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Image via WikipediaWhat would you say, however, if you found out that these categorizations of running shoes were meaningless? What if the tests employed by the salesperson weren't very good at determining pronation to begin with? Even more startling, what if the amount that you pronate wasn't even related to the likelihood that you might get injured? These are the types of questions that have been addressed in several recent scientific publications, and which were in turn summarized and reported on in a remarkable article by Gretchen Reynolds on the NY Times Well Blog. The results might be shocking to some, not so shocking to others, and they demand a response from those making the shoes that runners rely on to keep them running safe and injury free.
Lets take a look at some of the science. In this post I'm going to focus on a study published on-line in June 2010 by Ryan et al. in the British Journal of Sports Medicine. One of the co-authors of this study, Gordon Valiant, works for the Nike Sports Research Laboratory - he's the same biomechanist that Alberto Salazar and Dathan Ritzenhein worked with to modify Ritzenhein's footstrike from heel to midfoot. Keep this in mind as you read this - one of the co-authors works for the biggest sports shoe manufacturer in the world. In their introduction Ryan et al. state the following surprising detail: "...despite over 20 years of stability elements being incorporated in running footwear there is, as yet, no established clinically based evidence for their provision." They then go on to point out that "Motion control running footwear has yet to be proven to prevent running-related injuries." Pretty amazing, isn't it? Makes one wonder if the shoe makers actually have "proprietary data" supporting these designs, or if the whole pronation-control shoe paradigm is nothing more than a giant marketing gimmick.
Their goal in the study, therefore, was to determine how women assigned to the three categories of footwear based on their observed degree of pronation would fare in terms of pain and injury experienced while training for a half marathon.
A total of 105 women were classified as either neutral (51 women), pronated (36 women), or highly pronated (18 women). Now here's the really interesting part. In a shoe store, the neutral women would be assigned a neutral shoe, the pronated women a stability shoe, and the highly pronated women a motion control shoe - go it? In the study, however, the researchers took each of the three groups of women (neutral, pronated, and highly pronated), and subdivided them into sub-groups so that one-third would get a neutral shoe (Nike Pegasus), one third would get a stability shoe (Nike Structure Triax - incidentally, the Triax was my first "real" running shoe, assigned by one of those slow-motion eyeballs I mentioned earlier), and the final third would get a motion control shoe (Nike Nucleus). This was done for each of the pronation groupings, so that what we have here is some women in each pronation category wearing each type of shoe (i.e., many of them wearing the "incorrect" shoe for their foot).
The women in the study were then sent off to take part in a 13-week training program to prepare for a half-marathon to be run in Vancouver, BC. Estimated weekly training volumes started around 20km and rose to a peak of about 40-45km. Over the course of the training program, researchers recorded the number of missed workouts due to injury by each runner, and reportings of pain at rest, during daily living, and following runs. Ultimately, only 81 of the women wound up completing the study (for a variety of reasons, 24 women dropped out).
The results showed the following:
1. 32% of the women missed training days over the course of the study. Another way to think of this is that there was an injury incidence of 32% in this population of runners, which is in line with other studies on running injury.
2. Motion control shoes "resulted in both a greater number of injured runners and missed training days than the other two shoe categories." In other words, motion control shoes faired very poorly all-around.
3. Every runner in the highly pronated group who wore a motion control shoe reported an injury. In other words, all runners (yes, 100%) who were supposed to be wearing a motion control shoe based on their degree of pronation got injured. It's a small sample, but this is simply astonishing. In fact, highly pronated runners actually fared better in neutral shoes!
4. Neutral runners experienced greater pain after runs when wearing neutral shoes than they did when wearing stability shoes. Although the authors point out that the difference may not be clinically significant, it is once again amazing that neutral runners faired better with a shoe that would not have been "prescribed" for them in a shoe store based on their degree of pronation.
5. Pronated runners experienced more pain after runs if wearing a stability shoe than if wearing a neutral shoe. Again, they did better wearing the "wrong" shoe for their feet.
So what can we conclude from all of this? First, although they have an admittedly small sample, it appears that motion control shoes offer little benefit, and in fact are more likely to cause pain and injury than any of the other shoe types. That fact that every single severe overpronator exprienced an injury in their motion control shoes begs the question of why anybody would use them? The authors themselves conclude that "This study is unable to provide support for the convention that highly pronated runners should wear motion control shoes." Interestingly, Christopher McDougall indicated recently on his blog that the life of the motion control shoe might soon be coming to an end.
Second, this study showed that neutral runners did better in stability shoes, and pronated runners did better in neutral shoes. Try to make sense of that one...
So what do the authors themselves conclude? The final sentence of their paper states: "Current conventions for assigning stability categories for women’s running shoes do not appear appropriate based on the risk of experiencing pain when training for a half marathon." More clearly, they conclude their abstract with the telling statement that "The findings of this study suggest that our current approach of prescribing in-shoe pronation control systems on the basis of foot type is overly simplistic and potentially injurious." Now wait a second. If this is true, then why does almost every shoe store on this planet classify shoes based on pronation control (i.e., neutral, stability, motion control, etc...), and place runners in shoes based on their arch height (more on arch height in another post to come soon) or degree of "observed" pronation? This is bewildering stuff, and further strengthens my belief that maybe it's time for a change in how we choose or "prescribe" our shoes.
I'll finish by relating a few quotes from Dr. Ryan, the lead author of this amazing study, as reported by Gretchen Reynolds' on the NY Times Well Blog. When asked how to choose a running shoe given his experimental results, Ryan says (and recall that his co-author is a biomechanics expert at the Nike Sports Research Laboratory - I give Nike a lot of credit if they signed off on publication of this paper, though I have no idea if they had any say in the matter):
“If a salesperson says you need robust motion-control shoes, ask to try on a few pairs of neutral or stability shoes, too...” “Go outside and run around the block” in each pair. “If you feel any pain or discomfort, that’s your first veto.” Hand back those shoes. Try several more pairs. “There really are only a few pairs that will fit and feel right” for any individual runner... “My best advice is, turn on your sensors and listen to your body, not to what the salespeople might tell you.”That last quote is right on the money - "turn on your sensors and listen to your body." Your body evolved to run long distances, and it evolved to do so barefoot. The realist in me knows that most people will likely never run barefoot, so if that's not your thing, look for as little shoe as you can handle and still run comfortably. Your body will let you know if it's happy, be mindful and listen.
Update 7/23/2010: I just published a follow up to this post: What is Nike Doing?: Speculating on a Shoe Market in Motion
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