Note: Descriptions are shown in the official language in which they were submitted.
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COMPRESSIBLE STRUCTURE SECURED TO AN UPPER OF AN ARTICLE OF
FOOTWEAR
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to U.S. Patent Application No.
16/375,881, filed
April 5, 2019 and titled "COMPRESSIBLE STRUCTURE SECURED TO AN UPPER OF AN
ARTICLE OF FOOTWEAR," the disclosure of which is hereby incorporated by
reference in its
entirety.
INTRODUCTION
[0002] The presently disclosed technology is directed to cushioning and energy
return systems
for athletic shoes that increase athletic performance by engineering the
rebound characteristics of
the sole components to optimize the conversion of kinetic energy from the foot
of the wearer into
potential energy stored within the sole components and subsequently converting
that potential
energy back into useful kinetic energy. Given a vertical force magnitude from
the foot and a
specified proportionality limit for the sole, there is a unique value for the
spring constant, k
(N/m), which will yield the maximum energy return. The system is said to be
tuned when the
spring constant yields the maximum useful spring potential energy for a given
force and the
maximum spring compression.
[0003] The presently disclosed technology utilizes vertical ground reaction
force data for
discrete anatomical regions under the foot at a range of running speeds.
Energy return can be
maximized for different running speeds, by adjusting the spring constant
according to the force
from a foot region associated with a particular running speed. The presently
disclosed technology
allows for either the specification of the physical properties of sole
components to be tuned to a
running speed, or for the identification of running speeds that will
experience the greatest energy
return given the physical properties of the sole.
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BACKGROUND
[0004] Conventional articles of athletic footwear include two primary
elements, an upper and a
sole structure. The upper is generally formed from a plurality of elements
(e.g., textiles, foam,
leather, synthetic leather) that are stitched or adhesively bonded together to
form an interior void
.. for securely and comfortably receiving a foot. The sole structure
incorporates multiple layers that
are conventionally referred to as a sockliner, a midsole, and an outsole. The
sockliner is a thin,
compressible member located within the void of the upper and adjacent to a
plantar (i.e., lower)
surface of the foot to enhance comfort through the distribution of pressure
over the plantar
surface of the foot. The midsole is the compressible layer secured to the
upper and forms a
structure that attenuates ground reaction forces on the foot by doing work to
convert kinetic
energy of the foot into potential energy (i.e., imparts cushioning), and can
do work to turn stored
potential energy back into kinetic energy (i.e. energy return) during walking,
running, or other
ambulatory activities. The outsole forms a ground-contacting element of the
footwear and is
usually fashioned from a durable and wear-resistant material that includes
texturing to impart
traction. The outsole may constitute part of the compressible layer, may be
non-compressible,
and may cover a portion of the ground contacting surface.
[0005] The primary material forming many conventional compression layers is a
polymer foam,
such as polyurethane, olefin, or ethylvinylacetate. In some articles of
footwear, the compression
layer may also incorporate structures in the form of molded plastics or metal
alloys in the form
of conical, cylindrical, or leaf springs, or fluid/gas-filled chambers, which
modify the cushioning
and energy return properties of the compression layer. Many configurations of
polymer material
and incorporated structures purport to deliver varying degrees of cushioning
and energy return.
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[0006] Articles of footwear intended for sports activities such as running
have compressible
layers designed to respond to vertical compressive forces. Such compressible
layers may also be
designed to react to lateral and shear forces, and can be designed for either
or both purposes
simultaneously. Compressible layers acting in the vertical plane and behaving
much like springs,
can exhibit both cushioning and energy return properties. Together, the
compression phase and
the expansion phase are known as rebound.
[0007] Compressible layers with rebound properties can be modeled
mathematically according
to Hooke's Law [1] and Newtons 2nd Law [2]. Elastic 3-dimensional materials
have been shown
to exhibit spring-like qualities and to be accurately modeled mathematically
with simple
substitutions to translate from a 1-dimensional spring to a 3-dimensional
solid. For clarity of
explanation and universality of the concept, the 1-dimensional spring
equations will be presented
here. The term "spring" is interchangeable with "compressible layer" for the
purposes of
describing the presently disclosed technology. Substitution to a 3-D material
can be made in the
equations at any time using Young's modulus, the area and the thickness of the
compressible
layer [3].
F = kx [1]
F = ma [2]
YS
k = ¨ [3]
L
where k is the spring constant (N/m), x is the spring displacement from
equilibrium, m is the
mass of the body, a is the acceleration, Y is the Young's modulus (PA), S is
the surface area
(m2), and L is the thickness (m).
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[0008] When a stress (force) is applied to a spring, the spring exhibits
strain (displacement)
according to Hooke's Law. Hooke's Law describes a proportional relationship
between stress
and strain. The maximum displacement of the spring Xs-max is constrained by
the proportionality
limit of the particular spring. The proportionality limit is the maximum
amount of strain at which
the material still satisfies Hooke's Law. The proportionality limit also
applies to a solid used in a
compressible layer. When a strain is greater than the proportionality limit,
the material may
continue to compress until the elastic limit is reached. The elastic limit for
common compressible
layer materials is the point at which the material will no longer compress
under the normal range
of forces from athletic activities. The proportionality limit may range as a
percentage of total
material thickness for different formulations. Although Hooke's Law does not
strictly apply
when the strain exceeds the proportionality limit, an increased stress is
still required to create
further strain. The maximum spring displacement Xs-max is here defined as the
elastic limit.
[0009] One objective of running shoes is to provide shock attenuation
(cushioning) of the forces
imparted by the foot. Cushioning occurs when there is a change in kinetic
energy over an interval
of time and over a stopping distance. The stopping distance is equal to the
amount of
compression that occurs in the compressible structure. For a given change in
kinetic energy, an
average impact force can be defined as:
Wnet
Fimpact-avg = [4]
[0010] Where d is the stopping distance and Wnet is the net work done by the
change in kinetic
energy and defined as:
Wnet = mv2 1 initial -2mv2 final [5]
and vfinal is equal to zero. The larger the stopping distance d, the longer
the stopping time
interval.
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[0011] Cushioning is said to increase when the average impact force decreases.
Equation 5
shows that an increasing stopping distance results in a lower average impact
force. Therefore,
cushioning is said to increase with a larger stopping distance and a longer
stopping time interval.
[0012] Cushioning can also be understood as a negative acceleration
(deceleration) of a mass in
the context of Newton's second law F=ma. A lower deceleration, A lower
deceleration equates to
a lower average impact force and is also known as greater shock attenuation.
Running shoes
typically feature compressible layers with a range of thicknesses between 2mm
and lOmm in the
ball region, and lOmm to 20mm in the heel region, and a range of elastic
stiffnesses. Together,
the elastic properties and the thickness determine the effective spring
constant. The negative
accelerations can be analyzed assuming that the compressible layer behaves
like a spring.
Following Hooke's Law, the amount of cushioning (negative acceleration)
achieved will depend
on the force imparted and the spring constant of the compressible layer.
[0013] Another objective of running shoes is to limit the amount of energy
loss during
cushioning (compression of the spring) by returning energy to the runner.
While this energy
return is understood to be desirable, running shoe designs have not
successfully achieved this
goal. Energy return can occur in running shoes when the compressed spring
releases its stored
potential energy by expanding and providing a net upward force on the wearer's
foot. The net
upward force causes an acceleration and increasing kinetic energy. The total
amount of potential
energy (J) available for energy return can be computed from the spring
constant and the length of
compression:
PE = -1 kx2 [6]
2
[0014] The length of compression can be calculated from Hooke's Law [1]. Thus,
according to
Eqn. 6, for a given spring constant, a longer length of compression will
generate a higher
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potential energy. However, the maximum compression length, x, will be limited
by the
proportionality limit of the material. Thus, for any given shoe sole thickness
and associated
proportionality limit, there exists a maximum amount of energy available for
conversion into
kinetic energy in the runner (energy return).
[0015] Human running can be described as having a gait cycle which begins with
the toe-off of
the right foot, a flight period during which the left foot moves forward while
both feet are in the
air, a first contact period when the left foot is in contact with the ground
until toe-off of the left
foot, a second flight period during which the right foot moves forward while
both feet are
airborne, and a second contact period when the right foot is on the ground
until the moment of
toe-off. During each flight period, the center of mass for the body
accelerates downward under
the force of gravity an amount determined by the time period of the flight.
The center of mass
must, therefore, be accelerated back up during each contact period. A net
upward force must act
on the center of mass in order to produce the upward acceleration. According
to Newton's Third
Law, the net upward force will exhibit an equal and opposite downward force,
called the ground
reaction force. The runner's leg muscles generate the upward force. The ground
reaction force
can be measured over time with sensors placed under the runner's foot.
[0016] Slower running speeds are associated with longer ground contact times
and lower peak
ground reaction forces than faster running speeds. Conversely, faster running
speeds are
associated with shorter ground contact times and higher peak ground contact
forces than slower
running speeds. This can be understood from fundamental physics with the
center of mass
moving at a constant speed horizontally and for a specific cadence and flight
period: A faster
running speed allows less time for each foot to be in contact with the ground
than a slower
running speed. The shorter contact time means a shorter time to accelerate the
center of mass
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upward for the beginning of the flight period. The shorter period requires a
higher acceleration of
the mass and a higher ground reaction force to generate it. Such contact times
and ground
reaction force magnitudes associated with different running speeds are readily
observed in
studies measuring these parameters [Hunter et al. 2014, Concejero 2013, Kram
and Taylor
1990].
[0017] Ground reaction force data for barefoot runners using multi-nodal
measurement systems
(ex. Tekscan Inc. MatScan) show that the different parts of the foot (heel,
ball-of-foot, and toes)
each have unique and different force amplitudes and periods of impulse from
each other. Multi-
nodal measurement systems differ from a force plate measurement system in that
they collect
pressure data from a grid of many nodes [Figure 1] compared to a single point
using a rigid plate
[Figure 2]. Force plate systems measure an average of the force across the
entire foot, but do not
accurately measure the force at specific parts of the foot during the contact
phase of the gait
cycle. Multi-nodal systems have a typical spacing of 1 ¨ 5 mm and a sampling
frequency of 100
to 750 Hz. Multi-nodal force measurement allows the investigator to isolate
and compare the
force vs time sequences for different regions of the foot during the contact
phase [Figure 3]
revealing the important force characteristics of each anatomical part of the
foot. Such important
force characteristics are unobservable using a force plate measurement system.
[0018] Using the multi-nodal system by Tekscan Inc. MatScan VersaTekTm, the
following
observations were made.
[0019] First, the force amplitudes and force impulse frequencies differ for
each region of the foot
[Figure 4].
[0020] Second, the sum of the foot region force-time profiles produces the
same force-time
profile as a force plate measurement [Figure 4].
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[0021] Third, the forces during the contact phase include an impact force and
a propulsion force
and that these forces are present to different degrees in the different foot
regions [Figure 5]. The
impulse frequency associated with the impact force is high relative the
frequency of the
propulsion impulse and this is consistent with the common understanding of
impact forces from
falling objects.
[0022] Fourth, the propulsion force magnitude and frequency increase with
increasing runner
speed for each foot region, but specifically for the ball region [Figure 6].
This phenomenon can
be explained as the higher propulsion force required to achieve the higher
rate of vertical
acceleration associated with faster running speeds. The force impulse
generated from the muscle
activation during propulsion is defined here to be Fimpuise. The relationship
between peak force
amplitude and runner speed is central to the presently disclosed technology.
[0023] Fifth, the force amplitudes and frequencies from each foot region are
the same regardless
of strike pattern [Figure 7]. In other words, the measurements reveal that the
force-time profiles
for the heel, arch, ball, and toes, are the same whether the runner strikes
first with the heel or first
with the ball. This observation suggests that the ground reaction force
characteristics are not
driven by strike pattern.
[0024] These observations provide insights into the dynamic nature of the
ground reaction forces
during human running, walking, and jumping that were previously obscured. The
insights alter
the understanding of the kinematics and force dynamics involved in human
ambulatory
locomotion compared to the substantial body of previously published work in
the field. Scientific
studies and mathematical modeling based on force plate measurements support a
theory of
horizontal running where the ground reaction forces can be generally
attributed to the masses of
the runner's torso and legs segments and the force of gravity [Liu, Nigg 1999,
Clark et al. 2017,
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Lieberman et al. 2010]. Modeling based on this theory produces force vs time
profiles that
closely match force plate measurements. However, the models, like the force
plate measurement
system, do not differentiate between different regions of the foot, nor can
they explain peak force
differences at different running speeds. The low spatial resolution of a force
plate measurement
system causes a simplification to the theory and mathematical models for
running that doesn't
include forces generated by a) leg muscles, or b) the mechanical role of the
different regions of
the foot. The simplified theories fail to identify the different timing,
magnitude, and duration of
the forces from the four anatomical regions of the foot, for runners of
different masses, and for
persons running at different speeds. Since shoe materials can only respond to
forces directly
adjacent to them, knowledge of how the forces vary by foot region is essential
to engineering a
compressible layer with specific performance attributes. The multi-nodal force
measurements
and the insights gleaned from them, allowed the development of a theory and
mathematical
model needed to engineer a compressible layer for optimal performance. The
insights can be
exploited to maximize the cushioning and storage of potential energy in
running shoes by
identifying the unique spring constant that maximizes the potential energy in
the spring and
satisfies the boundary conditions imposed by the shoe dimensions, material
properties, runner
speed, and runner mass. Specifically, knowledge of the different force
magnitudes for different
foot regions according to running speed zones, determines a specific set of
boundary conditions.
Applying the boundary conditions and the laws of physics creates a unique
solution for the
spring constant that maximizes the cushioning and potential energy available
for energy return.
Additionally, the physical dimensions of the compressible layer vary by foot
region, creating
different boundary conditions for each region.
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[0025] The relevant boundary conditions include the compressible layer
component thickness,
the component's horizontal area, and the range of targeted body masses. Given
a set of boundary
conditions and a specified runner speed, a theoretical maximum potential
energy, PEmax, can be
calculated. For a given set of boundary conditions, PEmax will vary as the
specified runner speed
is changed. A graph of the ratio of the actual potential energy generated, PE,
at different actual
running speeds, to PEmax, illustrates how the amount of energy available for
energy return to the
runner drops off for ratios above and below 1.0 [Figure 8a]. For example, a
shoe designed to
maximize PE for a running speed of 3m/s will provide less cushioning and
energy return to the
runner at speeds of 2m/s or 4m/s. The result can similarly be viewed in the
graph depicting the
ratio of potential energy to maximum potential energy for a runner at a fixed
speed but with
different values of the spring constant inherent in the shoe (i.e., constant
PE and varying PE.)
[Figure 8h].
[0026] A compressible layer will decompress (expand) back toward the original
uncompressed
dimension when the force is decreased and/or removed. In the case of a rapid
removal of the
force, the amount of reexpansion will depend on the makeup of the compressible
layer. Materials
used in compressible layers in footwear exhibit a range of reexpansion amounts
relative to the
original uncompressed dimension, which can be measured and expressed as a
percentage.
Typical reexpansion percentages range from 10% to 90% within the first tenths
of a second after
removal of the force. The percentage of reexpansion is related to the amount
of stored potential
energy that is actually converted to kinetic energy in the wearer and
perceived as energy return.
[0027] Athletic footwear has been and continues to be manufactured for sports
like running
using compressible layers where the measured force magnitudes on the shoe at
different running
speeds are not considered during the design and engineering of the footwear
and, consequently,
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the cushioning and energy return available to the athlete is a mere fraction
of the potential
maximum. Furthermore, athletic footwear does not explicitly consider different
force elements
and their associated impulse frequencies in the heel, arch, ball-of-foot, and
toes, tending instead
to treat the foot as a monolithic entity with respect to forces. The over-
simplification of forces
and shoe design eliminates the possibility of maximizing cushioning and energy
return within the
shoe regardless of runner speed, running form, or wearer's mass. The
suboptimal results increase
the strain on the wearer's body during the cushioning phase and increase the
fatigue in the
muscles and metabolic system during the energy return phase.
SUMMARY
[0028] By tuning the rebound properties of the compressible layer to a
runner's speed and
optionally to specific regions of the compressible layer, cushioning can be
maximized and
energy losses minimized. Cushioning is maximized when the compressible layer
compresses to
near its elastic limit under the forces of running. Energy losses are
minimized when the vertical
(downward) component of the wearer's kinetic energy is converted into
potential energy in the
compressible layer during compression, and at least some of that stored
potential energy is
subsequently returned to the wearer by generating vertical (upward) kinetic
energy. The amount
of stored potential energy is determined by the amount of compression and the
maximum force
applied. Energy storage is maximized when the compressible layer is compressed
to near its
elastic limit.
[0029] It will be appreciated that a faster running velocity necessitates a
shorter ground contact
time and higher associated ground reaction forces to generate the higher
vertical acceleration of
the body center of mass necessary to lift the body back up for the flight
period between
successive ground contact intervals (steps). A slower running velocity has
longer contact times,
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requires a slower vertical acceleration of the center of mass, and is
associated with lower peak
ground reaction forces. The faster running speed will require that the
compressible layer be tuned
to the greater peak forces in order to store and return maximum energy to the
runner's foot, while
a slower running speed will require that the compressible layer be tuned to
lesser forces. It will
also be appreciated that any vertical kinetic energy not converted into stored
potential energy
will be lost and means that storing less spring potential energy will result
in more energy loss.
[0030] It will further be appreciated that the mass of the runner will
influence the forces
necessary to achieve the vertical acceleration associated with a specific
running speed. A higher
mass will require a higher force to achieve the vertical acceleration. Within
the normal range of
human body mass for runners, the differences in ground reaction forces are
primarily influenced
by the required vertical acceleration, because kinetic energy changes with the
square of the
vertical velocity and is linearly proportional to the mass. Consequently, a
given pair of running
shoes embodying the presently disclosed technology will be tuned to a specific
range of running
speeds and a given range of body masses. Runners will choose their running
shoes accordingly.
[0031] Different anatomical portions of the foot contact the ground at
different times in the
contact phase of the gait cycle, and also with different force magnitudes.
Consequently, it may be
beneficial to tune the portions of the midsole underlying distinct anatomical
portions of the foot
differently to take this into account. For example, the peak force in the heel
is significantly lower
than the peak force in the ball of foot region, requiring a lower spring
constant in the heel than in
the ball of foot in order to achieve similar amounts of compression.
Similarly, the arch and toes
regions experience lower peak forces relative to the ball and heel and require
relatively lower
spring constants.
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[0032] It will also be appreciated that the amount of potential energy stored
in the compressible
layer increases with increasing compression of the compressible layer roughly
according to
Equation 6. Furthermore, the maximum potential energy is limited by the limit
of elasticity,
which is defined as the maximum compression, Xs-max.
.. [0033] By means of the presently disclosed technology, a runner may recover
a significant
portion of the energy expended by the runner which would otherwise have been
lost. Instead, the
recovered energy will be used to provide a lift to the body as it accelerates
upward. This returned
energy will be small in each step but cumulatively will be a significant aid
when running long
distances.
.. [0034] An article of footwear is disclosed here as having an upper and a
sole structure secured to
the upper. The sole structure consists of one or more midsole components with
an inherent spring
constant such that the ratio of the midsole potential energy (PE) to the
maximum midsole
potential energy (PE.,,), approaches a value of 1Ø The range in ratio
represents a practical
range of variance a runner's ability to control running speed, variation in
body mass of +/- 10 kg,
manufacturing tolerances for typical midsole materials. The PE/ PEmax ratio is
computed using
the vertical propulsion peak force magnitude, Fimpuise, associated with
different running speeds
and a given set of physical parameters that includes the midsole dimensions
and a runner mass
range. It is possible to determine the spring constant mathematically for each
region of the
midsole that will yield the greatest cushioning and potential energy available
for energy return
(the maximum potential energy) by measuring or calculating Fimpuise for
different running speeds
from each adjacent point on the wearer's foot. In a preferred embodiment, the
PE/PEmax ratio is
between 0.95 and 1.05. In an alternative embodiment, the PE/PEmax ratio is
between 0.85 and
1.15. In another alternative embodiment, the PE/PEmax ratio is between 0.80
and 1.20.
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[0035] A midsole component can be tuned to a specific set of boundary
conditions at a point on
the midsole, an area of the midsole, or at multiple different areas of the
midsole. By treating the
midsole as having four regions in the transverse plane that correspond to the
heel, arch, ball-of-
foot, and toes of the wearer's foot, the midsole can be constructed with
separately tuned regions
[0036] In one embodiment of the presently disclosed technology, the midsole is
constructed with
four regions corresponding anatomically to the wearer's heel, arch, ball-of-
foot, and toes, each
region being comprised entirely of, or encompassing within it, a tuned midsole
structure.
Furthermore, the preferred embodiment will have midsole structures that are
tuned according to
the wearer running speed and wearer mass.
.. [0037] In an alternate embodiment of the presently disclosed technology,
the four anatomical
midsole regions can be further divided into subregions. The subregions may be
of any shape or
size that fit within the anatomically defined region. In one embodiment, the
subregions are
squares with dimensions of 4mm x 4mm. Each subregion can be tuned to the
specific forces
acting on it by the corresponding anatomical subregion of the wearer's foot.
[0038] By rearranging the terms algebraically, the PE/PE.,, ratio can be
expressed as a ratio of
the actual spring constant, k, to an ideal spring constant, kideai. The _kik-
Ideal ratio can practically be
applied to the manufacture of midsole components.
[0039] Midsole structures are comprised of one or more materials and assembled
in such a way
as to exhibit spring-like properties according to Hooke's Law when acted on by
a compressive
force. The effect may be achieved in a multitude of ways using materials and
constructions
common in the industry and with physical dimensions and masses suitable for
performance
athletic footwear. A practical engineering approach to determine the midsole
component physical
properties is to apply the relevant Fimpuise for the runner mass and speed,
the elastic limit for the
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compressible component, and Hooke's Law, to calculate the spring constant,
kideal, that equates
to the maximum spring displacement xs_max. Physical properties for an elastic
solid can by
derived from the spring constant and the conversion for Young's modulus.
Y = k [5]
where Y is the Young's modulus, L is the depth of the material, and S is the
surface area of the
material.
[0040] Springs and elastic solids exhibit varying degrees of energy loss
(damping) during a
rebound cycle. The amount of energy loss will constrain the efficiency with
which the spring
element can convert its stored potential energy into kinetic energy. However,
a high damping
coefficient, and therefore a high energy loss, does not change the
applicability of Hooke's Law
to spring displacements below the proportionality limit. It is understood that
the higher the
percentage of decompression in the compressible layer, the greater the amount
of the stored
potential energy that is returned to the wearer.
[0041] In one embodiment of the presently disclosed technology, any
compressible
component(s) incorporated into the shoe design will decompress (reexpand) to a
high percentage
of the original uncompressed dimension, reexpanding 90%. In an alternate
embodiment, any of
the compressible component swill decompress to a lesser percentage of 50%. In
a further
alternate embodiment, any of the compressible components we decompress to low
percentage of
25%. In all embodiments, the compressible components within a single shoe may
decompress by
different percentages from each other.
[0042] A running shoe consisting of (a) an upper that secures the foot to the
shoe, and (b) a
compressible sole structure under the upper that compresses in proportion to
the amount of
pressure applied during the gait cycle of the runner to no more than the limit
of elasticity and
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decompresses when pressure is decreased and removed from the compressible sole
structure
during the ground contact phase of the gait cycle of the runner, can be
constructed so that it is
tuned to a runner's running speed as follows.
[0043] This is done by taking into account the runner's gait cycle. The gait
cycle of the runner to
which the shoe is tuned consists of: first, a time when the shoe initially
contacts the ground;
second, a time during which gravity and the runner's leg muscles apply
increasing force to the
shoe; third, a time of maximum application of force to the shoe, fourth, a
time of application of
decreasing force to the shoe until the force applied to the shoe is zero but
the shoe remains in
contact with the ground; fifth, a time when the shoe is removed from contact
with the ground;
sixth, a time when the shoe is moved forward before again contacting the
ground.
[0044] The compressible sole layer is constructed so that it compresses to no
more than its limit
of elasticity upon application of increasing force to the shoe during the
initial stage of the stride,
and decompresses in response to decreasing force during the time after the
maximum application
of force to the shoe and until the shoe leaves the ground. The compressible
sole layer most
preferably decompresses substantially completely during the time after the
maximum application
of force to the shoe during the contact period of the runner and before the
shoe leaves the ground
during the gait cycle of the runner, but may decompress only 90% or even only
50%. In one
embodiment, the compressible sole layer consists of a plurality of regions,
each region of the
compressible sole layer below a corresponding region of the foot (e.g. the
heel, ball, and toe
.. regions) and tuned to the forces applied to that region of the compressible
sole layer by the
corresponding region of the foot. The shoe can be tuned so that the cushioning
and energy return
are maximized for a running speed zone by tuning the ratio of kik ¨Ideal to
approach a value of 1Ø
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A shoe according to this technology is tuned to match a runner's speed,
preferably +/- 0.3 m/s,
but may also be tuned to match the runner's speed +/- 1 m/s, or even +/- 2
m/s.
[0045] The advantages and features of novelty characterizing aspects of the
presently disclosed
technology are pointed out with particularity in the appended claims. To gain
an improved
understanding of the advantages and features of novelty, however, reference
may be made to the
following descriptive matter and accompanying figures that describe and
illustrate various
configurations and concepts related to the presently disclosed technology.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The presently disclosed technology will be better understood in light
of the
accompanying figures.
[0047] FIG. 1 depicts an array of pressure measuring nodes arranged in an
orthogonal matrix
with spacing of 5.8mm.
[0048] FIG. 2 is a schematic for a typical force plate used in biomechanical
studies.
[0049] FIG. 3 is a plot of peak vertical ground reaction force from the
plantar foot surface of a
human runner with the anatomical regions (heel, arch, ball, toes) demarcated
with boxes.
[0050] FIG. 4 is a graph depicting the vertical ground reaction force vs time
profiles of four
anatomical regions (heel, arch, ball, toes) of the foot for a single step of a
runner overlaid on the
profile for the sum of all forces vs time.
[0051] FIG. 5 is an annotated graph depicting vertical ground reaction forces
vs time profiles
from a human runner with callouts marking the impact forces and the propulsion
forces.
[0052] FIG. 6 is a graph of vertical ground reaction force vs time profiles
from the ball-of-foot
region of a runner for a series of steps with progressively increasing runner
speed.
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[0053] FIG. 7 is an annotated graph depicting vertical ground reaction forces
vs time profiles
from four regions of the foot experiencing a forefoot-strike pattern.
[0054] FIGS. 8a and 8b are graphs of PE/PEma,, vs runner speed and midsole
spring constant
respectively.
[0055] FIG. 9 is lateral side elevational view of an article of footwear.
[0056] FIG. 10 is a medial side elevational view of the article of footwear.
[0057] FIG. 11 is an exploded perspective view of a sole structure of the
article of footwear.
[0058] FIGS. 12a and 12b are cross-sectional views of the sole structure, as
defined by lateral
and longitudinal section lines 4A and 4B in FIG. 11.
[0059] FIGS 13a and 13b are cross-sectional views of the sole structure, as
defined by section
lines 4A and 4B in FIG. 11.
DETAILED DESCRIPTION
[0060] The following discussion and accompanying figures disclose various sole
structure
configurations for articles of footwear. Concepts related to the sole
structure configurations are
disclosed with reference to footwear that is suitable for running. The sole
structure
configurations are not limited to footwear designed for running, however, and
may be utilized
with a wide range of athletic footwear styles, including basketball shoes,
cross-training shoes,
cycling shoes, football shoes, soccer shoes, tennis shoes, and walking shoes,
for example. The
sole structure configurations may also be utilized with footwear styles that
are generally
considered to be non-athletic, including dress shoes, loafers, sandals, and
boots. The concepts
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disclosed herein may, therefore, apply to a wide variety of footwear styles,
in addition to the
specific style discussed in the following material and depicted in the
accompanying figures.
General Footwear Structure
[0061] An article of footwear 10 is depicted in FIGS. 9 and 10 as including an
upper 20 and a
.. sole structure 30. For reference purposes, footwear 10 may be divided into
four general regions:
a toes region 11, a ball-of-foot region 12, a midfoot region 13, and a heel
region 14, as shown in
FIGS. 9 and 10. Footwear 10 also includes a lateral side 15 and a medial side
16. Toes region 11
generally includes portions of footwear 10 corresponding with the phalanges.
Ball-of-foot region
12 generally includes portions of footwear 10 corresponding with the joints
between the
.. metatarsals and the phalanges and the metatarsal bones, midfoot region 13
generally includes
portions of the arch (both medial and lateral arches) in an area below the
tarsal bones, and heel
region 14 corresponds with the rear portion of the foot, including the
calcaneus bone. Lateral
side 15 and medial side 16 extend through each of regions 11-14 and correspond
with opposite
sides of footwear 10. Regions 11-14 and sides 15-16 are not intended to
demarcate precise areas
.. of footwear 10. Rather, regions 11-14 and sides 15-16 are intended to
represent general areas of
footwear 10 to aid in the following discussion. In addition to footwear 10,
regions 11-14 and
sides 15-16 may also be applied to upper 20, sole structure 30, and individual
elements thereof.
[0062] Upper 20 is depicted as having a substantially conventional
configuration incorporating a
plurality material elements (e.g., textiles, foam, leather, and synthetic
leather) that are stitched or
adhesively bonded together to form an interior void for securely and
comfortably receiving a
foot. The material elements may be selected and located with respect to upper
20 in order to
selectively impart properties of durability, air-permeability, wear-
resistance, flexibility, and
comfort, for example. An ankle opening 21 in heel region 14 provides access to
the interior void.
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In addition, upper 20 may include a lace 22 that is utilized in a conventional
manner to modify
the dimensions of the interior void, thereby securing the foot within the
interior void and
facilitating entry and removal of the foot from the interior void. Lace 22 may
extend through
apertures in upper 20, and a tongue portion of upper 20 may extend between the
interior void and
lace 22. Given that various aspects of the present discussion primarily relate
to sole structure 30,
upper 20 may exhibit the general configuration discussed above or the general
configuration of
practically any other conventional or non-conventional upper. Other devices,
such as Velcro
tabs, can be substituted for laces. Accordingly, the structure of upper 20 may
vary significantly
within the scope of the presently disclosed technology.
[0063] Sole structure 30 is secured to upper 20 and has a configuration that
extends between
upper 20 and the ground. In general, the various elements of sole structure 30
exhibit rebound
properties (impart cushioning and energy return), affect the overall motion of
the foot, and
impart traction during walking, running, or other ambulatory activities.
Additional details
concerning the configuration of sole structure 30 will be described below.
General Sole Structure Configuration
[0064] Sole structure 30 is depicted in FIG. 11 and includes a midsole element
40 and an outsole
50. In addition to these elements, sole structure 30 may incorporate one or
more plates,
moderators, or spring-like structures, for example, which further enhance the
ground reaction
force cushioning and potential energy storage characteristics of sole
structure 30 or the
performance properties of footwear 10. Additionally, sole structure 30 may
incorporate a
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sockliner (not depicted) that is located within a lower portion of the void in
upper 20 to enhance
the comfort of footwear 10.
[0065] Midsole element 40 extends throughout a length of footwear 10 (i.e.,
through each of
regions 11-14) and a width of footwear 10 (i.e., between sides 15 and 16). The
primary surfaces
of midsole element 40 are an upper surface 41, an opposite lower surface 42,
and a side surface
43 that extends between surfaces 41 and 42. Upper surface 41 is joined to a
lower area of upper
20, thereby joining sole structure 30 to upper 20. Lower surface 42 is joined
with outsole 50 in
regions 11-14. Surface 42 may also serve as outsole 50 in portions of regions
11-14, none of
surface 42 or the entirety of surface 42. Additionally, side surface 43 forms
an exposed sidewall
of sole structure 30 on both lateral side 15 and medial side 16.
[0066] A variety of materials may be utilized to form midsole element 40. As
an example,
midsole element 40 may be formed from a polymer foam material, such as
polyurethane or
ethylvinylacetate and exhibit the functional properties of rebound according
to desired design
specifications. In some configurations, midsole element 40 may also be (a) a
plate formed from a
semi-rigid polymer material or (b) a combination of a plate and foam material,
(c) a plurality of
foam-based and semi-rigid structures. In addition to the foam material,
midsole element 40 may
incorporate one or more foam elements defined spatially and with modulus Y,
semi-rigid
structures with spatial dimensions S and L and net modulus Y, for example,
that create the
rebound characteristics of sole structure 30 or the overall performance
properties of footwear 10.
In some configurations, midsole element 40 may also encapsulate foam-based,
semi-rigid, and
combination structures within a foam chassis 41. In other configurations,
midsole element 40
may encapsulate foam-based, semi-rigid, and combination structures within a
portion of regions
11 ¨ 14. Midsole element 40 may also comprise no encapsulating materials,
allowing the foam-
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based, semi-rigid, and combination structures to be exposed along the sidewall
43 and bonded
directly to upper 20 and to outsole 50, where an outsole 50 is present.
[0067] The midsole can be divided into several regions along the length of the
shoe as shown in
Figures 9 & 12. Individual midsole structural elements 60 encapsulated within
a foam chassis 41
may be configured as in Fig. 12a and 12b. Midsole elements 60 may be formed of
a wide range
of polymer materials with engineering properties of the materials (e.g.,
tensile strength, stretch
properties, fatigue characteristics, dynamic modulus, and loss tangent) as
well as the ability of
the materials to prevent the diffusion of any fluid contained within chamber
walls. The sum
behavior of all the materials comprising a single region (11, 12, 13, or 14)
located directly under
the corresponding foot anatomical feature will generate the net rebound effect
in the specified
region of the midsole. The particular placement, shape, and size of individual
elements 60 may
vary greatly between embodiments. The number of elements 60 and the
arrangement of the
elements within the chassis 41 as shown in Figs. 12a and 12b, represent a
single example and
does not represent the possible variety of configurations available to the
designers within the
context of the presently disclosed technology.
[0068] Midsole element 40 may be comprised entirely of structural elements 60
with no
encapsulating foam element 41, as depicted in Figs. 13a and 13b. Midsole 40
may include voids
of open space 61, and may expose any of the outer surfaces or may cover those
surfaces with
paint, film, cloth, or other polymer material 62 for the purposes of abrasion
resistance or
cosmetics. Outer surface coatings 62 may or may not contribute to the rebound
characteristics of
the structural elements 60 and the midsole element 40.
[0069] The presently disclosed technology is disclosed above and in the
accompanying figures
with reference to a variety of configurations. The purpose served by the
disclosure, however, is
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to provide an example of the various features and concepts related to the
invention, not to limit
the scope of the invention. One skilled in the relevant art will recognize
that numerous variations
and modifications may be made to the configurations described above without
departing from
the scope of the present invention, as defined by the appended claims.
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