Just How Significant are Heel Impacts at Causing Injury When Running?

I have always really struggled to understand why there is so much fuss about reducing impact forces to treat and prevent overuse injuries in runners. Everywhere you go in the crankosphere blogosphere heel impacts are the cause of all evil and have to be eliminated at all costs. Even in the scientific literature, for example, the very first sentence of the Lieberman et al (2010) article on barefoot running that made the cover of Nature was:

Running can be most injurious at the moment the foot collides with the ground.

You would have thought that such an emphatic statement, especially in a scientific publication would have a citation to support it. It doesn’t.

So, are impact forces, especially at heel contact a risk factor for injury or are those who claim it is, just engaging in the wishful thinking logical fallacy? In other words, they just state it as they wish it was true. Just what does the evidence say on impacts and injury in runners:

  • Nigg (1997) summarized his and other research and reported no differences in injury between those with higher or lower impact peaks and found a correlation between higher impact loads and less injuries; concluding that: “Impact forces have been associated with the development of musculoskeletal injuries. However, results of epidemiologic studies that assess the association between impact loading and the development of acute or chronic injuries do not support this notion“. In the initial chapter of his recent book (2010), Biomechanics of Sports Shoes, Nigg concluded: “Currently, there is no conclusive evidence that impact forces during heel-toe running are responsible for the development of running related-injuries
  • van Mechelen (1992) reported no differences in injury rates between those that run on hard or soft surfaces (where presumably the impact loads would have been different)
  • van Gent’s et al (2007) systematic review of published studies on the risk factors for running injuries did not identify impact loads as a risk factor.
  • Bredeweg et al (2013) looked at the asymmetry in impact loads between the left and right side of runners and found no correlation between higher impacts and the side of the injury.
  • The systematic review of the literature and meta-analysis by Zadpoor and Nikooyan (2011) on loading rates and stress fractures found that: “The currently available data does not support the hypothesis that there is a significant difference between the ground reaction force of subjects experiencing lower-limb stress fracture and control groups. Instead, the vertical loading rate was found to be significantly different between the two groups.” They reported that while impacts were not a factor, the loading rate was a factor. This was only for tibial stress fractures that make up ~4-5% of all running injuries¹.
  • In contrast, there was an abstract presented at the ASB meeting in 2010 by Irene Davis in which they reported that impact factors were associated with an increased risk for injury. There is no more information available on this study apart from the abstract.
  • Bredeweg et al (2012) in their prospective study did find that male injured runners had higher loading rates than noninjured male runners. They found no differences in the female cohort.

So I am unconvinced that impact loads and loading rates are even a problem or as big a problem as all the rhetoric and propaganda make them out to be. The evidence either way is not compelling. They are a problem for tibial stress fractures¹, that make up a small number of running injuries. It is possible to spin or cherry pick the research to try and make whatever point you are trying to make or story you are trying to tell. I am happy to be convinced otherwise, but the evidence is telling me that heel striking and high impacts are not the big evil that they often get painted to be. Even if they were and you change the running form or technique to reduce those impacts, to do so, you only increase the load in other tissues, exposing those tissues to increased risk for injury¹. Its six of one and half a dozen of the other.

As always, I go where the evidence takes me until convinced otherwise, and the evidence tells me that impact forces are either not really a big a problem as the rhetoric and propaganda says they are; or if they are, the evidence supporting that is far from compelling.

POSTSCRIPT: I was reminded of something via Twitter on this topic by@SethONeil: “Only time I worry about impacts is heel fat pad syndromes” (tweet). He is right. Despite all the rhetoric and propaganda that impacts are supposed to be so evil, clinicians when treating running injuries never take them into account! There is obviously a reason for that! Even if you look at all the risk factor studies for specific injuries, such as the most common running injuries of patellofemoral pain syndrome (runners knee) or medal tibial stress syndrome (shin splints), impacts are never mentioned or even found as being risk factors.

1. Even though the evidence shows that higher impact loading rates at heel impact are a risk factor for tibial stress fractures; forefoot striking probably increases the risk for metatarsal stress fractures. We keep being told that this is not a problem if the bone (metatarsals) are given time to progressively adapt to the loads. What I don’t understand is why the bone (tibia) can not be progressively adapted to the load of heel striking and adapt?

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About Craig Payne

University lecturer, runner, cynic, researcher, skeptic, forum admin, woo basher, clinician, rabble-rouser, blogger, dad. Follow me on Twitter, Facebook and Google+

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12 Responses to Just How Significant are Heel Impacts at Causing Injury When Running?

  1. John Keyes September 9, 2013 at 4:57 am #

    Do you know if any study has been performed to determine if heel-striking barefoot runners have more injuries than midfoot barefoot runners? I had a quick scan through some of the linked reports above, but came up empty.

    • Craig Payne September 9, 2013 at 5:02 am #

      There has been no study on that.

      Except we do now know that the preponderance of evidence is that the injury rate between heel strikers and non-heel strikers is probably the same and the injury rates between traditionally shod runners and barefoot/minimalist runners are probably the same.

      • John Keyes September 9, 2013 at 5:13 am #

        I find it that hard to believe that (don’t worry I trust science) as my intuition is telling me that the injury rate should be higher for heel strikers in that instance. Love a good old science put-down though – follow the evidence.

        • Craig Payne September 9, 2013 at 6:17 am #

          I to used to believe impacts were problem back in the 80’s! Niggs prospective study from the 90’s showed those with higher impact forces got less injuries! we have known about the Mechelen study on soft surface vs hard surface injury rates from the early 90’s. Two more recent studies Davies and Bredeweg – found a link —- its like one set of studies cancel out the other ….. that is why I call the evidence is not compelling one way or the other. It certainly does not match the strength of the propaganda and rhetoric that heel impacts are the source of all evil.

          • John Keyes September 9, 2013 at 7:58 am #

            If there is no compelling evidence for either side of an argument then both sides are arguing the same thing but for different reasons.

            I’ve transitioned from a heel striker to a mid-outside foot striker because I’d read so much about how much better barefoot running is. I’m a quicker runner (not competitive) because of it, but rarely get injured (long may that continue) so I couldn’t compare pre and post.

            I notice if I’ve been on a 15km+ run that I drift back to heel striking when I’m fatigued. So for me the main difference between the two is speed and stamina. Mid/outside strike for speed, and heel for stamina.

  2. simon Bartold September 9, 2013 at 6:38 am #

    Hi Craig.. I little while ago I wrote on this issue at http://www.bartoldbiomechanics.com/articles/athletic-footwear/a-discussion-on-cushioning-in-footwear
    I made the following comments amongst others: the vertical force peak is misleading because when you delay the peak with heel cushioning, it piggybacks on the developing force applied by the front of the foot and appears larger than it actually is. In other words, the height of the impact peak tends to be higher in more compliant cushioned shoes not because heel impact increases, but because impact gets stretched out over a greater time period and summates with rising vertical forces of the active peak.

    The part of this statement about the “piggybacking” makes a lot of sense, and this is pretty much exactly what I keep telling people about these so called “force transients” but they don’t seem to want to listen. The bottom of a shoe provides cushioning, which acts similar to a low pass filter in that it only allows through the low frequency, less rapid impact forces. Think of it like hitting a bit of hard metal with a hammer – if the hammer has a wooden grip you feel a sharp impact that hurts your hand and you feel a shockwave go through your bones. But if it has a soft cushioned grip you don’t feel it anywhere near as much, and it’s more of a “thud”. A shockwave is a rapid force spike, a thud is this shockwave being spread out over a longer time and with a lower peak value.

    Hope the sick one recovers soon.. best
    Simon
    http://www.bartoldbiomechanics.com

  3. Kevin A. Kirby, DPM September 9, 2013 at 4:36 pm #

    In 2011, Shorten and Mientjes showed quite conclusively that the heel impact peak seen in force plate studies is neither only due to shoe heel impact and also does not quantify the effects of the running shoe sole to be able to dampen impact forces with the ground (Shorten M, Mientjes MIV: The ‘heel impact’ force peak during running is neither ‘heel’ nor ‘impact’ and
    does not quantify shoe cushioning effects. Footwear Science, 3 (1):41-58, 2011).

    In other words, only about half of the impact peak seen in rearfoot-striking runners is actually due to the high frequency heel impact transient and the other half is due to the lower frequency loading of the more distal areas of the foot. This suggests that those researchers who look at only the loading rate and/or magnitude of the heel-impact transient seen in force running as a indication that rearfoot-striking running may somehow more harmful to runners are, at best, only half-right.

    http://www.tandfonline.com/doi/abs/10.1080/19424280.2010.542186#.Ui32Wsa9um4

    Here is a lecture I gave in Belgium from last year where I mentioned this research.

    http://www.arteveldehogeschool.be/elpa/podologie/lustrum/presentations/friday/15h15%20Kirby%20Barefoot%20vs%20Shod%20Running.Which%20is%20Best.Belgium.2012.pdf

  4. Peter Larson September 12, 2013 at 11:39 am #

    I would agree for the most part, though I am concerned about those who go barefoot or into ultra minimal shoes and continue to heel strike. Impact transients in that situation probably are not so good for the calcaneus as that one Vibram study had one subject develop a calcaneal fracture. My guess is past studies have not included runners exhibiting transients as big as those observed in barefoot heel strikers.

    • Simon Spooner September 13, 2013 at 7:13 am #

      Which begs the question: do you need to heel strike to develop a calcaneal stress fracture?

      • Craig Payne September 13, 2013 at 7:20 am #

        There are more than enough anecdotes and case reports of calcaneal stress fractures to show that you can get one without heel striking. I wrote about that here:
        http://www.runresearchjunkie.com/calcaneal-stress-fracture-forefoot-or-rearfoot-strikers/

        • Kevin A. Kirby, DPM September 13, 2013 at 3:31 pm #

          Achilles tendinitis/tendinosis and peroneal tendinitis/tendinosus are very serious and potentially chronic running injuries that may require surgery to rectify and are ones I see commonly in those runners who have been told by “running form experts” that they should not be heel-striking but rather should be midfoot-striking or forefoot-striking to minimize “shock” with the ground. From my clinical perspective of seeing thousands of runners as patients over the past 30 years, I’ll take a calcaneal stress fracture over a chronic Achilles/peroneal tendinitis/tendinosus any day since the calcaneal stress fractures I have seen always are able to return to running without pain….those with chronic Achillles and peroneal tendinosus often can’t….without surgery.

          Cheers,

          Kevin

        • Peter Larson September 13, 2013 at 3:44 pm #

          Sure, I don’t doubt that. But the title of the article is “How Significant are Heel Impacts at Causing Injury When Running?” My guess, and that’s all it is, is that heel impacts might be a problem for the heel if the heel is not cushioned on a hard surface.

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