There has been considerable interest recently in altering running technique to reduce impact loads and loading rates in the belief that this might reduce injury rates. There was a recent study I previously wrote about and now there is this one:
Impact reduction through long-term intervention in recreational runners: midfoot strike pattern versus low-drop/low-heel height footwear
Marlène Giandolini, Nicolas Horvais, Yohann Farges, Pierre Samozino, Jean-Benoît Morin
European Journal of Applied Physiology April 2013
Impact reduction has become a factor of interest in the prevention of running-related injuries such as stress fractures. Currently, the midfoot strike pattern (MFS) is thought as a potential way to decrease impact. The purpose was to test the effects of two long-term interventions aiming to reduce impact during running via a transition to an MFS: a foot strike retraining versus a low-drop/low-heel height footwear. Thirty rearfoot strikers were randomly assigned to two experimental groups (SHOES and TRAIN). SHOES progressively wore low-drop/low-heel height shoes and TRAIN progressively adopted an MFS, over a 3-month period with three 30-min running sessions per week. Measurement sessions (pre-training, 1, 2 and 3 months) were performed during which subjects were equipped with three accelerometers on the shin, heel and metatarsals, and ran for 15 min on an instrumented treadmill. Synchronized acceleration and vertical ground reaction force signals were recorded. Peak heel acceleration was significantly lower as compared to pre-training for SHOES (−33.5 ± 12.8 % at 2 months and −25.3 ± 18.8 % at 3 months, p < 0.001), and so was shock propagation velocity (−12.1 ± 9.3 %, p < 0.001 at 2 months and −11.3 ± 4.6 %, p < 0.05 at 3 months). No change was observed for TRAIN. Important inter-individual variations were noted in both groups and reported pains were mainly located at the shin and calf. Although it induced reversible pains, low-drop/low-heel height footwear seemed to be more effective than foot strike retraining to attenuate heel impact in the long term.
This was a good study, was thoroughly conducted and analyzed; being a prospective study rather than an acute intervention (which the other one was) it gives some strong data. It also provided some interesting snippets of information that jumped out at me when reading it (vide infra), but firstly, heading off on a rant: I really struggle to understand why there is so much fuss about reducing impact loads and loading rates. Everywhere you go in the crankosphere blogosphere heel impacts are the cause of all evil and have to be eliminated at all costs. As I always go where the evidence takes me, the evidence to me just does not support the strength of that contention:
- 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“.
- 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 impacts were not a factor, but the loading rate was. This was only for tibial stress fractures that make up ~4-5% of all running injuries.
- 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.
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 fractures, 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 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.
Having said that, back to the research above: They found that there was no change in loading rates during the 3 month transitions in either the lower-drop shoe or the midfoot strike pattern groups. For impact magnitude and peak acceleration at the heel, tibia and metatarsals, the transition from rearfoot to forefoot striking had no effect. However, for the transitions to the lower drop shoes (Salmon Sense S-Lab), there was a decrease in heel acceleration.
Some of the snippets that jumped out at me included:
- a large variation in the response in the lower drop shoe group (even though the mean response was no change in loading rates and a decease in the heel acceleration). This suggests that the response to the change in footwear is going to be individual and subject specific.
- some of the other loading parameters were significantly different at one month, but had gone back to pre-transition values at three months! This suggest that studies that use an acute intervention may not be very valid (ie the previous one I wrote about!)
- To quote the authors: “The conscious and progressive adoption of a midfoot strike pattern over the 3-month intervention had no effect on any of the mechanical variables studies (be it kinematic or impact variables)“. This is in contrast to other studies. The differences probably being that those studies that reported a decrease used a much more intensive laboratory based gait retraining program. This study used a more simpler and easy to perform method which is probably more reflective of what happens in the real world when runners transition.
- Rather than clarify things, this does muddy the water somewhat.
Take home message: Changing to lower drop shoes or changing to midfoot striking is not going to be a panacea or a one size fits all for reducing impact loads if you think impact loads are a problem. It is going to be subject specific.
As always, I go where the evidence takes me until convinced otherwise
Giandolini M, Horvais N, Farges Y, Samozino P, & Morin JB (2013). Impact reduction through long-term intervention in recreational runners: midfoot strike pattern versus low-drop/low-heel height footwear. European journal of applied physiology PMID: 23584279