Jan. 5: Do Running Shoes Cause Running Injuries? A Few Insights on a Dismal Science

I've spent the last several months buried in research papers about running injuries and their causes. (For a story that will appear in the March issue of Runner's World.) This has not been a happy period. The problem: Almost nothing is known.

For example, consider the best medical paper I could find on the subject--"Incidence and determinants of lower extremity running injuries in long distance runners: a systematic review"--which appeared in the British Journal of Sports Medicine in 2007. The Dutch research team began by identifying more than 1000 journal articles on running injuries. Then they tossed out the ones they found of poor design, poor analysis, and generally bad science. This left them with 17 papers. Get the picture?

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And what causes running injuries? The Dutch researchers felt confident about only two causes: previous injury, and high weekly mileage. Frankly, I'm growing weary of the studies, they contribute so little. The only thing I truly believe at this point are the words of Dr. George Sheehan: "We're all an experiment of one."

I only mention this because millions of runners are talking about injuries and running shoes today, based on a new study that surfaced yesterday. It's garnering headlines like: "Running shoes more dangerous than high heels" or "Barefoot running better than training shoes." I read the study quickly, and will give you a few comments below. But first, here's the key information you should know about running shoes and running injuries.

*** No one has ever proven that any running shoes prevent running injuries.

*** No one has ever proven that Army boots, basketball shoes or flip flops either increase or decrease running injuries.

*** No one has ever proven that barefoot running prevents running injuries.

*** Indeed, no one will ever prove any of the above. (It would be too complicated and expensive, and the only public health benefit might be fewer inflamed Achilles tendons).

*** Also, no one knows if the incidence of running injuries is increasing, decreasing, or staying the same. There are several simple reasons for this: 1) There's no commonly accepted definition for running injuries; and 2) the running population has changed substantially in the past 25 years (more women, more inexperienced runners, more slow runners, more overweight-obese runners, etc). So any and all comparisons are apples vs oranges.

Okay, how about that new "Running shoes are worse than high heels" study by D. Casey Kerrigan et al? The report found that runners experienced greater torques and forces when running in shoes than when running barefoot. This sounds bad. And it might be. Except that no one knows anything about how torques and forces are related to running injuries. It's all guesswork.

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Also, Kerrigan isn't exactly a disinterested party. She has designed some sort of "minimalist" running shoe, and stands to profit by attacks on conventional running shoes. The same is also true of Craig Richards, who last year published the widely-quoted study challenging shoe companies to produce evidence that their shoes actually prevent injuries. Apparently, none did. Richards has a stake in a minimalist shoe company. I'm not calling Kerrigan and Richards liars. Far from it, I agree with Richards's conclusion. But we should understand the motivation behind their writing and their research projects.

The other thing to understand about Kerrigan's study is that she didn't identify any running injuries. She didn't even look for them. Instead, she went looking for various torques and forces. This is an entirely reasonable approach, but it doesn't prove much, for the simple reason that we don't know how torques and forces relate to injuries. Some forces are bad; you can break a toe if you kick a rock while trail running. But other forces are good; think about what happens to the astronauts when they circle the globe with zero g's--their bones turn to mush.

I wish I had the space to attempt an explanation of how complicated this forces and injuries thing can get. In one amazing study, a researcher asked athletes to jump off a bench onto different-color floor mats that provided different degrees of cushioning. They were told when they were jumping onto a well-cushioned mat and when they were jumping onto a less-cushioned mat. Only this mat story was a complete sham, as all the mats were identical. Nonetheless, the athletes registered more shock forces when told they were jumping onto a well-cushioned mat than a less-cushioned one. Why? According to one hypothesis, the athletes relaxed more (they didn't "pre-activate" their muscles) when they thought they were headed for a soft landing. As a result, the cushioning increased the forces the athletes experienced rather than decreasing them.

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Based on this study, one might predict that Kerrigan's runners would register greater forces in shoes than barefoot. Obviously, they would expect the shoes to provide cushioning. They would relax. They wouldn't pre-activate. And the result would be greater forces, not smaller ones.

This is exactly what Kerrigan found in her study. She concluded that conventional running shoes might increase the risk of injuries. I conclude that there are lots of other factors involved.

Kerrigan also reported that barefoot runners adopted a six percent shorter stride than shod runners. Common sense tells us they did this to reduce forces. Only Kerrigan says that's not the case; she used some sort of mathematical analysis to eliminate shorter stride as a factor. I'm dubious, but I'd like to learn more.

Kerrigan also wrote that her running shoe study produced results "even greater" than work she has previously done with walking and high-heeled women's shoes. One should be careful about comparing the forces of running and walking, they're so different. In this case, the comparison led to many mistaken newspaper headlines and reports. Kerrigan didn't find that running shoes were worse than high-heel shoes; as I read her study, she found that running shoes produced greater differences vs. barefoot running, compared to high heel shoes vs. normal walking shoes.

In building her case that running might lead to arthritis, which she correctly notes has never been proven, Kerrigan particularly emphasizes a study of former East German elite marathoners. This is a population far afield from any normal running group. She should have noted this major difference rather than using the study to reinforce her own argument. Here's a conclusion directly from the East German study: "Osteoarthritis of the knee joint is rare in former elite marathon runners."

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I'm sure Kerrigan knows a lot more about running shoes and injuries than I do. I also suspect that neither one of us knows very much, because, frankly, no one does.

That said, I agree with her apparent position on one important point: Much of what we put under our feet has the potential to do more harm than good. You can't "raise the platform" without increasing instabilities. When you build one of those house-of-cards structures, the higher you go, the closer you get to collapse.

That's why I believe many of us should buy the lowest-tech running shoe we can get away with. For the few who live in Shangri-La, that might mean no shoe at all. For others, it might mean a simple racing flat. For others, the very Brooks Adrenalines that were used in Kerrigan&# 39;s study.

But some runners shouldn't even look at any shoe other the Brooks Beast, or a similarly built-up shoe. Because, in their experiment of one, that's the only shoe that will work for them.

[UPDATE, JAN, 8: I just found this nicely reported article on the Kerrigan study at WebMD. It includes an interview with Kerrigan, who says she isn't advising anyone to run barefoot, and with several other running experts who don't seem to find the study very helpful.


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