What kind of running shoe should I get to reduce my risk of getting injured?
For three decades, running shoes have been constructed to fulfill two basic missions: cushion your foot's landing and control its "pronation" - the amount that it rolls inward with each step.
"I was completely convinced that impact is something bad, and pronation is something bad, and I wanted to show that," recalls Benno Nigg, a biomechanics researcher and co-director of the University of Calgary's Human Performance Lab, who helped shape the original theory of pronation.
The initial studies were promising. Specialized running shoes, designed to address different degrees of under- or overpronation, could indeed reduce the impact forces shooting up through the legs of runners in lab testing. In the United States, sales of these high-tech shoes jumped from 25 million pairs in 1988 to 40 million in 2009, and growth was similar in Canada.
But there was just one problem: Running injuries didn't disappear. While reliable statistics are hard to find, it appears that levels of common running injuries, such as plantar fasciitis, Achilles tendinitis and runner's knee, have stayed roughly constant. Shoe researchers now face the possibility that the theory has been wrong all along - which would suggest we should either ditch shoes altogether, or look for simpler cues, such as comfort, to guide our shoe choices.
For Dr. Nigg, the realization came gradually. While study after study showed that shoes could manipulate impact forces, no one could produce any evidence linking these forces to injury rates.
The most telling test of the "pronation paradigm" came in a paper published last year in the British Journal of Sports Medicine by researchers at the University of British Columbia working with the Nike Sports Research Laboratory in Oregon. They studied 81 women enrolled in a 13-week training program prior to a half-marathon, dividing them into three groups based on their foot type and degree of pronation. But instead of fitting them with the "correct" shoe for their foot type, the researchers randomly assigned them to one of three types: neutral, stability or motion control.
"We were a bit nervous, because … if you see someone who is highly pronated, putting them in a neutral shoe may be a recipe for causing more pain," acknowledges Michael Ryan, the study's lead author, who is now a postdoctoral researcher at the University of Wisconsin.
He needn't have worried. Twenty-six of the 81 women, or 32 per cent, reported injuries, but there was very little correlation between foot type, shoe type and injury rate. In fact, subjects who received the "correct" shoe for their foot type were even more likely to get injured or report discomfort than those running in the "wrong" shoes. More than half of the subjects assigned to motion-control shoes - the heaviest and bulkiest category for severe pronators - reported injuries, including all five of those with highly pronated feet.
Chris McDougall, author of the 2009 bestseller Born to Run, greeted the results with a blog post titled "Breaking news from Nike: We've been talking a lot of crap, and selling it." In his view, the results were proof that we should be running barefoot, or at least in "minimalist" shoes that force us to mimic the gait of our caveman ancestors.
It's not that simple, though. It's true that minimalist shoes steer you away from the most common running mistake of overstriding (taking steps that are too long, so that your foot pounds into the ground far in front of your body instead of underneath your centre of gravity). But right now, barefoot running is at the same stage pronation-control shoes were in 1985: an intuitively attractive idea that makes sense, but hasn't yet been tested. (Dr. Ryan and his colleagues are planning a follow-up study that repeats their previous experiment and also includes a minimalist shoe.)
In fact, numerous studies have found that training decisions - how far you run, how fast, how much recovery you allow - are far more important than shoes in predicting injuries. Those factors account for about 80 per cent of injury risk, according to one prospective study by Dr. Nigg's group.
So where does that leave runners trying to choose a shoe? "The only thing we have is comfort," Dr. Nigg says.
A decade ago, he and his colleagues studied 206 soldiers who were given six different shoe inserts and allowed to choose whichever felt most comfortable. There was no apparent connection between the soldiers' foot types and the inserts they chose, but the number of injuries dropped significantly.
Dr. Ryan agrees: "The shoe should feel balanced. If it's over- or undersupported, your lower leg muscles will have to work harder, which will make it feel less comfortable."
As buying advice goes, that may seem a bit vague, but at least it's simple - and until further studies are completed, it's the best we've got.
Alex Hutchinson blogs about research on exercise at sweatscience.com. His new book, Which Comes First, Cardio or Weights?, will be published in May.