Archive for the ‘Evolution’ Category

Evolutionary Basis for Barefoot Running

May 27, 2011

The use of specialized running shoes is almost ubiquitous to modern society. It has until recently been the consensus of almost everyone involved in the fields of podiatry and sports medicine that some form of cushioned supportive shoe is necessary to perform any extended running activity. These concepts rested on the unfounded assumptions that running was either not an innate ability of humans and had never been integral to survival or that, despite its necessity for survival, humans were maladapted to perform it with any proficiency. In the athletic community running was, and still is, largely viewed as an activity made possible only by modern technology and technique.

This attitude is reinforced by some obvious facts about the human capacity for running when compared to that of other well known mammalian sprinters, such as dogs, cats and horses. In every case humans fall far short of the speeds reached by most other animals known for running.

The significance of human running only becomes apparent when we look at our times over long distances. While many running animals are good at short burst of great speed, others are specialized for slower speeds drawn out over very long distances. In the world of Endurance Running (ER), humans prove to be very competitive with most other animals.

The adaptations for ER and its possible role in our evolution as a species is covered in Daniel Leiberman’s Endurance running and the evolution of Homo . The article states that humans and some of our predecessors showed multiple adaptations not found in earlier species, or in modern great apes, that aid in the activity of ER. It also analyzes the human running abilities in comparison to those of other species. Leiberman shows that the speed range at which humans perform ER is slightly higher than most other running mammals, leading to the theory that humans evolved to use running as a form of hunting.  This is backed by the fact that, while uncommon today, endurance hunting was once widely practiced.

Included in the list of adaptations that assist in and are necessary for running are these major items: The Nuchal Ligament, The long Achilles Tendon, and the disconnection of breathing and stride functions. I will give a quick review of the significance of each of these adaptations and how they relate to how humans run.

The Nuchal Ligament runs from the base of the skull to the seventh vertebra in humans. What is unique about this ligament is that no other primate has it. The Nuchal Ligament is generally present in animals known for fast running, such as horses and dogs. The function of this ligament is to steady the head and keep it level during running. This adaptation was first seen in H. habilis and has carried into modern humans.

Next is the detachment of our breathing functions from our stride. In all quadrupeds, the breathing pattern is locked into the running stride. For every stride in a ‘gallop’, a quadruped has to take one breath cycle. This is a limiting factor in many ways for quadrupeds, but is significant in that it disallows the animal to effectively cool off by panting.  Additionally, because humans are not locked into a one-stride-one-breath ratio, we are able to use much higher stride rates instead of steadily increasing stride length. This is important in our ability to persistence hunt.

Finally, we have the long Achilles tendon which, again, is not present in our closest relatives, the chimpanzees. This tendon is absolutely essential to running any long distance. The function of the Achilles tendon is to absorb the initial shock of the foot fall and store that energy for return during push off. In this way the tendon acts like a spring or, more aptly, a rubber band. This rubber band action greatly increases the efficiency of running and thus reduces the metabolic cost of running.

All of these pieces of evidence come together to form a very vivid picture of our past as a species. Before we began using complex tools such as bows and arrows, we still had to hunt. Protein was a major part of our diets so we had to have a way of getting it regularly. One theory on how we managed to hunt without the aid of complex tools is we ran our prey to death.

To persistence hunt, group of human runners can split an animal from the rest of its herd and then chase it. The animal will gallop off as the humans approach but can only gallop for a very short time Before it must stop to rest. The humans use tracking to remain on the trail of the same animal. If the group keeps close enough to the animal to scare it into galloping every time it tries to rest, the animal will have no chance to cool off. In the African climate that humans evolved in, overheating is a serious problem. Humans can sweat to cool off even while running, so while the prey is dying of heat exhaustion, the humans remain able to perform. The pace that the humans maintain is just fast enough that the prey must gallop to get away, it cannot trot to conserve energy. After many miles and much time, the animal either slows enough to be caught and killed or dies due to heat exhaustion.

All of the adaptations needed to hunt this way are present in humans. These adaptations would not develop without some necessity. Thus, barring significant new understandings about the functions of these structures in human physiology, we must accept that humans regularly used running as a means of survival.

Next post will be the Mechanical Basis for Barefoot Running.