Heel Motion Inside A Running Shoe

When writing about running mechanics and injury prevention I do my best to provide information that’s supported by scientific research. In theory, using an evidence-based approach would be more valid and reliable than simple relying on personal opinion to give running advice. There are many pitfalls in conducting running studies however, so it’s also important to question the validity of the research itself.

Among the scientific literature published pertaining to running, there are many poorly designed studies which greatly limit our ability to draw any meaningful conclusion based on the results of those studies. Jason Robillard recently wrote about this problem on his blog as it pertains to correct running form: 

The very fact that there’s enough variability in the published literature should be a huge red flag for all parties involved. Specifically, the results of the entire body of research may not be as valid as we’d like to believe. In other words, if there’s research that supports both sides of an argument and no consensus that one side is “right”, we should question the research itself.

There is a wealth of expert advice available to runners but very little in the way of concrete evidence to support any single opinion. One of the reasons for this is that there is a huge variability among runners themselves, in terms of everything from body composition to shoe selection. The Running Physio wrote an interesting piece on how despite over 30 studies of 24,000 runners we still have no firm conclusions on training errors and running injury prevention. Science is a slow process, and all possible variables need to be considered in order to draw conclusions that can be generalized to the entire population of runners. Different individuals are going to run with different mechanics so it is not all that surprising that studies have been inconclusive. 

I’ve written before about the difficulty in determining the true injury risk associated with varying degrees of pronation of the foot. There is not a lot of evidence that would suggest a high degree of pronation raises the risk of developing an injury, but a question that needs to be asked is how accurately we are able to assess pronation during running. How a runner’s joints move when measured on a treadmill in a lab may be different from their mechanics 5 miles into a run. We could design a study that records video of runners at a certain point in a race, but even then information regarding foot motion would be obscured by the runners’ shoes.

To illustrate this, here are two videos of the same subject running. In the seconds clip, a small window has been made in the back of one of the runner’s shoes to show the movement of the heel (rearfoot).

Now with the heel window:

The second video appears to demonstrate the the motion of the shoe does not match the motion of the heel inside the shoe. Without the heel window the runner appears to have a lot of rear foot eversion (turning out of the heel), which is a component motion of pronation. With an unobstructed view of the heel we can see that the shoe is collapsing inward more so than the foot. I came across these videos in a forum thread discussing how the great distance runner Haile Gebreselassie is able to run so well despite what appears to be a substantial amount of pronation. Perhaps his running mechanics are not quite what his shoes make them appear to be. 

These videos are only of one runner, but the findings are consistent with the growing evidence that using external measures, such as shoe markers, will overestimate the true motion of the foot inside the shoe. So how does that change our knowledge about running mechanics and injuries? Footwear already complicates running research a great deal because different shoes can alter running mechanics in different ways depending on the individual. I can still rationalize and discuss how large degrees of pronation or rearfoot motion contribute to injuries, but a complex research design would be needed to prove or disprove that hypothesis. Because shoe movement may not match actual foot mechanics, more valid methods of assessing motion are required to draw meaningful conclusions regarding any possible link between joint motion, performance, and injury risk.  

Research is likely a long way from determining if there is a running style, a training schedule, or what type of shoe to buy to maximize performance while reducing injuries. Until that point what we have are different hypotheses, theories and scientific models regarding these issues. While it’s important to consider the available research, it’s equally important to realize the limitations of running studies. The discrepancy between shoe deformation and foot motion is just one of the many barriers in the way of developing a more complete understanding of these topics.

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