List of full length papers in peer-reviewed journals
TITLE: Running Related Injury Prevention Through Barefoot Adaptations 1987-1.pdf
Purpose: To test the hypothesis that measurable changes in foot morphology when bearing weight occurs when normally shod subjects adapt to barefoot locomotion.
Synopsis: Normally shod subjects modestly increased barefoot walking and running. Their feet were x-rayed before and after,while supporting weight on a platform that required the center of pressure to be sustained near the center of foot arches. Barefoot activity resulted in reduction in overall foot length due rising of the longitudinal arch. There was increase foot width at the metatarsal-phalangeal joints presumably due to development of interosseous muscles. Presumably plantar tactile sensations associated with even modest barefoot activity is capable of inducing changes that could add shock absorbency to the foot, improve stability widened base of support, and perhaps unload the plantar fascia, decreasing risk of plantar fasciitis.
It was the first report asserting the following postulates:
1) It was the first published report advancing the notion that the modern running shoe was a design failure because it failed to protect.
2) The human foot was not inherently fragile requiring protection from footwear.
3) The evolutionary necessity of a durable foot.
4) Walking and running barefoot might protect against injuries that are frequent when normally shod individuals run with shoes.
5) Plantar tactile information may be relevant to our understanding of safe human locomotion.
6) Some aspect of modern life - perhaps footwear and man made support surfaces were the source of the injury problem.
It was the first published report asserting the following hypotheses based on data from the experiment:
1) Surface irregularities of natural surfaces may be essential to our understanding of safe human locomotion.
2) "Pseudo-neuropathic" may adequately describe the injury mechanism of footwear related injuries associated with repetitive excessive impact.
3) “Intrinsic foot shock absorption” was present in the human foot.
TITLE: Overload Protection: Avoidance Response to Heavy Plantar Surface Loading 1988-1.pdf
Purpose: To test the hypothesis advanced in the first publication that plantar tactile information induced behavioral change resulting in foot adaptations to barefoot locomotion.
Synopsis: The plantar surface was loaded through applying load comfortably to the knee flexed at 90 degrees, and leg in a vertical position. There was evidence of an unconscious avoidance of heavy plantar loading that varied in relation to the surface irregularity of the support surface.
Significance: The hypothesis was supported.
The data further supported the following conclusions:
1) Humans possess an inherent feedback mechanism that serves to minimize impact in response to plantar sensory feedback from surface deformations.
2) Humans moderate impact through increasing amplitude of hip and knee flexion during locomotion.
3) Excessive extension at the hip and knee during locomotion is associated with overloading.
TITLE: Sensory Attenuation Induced By Modern Athletic Footwear 1988-2.pdf
Purpose: To test the "pseudoneuropathic" causation mechanism previously proposed which advanced the notion that athletic injuries associated with athletic shoes were caused by unknowingly overloading due to plantar sensory isolation caused by footwear.
Synopsis: A experiment was performed whereby subjects estimated plantar surface loads, up to the amplitude seen when running. There were three conditions: wearing modern running shoes, when their bare feet was placed on the smooth rigid surface of the testing apparatus and when gravel was placed between the foot and apparatus. Subjects underestimated load with athletic shoes and smooth rigid surface, but were accurate with the gravel condition. Localized skin deformations such as from gravel are required for precise load judgment.
This experiment supports the notion that the mechanism of injury for injury associated with impact while wearing shoes resembles neuropathic injury.
This experiment was the first to provide data suggesting that the SA II mechanoreceptor is used to judge plantar load.
TITLE: Running Related Injury Prevention Through Innate Impact Moderating Behavior 1989-1.pdf
Purpose: To test the hypothesis that foot morphology changes observed as normally shod subjects adapt to barefoot activity is explained as a response to plantar tactile stimulation.
Synopsis: The plantar was uniformly deformed by an penetrometer with spherical deforming ends of different sizes at three locations on the plantar surface: heel, metatarsal-phalangeal joints and distal digits. Pain threshold was recorded. Pain threshold to small deforming objects was lowest at the metatarsal-phalangeal joints and highest at the heel with the distal digits being intermediate. Difference in pain threshold across the plantar surface to contact with small rigid objects when barefoot can explain raising of the medial arch through intense plantar flexion of the digits, thereby sparing the area with the lowest pain threshold.
Significance: This report indicates that detailed foot mechanics when barefoot is a response to tactile information. It further supports the hypothesis that mechanics of locomotion when barefoot is largely mediated through tactile sensory input.
TITLE: Athletic Footwear and Chronic Overloading: A Brief Review 1990-1.pdf
Purpose: To summarize developments in related to plantar tactile mediated locomotory control to this time.
Synopsis: This paper allowed an opportunity to state the case that athletic footwear promotes overloading through insulating the plantar surface from sensory information. The effect of athletic footwear on stability, and the response of humans to instability with amplified impact, was not yet known - it was subject of experiments in the following years.
Significance: This paper best describes the state of our understanding of running related injuries associated with the use of modern athletic shoes, at the time of publication. Future research added greater complexity to this issue.
TITLE: Athletic Footwear: Unsafe Due to Perceptual Illusions 1991-1.pdf
Purpose: To evaluate the importance of shear stress in plantar sensory processes.
Synopsis: An experiment was performed in which heavy horizontal and vertical loads (the range seen in running) were applied to the sole of the foot supported by a rigid testing surface with various materials placed between the foot and surface. High levels of discomfort required application of both vertical and horizontal load and a support surface that causes small surface deformations (n this case small gravel).
Significance: This was this first published report indicating that the combination of vertical deformation and shear stress is essential to initiate behavior that can alter impact. This indicated it would be impossible to duplicate the barefoot condition in shoes because there is no conceivable way of adding plantar shear stress to footwear.
TITLE: Shoe Sole Thickness and Hardness Influence Balance in Older Men 1992-1.pdf
Purpose: The relation between balance and impact was suggested in reports indicating gymnasts land with greater impact when landing on soft mats compared to hard surfaces. This suggested a relation between balance and impact. The was the first report in this series which examined the effect of footwear on balance.
Synopsis: In this report dynamic balance was measured in an older cohort. Balance was found to be positively related to sole hardness and negatively related to sole thickness. Balance when barefoot was worse than any shoe condition.
Significance: This required was needed because data indicated that footwear in common use by older people presented a public health hazard. This was the first published report indicating that footwear associated with elevated impact also impair balance. It was the first report indicating that thick materials of low hardness significantly impair balance in older people. It also was the first report indicating that when normally shod older people commence barefoot activity, balance is dismal, probably due to rigid feet, used to the interior of shoes to accommodate to flat surfaces. This report was the first to suggest that the sense of comfort in well fitting footwear was the result low amplitude an uniform load distribution across the plantar surface.
TITLE: Protective Sensation of the Plantar Surface of the Foot 1993-1.pdf
Purpose: Two receptors are available to respond to vertical deformations and shear stress on the plantar surface: SA II mechanoreceptors and nociceptors with c-fibre afferents. The nociceptors have high thresholds and are thought to respond to impending tissue damage. To clarify which receptor is mainly used to eliciting behavior that alters locomotion we compared the relation between painful stimuli and signs of tissue damage on hairy skin and plantar skin.
Synopsis: Intense plantar surface (glabrous skin) horizontal and vertical loading was applied so as to reach pain threshold. The volley of 35 painful sequential plantar loads produced no visible signs of plantar surface damage whereas signs of damage was found on hairy skin similarly loaded. This indicates that pain threshold to plantar loading is set extremely low, and does not signal impending damage. This suggests that the SA II mechanoreceptors usually guide human locomotion.
Significance: This reports further advances the notion that plantar pain from localized plantar mechanical stimulation does not signal impending damage - rather it is used for another purpose such as guiding human locomotion. In addition, differences in pain threshold across the plantar surface directs loads from easily damaged structures. Marti's report which found a strong positive relation between injury frequency and shoe cost was first mentioned in this report.
TITLE: Athletic Footwear Affect Balance in Men 1994-1.pdf
Purpose: The relation between balance and impact was suggested in reports indicating gymnasts land with greater impact when landing on soft mats compared to hard surfaces. This suggested a relation between balance and impact. The was the second report in this series which examined the effect of footwear on balance.
Synopsis: Balance was tested in younger men. Shoe sole hardness was positively related to stability and thickness was negatively related to stability.
Significance: The importance of this report was related to data indicating that footwear in common use presented a public health hazard. This report was largely responsible for the movement to thinner and firmer materials in athletic footwear, particularly shoes in sports that have a high ankle sprains frequency, most notably basketball and football. This was the first report to indicate that in young men, balance is positively related to sole hardness and negatively related to sole thickness. This was the first report to suggest that the cause of the instability was oscillatory medial-lateral movement caused by these resilient materials. Balance was better when barefoot in a younger compared to older cohort, but continued to be poor - only better than one shoe condition.
TITLE: Proprioception and Stability: Foot Position Awareness as a Function of Age and Footwear 1995-1.pdf
Purpose: To test if the cause of loss of stability when wearing footwear was due to the influence of the shoe on proprioception - the sense of position and orientation of the plantar surface relative to the support surface. This proprioceptive sense was termed "foot position awareness".
Synopsis: Subjects of younger and older age cohorts were tested for foot position awareness barefoot and when wearing shoes. Subjects estimated surface slope when bearing weight based on a ratio scale. The psychophysical function when estimating slope was close to unity for young subjects when barefoot, but significantly lower with older barefoot subjects. It was also lower for both younger and older subjects with shoes.
Significance: This report suggests that young barefoot subjects use SA II mechanoreceptors for foot position sense when barefoot. Older subjects use muscle receptors in foot position judgement when both barefoot and older presumably due to SA II receptor decline. This was the first report to suggest significant SA II receptor decline at the plantar surface with age. It was also the first report to suggest that tactile receptors are used for proprioceptive sense with report to locomotion.
TITLE: Ankle Taping Improves Proprioception Before and After Exercise in Young Men 1995-2.pdf
Purpose: The above developments regarding the sense of position and orientation of the plantar surface relative to support surface (foot position awareness) had obvious application to the most common injury in sports - the ankle sprain. Many had speculated that the ankle sprain may be related to proprioceptive problems, but proprioception was never defined objectively and tested. No one had ever considered that footwear influence proprioceptive sense at the ankle. Also, interventions to prevent ankle sprains such as taping were never examined objectively in terms of proprioception.
Synopsis: The effect of ankle taping was examined before and after exercise in young men in a system whereby they were asked to estimate support surface slope according to a ratio scale. Standard ankle taping was performed prior to the exercise session to a random sample of subjects.
Significance: This report was the first to show that ankle taping improved foot position sense before and after exercise when wearing footwear, but but this sense was always better when barefoot. The conclusion was that ankle taping partly corrected the loss of foot position awareness caused by footwear. Traction of the tape on the hairy skin of the leg gave subjects a sensory cue especially when ankle angle was acute. This report suggested the risk of ankle spraining when barefoot should be extremely low. It also indicated that when wearing shoes foot position awareness declines as exercise increases, which may explain while ankle sprains are more common late in exercise sessions.
TITLE: Effect of Midsole Hardness and Thickness on Proprioception and Stability in Older Men 1997-1.pdf
Purpose: Previous reports suggested that when wearing footwear, humans rely of muscle receptors of the ankle and foot for foot position judgments. Muscle receptors are subject to "aftereffects" rapid high amplitude stimuli account for loss their sensitivity. This reports tests the hypothesis that rapid frontal plane (medial-lateral) movement caused by footwear sole materials causes loss in foot position awareness. Loss of foot position awareness is known to cause instability and a high amplitude behavioral response to instability that increases amplified impact.
Synopsis: Frontal plane foot movement and stability was tested in subjects wearing footwear that varied in midsole hardness and thickness. Optical testing system was used to measure frontal plane foot movement. Stability was tested using standard methods.
Significance: Frontal plane foot movement was closely correlated with stability. This supports the hypothesis that frontal plane movement caused by footwear results in loss of foot position awareness, with resulting loss of stability.
Title: Foot Position Awareness: The Effect of Footwear on Instability, Excessive Impact and Ankle Spraining 1997-2.pdf
Purpose: This paper gave an opportunity to integrate our rapidly evolving understanding of the complimentary role of SA II mechanoreceptors and foot and ankle muscle receptors in relation to locomotory mechanics and maintenance of stable equilibrium.
Significance: In the paper was the first to suggest the relation between stability and impact. Through integration of available data, the suggestion was made, that was later tested, that humans rely primarily on plantar tactile information for basic locomotory mechanics, which include maintenance of stability. Impact control is an unconscious consequence of stability maintenance and optimizing foot comfort. When tactile information is not available, such as when wearing shoes, or perhaps when the plantar surface is anesthetized by cold, locomotory mechanics is largely organized through muscle receptors. Loss of foot position awareness caused by shoes is the ultimate cause of ankle spraining.
TITLE: Hazard of Deceptive Advertising of Athletic Footwear 1997-3.pdf
Purpose: Bernard Marti published a epidemiological report in which he related running injury frequency with shoe model and manufacturer. After correcting for variables of age, gender, running mileage and previous injury, the most prominent finding was a relation between injury frequency and shoe cost - the more expensive shoes accounting for 123% greater injury frequency than the cheapest ones. The purpose of this experiment was to explain Marti's data. What made this relation intriguing was that both expensive and cheap shoes are made with almost identical sole materials, therefore their performance in terms of impact should be identical. The one difference between expensive and cheap shoes is how they are advertised - expensive shoes are advertised deceptively as possessing features that enhance protection, with no data to support any protective advantage. The running shoe is marketed mainly as a protective device with expensive ones have additional protective features than cheap ones. Novel footwear technology is usually found on more expensive models.
Synopsis: This experimental tests the influence of deceptive advertising suggesting protection on eliciting a false sense of security and dangerous behavior. Impact was measured when subjects stepped off of a low platform on to a rigid support surface covered the identical support surface encased by a fabric of different colors so as to look different. Prior to each conditional subjects were given a written message stating that the material they were landing on came from either cheap, expensive, or new high technology products. Impact varied significantly as a function of advertising message. Advertising message stating cheapest resulted in significantly less impact than the other conditions. Expensive and new technology messages resulted in significantly higher impact. Trends increased with repeated footfalls. The advertising message caused a false sense of security with expensive and new technology products and cautious behavior with those advertised as cheap.
Significance: This was the first report to provide data indicating that advertising of protective devices protective devices can strongly influence user behavior. In the case of athletic footwear, falsely and deceptively advertising expensive models as offering greater protection though advanced features appears to be the cause of the 123% greater injury frequency experienced by users of expensive models. This raises the need for honest advertising of protective devices.
TITLE: Balance and Vertical Impact: Role of Shoe Sole Materials 1997-4.pdf
Purpose: When plantar tactile information is extremely low such as when wearing shoes, impact is not constant - rather it varies considerably between shoe conditions all of which provide minimal plantar sensory feedback. In a previous report it was shown that shoes vary greatly in terms of the balance they provide users. This suggested that differences in impact between shoes was explained by differences in behavioral response which in turn resulted in variation in instability caused by shoes.
Synopsis: We hypothesized that there is a positive relation between impact on landing and instability as measured by balance failures when walking. Impact testing and balance testing was performed on the same material. Impact when landing and balance failures was found to be extremely closely correlated. This strongly supports variations in impact when wearing shoes is accounted for by the degree of instability with their use.
Significance: This report indicates that means of improving performance of footwear in terms of impact should be directed at enhancing stability with their use.
TITLE: Foot Position Awareness in Younger and Older Men: Influence of Shoe Sole Properties 1997-5.pdf
Synopsis: In this experiment balance testing was performed as well as foot position awareness in the form as accuracy in estimating foot position in the frontal plane (medial-lateral). Balance failures correlated well with error in plantar surface position judgement. This report indicates that instability in humans is a function of their ability to judge the position and orientation of the plantar surface in relation to support surface. It shows that footwear sole properties influence proprioception with decline in proprioception when soles become thicker and softer. It suggests that when plantar tactile information is low, such as when wearing shoes, humans rely probably on muscle receptors for foot position judgments. These judgments are influenced by the rapid oscillatory movements caused by footwear. Unlike tactile receptors, muscle receptors are subject to aftereffects causing them to code less precisely when subjects to rapidly changing high amplitude stimuli. Proprioception was amazingly precise when barefoot. Since the support surface was smooth tactile information was not used. Rather the precise proprioception was due to low amplitude of medial-lateral foot movement.
Significance: This strongly supports to earlier hypotheses that high resiliency sole materials cause loss in proprioception which results in loss of stability. It suggests that stability when wearing footwear would be improved if sole material were of low resiliency, thereby eliminating oscillatory foot movements when loaded.
TITLE: Improving Balance 1998-1.pdf
Purpose: The purpose of this experiment was to improve footwear in terms of balance and impact control and comfort, according to guidelines suggested in my previous research. Instability in footwear was previously found to be caused by loss of foot position awareness resulting from medial lateral-oscillations oscillations during the support phase of locomotion which overwhelm muscle receptors in making foot position judgments. Excessive impact is a behavioral response to loss of stability. It was hypothesized that a sole material that compresses but recover pre-compression thickness slowly would dampen oscillatory movements. The result would be improved foot position awareness, improved balance, lower impact while retaining comfort.
Synopsis: Balance was inferred by sway measures using a force platform. Comfort was estimated using a rating scale. Materials were examined that differed in the recovery to pre-compression thickness in 1 second. I was found that thin sole material of similar softness of current shoe insoles and midsoles, yet much lower in resiliency - allowing only 5% recovery in 1 second, provided superior balance, and equal comfort to high resiliency materials.
Significance: Previous reports indicated that thin soles made of harder material would improve balance, and consequently lower impact somewhat at the expense of comfort. This report the the addition of a thin layer of extremely loss resiliency sole material would further improve balance and retain comfort of current footwear composed entirely of high resiliency sole material.
TITLE: Factors Associated With Ankle Injuries 1998-2.pdf
Purpose: To present an understanding of th cause and possible prevention of ankle sprains - the most common injury in sports, according to developments regarding low sensory feedback while wearing footwear, reliance on muscle receptors in making foot position judgments while wearing footwear and influence of footwear of position awareness. Preventive measures are discussed including ankle taping and footwear that provide better foot position sense though reduction of oscillatory medial-lateral movement.
Synopsis: In this paper the previous work regarding plantar sensation and foot position awareness is applied to ankle sprains. It indicates that ankle sprain would be uncommon on surfaces that provide plantar tactile feedback of position and orientation of the plantar surface, such as the bare foot and naturally deposited ground. In footwear, tactile sensations are minimal and humans rely on muscle receptors for foot position judgments. This proprioceptive sense declines due to oscillatory movements caused by footwear with high resiliency. Ankle taping reduces the risk of ankle sprain through providing tactile information of plantar position and orientation through traction of the skin of the leg. A better solution would be footwear that provides plantar tactile feedback - a solution that seems currently impossible. An available solution is footwear that minimize oscillatory foot movement through the use of low resiliency material.
TITLE: Vertical Impact Increase in Middle Age May Explain Idiopathic Weight-bearing Joint Osteoarthritis 2001-1.pdf
Purpose: To test the hypothesis that ground reaaction force increases with age - an explanation of idiopathic osteoarthritis of the hip in humans.
Synopsis: Ground reaction force was measured while subjects performed a standard stepping task in young and older subjects. Ground reaction force when stepping was found to increase with advanvcing years. This increase may be explained by decline in plantar tactile sensibility. This may lead to impaired postural stability and behavior that amplifies impact in relation to instability.
Significance: This was the first report to show increase in vertical impact with advancng years. It may help explaining the rise in idiopathic hip osteoarthritis that occurs in late middle age.
TITLE: A common cause of diverticulitis and irritable bowel syndrome:chronic distal colon distention from sedentary behavior and excessive dietary fiber.2013-1.pdf
Purpose: To explain the cause of these conditions which was previously unknown, through a multi-disciplinary analysis.
Synopsis: Footwear use by all social classes commenced with the European Renaissance. Shoe use caused humans to change from being weight-bearing to sitting most wakeful hours. This attenuated the effect of gravitational force on distal colon mobility resulting in mild chronic intestinal obstruction. The excessive distention that followed caused synptoms of irritable bowel syndrome and intestinal wall damage resulting in diverticula formation. This process was exacerbated by the change from eating manly meat which humans are well adapted to digesting to excessive fiber which results in low pressure distention that functions in water homeostasis.
Significance: This report leads to prevention of irritable bowel syndrome and diverticulitis though increasing weight-bearing time, reducing fiber consumption and perhaps novel means to prevent low pressure colon distention.