A new study to be released tommorow by Lieberman in Nature takes an evolutionary look at barefoot running. In the study, they compared barefoot and shoe running on a whole variety of factors in both regular shoe wearers, regular barefoot runners, and even Kenyans!
The study is entitled and I HIGHLY recommend it:
Foot strike patterns and collision forces in habitually barefoot versus shod runners
This is a timely piece as it adds more evidence to the article I wrote a couple days ago below (click here). The implications are great as they extend beyond barefoot running to foot strike too (heel vs. forefoot,etc.)I’ll highlight some of the findings.
Foot strike and Elastic response and energy transfer:
As I speculated in my article, footstrike greatly effects the elastic energy return. In their study, it was found that forefoot and some midfoot strikes “reduces the effective mass of the foot and converts some translational energy into rotational energy; the calf muscles control heel drop, and the FFS runner can take fuller advantage of elastic energy storage in both the Achilles tendon and the longitudinal arch of the foot.”
On this topic, Liberman speculates that the arch plays a key role in reduced oxygen cost of running in barefoot runners. Essentially during a mid/fore foot strike the arch can stretch over the entire first half of the stance phase, while during the rearfoot strike, it has to wait until the last part of this phase, thus decreasing energy storage and return.
Also, forefoot and some midfoot strikes allowed for greater energy transfer. When heel striking a large portion of kinetic energy dissipates. With forefoot striking, some of the translational kinetic energy converts into rotational energy.
Barefoot/Forefoot runners have a “smoother” ride: Difference in collision forces:
Barefoot runners “take shorter strides and to run with greater vertical leg and ankle compliance (the lowering of the body’s centre of mass relative to the force of the impact). This serves to blunt the transient force and results in a less jarring, ‘smoother ride’.” (Jungers, 2010)
Basically this means that because of the footstrike difference, the body uses the lower leg in a more efficient shock absorbing way. The foot is more plantar flexed and the ankle is more compliant. This creates a situation where the collision is essentially absorbed and spread out better.
In heel striking the collision forces are concentrated in one area, and very sudden. Meaning a large amount of force in one place, very quickly. Meanwhile in a more flat footstrike, as mentioned above, the impact is spread out, absorbed better, and not so sudden. This leads to peak vertical forces 3x lower in barefoot vs. shoe wearing runners and a rate of loading that is half as much for barefoot compared to shoe wearing runners
This difference may lead to injury prevention, as some studies have suggested that it’s not necessarily the total impact forces but the high rate of force in a very short time. (Look at the drawings in my article below and remember that barefoot running doesn’t have the initial peak impact force). Still, the impact force debate can be VERY misleading. Just a word of caution to read my other blog post on running shoes and realize that peak impact forces do not relate to injuries
Concrete vs. Dirt:
Another interesting finding is the adjustment of impact forces that occurs based on the ground you are going to strike. The study found that barefoot running produced less collision forces on a hard surface than a cushioned shoe.
Similar to the conclusions I came to in the Running shoe article(here), they found that leg stiffness was adjusted to control impact. This created a situation where there was no difference in rate or magnitude of impact loading based on the surface they were running on. As I have said many times, the body has a built in adjustment mechanism. It controls impact via adjustment of several different mechanisms.
So all those people who are worried about the impact forces of running barefoot on concrete should consider that when they stick a cushioning shoe on and heelstrike, there collision forces are higher!
In his accompanying article Jungers eloquently stated:
“Although there is no hard proof that running in shoes, especially hitech or PCECH (pronation control, elevated cushioned heel) versions, causes injuries, in my view there is no compelling evidence that it prevents them either10,11. However, there are data that implicate shoes more generally as a plausible source of some types of chronic foot problems12,13.”
Speed and footstrike:
One other interesting finding was that speed was NOT related to foot strike type or ankle and foot angles. That means, how fast the runner was in the study did not relate to how he struck the ground. That helps to get rid of the old argument that I have heard time and time again that footstrike depends solely on speed and that only fast runners strike midfoot because they run fast. WRONG.
From a range of runners running at speeds varying from about 7minutes per mile to ~4:20 per mile, footstrike didn't depend on speed. Meaning that f
What causes heel strike?
“A major factor contributing to the predominance of RFS landings in shod runners is the cushioned sole of most modern running shoes, which is thickest below the heel, orienting the sole of the foot so as to have about 5u less dorsiflexion than does the sole of the shoe, and allowing a runner to RFS comfortably (Fig. 1). Thus, RFS runners who dorsiflex the ankle at impact have shoe soles that are more dorsiflexed relative to the ground, and FFS runners who plantarflex the ankle at impact have shoe soles that are flatter (less plantarflexed) relative to the ground, even when knee and ankle angles are not different.”Evolution:
“Differences between RFS and FFS running make sense from an evolutionary perspective. If endurance running was an important behaviour before the invention of modern shoes, then natural selection is expected to have operated to lower the risk of injury and discomfort when barefoot or in minimal footwear.”This essentially means, we’ve got millions of years of adjustment and fine tuning that went on to allow us to run barefoot with minimal risk. In addition, Lieberman points out several evolutionary changes that aid running. The development of the arch, which is essential for elastic energy return, is one of them.
Conclusion and Practical implications:
This study provides further evidence to some of the issues discussed previously in regards to barefoot running. For runners, the major implication could be on foot strike. It’s more than just barefoot running, it’s footstrike that matters. A lot of the differences in collision force are due to footstrike variations. For years, shoe companies and others have said that heel striking is the way to go. Elite runner Mark Plaatjes even made the same argument earlier this week in a well written paper. Lieberman’s article helps lend credence to what I and many others have always speculated. It’s not.
The human body was designed to run with a forefoot/midfoot strike and shoes cause us to run barefoot. In one of the nature barefoot articles there is a great picture illustrating this (Picture can be found here). It is of 2 Kenyan boys running on a dirt road. One is barefoot and landing whole foot, one in shoes, slamming his heel into the ground first. Shoes decrease proprioception, change ankle kinematics and allow the body to change it's landing habits.
Therefore, the major finding is that footstrike may be more important than running barefoot or not. Granted running midfoot is hard with heavy shoes. The study shows that footstrike was what mattered. Barefoot runners who landed heel first still had much higher impact forces than when striking forefoot/midfoot. Similarly, the rate of loading was still much higher in barefoot heel strikers than barefoot forefoot strikers. This finding that footstrike matters is something that track coaches have been saying for decades. One of my big mentors, Tom Tellez, has been preaching this for a long time.
More focus should be focused on changing footstrike with barefoot/minimalist running used as a way to aid that change.
A change to barefoot running should be accompanied by a change in running style to a midfoot/wholefoot/forefoot one. For information on how you should run read this (here) and watch these (here and here) (no I don't think Pose or Chi are wonderfull...)
Lastly, I think the take away message is that the human body is more complex than we give it credit for. The fact that it alters footstrike and pre-activation and numerous other mechanisms based on what is on the shoe or what ground you are going to strike is amazing. Think about that for a second. A couple years back Adidas tried to sell a shoe with an expensive microchip that adjusted cushioning each stride. The shoe cost several hundred dollars. The problem is, we already have a mechanism that does that for free….ourselves!
Lastly, a word of caution. This study will catch on fire. The major newsgrabbing headline will be the impact forces. However, that is likely a gross oversimplification of the process. Like with other variables (VO2max, lactate,etc.) don't get tied to one while missing the big picture.
If you enjoyed this or any other article, please help get the information out there and pass it on. Much appreciated.
To read more about barefoot running and running shoes read the below article on Why Running shoes do not work:
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I'll leave you with a wonderful video of barefoot forefoot striking from Dr. Lieberman: