Impact Related Factors and Running Injury

I have blogged before (Just How Significant are Heel Impacts at Causing Injury When Running?) and repeatedly commented that the evidence that links impact related factors to running injuries is far from compelling. I am not saying they don’t, it is just that the evidence supporting the link is not strong (and one study has even showed that there are less injuries in those with higher impacts). Since my previous post on this topic probably a day does not go by in which I read somewhere about impacts and injury and about the emphasis on reducing impact related factors in order to reduce injury. Why?

Since I addressed this topic back in 2013, its time for an update and please read the previous post to put this one into context so I do not have to re-litigate some of the same issues. Since I wrote that, there has been another systematic review and meta-analysis on the topic and two very recent studies (there have been others, but they are factored into that systematic review and the two recent ones came since that review was published, so I won’t discuss them).

The systematic review and meta-analysis by van der Worp et al in the BJSM reported that:

The loading rate was higher in studies that included patients with a history of stress fractures and patients with all injury types, both compared with controls. Only studies that included patients with a history of symptoms at the time of kinetic data collection showed higher loading rates overall in cases than in controls. There were no differences between injured subjects and controls for the active and passive peaks of the VGRF.

This pretty much confirms what I concluded previously. The evidence of the link between injury and impact related factors is either just not there or far from compelling (except for tibial stress fractures, which is far from being a common running injury).

The recent study by which was not included in the above review is by Davis et al, also in the BJSM (I did mention this one in my previous post, but back then all we had was the conference abstract and not the full paper which has now been published). This was a prospective study of 249 female runners and found that all impact-related variables were higher in those with medically diagnosed injuries. The only issue I have is how many non-medically diagnosed injuries where there and if they were included is there still a relationship? I have no evidence, but I get the impression that at least half of all running injuries are never medically diagnosed and are self managed. Regardless, this study does appear to come down on the side of the ledger that impact related factors are associated with running injury.

The other recent study by Kuhman et al which was not included in the above systematic review was also a prospective study, including only 19 runners. They collected a number of parameters including peak loading rate of the vertical ground reaction force. On that parameter there was no difference between the 10 that got and injury and the 9 that did not. This study does appear to come down on the side of the ledger that impact related factors are not associated with running injury.

So we not really any further ahead. Some studies show a link (especially for tibial stress fractures) and other studies show no link. My interpretation is that there is either just a weak link or the evidence of a link is far from compelling (in other words, nothing has changed since the 2013 post).

As always, I go where the evidence takes me until convinced otherwise …. and I am still not convinced that impact related factors are an important issue in running injuries except for tibial stress fractures.

van der Worp, H., Vrielink, J., & Bredeweg, S. (2016). Do runners who suffer injuries have higher vertical ground reaction forces than those who remain injury-free? A systematic review and meta-analysis British Journal of Sports Medicine DOI: 10.1136/bjsports-2015-094924

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3 Responses to Impact Related Factors and Running Injury

  1. romanair March 9, 2016 at 10:10 pm #

    Thanks for the update and genrally sharing your knowledge on this blog. I really appreciate that.
    Do you have any thought on why the GRF appears to be such a bad predictor for running injuries? I mean despite of running beeing such an entrenched and fundamental movement, the injury rates are surprisingly high and I would think it must have something to do with the forces. I didn’t look it up, but from the feeling non weight-bearing activities such as swimming or cycling, seem to have way lower injury rates compared to running. So maybe we just didn’t find the right tool to make the connection?
    Cheers,
    Roman

    • Craig Payne March 9, 2016 at 10:19 pm #

      In all honesty, I have no idea!
      I could speculate:
      – there are many factors involved (eg tissue vulnerability; etc) that the impact factors are just not that important in that context or mix of multiple factors
      – the GRF are only in that first 200ms …. there is a lot more than that going on when the foot is on the ground
      – loads in tissues are generally determined by lever arms that tissues have to joint axes – impact loads do not affect most of the lever arms and loads –> they are affected later in the stance phase.

  2. Matt Gooch June 10, 2016 at 7:54 pm #

    Craig,

    Thanks for all the work on this blog and PA. Fostering evidence based conversation between clinicians, researchers and the general public is no doubt a daunting task.

    I find these conflicting data sets would lend credence to the conceptual framework of an individual preferred movement pathway for each person. It would help to explain why at a given impact peak and loading rate some people have injuries and some do not.

    Also, since we know that reaction forces vary to some degree from step to step, surface to surface – as does joint coupling – in my mind it makes it difficult to place too much importance on simply the impact forces alone.

    There are so many other variables at play as well (shoe geometries, use of foot orthoses, training surface(s), tissue/joint health, etc.) that can dramatically alter the magnitudes, directions and temporal patterns of those GRF forces. All of these variables (and many others) could provide potential perturbations to a preferred movement path for some, or augment the preferred movement path for others.

    For those who experience a perturbation that counteracts the preferred movement path (and have a smaller envelope of healthy movement), they would potentially be outside of their healthy envelope of movement and potentially stressing a given tissue beyond the ZOOS. Those who have a larger envelope of healthy movement would potentially be able to maintain function of that same tissue within the ZOOS and remain un-injured.

    I thought the point you made above about tissue loads being determined by lever arms to joint axes is spot on and well stated. To me, impact forces are just the corner pieces of the puzzle. They help define the parameters of the picture, but the majority of the puzzle picture is more wholly defined by the other pieces.

    Thoughts?

    Thanks,

    Matt

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