If, like me, you run regularly enough to use customised trainers, the fun of choosing new ones can be outweighed by the embarrassment of having to run in public while shop assistants analyse your running style. Poor and lacking co-ordination would probably be the best way to describe my style, but the assistants aren’t looking for elegance. They are observing how much your feet turn inwards, or "pronate", when they hit the floor. I'm told that I'm a mild over-pronator and I need the right kind of shoes to prevent me from getting hurt. But is it true that people whose feet roll inwards more than others are at greater risk of injury? And if so, do special shoes help to solve the problem?
Most runners strike the ground first with the outside of their heels. As the foot comes down it rolls slightly to meet the floor. It's a normal mechanism that protects the feet and legs by distributing the forces exerted by impact with the ground. Flatter feet with low arches tend to roll more.
Over the last four decades manufacturers have been designing ever-more sophisticated shoes, which they claim can help those with less-effective natural shock absorption due to over-pronation (or, less commonly, under-pronation). The premise is special trainers that cushion the feet and raise the heels of pronators realigns the foot, keeping it more stable and reducing the impact of each step.
In June, researchers in Singapore published a meta-analysis of 29 previous studies on the relationship between foot type and the risk of injury. They found that those who under- or over-pronated were 23% more likely to suffer foot, ankle, knee and thigh injuries. One reason this has been such a controversial area is that researchers define and measure over-pronation in different ways. The recent analysis found a link to injuries for those defined as being outside the normal pronation range, according to visual or physical examination, and to the Foot Posture Index, a diagnostic tool that includes six individual components of pronation.
However, the authors pointed out that foot type was only weakly associated with increased risk of damage. In other words it only accounts for a small proportion of injuries. Somewhere between 37% and 56% of recreational runners hurt themselves during the course of a year, mostly due not to falling or tripping up but rather the repetitive nature of running.
When it comes to the question of whether customised footwear prevents injuries, the evidence is so sparse that some consider it to be a myth. In 2009 Craig Richards at the University of Newcastle in Australia trawled the scientific literature on the benefits of prescribing elevated cushioned heels and other measures to counter over-pronation. Surprisingly, even the evidence that running on hard surfaces led to more injuries was weak. At the time Richards found no randomised controlled trials assessing whether elevated heels prevented injury, and nothing in peer-reviewed journals on how shoe design affects injury, performance or enjoyment of distance running.
He and his co-authors suggest a treatment had been presented as standard for more than 20 years with no evidence to back it up, despite several authorities in the field having highlighted this lack of evidence. They don’t blame physiotherapists, coaches and specialist shoe-shop assistants who give advice, rather they blame footwear researchers for failing to conduct the research that would allow these views to be based on proper evidence.
A few studies have been carried out since then. In 2010, US Army scientists carried out research involving 1,600 US Marines recruits, in which around half received shoes designed to reduce their risk of injury based on their foot type. Those with low arches got shoes designed to actively reduce pronation, those with normal arches got "stability shoes" with moderate pronation control, and those with high arches got cushioned shoes. The other half all received stability shoes. After 12 weeks of training, being prescribed with special shoes made no difference to the risk of injury.
Research published in 2011 even found that runners given shoes that provide extra support to counter over-pronation spent more days injured. However, bear in mind it was a small study with just 12 over-pronators.
Built for comfort
This summer, the debate flared up again following the publication of a much bigger study involving a group of people new to running. Adverts in Danish newspapers and gyms attracted 927 participants, ranging in age from 18 to 65. Each person was assessed for their degree of pronation and then given the same lightweight running shoes without extra cushioning or raised heels. In effect, some were randomly assigned to what many shops and experts would consider to be the wrong kind of shoe.
For a year the participants ran for as little, or as far as they wanted to each week, chalking up 203,000 miles between them. A quarter were injured, but whether or not they had normal foot posture, or they under- or over-pronated made no difference. In fact of those who ran an average of at least 11.5 miles a week, over-pronaters were less likely to get injured.
While this study suggests that foot type is irrelevant for runners wearing ordinary shoes, it can’t tell whether special shoes make a difference. For all we know using them might have led to even fewer injuries among participants who over-pronated. Also those who already owned shoes with special insoles were excluded from the study. They might have been the most prone to injury and the most likely to benefit from special shoes.
So if the evidence for or against customised shoes is unclear, where does that leave the everyday runner? Some are turning away from fancy trainers altogether, and there’s a growing trend towards wearing very thin shoes or even running barefoot. I had a go at running without footwear myself and it felt like a very free way of running. But as I generally run on the dirty and often wet streets of London rather than on sun-kissed beaches, I'm not sure I'm ready to make a habit of it. There has been some research examining how barefoot running affects the angle at which the foot strikes the ground, but again there’s a lack of controlled trials, so we don’t know whether it leads to fewer injuries.
The author of the Danish study, Rasmus Nielsen, from Aarhus University, says clinicians should focus their advice on training, distance, duration and intensity, rather than shoe choice. In the meantime the results of a study by Benno Nigg from the Human Performance Lab at the University of Calgary suggests that if running shoes feel comfortable they may reduce the risk of injury. His team gave soldiers a choice of six different shoe inserts of various hardness, elasticity and shape of the arch and heel cup. They were then asked to keep diaries of any injuries over the next four months. Nielsen found that whichever insole they chose, injuries were lower than among participants in a control group who ran without insoles. The inserts varied a great deal in their shock absorption, so what seemed to matter was comfort.
Craig Richards says distance runners should be advised that the ideal type of running shoe is unknown, but that those who are not getting injured should stick with the type they already have, and only try different models if they are getting hurt. In the meantime the best advice for anyone starting out seems to be to try on lots of shoes and to choose the ones that are most comfortable. At the very least this might spare you the public humiliation of having your running style analysed by shop assistants while everyone else in the shop stares.
You can hear more Medical Myths on Health Check on the BBC World Service.
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