New Study by Dr. Daniel Lieberman on Barefoot Running Makes Cover Story in Nature Journal
A Review of Dr. Daniel E. Lieberman's study, "Foot strike patterns and collision forces in habitually barefoot versus shod runners"
~Includes an exclusive interview
By Michael Sandler
The long awaited study by Harvard Scientist Dr. Dan Lieberman, is hot off the press on the cover of the British Science Journal Nature.
For years Dr. Lieberman and his colleagues have been looking at the evolution of man in terms of his capacity to run and potential history as endurance or ‘persistence’ hunters, capable of running animals to exhaustion as they hunted their prey.
The hypothesis is that as ancient man left the trees and the jungle, he adapted and became more of a runner than a climber. Many adaptations and changes took place, including, but not limited, to changes in the lower leg and foot.
In his latest study, Dr. Lierberman and his colleagues looked at the difference between barefoot runners and shod runners to understand the differences in form, efficiency, impact, and to try and better understand how we evolved into the bipedal runners we are today.
Below is a review of this article, including a full abstract. To purchase the complete article and see their extensive illustrations and citations, please visit Nature.com. It’s well worth it.
By looking at populations of shod and unshod runners, researchers found that runners who land on their forefoot land with far less force and far greater efficiency than their heel-striking counterparts. They found that while modern running shoes afford greater cushioning and comfort for a rear-foot strike (and promote), it likely does little to mitigate the greater impact of this strike, or to reduce injuries. Further, they found that running barefoot has no greater impact when running on hard surfaces than soft.
In conclusion, modern running shoes may be dangerous because they promote a heel foot strike, which this study concludes produces far greater impact than landing on the forefoot. Combined with greater proprioception or ‘feel of the ground’ by running barefoot and stronger foot muscles, they believe barefoot running may help reduce the chance of injury, but that further studies are necessary to test this hypothesis.
With the average runner striking the ground almost 1000 times per mile, runners are highly susceptible to repetitive stress injuries.
In short, forefoot striking, whether in or out of a shoe is best, while today’s most common form of running ‘heel striking’, promoted by the running shoe industry and modern running shoe design, can get you in a lot of trouble.
Humans have engaged in endurance running for millions of years, but the modern running shoe was not invented until the 1970s. For most of human evolutionary history, runners were either barefoot or wore minimal footwear such as sandals or moccasins with smaller heels and little cushioning relative to modern running shoes. We wondered how runners coped with the impact caused by the foot colliding with the ground before the invention of the modern shoe. Here we show that habitually barefoot endurance runners often land on the fore-foot (fore-foot strike) before bringing down the heel, but they sometimes land with a flat foot (mid-foot strike) or, less often, on the heel (rear-foot strike). In contrast, habitually shod runners mostly rear-foot strike, facilitated by the elevated and cushioned heel of the modern running shoe. Kinematic and kinetic analyses show that even on hard surfaces, barefoot runners who fore-foot strike generate smaller collision forces than shod rear-foot strikers. This difference results primarily from a more plantarflexed foot at landing and more ankle compliance during impact, decreasing the effective mass of the body that collides with the ground. Fore-foot- and mid-foot-strike gaits were probably more common when humans ran barefoot or in minimal shoes, and may protect the feet and lower limbs from some of the impact-related injuries now experienced by a high percentage of runners.
How the Study was Performed:
Dr. Dan Lieberman set out to determine the differences between running barefoot and running in shoes.
He studied five subject groups, both indoors and outdoors at endurance speeds between 4 to 6 meters per second (Michael do the math). These groups included three adult groups, first habitually barefoot runners from the US, runners from the Rift Valley Province of Kenya who grew up barefoot but now run primarily in cushioned shoes (this is a region famous for it’s endurance athletes) and US runners who grew up in shoes but now run primarily barefoot or in minimalist footwear. It also included two adolescent groups from the Rift Valley, the first who have never worn shoes and the second who have worn shoes their entire lives.
Trials were done both indoors and outside. Indoor tests were performed along a 20 to 25 meter long indoor track where runners ran over a force plate. Outdoor tests were performed along a 20-25 meter outdoor track of hard dirt using a video camera.
(Full methods and any associated references are available in the online version of the paper at http://www.nature.com/nature/journal/v463/n7280/full/nature08723.html).
This study is geared to compare the foot strike mechanics (called kinematics) in habitually barefoot versus shod runners. In the past, studies have found that barefoot runners land ‘flatter’ than their shod compatriots, but a detailed study of the foot strike was never taken.
According to this study, running is most dangerous at the moment the foot contacts the ground, and there are three main ways this occurs. There is a heel foot strike (HFS), where the heel contacts first, a mid-foot strike (MFS), where the heel and forefoot strike simultaneously, and a forefoot strike where the forefoot comes down first.
While the majority of sprints are forefoot strikers, the vast-majority, 75-80% of all endurance runners are heel strikers.
The study found that ‘magnitudes of peak vertical force during the impact period are approximately three times lower in habitual barefoot runners who forefoot strike than in habitually shod runners who rear foot strike either barefoot or in shoes. In essence, that running barefoot has 1/3 of the impact of running with a rear foot strike in a shoe.
However, it also found that when comparing habitual barefoot runners to traditional shod heel strikers whose shoes are removed, the heel striker (when barefoot) hits the ground with 7 times the impact loading.
In an exclusive interview with Dr. Lieberman earlier today, here’s what he had to say about the forces involved and he difference between barefoot running and running in a shoe:
“Running is jumping from one foot to the other, one foot at a time, so when you run and your foot hits the ground, a certain part of your body comes to a dead stop. Force is mass times acceleration, there is mass that stops, and a certain change in velocity that occurs, too."
"In the barefoot runner who heel strikes, the typical impact force that you’ll get landing on your heel is two times your body weight, essentially the same as hitting your heel with a hammer with two times your body weight.”
“So if you land (with a heel strike) with a shoe on, you have basically the same force (perhaps 10% less as a little force is dampened by the shoe) so the magnitude of the force is the same, wearing a shoe or not when heel striking.”
“But when you land with a barefoot running style (much more of a forefoot strike), then the actual magnitude, or the height of that peak, is half the body weight, much less collision force is occurring.
If you look at the rate of loading of that force, how fast that force ramps up, which many people think is the primary cause of injury (nobody knows for sure), the rate of loading, when you run barefoot and heel strike is 450 bodyweights per second—that’s fast.
The reason a shoe is comfortable is that it has a lot of elastic elements in the heel and it slows the rate of loading when heel-striking to about 70 bodyweights per second.
However barefoot runners (most of them) had about 30 bodyweights per second.
The point is that when you run barefoot you can have magnitudes of loading that are much lower than running in a shoe, and rates of loading that are equal to or lower than wearing a shoe…which is why it’s comfortable and potentially less injurious.”
This is what we’ve been finding through our research for our barefoot running book and teaching at our clinics. As the study finds, when you get off of the heel, you can use your leg as a natural shock-absorber, rather than relying on a half-inch or inch of rubber under your heel to absorb all of the bone-jarring impact.
The study goes on to say that ‘modern running shoes are designed to make rear foot strike running comfortable and less injurious by using elastic materials in a large heal to absorb the force and spread it out over a longer time (in essence to make it less injurious).
The trials confirm reports that shod runners who grew up wearing shoes tend to stay with a heel strike (striking just slightly flatter) when out of a shoe, but that those who ‘grew up barefoot or switched to barefoot running most often used forefoot strike landings followed by heel contact (toe-heel-to running) in both barefoot and shod conditions. Mid-foot strike landings were sometimes used in barefoot conditions.
1st Point – Higher Impact and Lower Efficiency When Heel Striking
Based on the study, a heel strike converts little impact into forward or ‘rotational energy’ instead transmitting the energy up through the body. In contrast, a forefoot strike decreased impact by storing energy in the muscles of the calf and the achilles tendon, and rebounding it in rotational kinetic energy. In short, running on the heel increases impact (up to three times the impact force of forefoot landing, and up to 7 times the impact loading of running barefoot) and decreases efficiency (causing a braking effect with each stride) while running on the forefoot decreases impact and increases efficiency, by translating stored kinetic energy in the muscles into rotational or forward propulsion.
In essence, if you picture your stride as a wheel, when running with your heel down, you’re running with a cogged or geared wheel, hitting hard and stopping with each stride. When you’re running with a forefoot stride, your impact is less, and is translated into rotational force, spinning the wheel and moving you forward.
Second Point – Barefoot Runners Lower Center of Gravity to Reduce Impact
The study found that barefoot runners suffered no greater impact when landing on hard surfaces than soft surfaces. This is because forefoot runners lowered their centers of gravity more (bent their knees and ankles more) or were more ‘compliant’ to the ground than their rear foot striking compatriots. This allows barefoot runners to ‘adjust leg stiffness depending on surface hardnesses.
This point dispels the myth that we could once run barefoot on the Savanna, but cannot do so on harder ‘modern’ surfaces such as asphalt and pavement as the study found ‘no significant differences in rates or magnitudes of impact loading in barefoot runners on hard surfaces relative to cushioned surfaces’.
Point Three – We Evolved to Run on Our Forefoot
Natural selection suggests that if endurance running was important to our survival, then forefoot running come about to protect the foot and reduce the chance of injury.
While barefoot runners or those who wear minimalist shoes avoid rear foot landings and the associated impacts, in contrast, most shod runners today land almost exclusively on their heels.
From an evolutionary perspective, the study theorizes that ancient man, such as the early Australopithecus afarensis had an enlarged heel and probably walked with a rear foot strike, but was missing many features of the modern foot, such as a strong longitudinal arch.
They found that a strong longitudinal arch which acts as a spring, storing and releasing energy, would have increased performance in a forefoot strike or perhaps mid-foot strike, but not for a rear-foot strike. This not only would have better protected the runner, but likely accounts for the ‘lower (economical) cost of barefoot running relative to shod running’. In short, the longitudinal arch (if not locked in a shoe with arch support) helps us rebound with each stride, reducing the amount of energy necessary to run.
Dr. Lieberman believes this study may have far reaching health consequences and that further studies are necessary.
While ‘the average runner strikes the ground 600 times per kilometer, making runners prone to repetitive stress injuries.’ ‘the incidence of such injuries has remained considerable for 30?years despite technological advancements that provide more cushioning and motion control in shoes designed for heel–toe running.’
He believes that while cushioned, high-heeled running shoes may be comfortable, they limit the amount one can feel the ground, making it harder to mitigate impact, and easier for runners to land on their heels. He goes on to say that running shoes may weaken foot muscles and arch strength through reliance on arch supports and stiffened soles and that this weakness itself may contribute to ‘excessive pronation’ and plantar Fasciitis.
Both Dr. Lieberman and his colleagues, along with Dr. William L. Jungers who published a biomechanical editorial in this issue of nature (which we’ll be reviewing shortly) entitled ‘Barefoot running strikes back’ agree that more study is necessary on injury rates between barefoot runners and their shod compatriots.
‘Although there are anecdotal reports of reduced injuries in barefoot populations, controlled prospective studies are needed to test the hypothesis that individuals who do not predominantly RFS either barefoot or in minimal footwear, as the foot apparently evolved to do, have reduced injury rates.’
We agree and look forward to future studies.
More on this exciting topic to come, as well as more specifics on Dr. Lieberman’s new findings.
The Study: http://barefootrunning.fas.harvard.edu/
Harvard Magazine discussing barefoot running last Summer: http://harvardmagazine.com/updates/lieberman-barefoot-running-shoes
More of Dr. Dan Lieberman’s research: http://www.fas.harvard.edu/~skeleton/PDFList.html
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