• Invited lecture to be presented August 26, 2011, at the 2011 KAHPERD International Sport Science Congress (ISSC) Daegu, Korea

  
  

  How footwear caused humans to become sedentary

Steven E, Robbins, MD

Introduction

Humans currently suffer from a myriad of health disorders brought upon by lack of physical activity in their lives (sedentary) that range from afflictions that simply affect “quality of life” such as low back and foot pain, to coronary thromboses that kill. Based on the notion that this current state of physical activity indicates that humans are genetically inactive, serious investigators have hypothesized that humans are inherently idle, and are attempting to identify the “lazy gene.”(1) This would allow splicing in a few base pairs to change sloth to fitness.

The proposition that inactivity is genetically predetermined seems inconsistent with both human history and basic evolutionary concepts. Being inactive is inconsistent with survival as a hunter-gatherer as humans were for 95 percent of the time since they separated from a common ancestor perhaps 250,000 years ago. Furthermore, survival of humanity despite disorders that inactivity creates, such as compromised mobility and cardiac function, seems incompatible with scientific precepts regarding the origins of species first formulated by Darwin, since these conditions surely would represent a substantial selective disadvantage. Nevertheless, it seems inappropriate to dismiss ideas of prominent investigators on theoretical grounds alone without more evidence to the contrary, such as data indicating that humans have been highly physically active through most of their evolutionary history only to become inactive relatively recently. If human inactivity is not genetically based and its cause identified, it may be correctable, thereby advancing health. The objective of this report is to provide evidence to support the notion that the current human sedentary condition is external, and to identify its cause.

External cause

There is not a single anthropological report sourced from ancient writing, art or surviving artifacts indicating that humans spent a large part of their wakeful time either sitting or recumbent until the dawning of the Renaissance, which commenced as early as the fourteenth century in Italy, and as late as the mid-sixteenth century in England. For example, prior to the Renaissance, art and literature rarely depict or describe, respectively, subjects other than royalty seated. Absence of anthropological reports fails to support the thesis that humans are inherently inactive, but advances the opposing view that they were energetic through their evolutionary history, only to become sedentary recently. This suggests an external cause of human inactivity rather than a biological one.

There is evidence of a rapid transition from active to sedentary coinciding with the Renaissance. No measure of human behavior seems more relevant to overall activity levels than increase in wakeful time spent sitting. This point can be identified with some precision via the Oxford English Dictionary, which researches the English lexicon on the basis of historical word usage and meaning. Most new words are created as communication needs dictate, but soon disappear from use when the need to use them declines. A few relevant ones remain. Most words in modern English originated as a similar word in Old English, Middle English or a foreign language. A few words are considered “neologisms,” a completely new word without an equivalent historical example, which are created in response to novelty in the form of person, period or event.

The earliest recorded usage of sedentary was 1603, and its meaning was:

“of habits , occupations, etc.: Requiring continuance of the sitting position.”

A second, more pejorative usage was first documented in 1662, and is more consistent with its current meaning:

“Of persons : Accustomed or addicted to sitting still; engaged in sedentary pursuits ; not in the habit of taking physical exercise.”

Sedentary is a neologism. The year 1603 was during the reign of Elizabeth I, a period considered the English Renaissance. This suggests that the need to communicate this novel concept commenced at this time. The evolution of the meaning of the word indicates that within 60 years that the word was first used, sitting became perceived as excessive with negative health consequences, a condition that has not changed to the present time. This suggests that some novel condition commenced with the Renaissance in England and continues presently.

Recently,  anthropologists made an unfortunate word choice in assigning "sedentary" to also signify human groups at the beginning of the Neolithic Age (10,000 years ago) that changed from nomadic to living in a fixed location. There is no evidence that this change was associated with reduction in levels of weight-bearing time or physical activity. To avoid confusion, sedentary will be used here exclusively to mean inactive physically.

Further support of this Renaissance transition from active to sedentary comes from the history of the chair. According to Litchfield(2), technology of chair construction dates back perhaps five millennia, but its widespread use by a society is recent. For most of its history, chairs were highly decorative items used by the highest ranking few to denote status. Pre-Renaissance chairs are exceedingly rare finds, yet post-Renaissance seating is commonplace, indicating that the Renaissance marked a sudden transition to chair use by all social classes. Written records indicate that at this time chairs became omnipresent in the home, workplace and social gatherings. As demand exploded, guilds specializing in their construction came into existence. Since the technology to produce them was available but not used by many until the Renaissance, prior to the Renaissance humans chose voluntarily to be upright for most of their wakeful time rather than being seated. Humans were active by choice rather than inherently sedentary as has been hypothesized.

There is evidence that elite groups wore shoes dating close to the time humanity began the transition from nomadic hunter gatherers to residing in a fixed location - perhaps 10,000 years ago. The less advantaged majority were barefoot. In the feudal age, according to the Domesday Book of 1086, over 80% of the population of England were serfs of some form. Since serfs everywhere in Europe are portrayed as barefoot in written texts and the visual arts of that time, it can be assumed that most Europeans were barefoot during the Middle Ages.

This changed with the Renaissance. Zipfel & Berger(4) have shown that cohorts which were totally unshod preserve forefoot articulations whereas shod groups tend to damage them. Mafart(3) examined the hallux (great toe) of skeletal remains in a church graveyard in France that had been used as a burial site for greater than a millennium. He found that the percentage with indications of disorders of the hallux attributable to shoe wearing in males increased by approximately 400 percent between between the 11th - 13th centuries (pre-Renaissance) and the 16th - 17th centuries (post-Renaissance) cohorts. The true increase in footwear use in the overall population was probably greater than this number indicates because church ground was always used for burial by the upper classes who were more likely to wear shoes prior to the Renaissance, whereas barefoot groups such as serfs, debtors, bastards and criminals were denied burial on hallowed ground. Renaissance Europeans must have been eager to wear shoes considering that damage to the hallux usually results in pain on weight-bearing, and poor functionality of Renaissance footwear used by males limited users to walking with difficulty and no running because most shoes were highly stylized with significant heel rise and narrow toe box.

The energy behind the rapid transition to footwear use by all social classes is best explained as a consequence of the “Black Death,” a pandemic form of bubonic plague that ravaged Europe from 1347 to 1351, reducing humanity by 30 to 60 percent according to differing estimates. The resulting fear of death from disease became imprinted on the psyche of Renaissance man, leading to rapid change in many traditional practices, including loss of influence of the Catholic Church and the end of serfdom. With less repression of scientific thought came the reintroduction of classical Greek and Hellenistic ideas that were kept alive over medieval times by the Arabists.

Increase in income from a labor shortage caused by depopulation gave the lower classes the means to purchase simple varieties of footwear, but this does not adequately explain why so many turned to footwear use considering that footwear use entails a substantial cost in terms of ease of locomotion over the bare foot. The lower classes were not simply trying to be perceived as from a higher class through wearing shoes because their footwear were simple in design and construction, therefore easily identified as belonging to the poor. A more cogent explanation is that footwear use was considered a means of prevention of premature death from infectious disease according to notions of health at that time. Hellenistic ideas attributed infectious disease to environmental “filth” - visible evidence of environmental contamination, such as soil residues. Footwear wearing can be seen as an extension of this notion, since their use prevented filth contamination outside of the home.

Known causal relation between footwear use and sedentary behavior

There are two causal mechanisms linking footwear use to sedentary behavior. The first was previously identified. Footwear use leads to foot disorders (only some of which were documented by Mafart(3), and Zipfel & Berger(4)) that would make prolonged standing painful, thereby encouraging cessation of weight-bearing. A second causal system is essentially an inherent plantar skin protective mechanism. Plantar skin can sustain high amplitude brief loading associated with running without footwear, yet ulceration of plantar skin results from as little as the weight of the leg when supine if it is unremitting, as is the case when the unresponsive patient sustains “pressure ulcers.” Plantar surface loading is not sustained when walking and running, however, with prolonged standing, damage would occur without a behavioral mechanism to continuously change the plantar loading site.

Standing (weight-bearing without locomotion) is dynamic, with continual intense muscular activity maintaining stable equilibrium. This has perhaps been best examined via a “force platform” - an instrumented, rigid surface capable of measuring loading in six degrees of freedom (x, y, z, roll, pitch, yaw). Displacement of center of mass of the human body when standing is referred to as “sway,” with “sway velocity” perhaps the most widely used and validated.(5) When balance is stressed through blindfolding subjects, one footed standing or wearing footwear that invariably destabilize(7-9), all measures of sway are positively related to falls risk in all age groups. However, sway paradoxically increases sometimes exceeding levels seen in the unstable elderly as balance stress is removed from healthy adults under 40 years of age, the cohort with the best balance.(10) Therefore when humans with inherently good balance stand, sway serves a purpose other than maintaining stable equilibrium. Advancing pregnancy offers a controlled prospective study of this phenomenon. Measures of sway paradoxically decline with advancing pregnancy even as increase in body weight and altered posture make it more difficult to maintain stable equilibrium.(11). Amplified sway during relaxed standing is best explained as a sensory feedback mechanism used to prevent pressure ulceration. It is invoked only when vigilance is not required to prevent falling, such as in a stable cohort with no balance stress and a double support base. It disappears once falls risk increase either through natural decline in stability associated with age, or external factors that stress balance. Footwear eliminate this protective mechanism when standing by their destabilizing effect when standing. This explains why shod humans are unable to comfortably stand for long periods and must resort to sitting or reclining. Neurophysiological and psychophysical reports indicate that localized skin loading induces pain, therefore avoiding standing when shod is mediated through sensory feedback.(7,8)

A known physiological mechanism explains how sedentary behavior appeared addictive as early as 1662 in England, and is presently so pervasive that serious investigators have come to suspect humans to be genetically predisposed to it. Once weight-bearing time declines, musculature required to sustain prolonged weight-bearing degrade from lack of use. An example of this is atrophy of abdominal muscles we see today. Stability when standing in the upright position requires maintaining the center of mass of the body over the feet. This is accomplished by abdominal muscle contraction sufficient to “tilt the pelvis” so as to displace the hip articulation anteriorly near the center of mass for the entire period of standing. Since balance is not required when sitting, abdominal contraction is not required. Extensive sitting leads to a typical posture of sitting involving lax abdominals and shortening and stiffening of the opposing lumbar musculature, resulting in “lordosis” (hollow curved back). Once the sedentary person becomes upright, the now weakened atrophied abdominals must additionally struggle to overcome the resistance of stiff lumbar musculature. The upright posture becomes increasing difficult to sustain for prolonged periods, which further encourages more sedentary behavior.

Amplified inactivity through technology

With technological development in its infancy in 1662, the English already perceived inactivity to be a problem. Urbanization of populations that parallels advances in technology has shortened distances travelled preforming daily activities. Furthermore, urban setting are amenable to advances in public transportation systems that progressively has reduced the need to walk. Automation and computer technology tend to make the workplace sedentary. Energy saving devices at home attenuates weight-bearing time preparing food and performing household chores. The only extended weight-bearing time available for most is reserved for nominal “leisure time” - away from work and household chores.

Discussion

The significance of medical research is measured though size of the target population that the results affect, severity of disorders addressed (morbidity vs. mortality), and perhaps now also costs associated with implementation of remedy. Even before this report, published research suggested that shoes negatively affect health. Reports suggest that they destabilize humans, with footwear that destabilize the most, such as those with thick resilient soles, may account for significant morbidity and some mortality in the elderly. In addition, running shoes have been shown to account for substantial morbidity in runners. As previously mentioned in this report, all footwear damage foot structures that eventually leads to disabling osteoarthritis in most users.

The significance of the present report is of an order of magnitude greater than previous ones dealing with footwear, and of significance rarely found in medical research because the target population is essentially all of humanity because footwear has essentially become universal, and it deals with issues that cause morbidity but significant mortality as well through the influence of sedentary behavior on risk of death from circulatory disease. In addition, implementation of a remedy through education in order to erase the social norm of footwear use is not only cost effective, it may be cost saving through tarnishing the allure required to sell expensive examples.

Barefoot weight-bearing is the precondition to a return to an active lifestyle, since it allows use of the mechanism that permits comfortable prolonged standing. Extreme cold outdoors and dangerous working conditions are examples of situations where footwear use will continue, but barefoot activity is suitable in most other places where shoes are now used. Footwear use is rarely required - an explicit social norm enforced through penalties. It is mainly an implicit social norm therefore change to barefoot weight-bearing outside of the home will proceed through education of the public about risks of using footwear. Since the benefits to overall health of a more active lifestyle are massive and cost effective, public health agencies will undoubtedly play a role in this education process because it not only improves health of citizens but it portends significant fiscal deficit reduction.

It remains possible that footwear use is such an established social norm and fashion the statement that simply informing the public may be insufficient to invoke change. If this is the case, footwear use could be treated as use of other dangerous products - with warning labelling. This will probably be far more effective than, for example, labels on tobacco products because physical addiction is not an issue with shoes.

There are obstacles to increasing barefoot weight-bearing beyond social norms. As previously mentioned, the sedentary existence results in decline in musculature needed to sustain weight-bearing for extended periods, resulting in the need for gradual adaptation to greater weight-bearing time. Furthermore, many individuals who have been shod for most of their lives may have sustained sufficient foot damage to preclude prolonged weight-bearing. All groups balance better barefoot except the elderly which is explained by advanced foot arthritis caused by footwear making the foot unable to adjust to support surfaces. This group must continue to use footwear that offer optimal stability.

Perhaps the greatest obstacle to change will be resistance from vested interests. The footwear industry is vast with ample resources at its disposal to protect its market. These funds may be used to influence governments to delay public education as the tobacco industry did in the past. This industry has and will mislead through advertising. For example, footwear manufacturers have introduced “minimalist shoes,” to help retain the increasing large market of recreational runners who have been concerned about the safety of modern running shoes, and aware of advantages of barefoot locomotion. These products are marketed through advertising falsely claiming that minimal shoes use when weight-bearing is similar to being barefoot. This harkens back to the false claims made by the tobacco industry when they introduced “light cigarettes” as a safer alternative to normal ones.

The the urban environment will eventually have to be altered to be more amenable to barefoot weight-bearing with special attention to weight-bearing surfaces that remain cool when exposed to the heat of the sun, and allow friction with the bare foot when wet. The workplace is already starting to be altered to allow greater time bearing weight. Ergonomists have come to realize that standing is superior to sitting for the human body and have been responsible for the sensible introduction of desks designed to be used when standing. Their use has been modest perhaps because they have failed to realize that that comfortable prolonged standing requires being barefoot.

Changes must be made in venues used for athletic competitions. They all must be safe for those that are barefoot. Specialized footwear that offer competitive advantage to users of footwear, such as footwear with “spiked soles” used to artificially amplify traction on certain manmade and natural substrates should be treated as what they are - performing enhancing devices that interfere with measurement of true athletic performance.