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SINGAPORE - The sport of running seems as simple as putting on your shoes and heading out the door. But with the mind-boggling variety of shoes on the market today, just which pair should you be lacing up?
There are four general types of shoes: cushioning, stability/ motion control, neutral and minimalist, according to podiatrist Tiffany Chew of Tan Tock Seng Hospital's Sports Medicine and Surgery Clinic.
With companies introducing more specific features in the construction of their shoes, Ms Chew says extra care needs to be taken when choosing a pair as the wrong choice can increase the risk of sustaining running injuries.
"A feature can be beneficial for one person, but dangerous for the other," she says.
Innovation is certainly flourishing in a highly competitive running shoe market. Research company NPD Group reported that consumers worldwide spent US$15 billion (S$19.2 billion) on running shoes in 2011 - up 13 per cent over the previous year.
Minimalist shoes - ranging from the extreme "barefoot" shoes to slightly more cushioned variations - are still the hot trend. Shoemakers, however, realised that most people cannot get by in barely-there soles without injury and have introduced more forgiving models, resulting in the proliferation of the lightweight running shoe.
In the US, the market share of such lightweight shoes 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 country, according to NPD.
In traditional running shoes, the difference between the height of the heel and forefoot (known as a "heel-to-toe drop") can be 10mm to 12mm. By contrast, minimalist shoes feature a drop of between 0mm 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 Hong Kong.
The absence of an elevated heel - women, just think of how your walking style changes in stilettos - does away with what Mr Horne calls the "two-beat foot fall": a heel strike followed by a forefoot slap on the ground. This can be painful on the ankles and shins.
Minimalist shoes offer varying levels of cushioning, from just 3mm of rubber in the glove-like Vibram FiveFingers to 18mm of foam in the featherweight Mizuno Wave Evo Cursoris.
When deciding how much cushioning you need, Ms Chew says there are a few factors to consider.
First, the heavier you are, the more cushioning you need to absorb the impact on your feet and legs. "While running, (the impact) can be as high as three to six times one's bodyweight," says Ms Chew.
Second, the strength of your leg and foot muscles matter, because that affects how the impact forces are diffused. "Existing muscle imbalance or weakness will not be able to withstand or accommodate the lack of cushioning."
Lastly, if you are used to walking or running barefoot, then you could probably get away with less cushioning. "The foot is a highly adaptive structure, if given enough time to adapt without injury."
Cushioning aside, Ms Chew notes that another important factor is the amount of support a shoe provides. The heel counter and mid-shank of the shoe should be adequately firm with a securing mechanism around the ankle. This is especially crucial for runners with abnormal foot biomechanics and pre-existing overuse injuries.
Conventionally, foot types are simply categorised as flat, high-arched or normal. "However, the foot is not that simple," Ms Chew says.
"The structure and mechanics of the foot are determined by the interactions between the different joints and their alignment in relation to each other in the feet."
The motion and forces that occur due to misalignment often result in instability and stresses to structures in the feet and lower limbs, which then increase injury risk in runners, she says.
The type of shoe can immediately change your running style. A University of Kansas study 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 to racing flats, and 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.
If you are thinking of changing your running style, however, Ms Chew notes that there is not enough conclusive research on just which style lowers the risk of injuries or is more energy-efficient.
"It seems more that each style has its own risks for injury. It only makes sense to change one's natural running style if there is the presence of injury and the change in style is to reduce strains/stresses of the structures involved."
In finding your perfect running shoe, she says the key is to first understand your own foot biomechanics. Then, consider the following factors:
"Your level of commitment and interest in the sport - the type of footwear differs whether you're recreational or competitive.
"Level of experience - beginners may be better off with conventional running shoes for better support and cushioning to prevent traumatic and overuse injuries.
"Any past or pre-existing injury - if you do have one, it is best to seek a podiatrist's opinion on footwear.
"Your natural running style - forefoot, mid-foot or heel-toe? The latter would require more cushioning.
"Shoe fit - while standing with shoes laced, there must be a thumb's space in front of the longest toe for correct sizing."
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