Impacts and injury and the transition to minimalist running shoes

I struggled to come up with a title for this post as in the study below two key points came out and the points that come out of the study are not necessarily related to each other. Here is the study:

Injuries observed in a prospective transition from traditional to minimalist footwear: correlation of high impact transient forces and lower injury severity
Matthew J Salzler, Hollie J Kirwan, Donna M Scarborough, James T Walker, Anthony J Guarino & Eric M Berkson
The Physician and Sportsmedicine; 21 September
Background: Minimalist running is increasing in popularity based upon a concept that it can reduce impact forces and decrease injury rates. The purpose of this investigation is to identify the rate and severity of injuries in runners transitioning from traditional to minimalist footwear. The secondary aims were to identify factors correlated with injuries.
Methods: Fourteen habitually shod (traditional running shoes) participants were enrolled for this prospective study investigating injury prevalence during transition from traditional running shoes to 5-toed minimalist shoes. Participants were uninjured, aged between 22-41 years, and ran at least twenty kilometers per week in traditional running shoes. Participants were given industry recommended guidelines for transition to minimalist footwear and fit with a 5-toed minimalist running shoe. They completed weekly logs for identification of injury, pain using Visual Analogue Scale (VAS), injury location, and severity. Foot strike pattern and impact forces were collected using 3D motion analysis at baseline, 4 weeks, and 12 weeks. Injuries were scored according to a modified Running Injury Severity Score (RISS).
Results: Fourteen runners completed weekly training and injury logs over an average of 30 weeks. Twelve of 14 (86%) runners sustained injuries. Average injury onset was 6 weeks (range 1-27 weeks). Average weekly mileage of 23.9 miles/week prior to transition declined to 18.3 miles/week after the transition. The magnitude of the baseline impact transient peak in traditional shoes and in minimalist shoes negatively correlated with RISS scores (r= -0.45, p=.055 and r= -0.53, p=.026, respectively).
Conclusion: High injury rates occurred during the transition from traditional to minimalist footwear. Non-compliance to transition guidelines and high injury rates suggest the need for improved education. High impact transient forces unexpectedly predicted lower modified RISS scores in this population.

No big drama or issues with the study. Those who don’t like the results will have a go at the sample size of 14 (they wouldn’t have criticised it for that if they like the results). The study did not have a control group, but I do not necessarily see that as an issue. Ideally, there would have been a control group with the same characteristics of the group above (by randomization) that did not do the transition. That way, the injuries in that control group during the same time period could be compared to the group that made the transition. Given that almost all of the runners doing the transition got an injury, then that is a lot. Over a 30 week period, expectations based on what most injury prevalence studies put things at around 40% for year, then in a group of 14 runners over 30 weeks, you would probably expect to see around 2-3 injuries in a control group. Also of note above is that after the transition the runners were running less distances per week, which is consistent with other evidence that barefoot and minimalist runners run less (which theoretically lowers the injury risk).

The first point that comes out of the study is that very high injury rate during the transition, which is consistent with other studies. Is it worth it? Given that the evidence now also shows that there are no systematic benefits of minimalist running over shod running then any general recommendations or advice for minimalist running over traditional shod running really can’t be supported. That does mean that it should not happen, but any advice to do so probably should be subject specific and for the right reasons (eg to move the load from one set of tissues to another if there is a history of injury in one particular tissue). In other words, undertaking the transition should be done for the right subject specific reasons and not for any general systematic reasons.

A lot of that could be moot as interest in minimalist running has fallen so far that my latest attempt to get access to the sales figures at the run speciality level was greeted with a “they don’t register anymore”. In other words, they have fallen so far, they don’t show up in the statistics anymore. This is down from a peak of almost 10% of the run speciality market around 2011 to languishing around 2-3% of the market for around the years of 2013-2014. Hardly anyone is interested anymore.

The second point is the one: “High impact transient forces unexpectedly predicted lower modified RISS scores in this population“. They found that the worse injuries were associated with lower impact forces and the less worse injuries were associated with higher impact forces. I not sure why they thought it was ‘unexpected’ as I and others have been harping on about the lack of compelling evidence linking impact parameters to injury for years. The above study confirms that lack of compelling evidence, yet it still underpins the approach advocated by many. See my two previous posts on this: Impact Related Factors and Running Injury and Just How Significant are Heel Impacts at Causing Injury When Running?.

As always, I go where the evidence takes me until convinced otherwise …. and the risk of injury during the transition to minimalist running is high and is it worth it? And the evidence linking impact factors to running related injury is still not compelling.

Salzler, M., Kirwan, H., Scarborough, D., Walker, J., Guarino, A., & Berkson, E. (2016). Injuries observed in a prospective transition from traditional to minimalist footwear: correlation of high impact transient forces and lower injury severity The Physician and Sportsmedicine DOI: 10.1080/00913847.2016.1238282

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