TITLE: Running Related Injury Prevention Through Barefoot Adaptations 1987-1.pdf

Accessible Summary:

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.

Significance: 

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. 

Accessible Summary:

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

Accessible Summary:

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.

Significance:

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.

 1989

TITLE: Running Related Injury Prevention Through Innate Impact Moderating Behavior 1989-1.pdf

 1990

TITLE: Athletic Footwear and Chronic Overloading: A Brief Review 1990-1.pdf

Accessible Summary:

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.   

Accessible Summary:

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.

Accessible Summary:

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.  

1994

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.

Accessible Summary:

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. 

Accessible Summary:

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.