promenading along the seafront. And schools adopted the plimsoll as the all-purpose shoe for any kind of physical exercise, remaining a basic piece of school kit well into the years after the Second World War.
If the idea of young people playing sport in plimsolls now seems rather quaint, it's a tribute to the powerful marketing of trainers, which eclipsed their cheaper and simpler predecessors. In terms of how trainers managed to oust plimsolls from the nation's kitbag, perhaps a key difference was that plimsolls were not a brand. The name was a nickname, applied because people thought the high rubber sole looked like the Plimsoll line around the side of a ship.
The plimsoll was an easy-to-copy, universal type of shoe. But the companies that went on to become the trainer giants were built on the idea of exclusivity and a strong brand image. In the US, this process of branding "sneakers" had begun with the marketing of rubber-soled "Keds", launched in 1917 as a type of sport and leisure shoe.
But having established a brand name for a shoe, the other great success of the trainer companies was to link this name with the biggest names in sports, a tactic that has been applied again and again. In Germany, the Adidas company -named after its founder Adolf Dassler - provided the running shoes worn by Jesse Owen, the star athlete of the 1936 Olympic Games in Berlin. After the Second World War, this linking of brands to particular athletes continued.
But what really turned this into a global marketing exercise was the arrival of television coverage of sport. Every time a winner went up to collect a medal on a rostrum, the image-conscious shoe companies wanted to see their name in the picture. Whether it was the footballs being kicked in the World Cup or an athlete's running gear at the Olympic Games, they wanted their products to be part of the occasion.
Adidas and Puma (founded by Adolf Dassler's brother) were pioneers of this showcasing of their products and kept innovating to stay one step ahead. As well as getting medal winners to wear branded shoes, by the 1960s Adidas was producing branded tracksuits, so that people could dress like their sporting heroes.
Big names helped raise the stakes. In the 1970 World Cup, the Brazilian football legend Pele was wearing Puma boots. Adidas could hit back with Muhammad Ali wearing its clothes. It's easy to forget how quickly this branding of clothes spread throughout the sporting world and how quickly it left behind the world of the unbranded, low-cost pair of plimsolls in the duffel bag.
The first Nike-wearing Olympic medallist was the British runner Steve Ovett, in 1980. By the Barcelona Olympics in 1992, every US athlete who collected a medal was wearing something made by Nike. In the 1980s Nike took this marketing style to another level. In any popular history of the 1980s, Nike shoes are likely to get a mention, with the "Just do it" advertising slogan becoming part of the language. In multimillion-dollar sponsorship deals, Nike signed up US sporting icons such as tennis player John McEnroe and basketball's Michael Jordan.
And when Nike created an air-filled trainer to be worn by Michael Jordan - the Air Jordan - it fused the worlds of sport, sponsorship and designer clothing so that young people around the globe could literally walk in the shoes of a sporting legend. Of course, they were only a pair of shoes and they weren't going to turn a couch potato into a superstar athlete. But the brand name offered sporting glory by association, while at the same time retaining a sense of street-wise credibility.
It was in this era that the trainer began to emerge as a fashion item in its own right, with the luxury tag fitting in neatly with the decade of "conspicuous consumption". Instead of boasting about how little they had paid for their Oxfam coats, teenagers were boasting about how much more their "box-fresh" trainers had cost.
The different brands each had their own followers, with new types of shoe keeping the customers coming back for more. There was the Air Max and Air Force 1 from Nike, Reebok's Pump and the Adidas Superstar. While fashion was helping fuel the rise and rise of the trainer, the high retail price had to be justified. There had to be a clear difference between the highly expensive trainer and the bargain-basement plimsoll.
Trainer brands have always sold themselves as being innovative, whether it was Puma claiming the first Velcro fasteners in 1968 or Adidas using shark-skin for its sprint shoes in 1972.
But from the 1980s, trainers were sold as being a piece of high technology in a shoebox, with all kinds of elaborate claims for the performance-enhancing qualities of soles, heels and uppers. There was "forward thrust" for the sprinting and hi-tech shock absorbers to make the ride more comfortable.
They were marketed as being a product of refined engineering design, almost as if they were car engines rather than running shoes.
While much of this space hardware advertising seemed to be pitched at young men with an appetite for rap music and science-fiction, the 1980s also saw a huge boom in trainers for women, fuelled by the fashion for aerobics classes and work-out videos which could be played at home on the newly acquired VCR.
And Reebok in particular succeeded in selling female-friendly trainers, cut with softer materials and produced in less macho designs and colours.
Reebok's Freestyle trainer, launched in 1982 and specifically designed for women, became one of the biggest-selling trainers of all time.
But will trainers be able to retain their credibility? In their rise to prominence in the 1980s, they were sold as the embodiment of energetic living and ambition - footwear for winners in a tough world. As well as being the domain of high-achieving athletes, they were also sold as a symbol of inner-city street fashion, giving trainers a double-edged image.
The success of the marketing, pushed on by the rivalry between brands such as Nike and Reebok, was such that, in the 1990s and into the present decade, trainers have expanded into a much wider market. They might be advertised by edgy black teenagers playing basketball in an inner-city parking lot, but they're just as likely to be bought by plump white pensioners in Florida.
It's increasingly likely that they're being bought by someone living in a developing market, such as China. Nike might be steeped in American imagery, but for the first time last year it shifted more units overseas than inside the US. Operating in so many different global markets also makes them susceptible to upsetting local sensitivities. In December, Nike had to apologise for an advert in China after there had been complaints that a martial arts scene was demeaning to the national culture.
Trainers have become the footwear equivalent of blue jeans - a kind of global uniform. There are more than 350 million pairs sold in the US each year, as they've become the everyday shoe for millions of people who would never go near an athletic track.
Trainer brands have broadened their marketing to reflect this, putting their badges on all kinds of products that are unlikely to appear on any sports fields, whether it's baseball caps or designer watches. They've also broadened their endorsements beyond leading figures from popular sports.
Reebok has signed a deal with hip-hop performers in a project reinforcing the links between brands of trainers and music.
As trainer brands were absorbed into popular culture, they created their own unofficial mythology. The name Adidas was an abbreviation of its founder's name, but you can still find people who believe it's a secret acronym for "all day I dream about sex".Sports shoes have traded on their macho, urban image. And they've been used as a kind of code in ways that were unintended. In the US, baseball boots slung over a telephone wire were once supposed to be a sign that drug dealers were operating at that address. Street gangs and youth groups have worn different types of trainers, or used coloured laces as a symbol of affiliation. Wearing Air Jordans or Reebok Pumps was another way of sending a message. And musicians played on this by making sure that their expensive trainers were highly visible. In the 1980s, rap group Run DMC had a song called "My Adidas" with lyrics about their favourite brand and their trademark style of wearing their trainers unlaced. British football fans in the 1980s, the so-called "casuals", also adopted expensive trainers as part of their dress code.
For a product that is ostensibly about health and vitality, sports shoes have often also had a tough street image. This has been a longstanding feature of sports shoes. One version of how "sneakers" got their name was because robbers wearing these lightweight shoes were able to sneak up behind their victims without being heard.
In the 1980s, it became part of the urban mythology in the UK that young people were being mugged for their trainers. This reflected the status of trainers as the most desirable and expensive product likely to be in the possession of a teenager. And although young people are now more likely to be mugged for their mobile phones, trainers have continued to maintain their place as luxury goods. But such setbacks are unlikely to slow the spreading footprints of the trainer.
So is there any chance of a plimsoll revival? Not unless you can put on a hefty price tag and a clever logo, and call the rubber soles the "shox".
Teenagers, acutely aware of not wanting to wear the "wrong" type of clothes, are still looking at price tags on trainers of between pound;50 and Pounds 100. But when shoes are so dependent on their image, they are also vulnerable to bad publicity. And many manufacturers have been dogged by accusations that their expensive products are produced by cheap sweatshop labour in the developing world .
These claims, particularly prominent in the 1990s about conditions in the Asian factories where many trainer brands are produced, led to boycotts and calls for athletes to remove their endorsements. This has been a particularly uncomfortable problem for the companies. If they are selling trainers as expensive, hi-tech products, they don't want customers to think they cost very little to produce. For companies promoting an image of health and youthful vigour, it's a public relations nightmare to be linked to unhealthy, exploitative factories.
And so the big companies have made very public efforts to shake off the negative publicity about how their trainers are produced. This has meant signing up to monitoring systems and a variety of ethical trading agreements.