Science Literature

Over the years, there has been much interest in the design of running shoes, with product designers building in protection against impacts and other perceived hazards. However, continuing reports of repetitive strain injuries warrant further research and product re-design. The topic has come to the surface recently with a comparison of the forces experienced by feet of habitually shod versus habitually barefoot runners. It emerges that barefoot runners make contact with the ground in a way that avoids impact-related discomfort and injury.

On the left, a habitually shod Kenyan who is heel-striking; on the right, a Kenyan who has never worn shoes and who is forefoot striking in the way most barefoot runners land. Below are representative force traces (in units of body weight) showing how the two styles of running differ in the force generated when the foot collides with the ground. The barefoot runner lands with no collisional force. (Image: Daniel E. Lieberman, Source here)

As a matter of observation, most habitually shod runners first contact the ground with their heel. This is referred to as heel-striking or rear-foot strike. Modern running shoes have been designed to reduce the impact forces with the help of additional cushioning at the heel. Barefoot runners first contact the ground with the front part of their feet and bend their ankles more as they run. This is referred to as fore-foot or mid-foot strike. This mode of running results in reduced collision forces and enhanced comfort.

"People who don't wear shoes when they run have an astonishingly different strike," says Daniel E. Lieberman, professor of human evolutionary biology at Harvard University and co-author of a paper appearing this week in the journal Nature. "By landing on the middle or front of the foot, barefoot runners have almost no impact collision, much less than most shod runners generate when they heel-strike. Most people today think barefoot running is dangerous and hurts, but actually you can run barefoot on the world's hardest surfaces without the slightest discomfort and pain. All you need is a few calluses to avoid roughing up the skin of the foot. Further, it might be less injurious than the way some people run in shoes."

Since this is a topic where there are numerous agents with commercial interests, the authors of the research paper have felt the need to issue a disclaimer that their reported work is essentially empirical in nature.

"Please note that we present no data on how people should run, whether shoes cause some injuries, or whether barefoot running causes other kinds of injuries. We believe there is a strong need for controlled, prospective studies on these problems." (Source here)

However, the authors go well beyond the empirical data in their analysis when they ground their work in a framework of evolutionary biology. This is also the starting point for Jungers' commentary on the research: "A commitment to walking and running on two legs distinguishes humans from apes, and has long been the defining adaptation of the hominins - the lineages that include both humans and our extinct relatives. This form of locomotion (bipedalism) has been around for millions of years, and we have been unshod for more than 99% of that time." The view, therefore, is that the context for understanding running is that it has evolved as an adaptation under the influence of natural selection.

"Our feet were made in part for running," Lieberman says. But as he and his co-authors write in Nature: "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."

There is another perspective on this, which is that of design. Design advocates will affirm: 'Our feet were designed in part for running'. Humans live in many different environments, and the design issues are affected by the need to walk, jump, climb, carry and run in these different environments. A sensitivity to design means that we need to understand how our feet work best in different conditions, so it follows that runners should adopt a biomechanical and physiological approach to developing good running habits. Runners should train to develop the full potential of the design features of their bodies. An evolutionary story of how ape-like animals developed bipedalism is simply a veneer overlying the empirical data.

Foot strike patterns and collision forces in habitually barefoot versus shod runners
Daniel E. Lieberman, Madhusudhan Venkadesan, William A. Werbel, Adam I. Daoud, Susan D'Andrea, Irene S. Davis, Robert Ojiambo Mang'Eni & Yannis Pitsiladis
Nature 463, 531-535 (28 January 2010) | doi:10.1038/nature08723

First para: 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.

See also:

The Barefoot Professor: by Nature Video

Jungers, W.L., Barefoot running strikes back, Nature 463, 433-434 (28 January 2010) | doi:10.1038/463433a

Tyler, D. The human body is built for running, ARN Literature blog (29 October 2009)