Foot Strike & Injury Rates in Runners

4th March 2012
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A retrospective study comparing the injury rates of heel strikers and forefoot strikers amongst a group of cross-country runners, was recently published in the Journal of Medical Science and Sports Exercise. The co-authors of the study, led by Daniel Lieberman of Harvard’s Department of Evolutionary Biology, provided the following summary of their findings:

METHODS:
We measured the strike characteristics of middle and long distance runners from a collegiate cross country team and quantified their history of injury (over a 5-year period), including the incidence and rate of specific injuries, the severity of each injury, and the rate of mild, moderate and severe injuries per mile run.

RESULTS:
Of the 52 runners studied, 36 (59%) primarily used a rearfoot strike and 16 (31%) primarily used a forefoot strike. Approximately 74% of runners experienced a moderate or severe injury each year, but those who habitually rearfoot strike had approximately twice the rate of repetitive stress injuries than individuals who habitually forefoot strike. Traumatic injury rates were not significantly different between the two groups. A generalized linear model showed that strike type, sex, race distance, and average miles per week each correlate significantly (p<0.01) with repetitive injury rates.

CONCLUSIONS:
Competitive cross country runners on a college team incur high injury rates, but runners who habitually rearfoot strike have significantly higher rates of repetitive stress injury than those who mostly forefoot strike. This study does not test the causal bases for this general difference. One hypothesis, which requires further research, is that the absence of a marked impact peak in the ground reaction force during a forefoot strike compared to a rearfoot strike may contribute to lower rates of injuries in habitual forefoot strikers.”

So what does this mean?

This study is the first (likely others will follow) to look at injury rates based on running technique differences. Although their group size was relatively small, and looked at high level athletes, which may not be generable to recreational runners, their finding is still of considerable relevance to running injury debates.

This was the 2nd of a 3-part research project by Liebermans’s group, and both this and his initial study have been pounced-upon by the running industry and running bloggers everywhere. The study in my mind has received some unfair criticism, mostly because the findings have been entered into the barefoot running vs shod running debate. Infact, the study has nothing to do with barefoot running. Dr. Lieberman and Mr. Daoud, were quick to point out that their study did not in any way address the merits of going barefoot.

This is however a great, ground-breaking, study which demonstrates for the first time that running technique can have a significant effect on the likelihood of injury. Regarding footwear Dr Lieberman says that “all of the subjects wore shoes, and most, wore different shoes every day of the week. Some ran in well-cushioned shoes and became injured, while others did not. Likewise for those who usually ran in minimal racing flats. Some got hurt; some did not. And forefoot striking, over all, was not a panacea. Many of the forefoot strikers were felled by injuries. But in general, those runners who landed on their heels were considerably more likely to get hurt, often multiple times during a year.”

In Lieberman’s previous study it was shown that barefoot and shod runners produce different impact forces. The barefoot runners studied were generally landing towards their forefoot, whilst shod runners mostly made initial contact with their heels. In the diagrams below it can be seen that a heel striking shod runner produces a marked impact peak in the ground reaction force during a forefoot strike, whilst the forefoot striking barefoot runner has a much smoother impact curve, involving lower peak forces.

Impact forces for a heel striking shod runner

Impact forces for a barefoot runner

The larger initial impact transient seen with heel striking has been suggested as an possible explanation for the higher injury rates seen in these runners, however most running injuries, rather that seeming directly related to impact, are more likely caused by inappropriate torque (rotational) forces through joints such as the knee and hip. Over-striding rather than foot-strike will produce inappropriate torque.

So the finding that heel strikers have higher injury rates may actually be due to the fact that heel strikers are often also over-striding. It may not be about what hits first but more how you land in relation to your center of gravity. Other factors such as cadence and stride elasticity will also affect the forces involved in running gait.

The 3rd part of Liebermans study is going to look more specifically at technique (rather than just foot-strike) and also aims to investigate the effects of technique coaching on subsequent injury rates.

Summary- what we know so far:

– Heel strikers and barefoot runners produce different impact forces
Cushioned trainers reduce some but not all of the higher ground impact forces produced by heel striking

-Heel strikers have been shown to have 2x the injury rate of forefoot runners- the precise reasons why are still under investigation

-Running technique can affect both impact forces, and the likelihood of injury, but the two may not be directly related.

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