In addition to my normal topics of research I have taken on the choice task of studying the local crows. You can follow along with the day to day drama of Corvid life in my new blog Chasing Crows!
A common misconception that exists today is that the lifespan of early humans was extremely short. Often people quote numbers like 30 years as the average life span of early hunter gatherers and farmers. A look at modern day hunter-gatherer societies is the best way to examine the likely life span of early humans.
The study longevity Among Hunter-Gatherers: A Cross cultural Examination covers this topic with a look at the human life span in several different cultures. The study puts forward the hypothesis that there is a prototypical pre-industrial mortality profile in humans. Or in other words, there is a normal human lifespan that can be seen across many cultures and levels of pre-industrial development.
Our conclusion is that there is a characteristic life span for our species, in which mortality decreases sharply from infancy through childhood, followed by a period in which mortality rates remain essentially constant to about age 40 years, after which mortality rises steadily in Gompertz fashion. The modal age of adult death is about seven decades, before which time humans remain vigorous producers, and after which senescence rapidly
occurs and people die.
After reviewing a large amount of relevant data on the many aspects of running, I have come to the conclusion that barefoot running is an evolutionarily sound, biomechanically sound, and statistically plausible way of improving running and reducing injury.
- Endurance running was an important survival strategy for early humans and has left marks in our physiology.
- Humans possess many adaptations that allow for efficient running that neither our ancient ancestors nor out present evolutionary relatives have.
- The skeleture and musculature of the foot and leg are well adapted to handle the forces associated with running.
- There are no studies or clinical trials that show traditional modern running shoes as effective in reducing injury rates among runners
- Barefoot running has shown at least marginally better injury prevention rates than shod running
- More research is needed to ascertain the full extent and range of possible benefits from barefoot running as well as any possible risks related to it.
In the previous post we have covered both the evolutionary and biomechanical bases for running and in particular barefoot running. The evidence thus far has pointed towards barefoot running being not only possible but the preferable mode of running. This evidence has for the most part centered around the factor of injury prevention.
Due to the wide amount of variation between runners in factors such as speed and mileage, injury rate is the only common metric for effectiveness of a mode of running that can easily be measured. To add to this, injury is a very common occurrence that has only a few significant predictors or direct causes. This is to say that injuries tend to occur at a regular rate in all runners. This makes it a great tool to judge the effectiveness of a given technique as any change from the the statistical average would be easily apparent. Two polls taken roughly thirty years apart showed similar injury rates of 60% and 66% per year (Runners World). Reports of average injury rates today vary widely between 19.4% and 92.4% per year (Incidence and determinants of lower extremity running injuries in long distance runners: a systematic review), but the mode rate is around 50% per year. In other words, half of the running population gets injured in some way every year, and this estimate may very well be on the low side.
Injuries in this context are defined as any damage or disorder that causes significant change or even cessation of ones normal running routine. The large focus in most studies is on chronic injuries, or injuries that are not the result of sudden trauma and persist over long periods of time. Acute injuries are described as the result of sudden trauma and non persistent. Over use injuries largely fall into the category of chronic injury. Examples of these types of injuries would be: stress fractures, Iliotibial band syndrome, Patellofemoral Pain (runners knee), Achilles tendinitis, and plantar fasciitis to name just a few. The significance of these types of injuries is that the cause is usually systemic rather then the result of any one particular action. Systemic causes would include things such as personal physiology, running form, shoe type, and running surface.
The big question yet unanswered among all of the studies done on this subject is still why the injury rate of running is so high. To give some perspective on this we could imagine what would happen if another species shared this rate of injury. Lets imagine that one out of every two cheetahs in the wild got injured at least once a year, like humans. We all know how important running is to the survival of these cats, so its not hard to imagine that an injury might be the difference between life or death. We know that cheetahs do not have this high of an injury rate by the simple fact that they are still alive as a species. An injury rate, and subsequently a death rate of 50% would kill the species off faster then they could reproduce. Given the evidence I provided in the previous section about the importance of running to early humans, it would seem that there is a discrepancy between the paleoanthropological narrative and the modern day demonstration. If we hold the running man theory to be correct, then the only conclusion to be made is that a 50% injury rate is not inherent to our species. If it was in fact inherent to humans we would simply not been a viable species.
The question that immediately follows then would be what causes this injury rate if not the simple act of being a human. A number of factors can be eliminated easily. “Running injuries. A review of the epidemiological literature.” examined relevant medical literature and came to this conclusion:
[factors] Significantly not associated with running injuries seem age, gender, body mass index, running hills, running on hard surfaces, participation in other sports, time of the year and time of the day.
The association between running injuries and factors such as warm-up and stretching exercises, body height, malalignment, muscular imbalance, restricted range of motion, running frequency, level of performance, stability of running pattern, shoes and inshoe orthoses and running on 1 side of the road remains unclear or is backed by contradicting or scarce research findings.
None of the factors listed above show a high correlation with increased running injuries. In fact one of the factors, age, is found as a protective factor of injury in some studies.
A keystone study in this field (Is your prescription of distance running shoes evidence based?) did a systemic review of relevant medical literature and came to this conclusion in regards to modern running shoes, or in the terminology of this study “Pronation control, Elevated Cushioned Heel” PECH shoes:
Biomechanical and epidemiological studies have raised significant questions about the
capacity of running shoes incorporating either cushioning, heel elevation or sub-talar
control systems to prevent injury and have identified their potential to cause harm. We
identified no clinical trials which assessed the impact of the PECH design, which
incorporates all three of these features, on either running injury rates, running
performance or runner’s global health and wellbeing. Until such evidence becomes
available, PECH running shoes must be considered unproven technology with the
potential to cause harm. As such, the prescription of PECH shoes to distance runners is
not evidence based.
It is the intended purpose of this series of post to demonstrate that proper running form should reduce injury and that running barefoot encourages proper form. It is true that many proponents of barefoot running will claim that it almost eliminates injury all together. On this point however the actual data is very thin. Only one study could be found that included barefoot and “minimalist” runners in the sample group. This study (Relationships among Shoe Type, Foot Strike Pattern, and Injury Incidence) is, at the time of writing, still unpublished and has not gone under peer review. I did manage to make contact with the researcher heading the study, Don Goss, and he supplied me with the poster presented at ACSM in Denver this year. These preliminary results where as follows:
•1 yr injury incidence rate was 53.9% for all runners combined.
•1 yr overall risk of injury for those wearing traditional running shoes (55.4%) was greater than for those running barefoot or wearing minimalist running shoes (46.3%, relative risk = 1.19, X²=6.39, 1df, p=.01).
•Relative risk calculations indicate risk of foot injury among barefoot runners was 2.81 times greater than for those wearing traditional running shoes (X²=17.9, 1dF, p<.001).
•Incidence of knee injuries was not significantly different among foot strike groups (X²=2.19, 2dF, p=.34) or between traditionally shod and barefoot/minimalist runners (X²=1.24, 1dF, p=.27), however, relative risk calculations indicate risk of knee injury among traditionally shod runners was 1.3 times greater than for the barefoot/minimalist runners.
These numbers do support the case for barefoot and minimalist running as a means of injury prevention, even if the margins are very small compared to the lofty claims of many proponents of barefoot running. 46% injury rate still seems to be too high to fit with the evolutionary narrative though. It would seem that based on this, footwear alone is not the cause of the high injury rate in runners. Running barefoot may help reduce the risk of some injuries, but it also increases the risk of others. There are two factors that I hypothesize could be causes of the still very high injury rate. First is the exclusive use of minimalist footwear rather than true barefoot running. Second is the comparatively late adoption of running in life and the even later and more recent adoption of the barefoot mode of running.
This study also examined a similar point in asking whether people had changed their shoe type or foot strike pattern recently.
•35.2% (520) of runners taking the survey changed their shoe type in the last 2 yrs. Of those, 63.6% (331) also changed their foot strike pattern.
•33.4% (530) of respondents changed their foot strike pattern in the last 2 yrs. 63.9% (339) of those also changed their shoe type.
Adoption of a new mode of running can be difficult, and if not undertaken properly can lead to injury. I put forward the possibility that barefoot and minimalist runners make up a disproportionate amount of those who have either changed their foot wear and strike pattern. I base this hypothesis on two factors: The reported changes in shoes and strike patterns and the recentness of the barefoot/minimalist movement. 63% of those who changed their shoe type also changed their strike pattern. A change in strike pattern coinciding closely with a change in footwear fits the profile of adopting minimalist shoes, as these shoes require a very different strike pattern then conventional shoes. This was confirmed by Don although he could not give me exact number at this time. In addition, the book ‘Born to run” which is credited with the popularization of the barefoot movement was published in 2009 and there fore coincides closely with this two year period. If a large portion of barefoot and minimalist runners have only adopted this mode of running with in the past two years, then there is significant reason to expect an elevated injury rate over that of habitually barefoot people.
Use of minimalist shoe may also be responsible in part for the elevated rate of injury. In the study barefoot and minimalist runners are grouped into one category. While running in minimalist shoes such as vibrams is very similar to running barefoot, it is not exactly the same and lacks a few key qualities. Muted sensory feed back and limited range of motion in the foot are two major factors that set any shoe, minimalist or traditional, apart from true barefoot running. As discussed in the previous post, proprioception and flexion in the foot are important to reduce impact and subsequently protect against injury. Any limiting of these factors has the ability to increase the risk of injury. Ironically, barefoot runners seems to be in the minority among the barefoot/minimalist community. Because of this, interpretation of the statistics must take into account the uneven representation of barefoot runners.
Ultimately there is not enough information on the subject of barefoot running to come to a conclusive understanding of its effects on injury rates. There is similarly little to no information on traditional running shoes that indicates they could reduce the rate of injury. Based on the preliminary findings of one yet unpublished study, running shoes perform worse than barefoot or minimalist shoes in protecting against injury.
It is my hypothesis that habitually barefoot people who have a life long history of running are at the least risk of running injury, but as of yet no conclusive research exists to support this idea.
As discussed in the last post, there is significant evidence for running in humanity’s evolutionary past. Habitual shoe use only came onto the picture somewhere between 40,000 and 26,000 YA (BBC). Even then footwear was comparatively minimalist and would not have modified the biomechanics of the foot in the way that modern running shoes are made to do. So the question now would be: how did humans manage to make running a significant part of their survival strategy while being limited to running in bare feet. More simply put, how do humans run effectively with bare feet?
The mechanism of the human foot is a very complex and intricate one. There are 26 bones in each foot and even more muscles, tendons, and other connecting tissues. At first look, the muscles in the foot of the average habitually shod person would look atrophic as if they could serve no real function and where perhaps vestigial remnants from tree climbing ancestors. This appearance, however, is the result of continuous use of restrictive shoes rather than the natural state of the human foot. Examination of the feet of habitually barefoot people reveals significant morphological differences from those of habitually shod feet (The effects of habitual footwear use). These differences can be both in the skeletal formation of the foot and the muscular strength of the foot and surrounding structures. With the proper perspective of a healthy well formed foot in mind rather than the atrophied foot commonly depicted, we can shift our focus from protecting the foot toward using its innate mechanical properties.
The major factor that any runner has to overcome, whether they wear shoes or not, is the sudden vertical impact of the foot hitting the ground. Running is in essences a series of small jumps. Immediately after the foot meets the ground the weight of the entire body in motion is loaded onto that foot. On average the foot experiences over 2 times the body weight during and immediately after impact. This period is referred to as the stance phase of the running gait. The weight alone is not what makes this part of running significant, rather it is the rapidness with which that weight is applied that causes so much stress on the body. It is commonly accepted that most running injuries are the result of the large forces at play during the stance phase. Thus any sustainable approach to running must involve a way of adequately dealing with these forces in a way that does not lead to injury.
In the standard heel striking gait adopted by most shod runners, the foot is dorsiflexed (pointed upwards) making the Calcaneus (heel bone) the primary structure contacting the ground at touchdown. Because of the the positioning of the Calcaneus bone and the nature of the heel striking gait, all of the joints of the leg are lined up straight to receive the impact of the weight of the body, which is moving downward along the same vector as the leg. In this set up the energy from the initial impact cannot be dispersed at all and travel through the leg causing every joint involved to receive equal stress.
In barefoot running there are three major factors that allow the human body to endure the stress of running: the spring like structures of the foot and leg, the medial longitudinal arch, and the sensory feed back systems known as proprioception.
The foot and leg are positioned in a significantly different manner during barefoot running then the way just described for heel strike. This manner of landing is referred to as a forefoot strike. While there are variations on this technique, the basic principles remain the same. In the forefoot strike the bodyweight is largely positioned over the foot in stance phase. The knee is bent and the foot is plantarflexed (point down). In this way the leg forms a number of levers that can absorb the initial shock of impact. The primary lever is that of the foot, holding the ankle as the fulcrum. The forefoot, or ball of the foot, is the area comprised of the ends of the long metatarsal bones, or where the toes connect to the foot. Allowing this portion of the foot to fall first and then slow the decent of the rest of the foot and subsequently the rest of the body greatly cushions the loading of the rest of the bodyweight. In mechanical terms this is accomplished by converting linear momentum into angular momentum and then applying resistance. The same is mechanic is mirrored in the bent knee and to a lesser extent the hip.
Once again I refer to another article co-written by Lieberman titled Foot strike patterns and collision forces in habitually barefoot versus shod runners. In this article the forces of running are analyzed and Lieberman come to this conclusion:
At similar speeds, magnitudes of peak vertical force during the impact period … are approximately three times lower in habitual barefoot runners who FFS (forefoot strike) than in habitually shod runners who RFS (heel strike) either barefoot or in shoes
Both RFS gaits generate an impact transient, but shoes slow the transient’s rate of loading and lower its magnitude. FFS generates no impact transient even in the barefoot condition.
The next structure to aid in running is the medial longitudinal arch of the foot, or as it is commonly known just the arch of the the foot. Presence of this structure in early Proto-Humans is used as an indication of bipedalism (BBC). The arch is dealt with as a rigid structure in the case of most footwear. Most shoes have some form of arch support that is intended to stabilize the arch and keep it from moving. In the case of barefoot locomotion, however, the exact opposite is done for the arch. Studies of habitually barefoot people show that the arches of their feet are significantly higher on average then those of their habitually shod counterparts. When allowed to behave normally the arch of the foot deflects or spreads under weight. This topic is covered throughly in running related injury prevention through barefoot adaptations.
…medial arch rising and shortening due to activation of intrinsic musculature allows the foot to act as a dynamic impact dampening structure rather than merely as a lever for propulsion…
Because of this deflection it acts as yet another spring like structure absorbing shock and then returning energy on push off.
The deflection of the arch is facilitated by intrinsic muscles within the foot. As the muscles strengthen the arch becomes more prominent. Additionally as these muscles take over much of the load bearing function in the foot, stress on the plantar fascia is reduced. This can help prevent cases of Plantar fasciitis, a very common overuse injury.
Activation of this intrinsic musculature is in part or in whole initiated by sensory feedback the feet receive from the ground. The sensory feedback system is referred to as Proprioception.
The irregular character of the contact surface seemed to be the element that was present in the subject with the greatest adaptation. this is consistent with the hypothesis that plantar sensory feedback may induce intrinsic foot shock absorption.
Reduction of sensory feedback by means of a shoe or other device that keeps the foot from accurately feeling the impact of touchdown disallows the engagement of these adaptive features in the foot.
The modern running shoes and footwear in general have successfully diminished sensory feedback with out diminishing the injury inducing impact, a dangerous situation.The mode of injury follows the medical model of a neuropathic injury.
Given the function of the few structures and systems touched on here, as well as many others not discussed, it becomes clear that not only can humans run with bare feet effectively but that they may do so with better proficiency and safety then with shoes. From the perspective of evolution and from human physiology, barefoot running is solid. Never the less there remains a large number of practitioners of podiatry and sports medicine that recommend standard running shoes. These recommendations at best come from a fear that the case for barefoot running is only theoretical and may not be born out in practice. As with any procedure or new medicine, a fully controlled test of the effects in the real world is a must before it can be accepted. Unfortunately the reality of testing in the world of running is complicated and less then stellar.
In the next post I will be discussing the Statistical Analysis of Barefoot and Conventional Running.
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.
A number of sources have released articles on male and female perceptions of sexual attractiveness in nonverbal body language and more specifically facial expressions
PDF of article from University of British Columbia on body language and perceived attractiveness
Statistical analysis of facial expression from OkTrends
Statistical analysis of perception of attractiveness in opposite sex and response to perceived attractiveness
The basic gist of these findings are that men and women have distinct differences in deciding on sexual attractiveness when it comes to body language. While the common belief has been that smiling is the best way of appearing attractive, both the study from UBC and the statistics from OKTrends say otherwise.
For men, looking either prideful and triumphant or swaggering and brooding had a significantly positive effect on perceived attractiveness over a friendly smile.
For women a smile was still better then neutral and is comparatively perceived more attractive in women then men. A flirtatious face was the more attractive then a smile though.
The effects of eye contact where split between genders. Men on average benefited from not making eye contact in profile pictures on dating sites. Women benefited from the exact opposite. Combinations of eye contact with different facial expressions returned mixed results. Giving flirting signals with out making eye contact was over all the least beneficial combination and received on average the lowest responses.