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.