Note: Descriptions are shown in the official language in which they were submitted.
~ l l v~v -
FOOTW~AR WITH DIFFERENTIAL C~SHIONING REGIONS
FIELD OF THE lN V ~h . lON
The invention pertains to footwear, and especially athletic
footwear, wherein the sole includes differential cushioning regions
to provide both cushioning protection and stability for the
wearer's foot.
BACgGRO~ND OF T~E lNV~.~lON
To provide cushioning protection and support for the foot, the
sole of an athletic shoe commonly has a multi-layer construction
comprising an outsole, a midsole, and an insole. The outsole is
normally formed of a resilient and durable material to resist
wearing of the sole during use. In many cases, the outsole
includes lugs, cleats or other elements to enhance the cushioning
and traction afforded by the sole. The midsole ordinarily forms
the middle layer of the sole and is typically composed of a soft
foam material to attenuate and dampen impact energy and distribute
pressure placed upon the foot during athletic activities. The
midsole may be formed with or without the inclusion of other
cushioning elements, such as resilient inflated bladders. An
insole layer is usually a thin, padded member provided overtop of
the midsole to enhance the comfort afforded to the wearer. The
performance of such footwear depends in large part on the ability
of the sole to effectively cushion applied loads relative to the
anatomy and skeletal structure of the foot and to stabilize the
2 1 78282
movements associated with running and like activities.
The skeletal structure of a foot 1 provides the requisite
strength to support the weight of the body through a wide range of
activities (Figs. 1-4). The structure of the foot can be
categorized into three areas - namely, rearfoot area 2, midfoot
area 3, and forefoot area 4.
Rearfoot area 2 includes talus 13 and calcaneus 17. Tibia 10
and fibula 11 of the leg are movably attached to talus 13 to form
the ankle joint. In general, leg bones 10, ll form a mortise into
which a portion of talus 13 is received to form a hinge-type joint
which allows both dorsi and plantar flexion of the foot. Talus 13
overlies and is movably interconnected to calcaneus 17 to form the
subtalar joint. The subtalar joint enables the foot to move in a
generally rotative, side-to-side motion. Rearfoot pronation and
supination of the foot is generally defined by movement about this
joint.
Midfoot area 3 is anterior to rearfoot area 2 and comprises
navicular 20, cuboid 21 and outer, middle and inner cuneiforms 22-
24. The four latter bones-21-24 facilitate interconnection of the
tarsus to the metatarsus.
Forefoot area 4 is anterior to midfoot area 3 and includes:
proximal heads 3la, 3lb, 31c, 3ld, 3le, shafts 32a, 32b, 32c, 32d,
32e, and distal heads 33a, 33b, 33c, 33d, 33e of metatarsals 34a,
34b, 34c, 34d, 34e; metatarsal-phalangeal joints 35a, 35b, 35c,
35d, 35e; sesamoids 36a, 36b; and phalanges 45-47. Forefoot area
4 includes a ball area 42 and a toe area 43. Ball area 42 of the
,, , 1
``- 21 78282
foot is generally considered to include sesamoids 36a-b, distal
heads 33a-e, metatarsal-phalangeal joints 35a-e, proximal heads
44a, 44b, 44c, 44d, 44e of proximal phalanges 45a, 4Sb, 45c, 45d,
4Se, and the anterior portions of shafts 32a-e of metatarsals 34a-
e. Toe area 43 is generally considered to include distal phalanges
46a, 46b, 46c, 46d, 46e, middle phalanges 47b, 47c, 47d, 47e, and
the distal heads 48a, 48b, 48c, 48d, 48e and shafts 49a, 49b, 49c,
49d, 49e of proximal phalanges 4Sa-e.
Each metatarsal 34a-e is aligned with and attached via
connective tissue to one of the proximal phalanges 45a-e at
metatarsal-phalangeal joints 3Sa-e. For example, first metatarsal
34a is connected to proximal phalange 4Sa of the big toe 40a, and
fifth metatarsal 34e is connected to proximal phalange 45e of the
smallest or fifth toe 40e. First, second and third metatarsals
34a-c are largely attached on their proximal ends to outer, middle
and inner cuneiforms 22-24, respectively. Fourth and fifth
metatarsals 34d-e are both substantially connected to cuboid 21.
Toes 40a, 40b, 40c, 40d, 40e are hingedly attached to the
metatarsals for significant movement.
- The ground support phase of a running step generally includes
a braking phase, a stance phase, and a propulsive phase. The
braking phase occurs when the foot makes first contact with the
ground and the foot begins to flatten. The stance phase follows
the braking phase and is generally considered to consist of the
time when the foot flattens and the runner's center of gravity is
generally located above the foot. The propulsive phase is
`- 2 1 78282
characterized by the rising of the heel from the ground and the
shifting of the runner's weight to the ball and toes of the foot.
As to be expected of the running population, there are many
different running styles. Nevertheless, approximately eighty
percent of the running population makes first contact with the
ground along the rear lateral corner 53 of the sole when running at
moderate speeds. Individuals having this running style are
commonly referred to as rearfoot strikers. By and large, the
remaining twenty percent of the running population generally makes
first contact along the lateral side of the sole. Often, first
ground contact for these runners will occur at or between proximal
head 31e of fifth metatarsal 34e and metatarsal-phalangeal joint
3Se.
With respect to a rearfoot striker, the foot at heel strike is
typically oriented with big toe 40a pointing upward and slightly
outward (Fig. S). From the moment heel strikes the ground, and
through the braking and stance phases, the foot rotates inwardly
(i.e., the foot everts or pronates) and toward the midline of the
body (i.e., adducts). During the propulsive phase, the foot
rotates outward (i.e., inverts or supinates) and away from the
midline of the body (i.e., abducts). This general description,
however, varies with differing circumstances. For instance,
running on an uphill grade tends to cause the footpath to deviate
in a manner so as to cause greater abduction of the foot. Running
on a downhill grade tends to cause the footpath to deviate in a
manner as to cause greater adduction of the foot.
~ 2 1 78282
For a rearfoot striker, the plantar center of pressure path
55a normally proceeds from the point of first contact 53 towards
the midline of the foot and exits between the first and second toes
40a, 40b (Fig. 6). This action reflects the fact that the
individual has maintained balance and stability during the ground
support phase. While eversion of the foot in this context is a
natural action, excessive eversion or an excessive rate of eversion
is sometimes associated with injuries among runners and other
athletes. A deviation of the center of pressure path to beneath
the first toe 40a can be indicative of excessive eversion.
Figures 15-17 each sets forth a map of plantar pressures
applied to the foot of a rearfoot striker running at slow speeds.
The provided results are a composite of the pressures applied
during the entire ground support phase. These results are single
samples to represent the general distribution of pressures during
running. Figure 15 indicates the pressures applied for an
individual having a normal or average arch. Figure 16 illustrates
the pressures applied for an individual having a high arch. Figure
17 sets for~h the pressures applied for an individual having a flat
foot. The incremental units in each illustrated map represent
approximately a 25 square mm area. As indicated in the figures,
the represented pressure readings are indicated in kilopascals
(KPa). As is evident in all of the examples, the areas of highest
pressure are located generally under the heel, the ball area and
the big toe. Nevertheless, these maps are representative of
applied pressures, irrespective of whether any of the pressures are
21 7~282
applied as impact loads.
For a midfoot striker, first contact with the ground S6 is
commonly made near proximal head 31e of fifth metatarsal 34e (Fig.
7). With these runners, the plantar center of pressure path SSb
generally moves to the midline of the foot and then exits between
the first and second toes 40a, 40b. For a forefoot striker, first
contact with the ground 57 is often proximate the fifth metatarsal-
phalangeal joint 35e (Fig. 8). The center of plantar pressure path
55c for this type of runner often moves rearward towards the
midline of the foot before moving forward and exiting between the
first and second toes 4Oa, 4Ob.
Moreover, an individual characterized as a rearfoot striker
when running at slow or moderate speeds will often modify their
technique to become a midfoot striker, and subsequently, a forefoot
striker when running at ever increasing speeds. Further, when an
individual is in a full sprint as on the straightaway of a running
track, the initial point of contact between the foot and the
support surface 58 may be near the distal head 33b of the second
metatarsal 34b (Fig. 9). The plantar center of pressure path 55d
can then proceed directly anteriorly between the first and second
toes 4Oa, 4Ob.
Up until about the 1970's, athletic shoes by and large lacked
sufficient cushioning. Consequently, injuries were sustained by
those engaging in athletic activities. To overcome these
shortcomings, manufacturers focused their attention upon enhancing
the cushioning provided by athletic shoes. To this end, midsoles
- 21 78282
have over time been increased in thickness. These endeavors have
further led to the incorporation of other cushioning elements
within the midsoles and other sole configurations intended to
provide enhanced cushioning effects. The industry's focus on
improving the cushioning effect has resulted in a marked
improvement of shoes in this regard. Nevertheless, footwear
stability with respect to lateral and rotative movements has not
always been successfully addressed. In fact, the benefits realized
in cushioning have sometimes led to a degradation of the shoe's
stability.
Inadequate running stability, like inadequate cushioning, can
result in an increased risk of injury. As discussed above, undue
amounts of eversion or inversion, or excessive rates of eversion or
inversion, can lead to injuries for runners. Moreover, forces
generated between the foot and the ground during the ground support
phase can also produce visible and generally equal and opposite
physical reactions in the lower extremities during the subsequent
flight phase. For example, severe inward or outward rotation of
the foot during thé propulsive phase can produce rotative or
counter-rotative movements in the lower extremities during the
flight phase. These generally inefficient movements, commonly
called whips~ by athletic coaches, can also be associated with an
increased potential for injury.
In an effort to provide greater stability, some shoe soles
have in the past included cushioning materials having differing
degrees of stiffness. In general, the stiffer materials have been
i 21 78282
provided in an effort to prevent excessive eversion of the
forefoot. As one example, U.S. Patent No. 4,364,189 to Bates
discloses a sole wherein a stiffer foam material is provided along
the medial side of the foot. This design, however, fails to
recognize and adequately address impact forces, high vertical
loading, and plantar pressures found under the distal heads of the
first and second metatarsals, the sesamoids, and the proximal heads
of the proximal phalanges of the first and second toes. As a
result, enhanced stability is gained at the price of degrading the
quality of cushioning afforded to the user's forefoot.
U.S. Patent Nos. 4,551,930 to Graham et al. and 4,128,9S0 to
Bowerman et al. disclose athletic shoes wherein the soles have a
plurality of foam materials which provide different degrees of
stiffness in compression. In the Graham shoe, the stiffer foam
material is positioned about the entire perimeter of the sole. In
the Bowerman shoe, the stiffer foam material is positioned about
the perimeter of the heel area. While enhanced stability is
provided by these shoes, the stability is again gained at the
expense of cushioning. In particular, the introduction of
materials having a greater relative stiffness in compression about
the heel reduces the potential cushioning available during heel
strike.
SUMMARY OF TRE lNv~N~lON
Numerous studies have been conducted to determine which areas
along the foot experience the highest plantar pressures during
running. However, the mere existence of a high plantar pressure is
``- 21 78282
not necessarily indicative of a need for enhanced cushioning
materials or devices affording relatively low stiffness in
compression. A high pressure area which is not the result of a
sudden impact is not associated with the same level of acceleration
and shock as one which is associated with a sudden impact.
The present invention pertains to a sole having the ability to
provide both stability and cushioning in order to enhance
performance and lessen the risk of injury. The sole of the present
invention includes cushioning regions with different levels of
stiffness at selected locations with respect to the anatomy and
skeletal structure of the foot. Cushioning elements with a lesser
relative stiffness in compression are positioned at locations most
likely to experience impact loads during running and like
activities. Cushioning elements with a greater relative stiffness
in compression are positioned at locations where impact loads are
unlikely and greater resistance is needed to stabilize the running
motion.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a top or dorsal view of the bones of a foot.
Figure 2 is a medial side view of the bones of a foot.
Figure 3 is a bottom or plantar view of the bones of a foot.
Figure 4 is a lateral side view of the bones of a foot with
the second through fifth phalanges omitted for clarity of view of
the hallux.
Figure 5 is a rear view of a typical rearfoot striker.
Figure 6 is top view of the bones of a foot (with only the
-- 2 1 78282
bones of the forefoot shown in detail) illustrating the plantar
center of pressure path for an individual characterized as a
rearfoot striker.
Figure 7 is top view of the bones of a foot (with only the
bones of the forefoot shown in detail) illustrating the plantar
center of pressure path for an individual characterized as a
midfoot striker.
Figure 8 is top view of the bones of a foot (with only the
bones of the forefoot shown in detail) illustrating the plantar
center of pressure path for an individual characterized as a
forefoot striker.
Figure 9 is top view of the bones of a foot (with only the
bones of the forefoot shown in detail) illustrating the plantar
center of pressure path for an individual in a full sprint on a
straightaway.
Figure 10 is a top view of the sole of one embodiment of the
present invention illustrating the locations of the differential
cushioning regions with respect to the skeletal structure of the
foot (with only the bones of the forefoot shown in detail).
Figure 11 is a top view of an alternate construction of the
sole.
Figure 12 is a top view of a sole of another embodiment of the
present invention illustrating the locations of differential
cushioning regions with respect to the skeletal structure of the
foot (with only the bones of the forefoot shown in detail).
Figure 13 is a top view of another alternative construction of
`- 2 1 78~82
the sole which includes the use of a moderator.
Figure 14 is a cross-sectional view of an athletic shoe taken
along line 14-14 in Figure 13.
Figure 15 is a map of plantar pressures for a rearfoot striker
having a normal arch.
Figure 16 is a map of plantar pressures for a rearfoot striker
having a high arch.
Figure 17 is a map of plantar pressures for a rearfoot striker
having a flat foot.
DET~TT~n DESC~IPTION OF THE PREFE~RED EMBODIMENTS
The present invention pertains to footwear 60 having an upper
63 and a sole 70 (Fig. 14). The upper can have a number of
different constructions. In the preferred embodiment, upper 63 has
a conventional athletic shoe construction including a rear or heel
end 64, a front or toe end 65, a tongue 66 and a row of eyelets 67
(Fig. 14). Nonetheless, the upper may also consist of straps
(e.g., a sandal) or other constructions suitable for securing the
footwear to a foot. Upper 63 is secured to sole 70 having an
outsole 68, a midsole 69 and an insole 74.
The sole of the present invention is formed with regions which
exhibit differential stiffness in compression. The regions which
provide a lesser relative stiffness in compression are positioned
beneath those portions of the foot which are most likely to
experience sudden impacts during running and like activities.
Shock waves generated by an impact travel at a rate exceeding 1500
meters/second in soft tissue, and at a rate exceeding 3000
~`_ 2 1 78282
meters/second in bone. - Accordingly, a soft cushion is needed
proximate the point of impact to provide a rapid and sufficient
cushioning response. Cushions with a greater relative stiffness in
compression are positioned at locations where sudden impacts during
running activity are unlikely, and where running stability can be
enhanced.
In one preferred embodiment, a sole 70 for footwear has a
forefoot portion 71 formed with cushioning regions 72, 73 having
different degrees of stiffness in compression (Fig. 10).
Cushioning region 72 has a lesser relative stiffness in compression
than cushioning region 73 in order to provide greater cushioning
during running. Cushioning region 73 offers a firmer cushion in
order to provide the foot with greater stability.
Cushioning region 72 is generally shaped to underlie second
and third toes 40b, 40c in toe area 43, a substantial portion of
ball area 42, an anterior portion of shafts 32a-c, and shafts 32d-e
and proximal heads 31d-e of fourth and fifth metatarsals 34d-e. As
discussed earlier, ball area 42 includes sesamoids 36a-b, distal
heads 33a-e of metatarsals 34a-e, metatarsal-phalangeal joint 35a-
e, and proximal heads 44a-e of proximal phalanges 45a-e.
Cushioning region 72 extends along the lateral side wall 76 of the
sole so as to cushion the shock associated with first ground
contact for midfoot and forefoot strikers. Since the first ground
contact is made along the lateral side wall 76, cushioning region
72 could be limited to underlie only fifth metatarsal 34e, instead
of both metatarsals 34d-e. However, in order to enable easier
`-- 21 78282
manufacturing and a better transition during running activity,
cushioning region 72 can underlie fourth metatarsal 34d as well.
Cushioning region 73 preferably includes a pair of discrete
sections 73a, 73b. Cushioning section 73a is C-shaped and is
positioned underneath a portion of the foot as to generally
surround metatarsal-phalangeal joint 35a adjacent medial side wall
77, and underlies first toe 40a, and the posterior portions of
metatarsals 34a-c. Cushioning section 73b underlies fourth and
fifth toes 40d-e. More specifically, cushioning region 73
underlies: shafts 49a, 49d, 49e and distal heads 48a, 48d, 48e of
proximal phalanges 45a, 45d, 45e; middle phalanges 47d, 47e; distal
phalanges 46a, 46d, 46e; the medial side portion 79 adjacent
metatarsal-phalangeal joint 35a; and proximal heads 31a-c and a
portion of the shafts 32a-c of metatarsals 34a-c.
Although high pressures are associated with the medial side of
the sole, particularly under big toe 40a and adjacent first
metatarsal-phalangeal joint 35a, these areas are not likely to
experience substantial and sudden impact loading during running.
As discussed above, first contact with the ground ordinarily occurs
in the rearfoot area as shown in Fig. 6 at 53, along lateral side
wall 76 as shown in Figs. 7 and 8 at 56 and 57, respectively, or in
the center portion of ball area 42, as shown in Fig. 9 at 58. As
a result, the level of shock generated along medial side wall 77 of
the sole is much less as compared with that generated along lateral
side wall 76. Consequently, use of a firmer cushion along the
medial side wall does not detrimentally affect the sole's ability
``- 21 78282
to provide adequate cushioning protection for the foot.
By providing a firmer cushion along medial side wall 77, the
sole is able to offer resistance to the lateral rolling of the
foot, i.e., eversion, and provide a better support for the foot.
The medial portion of the foot, and especially big toe 40a, play a
predominant role in an individual's ability to prevent excessive
eversion and stabiiize the foot.
Cushioning region 73 also includes cushioning section 73b
along lateral side wall 76 to underlie toes 40d-e. More
specifically, cushioning section 73b of cushioning region 73
underlies shafts 49d-e and distal heads 48d-e of proximal phalanges
45d-e, middle phalanges 47d-e, and distal phalanges 46d-e.
Although impact forces are ordinarily associated with lateral side
wall 76, first contact with the ground generally occurs rearward of
toes 40d-40e. Accordingly, a firmer cushion can be provided
beneath toes 40d-40e to resist excessive inversion of the foot
during the latter portion of the propulsive phase as the foot is
commonly inverted and abducted.
Extending cushioning region, 72 which provides a lesser
relative stiffness in compression, to underlie toes 40b, 40c can be
advantageous. Although, substantial impact forces are not likely
to be imposed on toes 40b, 40c, the use of a softer cushion between
the two firmer sections 73a, 73b of cushioning region 73 can
provide a cradling effect to assist in guiding the center of
pressure in relation to the foot so as to afford stability.
Nevertheless, there are times when a firmer cushion may be
14
21 78282
desired under the entire toe area 43, including the portion
underlying toes 40b, 40c. For instance, at high running speeds
(e.g., sprinting activity) a reduction in ground contact time is a
high priority, as such generally results in faster running
performances. The use of a firmer toe area can provide a faster
transition during the propulsive phase.
While the above-described embodiment is the preferred
construction, the size and shape of regions 72, 73 can be varied.
For instance, regions 72, 73 can be limited to forefoot areas
located rearward of toe area 43, or, to areas forward of about the
midpoint of shafts 32a-e of metatarsals 34a-e. In either case, the
shape of the regions would remain generally the same as in the
preferred embodiment, except for the noted limitations.
As another alternative, the cushioning regions could also be
limited to an area substantially about ball area 42 (Fig. 14). In
this construction, a cushioning area 72' of lesser relative
stiffness in compression generally underlies the anterior portions
of shafts 32b-e, a small anterior portion of the shaft 32a, and a
substantial portion of ball area 42 including the metatarsal-
phalangeal joints 35a-e and sesamoids 36a-b. Cushioning area 73'
of greater relative stiffness in compression has a generally C-
shaped configuration which underlies a portion of shaft 49a, medial
side portion 79 adjacent metatarsal-phalangeal joint 35a, and a
portion of shaft 32a. As with the other embodiments, cushioning
area 72' extends to lateral side wall 76' of sole 70', but lies
short of medial side wall 77'. The C-shaped configuration of
21 78282
cushioning region 73' then wraps about the medial end 80' of
cushioning region 72'.
The differential cushioning provided by regions 72, 73 or 72',
73' can be provided in a wide variety of ways. In the preferred
construction, differential cushioning is substantially provided by
the cushioning elements of the sole. These cushioning elements can
be composed of foam materials, fluid-filled bladders, or other
cushioning devices used singularly or in combination with other
elements. In the most preferred embodiment, the sole is
substantially composed of fluid-filled bladders. The fluid-filled
bladders can be at least partially encapsulated in a foam material.
The bladders are preferably fabricated in accordance with the
teachings of U.S. Patent Nos. 4,183,156, 4,219,945, and 4,340,626
to Rudy, which are hereby incorporated by reference. Nevertheless,
other types of bladder constructions could also be used.
According to the preferred construction, bladders inflated to
different internal pressures are arranged to cover the two
respective cushioning regions 72, 73. Preferably, the bladder (or
bladders) defining cushioning region 72 is inflated to an internal
pressure of 1-15 psi, and most preferably about 10 psi. The
bladder (or bladders) defining cushioning region 73 is preferably
inflated to 15-50 psi, and most preferably about 25 psi.
Nonetheless, other pressures could be used depending upon the
volume of the respective bladders and the intended athletic
application. The different inflation pressures provide the
different degrees of stiffness desired to obtain the above-
16
"~ 21 78282
discussed cushioning and stability objectives. Generally, asdiscussed in U.S. Patent Nos. 5,343,639 and S,3s3,523, which are
hereby incorporated by reference, the pressure and volume of the
bladders are chosen to provide an air spring stiffness in
compression on the order of less than or equal to about 20 N/mm at
the time of initial impact and about 70-100 N/mm at the time of
maximum loading for cushioning region 72, and on the order of about
twice that stiffness in compression for cushioning region 73. of
course, cushioning elements with different levels of stiffness in
compression could be used.
The cushioning elements forming cushioning regions 72, 73 can
be composed of a single element or a plurality of elements. For
instance, each region 72, 73 can be formed of a single open
bladder, a single bladder with a plurality of chambers, or a
plurality of bladders. The chambers may be fluidly-interconnected
or closed to one another. In the preferred embodiment, cushioning
region 72 is covered by a fluid-filled bladder 176 having a
plurality of closed chambers 176a, 176b, 176c, 176d (Fig. 11). Of
course, other combinations and numbers of chambers could be used.
Similarly, cushioning region 73 is covered by a fluid-filled
bladder 177 having closed chambers 177a, 177b. During fabrication,
chambers 177a, 177b are interconnected via conduit 181. In the
preferred construction, chambers 176a, 176b, 176c, 176d, 177a, 177b
are inflated at ports 183. Bladders 176, 177 can be fab~cated in
accordance with U.S. Patent Nos. 5,353,459 or S,40~ 179,j hereby
incorporated by reference. However, other known manufacturing
2 1 78282
techniques could also be used.
Alternatively, in accordance with U.S. Patent No. 5,406,719,
the bladder or bladders covering regions 72, 73 may all be inflated
to the same internal pressure. As an example, a single bladder
having a plurality of chambers can extend to cover both regions 72,
73. During fabrication, the chambers are fluidly interconnected to
facilitate easy inflation. However, once inflation is complete,
the ports interconnecting the chambers are closed by radio
frequency welding or other means. Of course, if desired, one or
more of the ports could be left open or partially open to permit
the fluid to flow between the chambers. In this construction, the
chambers covering region 73 would have a smaller volume than the
chambers covering region 72 in order to provide a greater relative
stiffness in region 73. In this way, the desired differential
degrees of stiffness can be obtained with chambers inflated to the
same internal pressure.
Further, the different degrees of stiffness in the sole may
also be provided by other means. For example, stabilizers as
taught in co-pending U.S. Patent Application Serial No.
by Robert M. Lyden, entitled Footwear With Stabilizers," filed the
same day as the present application, could be used to provide at
least a portion of the desired differential cushioning. Also, as
an example, moderators 83 can be used to provide the desired
differential cushioning regions 72, 73 (Figs. 13 and 14). The
moderators could be shaped to overlie the entire region 73 in order
to spread the loads out over a greater surface area and thereby
18
" 21 78282
increase the stiffness of the cushion. Nevertheless, if desired,
the moderator 83 could be used to cover only a portion of region
73, such as the rearward parts of section 73a. The stiffer
portions of the toe area 43 could be formed with the use of stiffer
midsole cushioning elements. The moderators 83 can lie between the
midsole 69 and the insole 74, but could also be located in other
areas of the sole. A thin auxiliary pad 84 can be provided to
cover the areas left open by moderators 83 to provide an even
support surface for the foot when the moderators lie over the
midsole. The moderators can also be used in combination with
midsole cushioning elements, such as fluid-filled bladders 85a,
8Sb, which may, if desired, provide different degrees of stiffness
to obtain the desired overall stiffness levels. As an example, the
moderators can be constructed as taught in U.S. Patent Nos.
4,506,460 and 4,486,964, which are hereby incorporated by
reference. The moderators can be formed of a wide variety of
materials including thermoplastics or other resins, cardboard,
carbon fiber composites, or other suitable material.
The differential cushioning effect could also be provided by
the outsole construction. For example, the outsole may be provided
with lugs of differing sizes or shapes arranged in accordance with
cushioning regions 72, 73. As an example, in a shoe wherein the
lugs bear against a conventional foam midsole, lugs having greater
surface area could be provided in region 73 as compared to the lugs
in region 72. In this way, the lugs of the outsole in cooperation
with the rest of the sole could provide the different levels of
19
2 1 78282
stiffness for cushioning regions 72, 73. Of course, other suitable
outsole structures for providing the desired differential
stiffening could also be used.
Soles fabricated in accordance with the present invention can
also be provided with one or more lines of flexion in the forefoot
area. For example, a longittl~;n~l line of flexion 190 can extend
rearward from the anterior end 192 of the sole such that big toe
40a and metatarsal-phalangeal joint 35a are located on one side of
line 190 and medial toes 40b-40e and other metatarsal-phalangeal
joints 35b-e on the other side (Fig. 11), as taught in U.S. Patent
No. 5,384,973, which is hereby incorporated by reference. As
another example, a line of flexion 194 can be provided along the
base of toes 40a-e (Fig. ll), as disclosed in U.S. Patent No.
4,562,651, which is also hereby incorporated by reference.
In the preferred embodiment, sole 70 further includes a
cushioning region 201 of lesser stiffness in compression in the
lateral, rear corner 203 (Fig. 11). This construction defines a
rearfoot strike zone 205 as described in co-pending U.S. Patent
Application Serial No. 08/038,950, filed March 29, 1993 and
entitled ~Athletic Shoe With Rearfoot Strike Zone," and co-pending
U.S. Patent Application Serial No. (CIP of Serial No.
08/038,950) filed the same day as the present application, which
are hereby incorporated by reference. The rearfoot strike zone 205
is a portion of the heel area of the sole delimited by a line of
flexion 207 about which the rearfoot strike zone is articulated in
relation to the remaining heel area. Independent articulation of
- 2 1 78282
strike zone 205 increases the surface area of ground contact
occurring at heel strike from a narrow edge-like strip extending
along the rear lateral sidewall of the sole to a wider planar area
extending inwardly of the sidewall. This construction reduces
medial moment and enhances both cushioning and stability. The
shock associated with heel strike is reduced by the provision of
cushioning means having a lesser relative stiffness in strike zone
205. As seen in Fig. 11, a soft cushion is also preferably
provided in a section 206 directly beneath the heel.
A primary objective in the placement of the line of flexion
207 is to properly delimit a rearfoot strike zone having enhanced
cushioning. The rearfoot strike zone should encompass the range of
heel strike locations for most rearfoot strikers, without adversely
affecting medial and lateral stability during the braking, stance
and propulsive phases. Since the orientation of the foot for
rearfoot strikers normally causes the lateral rear corner of the
sole to first engage the ground, the rearfoot strike zone is
located in this corner.
On the lateral side 76 of sole 70, there is no need for the
rearfoot strike zone to extend beyond the jun~tion 209 of calcaneus
17 and cuboid 21. The medial point of rearfoot strike generally
occurs well rearward of this point so that the rearfoot strike zone
may be shortened if desired. Extension of a more compliant
rearfoot strike zone beyond junction 209 could begin to degrade
lateral stability in the midfoot region, particularly during the
stance and early stages of the propulsive phase or for those
- 21 78282
exhibiting a propensity for excessive inversion. A region
providing a higher relative stiffness in compression is preferably
located along lateral side 76 between junction 209 and the rear
lateral corner of cushioning region 72 (i.e., by proximal head
31e).
Rearfoot strike zone 205 generally need only extend toward the
medial side a short distance beyond the longitudinal center of the
rear side of the heel in order to accommodate the heel strike of
most runners. The medial side termination point 211 of the
rearfoot strike zone is conveniently described in relation to the
nominal weight bearing center 213 of the heel. More specifically,
medial side termination point 211 may be described in terms of an
angle ~ formed between a longitudinal center axis of sole 70 and a
line drawn from the weight bearing center 213 of the heel to
termination point 211. Placement of the medial side termination
point 211 which creates an angle ~ of 10 is satisfactory to
accommodate the heel strike of most rearfoot strikers. The angle
~ may be increased up to about 50 for greater inclusiveness of the
range of possible heei strikes. However, extension rearfoot strike
zone 205 beyond this point can degrade stability, particularly for
those runners exhibiting a tendency towards excessive eversion
(i.e., over pronation). Therefore, cushioning elements positioned
directly forward of line of flexion 207 preferably provides a
greater relative stiffness in compression.
The term line of flexion in the application is intended to
refer to a line of action, rather than a physical element of the
2 1 78282
sole about which the rearfoot strike zone occurs~ The location and
path of line of flexion 207 are determined by physical elements of
the sole (e.g., grooves) that cooperate to provide a relatively
independent articulation of rearfoot strike zone 205 relative to
the remaining heel area. By delimiting rearfoot strike zone 205
with a line of flexion 207, increased compliance within the strike
zone is obtained because the strike zone is able to pivot as a
whole in addition to compressing.
With this whole sole construction, the sole can provide botn
cushioning and stability for all kinds of runners (including
rearfoot, midfoot and forefoot strikers) and at different levels of
speed or running velocities. The above-discussion concerns the
preferred embodiments of the present invention. Various other
embodiments as well as many changes and alterations may be made
without departing from the spirit and broader aspects of the
invention as defined in the claims.
