It's been a dirty word among runners for decades, but it turns out that pronation – the inward roll of your foot as it hits the ground – may not be such a bad thing after all, according to a new study in the British Journal of Sports Medicine.
As interest in barefoot, minimalist and other unconventional running styles has grown, researchers have taken a harder look at running-shoe technologies such as soft cushioning, an elevated heel and "motion-control" designs that limit excessive pronation. The latest study, by researchers at Aarhus University in Denmark, takes aim at the idea that runners should be fitted with different types of shoes based on the degree of pronation in their feet.
The study design was simple: 927 beginners who were interested in starting a running program were issued with identical shoes and GPS watches, and divided into five groups from least pronated to most pronated based on their "foot-posture index," a measure of foot angle when standing still. They were given no instructions on how much to run or how often; over the following year, their running distance and injuries were carefully tracked.
The current advice from shoe companies is that runners with the most pronation should opt for motion-control shoes, those with the least pronation should wear "neutral" shoes and those somewhere in the middle need "stability" shoes. In this case, the shoe issued to all the runners was a neutral one (provided to the study at reduced cost by Adidas) – a recipe for disaster for subjects with severe pronation, you might think.
By the end of the year, 252 of the participants had sustained running-related injuries – but when the results were broken down by pronation group, there were no significant differences in injury rates. If anything the "pronated" group suffered fewer injuries per kilometre run than the "neutral" group, despite the lack of pronation control in their shoes.
The study has several strengths that are unusual in running research, such as the large number of subjects, the long follow-up period and the fact that clinicians assessing the injuries were blinded to their patients' pronation score, says Blaise Dubois, a physiotherapist at the Running Clinic in Quebec City.
"We need more of this type of study," says Dubois, who is currently planning his own large-prospective trial on the links between shoe choice and running injuries, in affiliation with Laval University. "It's important to reconsider the 'old dogmas.'"
On the other hand, anyone using orthotics was excluded from the study, Dubois points out. This may have eliminated precisely those subjects most likely to suffer injuries when running without pronation control. Also, the subjects had no running injuries to begin with. In runners who are injured or have previously been hurt, it's possible that assessing foot posture and reducing (or in some cases increasing) pronation could help eliminate the imbalances contributing to the injury, says the study's lead author, Rasmus Ostergaard Nielsen.
Still, the results offer the strongest evidence yet that pronation shouldn't be the determining factor in how you choose your shoes. This is consistent with a 2011 University of British Columbia study, in which runners were randomly assigned to one of the three main shoe types. In that study, those who happened to get the "correct" shoe for their foot type were no less likely to get injured than those in the "incorrect" shoe.
All of which leaves runners with little to go on when they choose their shoes – except one obvious factor. Research by Dr. Benno Nigg at the University of Calgary has offered preliminary evidence that the feeling of comfort when you try on a pair of shoes relates to how well the shoe is suited to your foot, and ultimately to your injury risk.
Though it sounds simple, this approach integrates your body's feedback about how much your foot is pronating, how it strikes the ground and how well the shoe fits your particular foot type. (Note that comfort needs to be assessed while actually running in the shoes.)
And there's also a more general message, Nielsen and his colleagues point out: When you get injured, you can't always blame the shoes. The underlying cause of most injuries, whatever you have on your feet, is simply "too much, too soon."