Running Mechanics: Challenging the Forefoot Stereotype (Part 2)
For those of you who read my last blog post about running mechanics, you’ll remember I presented some pretty significant evidence to suggest that forefoot striking (FFS) is the best way of running. The main takeaways for that evidence are as follows:
- The passive structures of the foot, including the arches, tendons and musculature are both protected and enhanced with a FFS.
- Our ancestors ran with this FFS.
- Average and maximal vertical loading rates are decreased using FFS.
As promised, in this post I am going to present some evidence that might make you think twice about the evidence above. Almost all of the authors in my previous post advocated for a slow, gradual shift towards FFS for the upwards of 90% of runners that still currently run with a rearfoot strike (RFS) pattern. As I mentioned before, I’m not convinced that this shift will either; make me less prone to injury, or improve my running performance. However, the evidence presented above has me doubting myself and so I went and did some digging…
I always tend to look towards elite runners as my first port of call (not sure why) and I found that a larger percentage than normal (i.e. amongst us amateur runners) tend to have either a mid or forefoot strike (anecdotal evidence from analysing photos like the one below). Does this represent the shift spoken about above? Are these runners on to something that we amateurs are still catching up on? I mean there’s a larger proportion of them using FFS than in the general population…are they all busy shifting towards FFS – and is this part of the reason why they are elite runners? Or is this just a tiny sample of elite runners that shows us that our foot strike pattern does not affect our performance? Did the winner use a RFS or a FFS? Does it even matter? Lots of questions…let me try and provide some answers.
Image of lead runners from New York Marathon 2011 taken from naturalrunningcenter.com
One piece of research that I immediately think of when discussing this topic is the invited review by Hamill and Gruber (2017) with the title, “Is changing foot strike pattern beneficial to runners?”. This raises an interesting question because the argument surrounding foot strike pattern has evolved from simply ‘FFS is better than RFS’ to ‘RFS should change to FFS’ – and there is a big difference between the two. It’s kind of like a banter/paleo diet follower telling a vegan that not only is their diet better than a vegan diet – but that the vegan should change diets to a banting/paleo diet. As soon as we start telling people what they should or shouldn’t do – people put walls up and immediately are less inclined to follow your advice. A strategy many people prefer to use is to present the evidence and let the person make the decision themselves – that’s the route I try and use.
Hamill and Gruber (2017) begin by presenting some conflicting evidence stating that,
- In Africa, habitually barefoot people (humans who have never worn shoes) are FFS while their shod counterparts are RFS (Lieberman et al. 2010), and
- 72% of habitually barefoot runners in Africa are RFS with only 28% preferring a FFS (Hatala et al. 2013).
Regardless of conflicting evidence like this – many coaches, practitioners and academics have called for a shift towards FFS amongst their athletes/coaches/peers. The question is, does this change make runners (1) more economical, (2) reduce the impact peak and loading rate in ground reaction forces, and (3) reduce running related injury risk (Hamill and Gruber, 2017)? Let’s examine each of the claims:
Is running economy improved when changing to FFS?
In my first post I presented evidence that suggested that FFS is more economical than RFS because elastic energy is stored and released more efficiently in the passive structures of the foot than with RFS. Hamill and Gruber (2017) suggest that there is enough evidence to refute this claim as other studies have examined the effect of runners shifting from RFS to FFS with no difference found in intra-subject oxygen consumption between these foot strike patterns. These studies have been criticized owing to the fact that they had habitually RFS runners changing to a FFS pattern which is thought to bias the results of the study. However, other studies have shown that when comparing FFS and RFS runners using their preferred/habitual foot strike pattern across running speeds, there is no difference in oxygen consumption rate or net metabolic rate (Hamill and Gruber, 2017).
Furthermore, a study by Gruber et al. (2013) compared a habitually RFS and FFS sample group and asked each group to run both with their habitual foot strike and with the unnatural foot strike. What they observed was that the habitually RFS group became significantly less economical when running with a FFS, while the habitually FFS group had the same economy across foot strike patterns. This is an interesting finding considering most researchers have suggested that shifting to a FFS (as a RFS runner) should improve running economy. While not scientifically founded, my interpretation of these results is that for RFS runners, the unnatural way of striking with the forefoot makes them ungainly and inefficient and that the FFS group have no struggle shifting to the RFS pattern while still maintaining efficiency. This makes me question what the most “natural” state of foot strike really is – if it was FFS, we should surely have observed the opposite – with FFS feeling unnatural or ungainly when switching over to the RFS pattern? Gruber et al. (2013) further analysed their sample data and found that at several submaximal speeds, the FFS group had greater carbohydrate oxidation than their RFS counterparts. This suggests that FFS may actually stand to benefit from switching to a RFS pattern as they would be able to train/race at submaximal speeds for longer. This once again points to the concept of metabolic efficiency (RFS) against mechanical efficiency (FFS) – perhaps those seeking to run for longer should adopt a RFS pattern after all!
Finally, Jewell et al. (2017) observed that habitually FFS and midfoot striking runners tend to land more and more posteriorly during a progressively fatiguing run. Could this shift be the FFS runner gradually shifting to a more metabolically efficient running gait as the relative cost of running increase?
Does a lower impact peak and loading rate in vertical ground reaction forces decrease risk of running related injury?
The idea that RFS runners are at more risk of injury comes from the very true fact that the vertical loading profiles of a RFS and a FFS runner are very different (see figure 1 below). The first peak seen in a RFS runner is non-existent in a FFS runner as well as a “steeper” loading rate (sharp incline) compared to RFS runners. Researchers have implied that this lack of impact peak and slower loading rate will decrease the risk of injury to FFS runners (Hamill and Gruber, 2017). The reality is that the forces visible in figure 1 below are easy to explain. The initial spike/peak seen in RFS runners amounts from initial contact with the respective foot, while the second peak is the result of the full body weight acting on the ground. In the FFS runner this first “contact” peak seems non-existent, but Hamill and Gruber (2017) argue that it is still there – it just happens later on in the time aspect (x axis) and is therefore “hidden” by the larger second peak. Furthermore Hamill and Gruber (2017) argue that although it has been argued that reducing the impact peak and the loading rate is important in preventing injuries, the relationship between these impact characteristics and injuries is not conclusive. In fact, several researchers have found that runners who have higher impact peaks and loading rates are actually more robust against injury possibly owing to the fact that force application can be either beneficial or detrimental for bone health depending on the extent of the impact (and that crossover point is not known). Seemingly there is a greater stress on the knee joint and surrounding muscles when using a RFS and a greater demand on the ankle joint and musculature with a FFS. This points towards a differing profile for injury risk (knee area for RFS, ankle area for FFS) rather than one being better than another.
Figure 1 taken from clinicaladvisor.com indicating the difference in vertical loading (force, y axis) across strike patterns over time (x axis).
Do runners changing from a RFS to a FFS have reduced injury risk?
The only way to truly tell whether a shift from a RFS to a FFS will reduce injury risk is by doing a prospective research study with a large study sample of runners who have made the shift from a RFS to a FFS pattern. Typically this is not very common amongst research on runners as it is difficult to get hold of a large number of runners who have all changed foot strike pattern and monitor them over a considerable period of time while they report on injury rates (Hamill and Gruber, 2017). In 3 such studies with samples of 341 – 1203 runners, no significant differences were found in injury rates between habitual rear, fore or mid-foot strike runners (Hamill and Gruber, 2017). The reality is that more research is needed to confirm this claim as it is largely built off the work of Daoud et al. (2012) who retrospectively reported that FFS runners had reduced rates of injury per 10,000 miles than their RFS counterparts. Unfortunately, the nature of this study (retrospective) coupled with a limited sample size (collegiate cross country athletes), makes the findings of this study hard to generalize.
The reality is that foot strike pattern may well be determined by the goal of the runner, with those opting for a RFS having the goal of minimizing metabolic cost and those with a RFS wanting to improve their speed using a FFS (Hamill and Gruber, 2017). This is the concept of mechanical vs metabolic efficiency in which on a continuum of 100m sprinter to ultra-marathon runner we find the most mechanical and least metabolic efficient to the least mechanical and most metabolic efficient. Have you ever asked yourself – “should more sprinters land with a RFS?” probably not – and that is why almost all sprinters use a FFS, and perhaps why almost all (75-95%) marathon and ultra-marathon runners use a RFS. I think there is enough evidence to not only argue that FFS is not the optimal foot strike pattern for habitually RFS runners, but also that RFS may actually be the most optimal foot strike pattern for runners. The fact that FFS runners tend to shift towards a more RFS pattern is a big warning sign for me suggesting that as much as people might try to land with a FFS – they are actually more efficient using a RFS. At the very least I would encourage runners to run with whatever foot strike pattern feels the most comfortable for them – and certainly at this point would I never tell someone to change their foot strike pattern because, “this one is better than that one”. Happy running!
Daoud, AI., et al. 2012. Foot strike and injury rates in endurance runners: a retrospective study. Journal of Medical Science in Sports and Exercise. 44 p. 1325-1334.
Hamill, J., and Gruber, AH. 2017. Is changing footstrike pattern beneficial to runners? Journal of Sport and Health Science. 6 p. 146-153.
Hatala, KG., Dingwall, HL., Wunderlich, RE., and Richmond, BG. 2013. Variation in foot strike patterns during running among habitually barefoot populations. PLoS One. 8 e. 52548.
Gruber, AH., Boyer, KA., Silvernail, JF., and Hamill, J. 2013. Comparison of classification methods to determine footfall pattern. Footwear Science. 5 p. 103-104.
Jewell, C., Boyer, KA., and Hamill, J. 2017. Do footfall patterns in forefoot runners change over an exhaustive run? Journal of Sports Sciences. 35 p. 74-80.
Lieberman, DE., et al. 2010. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature. 463 p. 531-535.