Note: Descriptions are shown in the official language in which they were submitted.
73~
DYNAM~C SIJPPO~T SYSTEM
FOR AT~ILFTIC SHOES
Fie]d of Inventiorl
This inven~ion relates to athletic shoes ~nd is ~articu-
larly concerned with running or jogging shoes of the type
having a closed cell polymeric foamed rnidsole.
Backgrouncl
Present day sliplasted and boardlasted running and jogging
shoes, as well as other types of athle~ic shoes, are customarily
manufactured with a laminate bottom construc~ion having a closed
cell polymeric foam midsole overlying and adhered to a fle~:ible
outsolev Sliplasted athletic running shoes mainly differ from
boardlasted athletic shoes in that they have no insole board
and instead have a closed fabric bottom to extend completely
around the foot like a slipper. In the boardlasted athletic
running shoes, the uppex has an open bottom which is closed by
an insole board overlying the midsole. The foamed midsole is
used in both types of shoes because of its lightness 2nd shock
absorbing propexties to cushion the wearer's foot ayains-t im-
pacts during runningO
Sliplasted athletic shoes ~re generally preferred over
boardlasted athletic shoes because they usually are more com~
fortable than boardlasted athletic shoes. Due to the absence
of an insole board, however, sliplasted athletic shoes are
usually less stable than boardlasted athletic shoes because
concentra~ed stresses are developed in the fo~ned midsole
during xunnirlg to non-uniformly clegrade the foamed midsole to
an objectionable extent. The foamed midsole therefore loses
much of its effectiveness as a shock absorber because o the
non-uniform deyradation~
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,~
Degradation of the foamed midsole arises from con-tinual
stresses which are developed by the repeated and cyclic defor-
mation and relaxation of the midsole during the course o~
running. The degradation may take ~he form of a permanent
compressive deformatiorl or compression set, as it is called,
of the midsole. It mayialso occur without compression set ~here
there is a breakdown or loss of the closed cells in the foamed
midsole.
Midsole degradation is frequently localized due to con-
cen~rated Eorce patterns which arise from a runner's particular
running style. For example/ localized midsole degradation may
occur at the rear outside border of the shoe in the region of
the back of the heel. Midsole degradation also occurs through-
ou~ the impact absorbing region of the midsole as a result of
the compressive forces which cause the midsole to expand
laterally outwardly of the shoe.
Localized midsole degradation along either the medial
inside or lateral outside shoe edges is particularly trouble-
some because it tends to cause the shoe to lose its stability
by tilting as the runner's foot strikes the ground. To
compensate for the instability, the runner may adjust his running
style which, in turn, could lead to foot or ankle injuries.
Furthermore, the problem of midsole degradation is compounded
by the fact that it frequently occur5 before the outsole loses
its service life.
The foamed midsole in a boardlasted athletic running shoe
will also degrade as a result of usage, but the degradation is
no~ as non-uniform as the midsole degradation in a s:Liplasted
athletic shQe becau~e ~he insole board of the boardlasted ath-
le tic shoe disperses ~he ~orces a~ting on the midsole to some
extent as long as ~he 1n~1~ b~rd i~el~ do~ ~ot degrade.
.. . . . . . . .
, . . ," , s , ~
-2
. . . . . .
A1-though an insole hoarcl does d.isperse the forc-es
ac-ting on the foamed midsole -to some ex-tent, it was found tha-t
if the insole board is made stiff enough to adequately spread
the forces over the Eoamed midsole, the shoe becomes -too hard,
causing appreciable discomfor-t to the wearer. On the other
hand, low strength insole boards which meet the wearer's com-
for-t requirements are likely to degrade, -thus giving rise to
excessive non-uniform midsole degradation even in boardlasted
shoes.
Summary of the Invention
The inven-tion provides in an athletic shoe for running
and other sports involving running, an upper and a bot-tom, said
upper overlying and being attached to a part of said bottorn,
said bottom comprising a flexible outsole and a flexible shock-
absorbing midsol.e overlying and secured to said outsole, and
said midsole being formed from a foamed polymeric material, the
improvement comprising formation means formed separately of
said midsole and engaging said midsole along a pre-selec-ted
surface area underlying the wearer's foot and loca-ted inter-
mediate -to the upper and lower surEaces of said midsole for
stiffening said midsole along said pre-selected surface area.
The novel structure is designed to improve the
stability of -the athletic shoe, reduce midsole degradation, and
enhance the anatomical suppor-t for the wearer's foot, all with-
out making the shoe uncomfortably hard and without using any
parts which reduce the foot-receiving volume of the upper. The
structure can substantially reduce the non-uniform rnidsole
degradation of a sliplasted athletic shoe without resorting -to
an insole boar~ and without otherwise impairing the comfor-t pro-
perties of a slip]asted athle-tic shoe.
In the illustrated embocliment, the forma-tion means
takes the form of a thin, stiff, subs-tantial:ly non-s-tre-tchable
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73~
layer or stif:Eening board, as it may be called, which lies
between and is adhered to two midsole layers at a level lying
between -the upper and lower surfaces of the midsole. 'L'he
stiffening board is required to be sufficiently s-ti:f.E to
ef:Eectively disperse the forces acting on the shoe -throuc3holl-t
the region covered
-3a-
~2~3~
by the board to thereby provide for a more uniform distribution
of the Eorces acting on the shoe.
Because the stiffening board of this invention is effect~
ive in stiffening the foamed midsole support underneath the
foot, its geometrical shape is particularly important. In
the illustrated embodiment, the shape of the stiffening board
is such that it underlies the wearer's entire rearfoot or heel
region and ex~ends forwardly approximately to the first, second
and third metatarsal heads to underlie the inside arch, but not
the outside arch of the wearer's midfoot.
Because of the selected region covered by the stiffening
board! the board does not interfere with the required flexure
of the shoe~ It therefore may be made as stiff as possible ~ut
not so stiff that it becomes brittle.
By dispersing the forces acting on the midsole, the
stiffening board of this invention significantly reduces dele-
terious, non-uniform midsole degradation and substantially
lengthens the useful life of the shoe. The adherence of the
stiffening board to the opposing midsole layers by itself has
the effect of restraining the outward lateral expansion of the
midsole due to compressive forces, thereby reducing midsole
degradation due to such outward expansion. The degradation
resulting from outward expansion of the midsole takes the form
of cell wall fail~es which are caused by shear orces acting
on the midsole material.
By locating the stiffening board of this invention at a
level intermediate to the upper and lower surfaces of the mid-
sole and by utilizing a boardless insole (i.e., a sliplasted
construction without an insole board~, the foot support system
is advantageously lowered. The foamed midsole layer underlying
the stiffening boa~rd is used solely for absQrbing forces resultiny
~4
3~
from the impact of the foo-t on the ground. The midsole l,ayer
overlying the stiffening board a]so ac-ts as a shock ab.sorber
and additi.onally cushlons the wearer's foot so that the shoe
does not feel hard due to the presence o:E the stifEening board.
Furthermore, the foamed midsole ],ayer overlyiny the sti,Efening
board in the region of the wearer's rearfoot is of suEficient
thickness to closely conform -to -the shape of the wearer's heel,
thereby enhancing the cornfort qualities of -the shoe.
By stiffening the foamed midsole in the manner
described above, the extent of penetration of the runner's foot
into the midsole is advantageously reduced by selectively
increasing the stiffness of the midsole material. By extending
the stiffening board to a region where it underlies the inside
or medial arch-supporting region of the midsole, the stiffening
board and foamed midsole also advantageously acts as a comfort-
able dynamic arch support~ This aspec-t of the present invention
eliminates the need for arch cookies or other conventional arch
supporting inserts which disadvantageous]y reduce the foot-
receiving volume of the shoe upper.
The midsole stiffening formation of -this invention
may advantageously be manufactured separately from the shoe as
a customized product for use by podiatrists and orthopedists in
modifying existing running shoes to compensate for leg and foot
asymmetries or other problems. Heretofore, various shoe inserts,
such as heel cushions, arch supports and other so-called
orthotic devices, have been used for this purpose. I'hey all
have the common disadvantage of causing some discomfort because
they take up foot-receiving space in the shoe upper.
In contrast to these prior shoe inser-ts, the stiffen--
30 ~ ing forma-tion of -this invention lies in the midsole, and not in
the upper so that the full volurne of the upper remains available
--5--
for comfor-tably covering -the wearer's foo-t.
The athletic shoe disclosed has a novel midso]e con-
struction wherein a special formation engages the Eoamed mid-
sole body to reduce or retard deleterious, non-uniform degrada--
tion oE the foamed midsole. The novel midsole has a dynarnic
arch support. The midsole construc-tion is economical and easy
to manufacture.
The invention also provides a method of modifying an
exis-ting athletic running shoe having a polymeric foamed mid-
sole, comprising the steps oE cutting the midsole to provide aformation-receiving space lying between the upper and lower
surfaces of the midsole, inserting a stiff formation of pre-
selected configura-tion into said space -to stiffen the midsole
along a pre-selected surface area, and adhering the formation
to the rnidsole.
The invention can provide a novel, customized forma-
-tion for modifying existing athletic shoes for -the purpose of
accommodating a wearer's particular anatomy or asymmetries, and
to compensate for different body weights and/or difEerent leg
lengths.
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7~ ~
Description of Drawings
Figure 1 is a perspective view of a left-hand athletic
running shoe incorporating the p.rinciples of this invention;
Figure 2 is a lonyitudi.nal section of the athletic runnirlg
shoe shown in Figure l;
Figure 3 is a horizontal section taken substantiall~
along lines 3-3 of Figure 2 and showing the configuration of
the stiffening formation according to one embodiment of this
invention;
Figure 4 is a transverse seckion taken substantially
along lines 4 4 of Figure 2;
Figure 5 is a further transverse section taken substan-
tially along lines 5-5 of Figure 2;
Figure 6 is a transverse section similar to Figure 4 but
showing a variation which is applicable for runners who pronate
excessively; and
Figure 7 is another transverse section similar to Figure
4 but showing a further variation which is applicable to
runners who supinate excessively.
Detailed Description
In this specification, the term "rearfoot" is used to
identify the heel portion of the foot containing the heel bone,
the term "midfoot" is used to identify the intermediate portion
of the foot lying adjacent to the rearfoot and containing the
five bones which are connected together to form the beginning
of the arches in the foot, and the term "forefoot" is used to
identify the foot portion lying adjacent to the midfoot and
containing the metatarsals.
Although the midsole stif~ening formation of this
invention i~ incorporated lnto a slipla~t~d athletic running
shoe in the illust.rated embodimén~l it will be appreciated ~hat
,
;
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73~
the principles of the subjec-t invention are also applicable
to athletic shoes having an insole board where the insole
board is made sufficiently flexible so that it does not
impair the f~tnctions of the special stiffeniny formation o~
this invention.
Referring to Figure5 1 and 2, the athletic running shoe
incorporating the principles of this invention comprises a
flexible, sliplasted upper 10, a bottom 12 underlying upper
10 and a soft, pliable sliplasted insole 13 (see Figure 2).
Upper 10 has a closed fabric bottom 15 so that it extends
completely around the foot in the customary manner. Insole
13 is received in upper 10 and overlies the fabric bottom 15.
The upper 10 may be of any suitable, conven-tional con-
struction and is shown to comprise a toe portion or toe box
14, a vamp portion 16, a heel portion 18, foxing 20 wrapped
around the back of the heel portion, a throat 22 extending alony
the vamp portion 16 for the lacing which is indicated at 24,
a padded tongue 26 extending along throat 22, and a padded collar
28 extending aroun~ the shoe's foot-receiving opening.
The shoe bottom 12 i9 a laminated construction having a
flexible, ground-engaging outsole 32 and a shock-absorbing
midsole 33 ovsrlying and bonded to the outsole 32. The outsole
32 may be of any suitable construction and may be fabricated
from synthetic or natural rubber material. The ground-engaging
surface of outsole 32 is preferably formed with a suitable
tread pattern 36. The midsole 33 is substantially coextensive
with the outsole 32. The upper 10 is bonded or otherwise
suitably secured to midsole 33 along its fabric bottom 15.
The midsole 33 is formed from any suitable closed cell
polymeric foam shock absorbing material. For example~ the mid-
sole 33 may be formed ~from a blend of ethylene vinyl acetate
~ f~
f~ J~
and polyethylene and then cross-linked with a peroxi~c dUl^illCJ
molding. The foam material is preferably lightweight haviny
a density on the order of 0.2 grams per cubic centim~ter or
somewhat less.
MidsoIe 33 is the ~hickes~ at its rearfoot or heel
portion 39 where it undérlies the wearerls heel or rearfoot.
In the illustrated embodiment, the midsole's heel portion 39 `
is of substantially uniform thickness. Midsole 33 tapers for-
wardly at an intermediate region lying forwardly of the heel
portion 39 to form a wedge as shown in Figures 1 and 2. The
wedge may be formed separately of midsole 33 and it may
overlie or underlie the midsole.
In the illustrated embodiment, the midsole stiffening
formation of this invention is in the form of a thin, stiff,
planar, flat-sided layer 37 or stiffening board, as it may
also be calledO The stiffening board 37 is formed separately
of the foamed midsole 33 and is incorporated into the midsole
in a manner to be described in detail later on.
In the illustrated embodiment, the insole 13 comprises
a soft, flexible, flat cushion liner 38 for the wearer's
sock. Liner 38 overlies the fabric bottom 15 of upper 10 and
may be formed from any suitable pliable material such as a foam
material or terrycloth. Insole 13 is characterized by the
fact that it does not have an insole board.
As shown in Figures 1-5, stiffening board 37 is recei~ed
in a slit 42 which is formed in midsole 33 between the upper
and lower surfaces of the midsole to partially divide midsole
33 into upper and lower layers 44 and 46, respectively. Stiff-
ening board 37 is glued or otherwise su'tably adhered to the
bott~m sur~ace o~ the midsole layer 44 and to the upper surf aee of
the lower midsole 1ayer 46. ~ny suitable adhesive may be used
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27~3~ ~
for adhering stiffening board 37 to the midsole layers 44
and 46. Preferably, the adhesive is applied throuyhout the
entire interface between stiffeniny board 37 and the midsole
layer 44 and also throuyhout the entire interface betwe~n
the stiffening board 37 and the lower midsole layer 46.
Slit 42 extends parallel to or at least yenerally
parallel to the outsole 32 when the shoe bottom is in its
straiyht, unflexed condition.
With the possible exception of the midsole's rearmost
heel reyion which may be tapered as shown in Fiyure 2, the
lower midsole layer 46 is provided with a substantially uniform
thickness throughout the length and width o~ slit 42. The
rearfoot section of the upper midsole layer 44 underlying the
wearer's rearfoot or heel also has a substantially uniform
thickness.
Slit 42 is formed in midsole 33 at a level lying about
midway between or slightly below the upper and lower edges of
the midsole's rearfoot section. The level of slit 42, in any
case, is required to be low enough to provide the upper midsole
layer 46 with a thickness that is sufficient to keep the
weareris foot rom bottomlng on stiffening board 37 during
m~;mum expected impact on the midsole. The thickness and other
dimensions of midsole 33 may be customary, suitable values
presently used in the shoe industry to manufacture running shoes.
At a region centrally underlying the wearer's rearfoot
or heel, the overall thickness of midsole 33 may, for example,
be about 3/4 inches and the height of slit 42 above the lower
edge of the midsole may be about 5/16 inches.
As shown in Figures 1-3, the configuration or outline of
slit 42 conforms to that of stiffening board 37 to snugly and
ully receive the stiffening board. Slit 42 extends throughout
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~9~73'~ ~
the rearfoot or heel portion of midsole 33 so that it opens
completely around the midsole's rearfoot portion at the hack
and also at both sides. From the rearfoot portion of midsole
33, slit 42 extends forwardly along and opens at the inside or
medial border of the shoe approximately to the first metatarsal
head to underlie the we.irer's inside arch.
It will be appreciated that stiffenirly board 37 may be
assembled with midsole 33 in any suitable manner. For e~ample,
after slit 42 is formed in the midsole and an adhesive is
applied to both sides of stiffening board 37, the stiffening
board may be fully inserted into slit 42. The mldsole layers
44 and 46 and stiffening board 37 may then be pressed together
to firmly adhere the stiffening board to the midsole layers
44 and 46.
Stiffening board 37 is formed from any suitable, durable
substantially non-stretchable material. For example, it may
be a sti~f composite material sheet formed from polyester resin
and woven or chopped fiberglass in which the amount of fiber-
glass present is equal to approximately 25 percent by volume
of the sheet.
The stiffening board's minimum flexural or bending
modulus required for an adequate dispersion or spreading of
the forces acting on midsole 33 is dependent on the thickness
of the stiffening board. The thickness for stiffening board 37
should normally be at least approximately 0.05 inches and
preferably is approximately 0.06 inches (about 1~16 inch). r'Ol-
a stiffening board thickness of 0.05 inches, the bending or
flexural modulus is required to be at least 1,000,000 psi and
is more preferably about 2,000,000 psi.
As sho~n in Figure 31 stiffening board 37 extends through-
out the rearfoot region of the ~hoe bottom to the outer edge
3~
o~ th~ hecl alld from o~ le of ~l~c midsole ~o ~l~e oLIIer.
From the rear of midsole 33, stiffening board 37 e~ellds
forwardly along the shoe's medial or inside 'oorder to the
location 50 which is proximal to the wearer' 5 first metatarsal
head. ~rom here, the edge or perimeter of sti.ff~ning board 37
arcs posteriorly and .Latera:Lly along a line 51 which i5 proxirnal
to the wearer's second and third metatarsal heads. The edge
of the stifening board then turns to take a direct longitu-
dinally extending line 52 posteriorly to a region underlying
the wearer's cuboid where it arcs out at 53 to extend laterally
to the lateral or outer border of the shoe bottom along a line
54 lying approximately normal to the shoe's longitudinal axis
at the forward end of the midsole's rearfoot or heel section
39.
By the foregoing construction, it is clear that stiffen-
ing board 37 underlies the wearer's entire rearfoot and extends
forwardly to underlie the wearer's inside arch along the medial
border, but not khe wearer's outside arch or the forefoot
region extending forwardly of the wearer's first, second and
third metatarsal heads. Because of the selected area covered
by stifrening board 37, the board does not in~erfere with the
requiredflexure of the running shoe. It therefore may be made
as stiff as desired without making ik brittle.
Stiffening board 37 is preferably feathered or skived
to a taper along .its curved, forward edge (see lines 51-54)
as indicated at 56 in Figure 3 to keep the wearer from sensing
or feeling an abrupt change in stiffrless due to the stiffening
board edge as he presses clown on the shoe bottom. Additionally,
the rear lateral or outside corner 58 (see ~igure 3) may also
be similarly skived ko avoid the development of stress concen-
~trations at the most con~on first heel strike region and also
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~ Z~3~
-to eliminate or signlficantly reduce accelerated, deleterious
sole wear due to the presence of stif~eni.ng board 37.
The lower midsol~ layer 46 functions solely as a shock
absorber for absorbi.ny the forces resultiny rom impact of
the runner's foot on the ground. The upper midsole layex 44
also acts as a shock absorber for absorbing such forces and
additionally cushions the wearer's foot so that the shoe does
not feel hard due to the presence of stiffening board 37.
Furthermore, the thickness of the upper midsole layer 44 in
the region of the wearer's rearfoot or heel is sufficient to
closely conform or mold itself to the shape of the wearer's
heel to provide additional comfort for the wearer.
By stiffeniny midsole 33 in the manner described above,
the extent of penetration of the runner's foot into the upper
midsole layer 44 overlying stiffening board 37 is advantageously
and significantly reduced as compared with a conventional shoe
without the stiffening formation of this invention. The
stiffening effect encountered at initial deformation or pene-
tration of ~he wearerls foot into the upper midsole layer 44 is
approximately douhled by the presence o stiffening board 37
in midsole 33, with the result that energy is absorbed at about
twice the rate of a conventional shoe. Although the maximum
force will be increased over a new conventional shoe, it never~
theless will still be acceptably low. In addition, conventional
shoes are known to frequently lose about half of their energy
absorbing properties due to continuous use as, for example,
while running a marathon distance~
Reducing the extent of rearfoot penetration into midsole
33 has the advantageous effect of enabling the runner ~o have
greater control o~er h.is rearfoot motion, thus .improviny rear-
foot .stahility withouk any significant tradeoff of the shock
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3~ ~
absorbing properties of the midsole 33.
By extending stiffening board 37 to a region where it
underlies the runner's inside or med.ial arch, the composite
of -the midsole 33 and the stiffening board 37 ~mderlyiny the
inside arch establishes a comfortable arch suppo.r-t fo.r the
wearer which .is dynamic in -the sense that .it is felt only ~7ith
the application of substantial forces. This eliminates the
need for arch cookies or other conven-tional arch-supporting
inserts which are placed in the shoe upper and which dis-
advantageously reduce the foot-receivi.ng volume of the shoe
upper.
Stiffening board 37 acts to reduce midsole degradation
in two ways. First, it is sufficiently stiff to effectively
disperse or spread out the forces acting on midsole 33 through-
out the area or region of the stiffening board to thereby
provide for a more uniform distribution of the forces acting
on midsole 33 in the region of the stiffening board. Stiffen-
ing board 37 thus eliminates or substanti~lly reduces large,
concentrated force patterns resulting from a runner's particu-
lar running style and consequently reduces non~uniform degrada-
tion of midsole 33.
Second, stiffening board 37 has the effect of restrain-
ing outward lateral expansion of midsole 33 under the influence
of compressive forces because of its adherence to the midsole
layers 44 and 46 and because of its substantially non-stretchable
properties. The tensile properties of the midsole foam cel]
walls lying contiguous to the adhesive surfaces will therefore
act to restrain the outward expans.ion under the influence of
the compressive forces. While some outward midsole expansion
will occur because of these compressive forces/ the extent of
the outward expansion in each of the midsole layers 44 and 46
2~3~
will never-theless be subs-tantially less than the c~pansion
that would talce place without -the stiffeniny formation of
the present inventlon. Midsole degradation resulting frorn
such outward expansion is therefore correspondingly reduced
with the present invention.
From the foregolng construction, it is important to
observe that the stiffening board 37 has the effect of signifi-
cantly improving the stability of a new running shoe in which
no midsole degradation has occurred. In this regard, stiffen-
ing board 37 has the effect of dispersing off-centered or
unbalanced forces created by a particular running style. Such
dispersement produces a restoring force which opposes an un-
balanced or off-centered landing of the foot where, for example,
the runner lands on the ground along the outside or lateral
border of the shoe instead of landing flat. Furthermore,
stiffening board 37 provides an improved foot support during
running by employing the midsole layer 44 as a cushion which
comfortably conforms to the configuration of the wearer's heeL
while running and by further establishing a dynamic arch
support for the runner's inside or medial archO In addition to
the foregoing, stiffening board 37 significantly reduces non-
uniform midsole degradation to substantially improve the
stability of the running shoe over the long term and to sub-
stantially lengthen the problem-free life of the shoe.
Because the outward expansion of the midsole is restrained
just by the non-s-tretchable or tensile properties of stiffening
board 37 and by the adherence of the stiffening board -to the
midsole layers ~4 and ~6, such ou'ward midsole expansion may
be reduced by using a fleXible, substantially non-stretchable
layer or formation in place of stiffening board 37 and by adhering
such a non-stretchable flexible formation or layer to the
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7'~3~
midsole layers 44 and 46.
Instead of beiny molded in one piece and thereafter
slit -to accommodate stiffening board 37, midsole 33 may be
manufactured with two separately formed Eoamed layers, and these
layers may have different densities. Because of the stiffeniny
formation of this invention, differen-t foam materials not pre-
viously thought to be suitable for midsoles may be used in the
manufacture of the running shoe.
Stiffening board 37 is not required to lie horizontal-
ly as shown in Figures 1-5. Instead, it may be tilted or
rotated in one direction or the other about a longitudinal axis
as shown in Figures 6 and 7.
In Figure 6, stiffening board 37 is tilted in a direc-
tion to locate its side edge at the lateral or outside shoe
bottom border at a level that is lower than i-ts side edge a-t the
media] or inside shoe bottom border to compensate for the forces
which are created by runners who pronate excessively. In Figure
7, stiffening board 37 is tilted in the opposite direction such
that the side edge of the stiffening board at the medial or
inside shoe bottom border is at a level lower than the opposite
stiffening board side edge at the lateral or outside shoe
bottom border to compensate for the forces created by runners
who supinate excessively.
The midsole stiffening formation of this invention is
not required to be flat or planar as is the case with s-tiffening
board 37~ Stiffening board 37 may therefore be replaced with
differently shaped stiffening formations. For example, the
stiffening formation may have a curved or contoured configura-
tion, and it may also be molded. Furthermore, var:ious factors
associated with the s-tiffening formation of this invention may
~~ be suitably varied depending upon the circurnstances. For
example,
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3~
such factors as the thickness of the stiffening formation,
the stiffness of the formation, -the geometrical ex-tent or
area covered by the stiffening format.ion, and the p].acement
height o the formatlon may all be varied -to accommodate
different running styles, leg and foot asymmetries ancl body
weights. ..
It also will be appreciated tha-t the stiffening formation
of this invention avoids difficult and costly attempts to vary
the suppor~ pattexn of the running shoe by introducing diferent
elastomeric materials into the midsole foam.
~ urthermore, the midsole stiffening formation of this
invention may advantageously be manufactured separately from
the running shoe as a customized product or use by podiatrists
and orthopedists for modifying existing or fully constructed
shoes after they are manufactured to compensate for leg and
foot asymmetries or other problems and to thereby customize the
shoe to the individualO For example, the midsole stiffening
formation of this inven-tion may be used to compensate for
different leg lenyths with the added advantage of not requiring
the insertion of any parts of components into the shoe upper
itself. The method of using the stiffening formation in this
manner mainly comprises the steps of first slitting the foamed
midsole of an existing athletic shoe or otherwise forming a
cavity in the midsole for receiving the stiffening formation,
and thereafter inserting the specially formed stiffening for-
mation into the slit or cavity and adhering the stiffening
formation to the midsole~
It will be appxeciated that the parts of the athl.etic
rl~nning shoe for ~he right foo~ are the mirror image of the
previously described parts of the shoe or the left foo~.
The invention may be embodied in other specific forms
~17~
~2'~
wi-thout departing from the spirit or essential characteristics
thereof. The present embodiment is therefore to be considered
in all respects as illustratlve and not restrictive, the scope
of the invention being indicated by the appended claims rather
than by the foregoing description, and all changes which come
within the meaning and range of equivalency of the claims are
therefore intended to he ernbraced therein.
What is claimed and desired to be secured by Let-ters
Pa~ent i5:
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