People are taking to running in record numbers, so it's no surprise that selling running shoes - the only essential gear you need for the sport - has become a lucrative business.
Research company NPD Group reported that consumers worldwide spent US$15 billion on running shoes in 2011, up 13 per cent over the previous year. Running is worth almost twice as much as soccer globally, driven by hardcore runners, newbies and fashionistas alike, according to a recent report by Bloomberg.
In the United States, which accounts for 40 per cent of the global total, running shoe sales grew 8 per cent last year. More than 38 million pairs were sold in America in 2011, according to a US National Sporting Goods Association report.
In a highly competitive market where traditional footwear giants are being challenged by niche brands, innovation is flourishing. Here's a look at the hottest trends.
Featherweight road racing shoes, also known as "racing flats", have been around for decades and are used mainly by distance runners. But it was the glove-like shoe Vibram FiveFingers that really sparked the minimalist running shoe trend and made it mainstream around 2005.
This year, pretty much every major brand has its own range of super-lightweight trainers. These include adipure by Adidas, Brooks' Pure line, Nike's Free and Saucony's Natural range, among others.
Compared to traditional running shoes where the difference between the height of the heel and forefoot (known as a "heel-to-toe drop") could be 10 to 12mm, minimalist shoes feature a drop of between zero and 6mm.
"The theory behind this is that it allows, or promotes, a more natural running style, with a smoother transition from rear-foot to mid-foot to toe-off," explains podiatrist Douglas Horne, who runs a private practice in Discovery Bay.
"This lower heel-to-toe drop reduces the occurrence of the two-beat foot fall - a heel strike followed by an uncontrolled shift of the foot into a forefoot slap on the ground - which can become painful on the ankles and shins."
These shoes range from the extreme "barefoot" shoes to slightly more cushioned variations. Barefoot shoes, such as the FiveFingers or New Balance Minimus, have a very thin rubber sole (just 3mm) for protection. They weigh about 140 grams per pair, or less than half the weight of a typical running shoe.
Other minimalist shoes offer a bit more cushioning, while still allowing the foot to flex naturally. Mizuno, considered a brand for serious runners, for example, finally jumped on the trend, designing from scratch two new models: the Wave Evo Cursoris and Wave Evo Levitas.
Both shoes have zero drop, but offer 18mm and 14mm of cushioning respectively. In comparison, the brand's traditional staple, the Wave Rider 16, has a 28mm high heel and 16mm high forefoot, and weighs 283 grams.
The minimalist trend is not for everyone - and may cause injury. Hence, brands are responding by producing more forgiving models while still allowing for the sensory connection between the foot and the ground.
The result is the proliferation of the lightweight running shoe, whose market share in the US has more than tripled year on year to reach 14 per cent in February last year. This growth contributed nearly 60 per cent of the total gain in running shoe sales in the US, according to NPD. Examples include the Saucony Virrata, Brooks Pure Flow 2 and Salomon S-Lab Sense Ultra. "This is an inevitable change from the super-skinny minimalist shoes, which was mainly marketing led, to something a bit more useful to a greater percentage of runners," says Horne. "Not everyone has the mechanics or the body weight to run on concrete with a 3mm sole on their shoes."
Karlyn Harfoot, a private practice podiatrist in Hong Kong, adds: "Due to the amount of cushioning in previous running shoes, the natural running style is altered and becomes a habit. Like any habit, it is difficult to break. Some will find it easier to make the changes than others. But due to hard surfaces with no give, such as marble granite and concrete, we do need some cushioning."
Transitioning to a minimalist shoe takes time - more than 10 weeks of low-intensity running is advised, according to a new Brigham Young University study in the journal Medicine & Science in Sports & Exercise. It's a lot of effort for the regular runner, notes Horne, "most of whom just want to run".
Horne also suggests that "the science which was touted as the reason for moving towards a more forefoot strike [as promoted by minimalist shoes] is now being questioned and challenged by other research, which in some cases seems to say the complete opposite".
The demise of motion control
Controlling how your foot rolls between landing and pushing off the ground - a motion called pronation - had been a focus of running shoe designers. If your foot rolled in too much (overpronation), you'd be told to get a motion-control shoe that was stiff and heavy, with plastic inserts and/or extra-dense foam ("medial posts") in the sole under the arch.
Now, influenced by minimalism, such shoes are getting svelter. For example, the latest incarnation of Nike's 17-year-old flagship stability shoe, the Structure Triax, loses the very technologies that changed the industry in its early years. A new type of foam that enhances the foot's natural mechanics has replaced the medial post. Lightweight mesh has replaced restrictive materials in the upper of the shoe. The Nike Air sac in the heel has disappeared. The result: a shoe that's 15 per cent lighter.
"[Christopher McDougall's] book Born to Run caused a lot of people to question whether they needed motion-control technology in their shoes," says Japan-based sports physiotherapist and triathlon coach Bevan Colless. "Now, most serious runners are looking for more flexible shoes to allow the foot more of its normal movement, and hence to let the body become stronger and more adept at absorbing shock."
New materials for cushioning and shoe uppers, and new manufacturing processes such as welding instead of stitching, have led to lighter and more comfortable shoes that shoe companies claim perform better than ever.
Last month, Adidas launched the Energy Boost in Hong Kong, which features a type of cushioning said to return energy to the wearer. Instead of the standard ethylene-vinyl acetate (EVA) foam, Adidas partnered with German chemical giant BASF to create a thin, lightweight yet bouncy midsole made of tiny melted "energy capsules" that help the wearer run for longer with less effort. The material is also said to have tremendous resistance to heat and cold, and is more durable than EVA.
The upper on the Energy Boost features a stretchy, breathable mesh material that fits like a sock, while elastic polyurethane strips across the upper provide targeted support and stabilise the foot.
Nike, too, launched its own sock-like upper called Flyknit last year. The material is made in one piece, using polyester yarns and cables that are threaded together. The FlyKnit Racer made Time magazine's Best Inventions of 2012 list.
Nike recently launched the "Steaming Lounge", where FlyKnit shoes are heated in a machine and then slipped onto customers' feet, moulding to the exact shape of the wearer.
For New Balance, welding ultrathin synthetic overlays instead of sewing heavier ones helped the brand make the 91-gram RC5000 flats.
Newton Running, Hoka One One, Inov-8, On, Skora, Topo Athletic and Altra - you may not have heard of these brands, but you should probably keep them on your radar the next time you go shoe shopping.
"These new trends have opened up the market for new companies to come in and challenge the established heavyweights," says Colless. "Some big companies are trying harder to adapt, such as Brooks and New Balance, and other companies have been sitting back and waiting for the fad to end. It is going to be really interesting to watch it develop."
Horne adds: "The rise of niche brands, often with their own specific scientific approach - or gimmick - shows that not all shoes work for everybody. Many of the niche shoes have moved away from the forefoot/mid-foot strike theory to the more natural running style - a simple claim to make, as what is natural has yet to be properly classified. For me, it's running in a way that's comfortable for you, fulfils your needs and doesn't cause injury."
The type of shoe can immediately change your running style. A University of Kansas study to be published in the Journal of Paediatric Orthopaedics put 12 teenage track athletes on a treadmill at four speeds, wearing different shoes from classic cushioned running shoes with a heel or racing flats, or even barefoot.
The change in gait was instantaneous. For those with cushioned shoes, their heel struck first nearly 70 per cent of the time, compared to less than 35 per cent of the time while in racing flats and less than 30 per cent of the time when barefoot.
Harfoot's advice: find a shoe that fits you, is suitable for your sport, and disregard the brand.