[TECHNICAL FIELD]
[0001] The present invention relates to shoe bottoms of shoes.
[BACKGROUND ART]
[0002] In the related art, attempts have been made for providing various functions to shoes
by devising soles of shoe bottoms (e.g., see Patent Document 1).
[0003] [Patent Document 1] International Publication No.
2017/046959
[DISCLOSURE OF THE INVENTION]
[PROBLEM TO BE SOLVED BY THE INVENTION]
[0004] When doing a front bridge motion or the like during core training, a wearer of shoes
(hereinafter simply referred to as a wearer) may take a standing on tiptoe posture.
The expression "standing on tiptoe posture" in the present specification means a posture
in which at least a rearfoot portion of the sole is lifted from the ground under the
condition that a forefoot portion of the sole described later is in contact with the
ground. There is no particular limitation on the angle that the sole makes with the
ground at parts other than the part in contact with the ground.
[0005] If the muscular strength of the wearer's legs is weak, it tends to be difficult to
stably maintain the standing on tiptoe posture. From the viewpoint of supporting the
exercise of the wearer, it is desirable to propose shoe bottoms that allow for good
stability while taking a standing on tiptoe posture. As a result of study based on
such a viewpoint, the inventors of the present invention have come to realize that
there is room for improvement in the shoe bottoms described in Patent Document 1,
as described later in detail.
[0006] One embodiment of the present invention has been made in view of such problems, and
one of the purposes of the invention is to provide shoe bottoms that are capable of
improving the stability of a standing on tiptoe posture.
[MEANS TO SOLVE THE PROBLEM]
[0007] One embodiment of the present invention relates to a shoe bottom that is a shoe bottom
comprising a sole, wherein when a midfoot portion of the sole is divided by a predetermined
sole center line into an medial midfoot region and a lateral midfoot region one on
each side in the foot width direction, the shoe bottom has a rigidity lowering portion
that is provided in the medial midfoot region, and wherein, in such a manner that
the bending rigidity of the medial midfoot region around a foot width direction axis
becomes smaller than that of the lateral midfoot region, the rigidity lowering portion
in the medial midfoot region reduces the bending rigidity of the medial midfoot region
due to another factor other than the shape of the medial edge and the shape of the
lateral edge of the sole in a planar view.
[ADVANTAGE OF THE INVENTION]
[0008] According to the present invention, shoe bottoms that are capable of improving the
stability of a standing on tiptoe posture can be provided.
[BRIEF DESCRIPTION OF THE DRAWINGS]
[0009]
Fig. 1 is a plan view of a sole that serves as one invention example;
Fig. 2 is a plan view showing the skeleton of a foot of a human body;
Figs. 3 are diagrams in which the skeleton of the right foot of a wearer is viewed
from the front side in the foot longitudinal direction; Fig. 3A shows a positional
relationship when the toes and heel of the wearer are in contact with the ground;
Fig. 3B shows a state where a crossing angle is larger compared to the positional
relationship of Fig. 3A;
Figs. 4 are diagrams showing the calcaneocuboid joint surface and talonavicular joint
surface of the right foot of the wearer; Fig. 4A shows a positional relationship when
the toes and heel of the wearer are in contact with the ground; Fig. 4B shows a state
where a crossing angle is larger compared to the positional relationship of Fig. 4A;
Figs. 5 are diagrams for explaining the axis of motion of a Chopart joint; Fig. 5A
is a plan view of the skeleton of the right foot; Fig. 5B is a view of the skeleton
thereof viewed from the medial side in the foot width direction;
Fig. 6 is a bottom view showing another invention example of a sole provided with
rigidity lowering portions;
Fig. 7 is a bottom view of a sole that serves as still another invention example;
Fig. 8 is a perspective view schematically showing a model simulating a sole used
for analysis;
Fig. 9 is a diagram showing the result of the analysis;
Fig. 10 is a diagram for explaining an external torsional resistance expected region;
Fig. 11 is a diagram showing a sole according to a reference example used for the
analysis;
Fig. 12 is a graph showing torsional frequencies obtained by the analysis;
Fig. 13A is a diagram showing the measurement result for torsion angles obtained by
an experiment; Fig. 13B is a diagram showing the measurement result for the amount
of the ankle unstableness;
Fig. 14 is a bottom view of a sole according to a first exemplary variation;
Fig. 15 is a side view of a shoe using a shoe bottom according to a first embodiment
as viewed from the medial side in the foot width direction;
Fig. 16 is a bottom view of a sole according to the first embodiment;
Fig. 17 is a bottom view of a sole according to a second embodiment;
Fig. 18A is a side view of the sole according to the second embodiment as viewed from
the medial side in the foot width direction; Fig. 18B is a side view of the sole viewed
from the lateral side in the foot width direction;
Fig. 19A is a bottom view of a sole according to a second exemplary variation; Fig.
19B is a bottom view of a sole according to a third exemplary variation; Fig. 19C
is a bottom view of a sole according to a fourth exemplary variation;
Fig. 20 is a side view of a shoe bottom according to a third embodiment as viewed
from the same viewpoint as that of Fig. 15; and
Fig. 21 is a side view of a shoe bottom according to a fourth embodiment as viewed
from the same viewpoint as that of Fig. 15.
[MODE FOR CARRYING OUT THE INVENTION]
[0010] Terms used in this specification will be explained. Fig. 1 is a plan view showing
a sole 10, which serves as one invention example. A "foot longitudinal direction Lx"
in the present specification means a direction along a straight line connecting a
tip 10a on the toe side and an end 10b on the heel side of the sole 10. The toe side
in the foot longitudinal direction Lx is also referred to as the front side, and the
heel side is also referred to as the back side. A "foot width direction Y" refers
to a horizontal direction orthogonal to the foot longitudinal direction Lx. A first
toe side of the foot of a wearer supported by the sole 10 is referred to as the medial
side, and a fifth toe side is referred to as the lateral side. A "full length La"
in the foot longitudinal direction Lx is the longest length in the foot longitudinal
direction Lx, and a "full width Lb" in a foot width direction Ly is the longest length
in the foot width direction Ly.
[0011] Fig. 2 is a plan view showing the skeleton of a foot of a human body. The foot of
a human body is mainly composed of cuneiform bones Ba, a cuboid bone Bb, a navicular
bone Bc, a talus Bd, a calcaneus Be, metatarsal bones Bf, and phalanges Bg. The joint
of the foot includes an MP joint Ja, a Lisfranc joint Jb, and a Chopart joint Jc.
The Chopart joint Jc includes a calcaneocuboid joint Jc1 formed by the cuboid bone
Bb and the calcaneus Be and a talonavicular joint Jc2 formed by the navicular bone
Bc and the talus Bd. A "midfoot portion" of a wearer (hereinafter, simply referred
to as a human midfoot portion) in the present specification means the portion from
the MP joint Ja to the Chopart joint Jc.
[0012] Fig. 1 is referred back. A straight line along the foot width direction Y, which
is assumed to pass the heel side end of the MP joint Ja of the wearer, is defined
as a line p. A straight line along the foot width direction Y, which is assumed to
pass the toe side end of the Chopard joint Jc of the wearer, is defined as a line
q. The line p and the line q are, for example, straight lines along the foot width
direction Y that divide the full length La of the sole 10 in the foot longitudinal
direction Lx into 1.5:1.0:1.1 from the toe side to the heel side. A "forefoot portion
12" of the sole 10 in the present specification means a region on the toe side of
the line p, a "midfoot portion 14" (hereinafter simply referred to as a sole midfoot
portion 14) of the sole 10 means a region from the line p to the line q, and a "rearfoot
portion 16" of the sole 10 means a region on the heel side of the line q. The sole
midfoot portion 14 can be also considered to be a region that is assumed to overlap
with the range from the heel side end of the MP joint Ja to the toe side end of the
Chopard joint Jc of the wearer, that is, a range that is assumed to overlap with the
human midfoot portion.
[0013] The background for how the shoe bottom according to the present embodiment has been
conceived of will be explained. As described above, if the muscular strength of the
wearer's legs is weak, it tends to be difficult to stably maintain the standing on
tiptoe posture. Further, if the muscular strength of the wearer's legs is weak, a
decrease in propulsive force in a pushing-off motion during the terminal stance of
a gait cycle is known as a factor for falling down. This wearer is, for example, a
woman, an elderly person, or the like.
[0014] From the viewpoint of solving these problems, the inventors of the present invention
found out, based on the anatomical viewpoint of the foot of the human body, that it
was effective to induce a bony locking mechanism in the human midfoot portion of the
wearer.
[0015] Figs. 3 and 4 are diagrams in which the skeleton of a right foot of the wearer is
viewed from the front side in the foot longitudinal direction Lx. Figs. 3 are external
views of the skeleton, and Figs. 4 are diagrams showing a calcaneocuboid joint surface
Sja and a talonavicular joint surface Sjb of the right foot. Figs. 3A and 4A show
a positional relationship when the toes and heel of the wearer are in contact with
the ground, and Figs. 3B and 4B show a state where a crossing angle θc described later
is larger compared to the positional relationship of Figs. 3A and 4A, respectively.
The crossing angle between a joint axis Aj1 of the calcaneocuboid joint Jc1 of the
Chopart joint Jc viewed from the front in the foot longitudinal direction Lx and a
joint axis Aj2 of the talonavicular joint Jc2 is defined to be θc.
[0016] Figs. 5 are a diagram for explaining the axis of motion of the Chopart joint Jc.
Fig. 5A is a plan view of the skeleton of the right foot, and Fig. 5B is a view of
the skeleton thereof viewed from the medial side in the foot width direction. The
Chopart joint Jc has a longitudinal axis and a clinoaxis as two axes of motion, of
which the longitudinal axis serves as the joint axis Aj1 of the calcaneocuboid joint
Jc1 and the clinoaxis serves as the joint axis Aj2 of the talonavicular joint Jc2.
Although there are individual differences in terms of a skeleton, in general, the
calcaneocuboid joint Jc1 is an axis obtained by tilting the toe side inward by 9 degrees
in the foot width direction with respect to the horizontal plane and tilting the toe
side upward by 15 degrees with respect to the sagittal plane, based on the state where
the toe and the heel are in contact with the ground. Normally, the talonavicular joint
Jc2 is an axis obtained by tilting the toe side inward by 57 degrees in the foot width
direction with respect to the horizontal plane and tilting the toe side upward by
52 degrees with respect to the sagittal plane, based on the state where the toe and
the heel are in contact with the ground.
[0017] As shown in Fig. 3B, the bony locking mechanism is realized when the crossing angle
θc is increased to a certain extent compared to that obtained when the wearer's toe
and heel are in contact with the ground. Due to an increase in this crossing angle
θc, the mobility of the Chopart joint Jc is reduced compared with a case where the
crossing angle θc is small, and the Chopart joint Jc can be turned into a rigid body.
This allows unstable between a plurality of bones constituting the Chopart joint Jc
to be prevented when taking a standing on tiptoe posture, and the stability of the
standing on tiptoe posture can be improved. Further, as a result of turning the Chopart
joint Jc into a rigid body, the propulsive force transmission between the plurality
of bones constituting the Chopart joint Jc becomes smooth, and the propulsive force
in the pushing-off motion can be improved.
[0018] The crossing angle θc of the plurality of joint axes forming the Chopart joint Jc
described above is known to increase as the amount of external torsion at the human
midfoot portion increases. Therefore, in inducing the bony locking mechanism, it is
necessary to increase the amount of external torsion at the human midfoot portion.
The external torsion means that the heel is twisted in the supination direction with
respect to the toes based on the positional relationship obtained when the toes and
heel of the human body are in contact with the ground. The present inventors have
found that it is preferable to satisfy the following condition in order to achieve
such an increase in the amount of external torsion at the human midfoot portion.
[0019] When the human midfoot portion is attempted to be twisted outward (external torsion),
the sole 10 is also attempted to be twisted outward in a range including the sole
midfoot portion 14 following the deformation of the human midfoot portion. Therefore,
in order to increase the amount of external torsion at the human midfoot portion,
it is desirable to reduce the external torsional resistance of the sole 10 within
the range including the sole midfoot portion 14.
[0020] In order to respond to such a demand, the inventors of the present invention found
out that it is effective to provide a rigidity lowering portion 32 for lowering the
bending rigidity around a foot width direction axis (hereinafter, simply referred
to as "bending rigidity") in an medial midfoot region 20 of the sole midfoot portion
14, as shown in Fig. 1. The medial midfoot region 20 means a region located on the
medial side when the sole midfoot portion 14 is divided into two regions one on each
side in the foot width direction by a predetermined sole center line s. Of these two
regions, the region located on the lateral side is referred to as a lateral midfoot
region 22.
[0021] This sole center line s is defined as a line passing through the center part of the
sole 10 in the foot width direction Y. In this example, a straight line along the
foot longitudinal direction X that divides the full width Lb of the sole 10 into 1.2:1.0
from the medial side to the lateral side in the foot width direction is defined as
the sole center line s. The sole center line s in this example is also a part on which
a foot width direction center part of the foot of the wearer is assumed to be located.
The foot width direction center part is assumed to be a part located on a straight
line passing through a third metatarsal bone Bf3 and a medial process of calcaneal
tuberosity Be1 of the calcaneus Be of a human body. Fig. 1 shows a range in which
the medial process of calcaneal tuberosity Be1 is assumed to be located.
[0022] Rigidity lowering portions 32 of the medial midfoot region 20 reduce the bending
rigidity of the medial midfoot region 20 such that the bending rigidity of the medial
midfoot region 20 becomes smaller than that of the lateral midfoot region 22. The
expression "the bending rigidity of the medial midfoot region 20 becomes smaller than
that of the lateral midfoot region 22" includes the following two cases. The first
case is a case where, in the lateral midfoot region 22 and the medial midfoot region
20, only the bending rigidity of the medial midfoot region 20 is reduced. The second
case is a case where, when reducing the bending rigidity of both the lateral midfoot
region 22 and the medial midfoot region 20, the amount of decrease in the bending
rigidity in the medial midfoot region 20 is set to be larger than that in the lateral
midfoot region 22.
[0023] The rigidity lowering portions 32 in the medial midfoot region 20 reduce the bending
rigidity of the medial midfoot region 20 due to another factor other than the shape
of an medial edge 10c and the shape of a lateral edge 10d of the sole 10 in a planar
view. This "another factor" is, for example, any one or a combination of two of recessed
portions that are open on the ground contact surface of the sole 10 and the elongation
characteristic of the material constituting the sole 10 such as those explained in
the following.
[0024] The expression "recessed portions that are open on the ground contact surface of
the sole 10" means those that are recessed upward from the ground contact surface
of the sole 10, which comes into contact with the road surface. The recessed portions
may be groove portions continuous in the in-plane direction of a ground contact surface
10e of the sole 10 or may not be continuous in the in-plane direction thereof. Fig.
6 is a bottom view showing another invention example of the sole 10 provided with
rigidity lowering portions 32. When the recessed portions constituting the rigidity
lowering portion 32 are not continuous in the in-plane direction, the recessed portions
may be provided intermittently so as to be aligned on a virtual line such as a straight
line, a curved line or the like. As the recessed portions, Fig. 1 shows medial transverse
groove portions 34 extending from the medial edge 10c of the sole 10 in the foot width
direction Y. When such recessed portions are provided in the medial midfoot region
20, the bending rigidity of the medial midfoot region 20 can be lowered compared to
that in a case where such recessed portions do not exist. The bending rigidity of
the medial midfoot region 20 being reduced due to the recessed portions means such
a situation. When the recessed portions are the medial transverse groove portions
34, the bending rigidity can be effectively reduced.
[0025] Further, the expression "the elongation characteristic of the material constituting
the sole 10" means, specifically, the Young's modulus [N/mm
2] in the foot longitudinal direction X of the material constituting the sole 10. The
rigidity lowering portions 32 are formed using a second material having a smaller
Young's modulus in the foot longitudinal direction X than that of a first material
constituting portions adjacent to the rigidity lowering portions 32 of the sole 10.
This allows the bending rigidity of the medial midfoot region 20 to be lowered compared
to a case where the rigidity lowering portions 32 are formed using the first material.
The bending rigidity of the medial midfoot region 20 being reduced due to the elongation
characteristic of the material constituting the sole 10 means such a situation.
[0026] On the medial edge 10c of the sole midfoot portion 14, a curved-in part 10f recessed
outward in the foot width direction X is formed. The bending rigidity of the medial
midfoot region 20 of the sole 10 is often smaller than the bending rigidity of lateral
midfoot region 22 due to the influence of the curved-in part 10f. In order to exclude
the influence of this curved-in part 10f, the shape of the medial edge 10c and the
lateral edge 10d of the sole 10 in a planar view is excluded from the above-mentioned
factors, which cause a decrease in bending rigidity.
[0027] By providing such a rigidity lowering portion 32 in the medial midfoot region 20,
it is easier to lower the bending rigidity of the medial midfoot region 20 than that
of the lateral midfoot region 22 as compared with the case where the rigidity lowering
portion 32 is not provided. As the bending rigidity of the medial midfoot region 20
is lowered compared to that of the lateral midfoot region 22, the elongation amount
of the medial midfoot region 20 at the ground contact surface can be increased compared
to that of the lateral midfoot region 22 when the sole 10 is bendingly deformed around
the foot width direction axis. This means that when the wearer is taking a standing
on tiptoe posture, the medial midfoot region 20 can be more easily deformed in an
extended manner in the foot longitudinal direction X than the lateral midfoot region
22, that is, the medial midfoot region 20 tends to be easily twisted outward. In other
words, it means that external torsional resistance at the sole midfoot portion 14
can be lowered compared with the case where an medial midfoot region 20 is not provided
with a rigidity lowering portion 32. Therefore, by providing a rigidity lowering portion
32 in the medial midfoot region 20, when the wearer attempts to twist his/her human
midfoot portion while taking a standing on tiptoe posture, the amount of external
torsion can be increased compared to the case where a rigidity lowering portion 32
is not provided. As a result, it is possible to induce the bony locking mechanism
and thus improve the stability of the standing on tiptoe posture and improve the propulsive
force in the pushing-off motion.
[0028] The medial midfoot region 20 is formed such that the bending rigidity thereof is
smaller than that of the lateral midfoot region 22. This is realized by providing
a rigidity lowering portion 32 in the medial midfoot region 20 or due to the shape
of the medial edge 10c or the lateral edge 10d of the sole 10 in a planar view. These
bending rigidities may be evaluated based on the strain amount of the ground contact
surface in the foot longitudinal direction obtained when a bending moment of a predetermined
size around the foot width direction axis is applied toward the upper surface of the
sole at a toe side end portion and a heel side end portion of the midfoot region being
mentioned. It means that the bending rigidity becomes small as this strain amount
increases. The bending rigidity of the medial midfoot region 20 being smaller than
that of the lateral midfoot region 22 means that the strain amount in the medial midfoot
region 20 is larger than the strain amount in the lateral midfoot region 22. The strain
amount may be acquired by actually cutting out the midfoot region being mentioned
from the sole 10 and measuring the strain amount using the piece that has been cut
out.
[0029] Further, as described above, the line q indicates a portion where the Chopard joint
of the foot of the wearer is assumed to be located. As a rigidity lowering portion
32 is located closer to this line q, the sole midfoot portion 14 becomes more likely
to be twisted outward at a location closer to the Chopart joint Jc, and the bony locking
mechanism is more likely to be induced accordingly. Therefore, the rigidity lowering
portion 32 is preferably provided in a region on the heel side of a straight line
y along the foot width direction Y, which bisects the full length of the sole midfoot
portion 14 in the foot longitudinal direction, in the medial midfoot region 20 of
the sole midfoot portion 14.
[0030] During the standing on tiptoe posture, a load for twisting the sole 10 outward is
applied to the sole 10 via the upper of the shoe in a state where the forefoot portion
12 of the sole 10 is restrained. At this time, the toe side end portion of the sole
midfoot portion 14 is fixed, and an external torsion load is applied to the heel side
end portion thereof. At this time, the most deformed portion of the sole midfoot portion
14 is a region on the toe side of the sole midfoot portion 14 close to the forefoot
portion 12 restrained in the sole 10. In this region on the toe side of the sole midfoot
portion 14, it is possible to effectively twist the sole midfoot portion 14 outward
by having different bending rigidity on the medial side and the lateral side in the
foot width direction of the sole midfoot portion 14. Therefore, the rigidity lowering
portion 32 is also preferably provided in the region on the toe side of the straight
line y bisecting the sole midfoot portion 14 in the foot width direction.
[0031] Next, another condition will be described that is preferably satisfied in order to
increase the amount of external torsion at the human midfoot portion. A case is taken
into consideration where an external torsional load for twisting the sole 10 outward
is applied to the sole 10 via the upper of the shoe when the wearer is taking a standing
on tiptoe posture. A case is taken into consideration where a transverse groove portion
extending from the medial edge 10c to the lateral edge 10d is formed in the rearfoot
portion 16 of the sole 10. In this case, even when the external torsional load described
above is applied to the sole 10, the bending deformation at the transverse groove
portion of the rearfoot portion 16 thereof becomes dominant, and the amount of external
torsion at the sole midfoot portion 14 becomes small. As a result, when the wearer
attempts to twist his/her human midfoot portion outward while taking a standing on
tiptoe posture, it is difficult to increase the amount of external torsion at the
human midfoot portion due to resistance from parts other than the sole midfoot portion
14.
[0032] Fig. 7 is a bottom view showing a sole 10, which serves as another invention example.
In order to solve the above problems, as another condition, it is defined that a continuous
surface 16c continuous in the foot longitudinal direction from a toe side end portion
16a to a heel side end portion 16b of a rearfoot portion 16 of the sole 10 is formed
on the ground contact surface of the sole 10. In this figure, the range in which the
continuous surface 16c is formed is indicated by hatching with two-dot chain lines.
This means that a transverse groove portion extending from an medial edge 10c to a
lateral edge 10d is not formed in the rearfoot portion 16 of the sole 10. In the illustrated
example, this continuous surface 16c is formed in the entire range in the foot width
direction Y; however, the continuous surface 16c may be formed in at least a part
of the range in the foot width direction Y.
[0033] Thereby, when the wearer attempts to twist the midfoot portion outward while taking
a standing on tiptoe posture, the bending deformation of the sole 10 at the rearfoot
portion 16 can be suppressed by the continuous surface 16c, and a situation can be
prevented where the amount of external torsion at the sole midfoot portion 14 becomes
small in accordance with the bending deformation. Accordingly, by satisfying the above-mentioned
conditions, it becomes easier to obtain the effect of reducing the external torsional
resistance at the sole midfoot portion 14, and it thus becomes easier to increase
the amount of external torsion at the human midfoot portion.
[0034] When a reinforcing member such as a shank is attached to the sole midfoot portion
14, the bending rigidity of the shoe bottom becomes excessively increased, and the
external torsional resistance of the sole midfoot portion 14 thus becomes excessively
increased. Therefore, in the shoe bottom according to the present embodiment, a reinforcing
member such as a shank is preferably not attached to the sole midfoot portion 14.
This prevents an excessive increase in the bending rigidity of the sole midfoot portion
14 and allows the external torsional resistance of the sole midfoot portion 14 to
be easily reduced.
[0035] The reinforcing member used in this case is those other than a midsole 56 and an
outer sole 58 of the sole 10 described later. This reinforcing member is used, for
example, for enhancing bending rigidity around the foot width direction axis of the
shoe bottom just like a shank or the like and is formed using a material whose hardness
is larger than the maximum hardness of the sole 10. This material is, for example,
various metals or synthetic resins having a JIS A hardness of 80 degrees or more.
The JIS A hardness is a value obtained by measurement using an A type hardness meter
in compliance with JIS K 6301. The hardness of the midsole 56 is, for example, 35
to 75 degrees in terms of JIS C hardness, and the hardness of the outer sole 58 is,
for example, 50 to 75 degrees in terms of JIS A hardness. The JIS C hardness is a
value obtained by measurement using a C type hardness meter in compliance with JIS
K 6301.
[0036] Even when the reinforcing member is not attached to the sole midfoot portion 14,
a reinforcing member may be attached to the sole forefoot portion 12 and the sole
rearfoot portion 16. Even under this configuration, the external torsional resistance
of the sole midfoot portion 14 can be easily reduced.
[0037] Next, an analysis performed for coming up with the shoe bottom according to the embodiment
will be explained. Fig. 8 is a perspective view schematically showing a model simulating
a sole 10 used for the analysis. In this analysis, a sole having the same size as
that of the sole 10 shown in Fig. 7 was used. The sole 10 had a full length La of
280 mm, a full width Lb of 200 mm, and a uniform thickness of 20 mm. The physical
conditions of the sole 10 were set to have a Young's modulus of 6 [N/mm
2], a Poisson's ratio of 0.25 [-], and a density of 3 x 10
2 [kg/m
3]. It is assumed that this analysis reproduce the deformed state of the sole 10 during
a front bridge motion. For this reason, a region Sa in which the ball of foot of the
toes of the wearer were assumed to hit was completely restrained, and an upward load
Fz was applied to the rearfoot portion 16 of the sole 10. In order to apply an external
torsional load to the sole 10, a load Fy directed outward in the foot width direction
Y was applied to the rearfoot portion 16 of the sole 10.
[0038] Fig. 9 is a diagram showing the result of this analysis. In this figure, the distribution
of the maximum principal stress at the bottom surface of the sole 10 obtained under
the above-described conditions is shown. The higher the density of dots, the greater
the stress. It can be confirmed that when the external torsional load is applied to
the sole 10, the stress becomes larger in a region 24, which includes the medial midfoot
region 20 and the peripheral region of the sole 10, than those in other regions. This
means that this region 24 is strongly resisting the external torsion of the sole midfoot
portion 14. Therefore, it is considered that the external torsion at the sole midfoot
portion 14 can be effectively reduced by providing a rigidity lowering portion 32
in the foregoing region 24 (hereinafter referred to as an external torsional resistance
expected region 24), which is assumed to be resisting the external torsion of the
sole midfoot portion 14. Therefore, as a region in which a rigidity lowering portion
is preferably provided, the external torsional resistance expected region 24 obtained
by this analysis is used.
[0039] Fig. 10 is a diagram for explaining the external torsional resistance expected region
24. The external torsional resistance expected region 24 is geometrically specified
in relation to the shape of the sole 10. Hereinafter, an explanation will be given
with reference to the positional relationship of the sole 10 in the planar view.
[0040] The definition of a line s, a line p, and a line q is the same as the definition
described above. A straight line along the foot width direction Y that divides a region
on the heel side of the line q of the sole 10 into 0.2:0.9 is defined as a line r.
Being viewed from a point o1, which is the intersection point of the line p and the
line s, a straight line obtained by rotating the line p by 13 degrees around the point
o1 in an outward direction Pa, which rotates the toe side outward in the foot width
direction, is defined as a line t. Being viewed from the point o1, which is the intersection
point of the line s and the line p, a straight line obtained by rotating the toe side
of the line s by 8 degrees around the point o1 in the aforementioned outward direction
Pa is defined as a line u. Being viewed from a point o2, which is the intersection
point of the line u and the line q, a straight line obtained by rotating the line
q by 5 degrees around the point o2 in the outward direction Pa is defined as a line
v. Being viewed from a point P, which is the intersection point of the line r and
the line u, a straight line obtained by rotating the line r by 4 degrees around the
point P in the outward direction Pa is defined as a line w. A straight line connecting
a point o5, which is the intersection point of the medial edge 10c of the sole 10
and the line w, and the point o2 is defined as a line x.
[0041] At this time, the external torsional resistance expected region 24 is defined to
be formed of a first region 26 surrounded by the line t, the line u, the line v, and
the medial edge 10c of the sole 10. This external torsional resistance expected region
24 is provided on the ground contact surface of the sole 10 in the planar view of
the sole 10. A rigidity lowering portion 32 is preferably provided in the foregoing
external torsional resistance expected region 24. It is considered that by providing
the rigidity lowering portion 32 in this external torsional resistance expected region
24, the external torsional resistance of the sole midfoot portion 14 can be effectively
reduced.
[0042] The rigidity lowering portion 32 is preferably provided in a part (the part indicated
by a range S1) that belongs to the external torsional resistance expected region 24
outside the medial midfoot region 20, other than the part that belongs to the external
torsional resistance expected region 24 in the medial midfoot region 20. The rigidity
lowering portion 32 provided in the part belonging to the external torsional resistance
expected region 24 outside the range of the medial midfoot region 20 also lowers the
bending rigidity of the part due to a recessed portion that is open on the ground
contact surface of the sole 10, the elongation characteristic of the material constituting
the sole 10, and the like.
[0043] Referring to the analysis result of Fig. 9, the first region 26 defined as the external
torsional resistance expected region 24 of the sole 10 mainly spreads largely in a
direction Lb heading toward the heel side of the foot longitudinal direction Lx. Further,
the first region 26 also spreads somewhat in a direction Lc heading toward the outside
in the foot width direction Y. This analysis is intended for a front bridge motion.
It is expected that a larger external torsional load will be applied to the sole 10
in other motions such as running or the like. If a large load is applied to the sole
10, the external torsional resistance expected region 24 is considered to first spread
in the direction Lb heading toward the heel side in the foot longitudinal direction
Lx. Further, the external torsional resistance expected region 24 is considered to
spread in the direction Lc heading toward the outside in the foot width direction
Y in an extent smaller than how the external torsional resistance expected region
24 spreads toward the heel side of the foot longitudinal direction Lx.
[0044] Therefore, as shown in Fig. 10, the external torsional resistance expected region
24 may be defined to be formed of the first region 26 and a second region 28 surrounded
by the line v, the line x, and the medial edge 10c of the sole 10 in planar view.
It is considered that by providing the rigidity lowering portion 32 in the foregoing
external torsional resistance expected region 24, the external torsional resistance
of the sole midfoot portion 14 can be effectively reduced when a large external torsional
load is applied to the sole 10.
[0045] This rigidity lowering portion 32 is also preferably provided in parts (the range
S1 and the part indicated by a range S2) that belong to the external torsional resistance
expected region 24 outside the medial midfoot region 20, other than the part that
belongs to the external torsional resistance expected region 24 in the medial midfoot
region 20.
[0046] Further, the external torsional resistance expected region 24 may be defined to be
formed of the first region 26, the second region 28, and a third region 30 surrounded
by the line s, the line u, the line x, and the line w in planar view. It is considered
that by providing the rigidity lowering portion 32 in the foregoing external torsional
resistance expected region 24, the external torsional resistance of the sole midfoot
portion 14 can be effectively reduced when a larger external torsional load is applied
to the sole 10.
[0047] This rigidity lowering portion 32 is also preferably provided in parts (the range
S1, the range S2, and the part indicated by a range S3) that belong to the external
torsional resistance expected region 24 outside the medial midfoot region 20, other
than the part that belongs to the external torsional resistance expected region 24
in the medial midfoot region 20.
[0048] Next, the effects of the invention based on the presence or absence of the above-described
conditions will be explained using analysis. Fig. 11 shows a sole 100 of a reference
example used for the analysis. The sole 10 according to an exemplary embodiment is
shown in Fig. 7. The dimensional conditions and physical conditions of the soles 10
and 100 were set to be the same as those in the analysis of Fig. 8.
[0049] In each of the sole 100 according to the reference example and the sole 10 according
to the exemplary embodiment, a transverse groove portion 40 is provided at a part
corresponding to the MP joint in the forefoot portion 12 of the sole such that the
sole is bent at the forefoot portion 12 of the sole around the foot width direction
axis during a standing on tiptoe posture. In the sole 10 according to the exemplary
embodiment, two medial transverse groove portions 34 are provided as rigidity lowering
portions 32 that lower the bending rigidity of the medial midfoot region 20. Further,
in the sole 10 according to the exemplary embodiment, one more medial transverse groove
portion 34 is provided as a rigidity lowering portion 32 that lowers the bending rigidity
of the external torsional resistance expected region 24 in the part S1 located outside
the range of the medial midfoot region 20. The three medial transverse groove portions
34 extend in the foot width direction Y from the medial edge 10c of the sole 10 and
are provided at intervals in the foot longitudinal direction Lx. No similar rigidity
lowering portion 32 is provided in the sole midfoot portion 14 according to the reference
example.
[0050] The respective deformation characteristics of the soles 10 and 100 with respect to
external torsion were evaluated by eigenvalue analysis. More specifically, the respective
torsional frequencies, which were the respective natural frequencies occurring when
the characteristic vibration mode of the soles 10 and 100 was torsional vibration,
were obtained by the eigenvalue analysis, and the deformation characteristics of the
soles 10 and 100 were evaluated using the respective torsional frequencies. It means
that the smaller the torsional frequencies become, the smaller the respective external
torsional resistances of the soles 10 and 100 become.
[0051] Fig. 12 is a graph showing the torsional frequencies obtained by this analysis. As
shown in this figure, the torsional frequency of the sole 10 according to the exemplary
embodiment was smaller than that of the sole 100 according to the reference example.
This indicates that the sole 10 according to the exemplary embodiment had smaller
external torsional resistance than the sole 100 according to the reference example.
[0052] Next, the effects of the invention based on the presence or absence of the above-described
conditions will be explained using an experiment example. In this experiment, a sole
whose size and physical properties as the same as those of the two types of soles
shown in Figs. 7 and 11 was used. In this experiment, shoes using these soles were
worn. Using these shoes, the wearer kept a posture for 40 seconds where the wearer
focused on keeping his/her body torso lifted from the ground contact surface while
having his/her elbows touching the ground and having the respective forefoot portions
12 of the soles touching the ground such that the body parts from the head to the
heel became straight.
[0053] The result of this experiment was evaluated using the torsion angle of the sole midfoot
portion 14 and the amount of the ankle unstableness of the wearer. Using a motion
capture system, this torsion angle was measured by acquiring three-dimensional positional
information of markers attached to a plurality of parts of the sole 10. This torsion
angle is defined as the angle formed by the ground contact surface of the sole midfoot
portion with respect to the ground contact surface of the sole rearfoot portion. In
the same way as in the torsion angle, the amount of the ankle unstableness of the
wearer was also measured by acquiring three-dimensional positional information of
markers attached to the ankle.
[0054] Fig. 13A shows the measurement result for torsion angles obtained by the experiment,
and Fig. 13B shows the measurement result for the amount of the ankle unstableness.
As compared with the sole 100 according to the reference example, it can be confirmed
that the sole 10 according to the exemplary embodiment had a larger torsion angle
of the sole midfoot portion 14. Based on this, it can be confirmed that the sole 10
according to the exemplary embodiment had smaller external torsional resistance than
the sole 100 according to the reference example. Further, it can be confirmed that
the sole 10 according to the exemplary embodiment had a smaller amount of the ankle
unstableness than the sole 100 according to the reference example. Based on this,
it can be confirmed that good stability can be obtained during a take standing on
tiptoe posture by the shoe using the sole 10 according to the example. This is considered
to be due to the bony locking mechanism being able to be induced in accordance with
an increase in the torsion angle of the sole midfoot portion 14, as described above.
[0055] Fig. 14 is a bottom view showing a sole 10 according to a first exemplary variation.
Lateral transverse groove portions 44, which are open on the ground contact surface
10e of the sole 10 and extend from the lateral edge 10d of the sole 10 in the foot
width direction Y, are formed in the sole midfoot portion 14 and the rearfoot portion
16 of the sole 10 according to the first exemplary variation. In this case, the bending
rigidity decreases in a range including a lateral midfoot region 22 of the sole 10.
In accordance with this, it is difficult to provide a sufficient difference in bending
rigidity between the medial midfoot region 20 and a lateral midfoot region 22 of the
sole 10. In order to sufficiently obtain the effect of reducing the external torsional
resistance at the sole midfoot portion 14, this difference in the bending rigidity
is preferably as large as possible.
[0056] Therefore, the lateral transverse groove portions 44 extending from the lateral edge
10d of the sole 10 in the foot width direction Y are preferably not formed in a partial
range Sb of the sole 10 in the foot longitudinal direction X. The partial range Sb
includes a range Sb1 in the foot longitudinal direction X where all rigidity lowering
portions 32 are provided and all of a range Sb2 on the heel side of the range Sb1.
This allows a sufficient difference in bending rigidity to be provided between the
medial midfoot region 20 and the lateral midfoot region 22 of the sole 10, and the
effect of reducing the external torsional resistance at the sole midfoot portion 14
can thus be more easily obtained. From the same point of view, it can be considered
that the lateral transverse groove portions 44 are preferably not formed in a range
Sc, which is located on the heel side of the line y described above.
(First Embodiment)
[0057] Fig. 15 is a side view of a shoe 52 using a shoe bottom 50 according to a first embodiment
as viewed from the medial side in the foot width direction. The shoe 52 is used, for
example, for exercise in a room such as a gym; however, the usage thereof is not particularly
limited. The shoe 52 includes a shoe bottom 50, which supports the wearer's foot,
and an upper 54, which covers the wearer's foot.
[0058] The shoe bottom 50 includes a sole 10. The sole 10 according to the present embodiment
includes a midsole 56. The sole 10 has a ground contact surface 10e, which comes into
contact with the road surface. The ground contact surface 10e according to the present
embodiment is formed by the lower surface of the midsole 56. The midsole 56 mainly
has a role of alleviating the impact of landing. The midsole 56 is formed using, for
example, a foam or non-foam resin, or the like.
[0059] Fig. 16 is a bottom view of the sole 10. A plurality of medial transverse groove
portions 34 are formed on the sole 10. The plurality of medial transverse groove portions
34 are formed so as to be open on the ground contact surface 10e of the sole 10 and
to extend in the in-plane direction of the ground contact surface 10e. The plurality
of medial transverse groove portions 34 extend in the foot width direction Y from
the medial edge 10c of the sole 10 toward the lateral edge 10d. The plurality of medial
transverse groove portions 34 are provided at intervals in the leg longitudinal direction
Lx. The respective end portions of the plurality of medial transverse groove portions
34 on the lateral side in the foot width direction Y are provided at intermediate
positions in the foot width direction Y of the sole 10.
[0060] The extending direction of the medial transverse groove portions 34 is set to be
a direction oblique to the foot width direction axis. More specifically, the extending
direction is set to be a direction that is the same as the direction along a line
t in the planar view. As shown in Fig. 2, this direction along the line t is a direction
that is the same as the direction along a straight line Ld connecting the rear end
portion of the first metatarsal bone Bf1 to the rear end portion of the fifth metatarsal
bone Bf5 constituting the Lisfranc joint Jb. The expression "the same" includes not
only the case where the directions are the same as interpreted literally but also
the case where the directions are almost the same. When this condition is satisfied,
the heel side end portion of the sole 10 easily turns in the supination direction,
and as a result, the sole midfoot portion 14 can be easily twisted outward.
[0061] The depth of the medial transverse groove portions 34 from the ground contact surface
10e is preferably as deep as possible from the viewpoint of effectively reducing the
bending rigidity of the medial midfoot region 20 of the sole 10. From this viewpoint,
the depth of the medial transverse groove portions 34 is preferably 1% or more, more
preferably 5% or more, and particularly preferably 10% or more, with respect to the
average thickness of the entire sole 10.
[0062] The groove width of the medial transverse groove portions 34 is preferably 1 mm or
more. The groove width means the opening width of the medial transverse groove portions
34 at the ground contact surface 10e of the sole 10. The groove width is set to 1
mm or more in order to effectively reduce the bending rigidity of the medial midfoot
region 20 of the sole 10. Although the upper limit value of the groove width is not
particularly limited, the groove width is preferably, for example, 20 mm or less.
[0063] An example is shown in which the shape of the medial transverse groove portions 34
is a straight line shape extending in the in-plane direction; however, the shape is
not limited thereto. For example, a curved shape extending in the in-plane direction
or a shape such as a combination of a straight line and a curved line may be employed.
[0064] Each of the plurality of medial transverse groove portions 34 constitutes a rigidity
lowering portion 32, which lowers the bending rigidity of the medial midfoot region
20. A plurality of rigidity lowering portions 32 are thus provided. One medial transverse
groove portion 34, which is a part of the plurality of medial transverse groove portions
34, is formed so as to extend from the medial midfoot region 20 to the lateral midfoot
region 22. As described above, the rigidity lowering portions 32 are assumed to be
provided in the medial midfoot region 20; however, the rigidity lowering portions
32 may be provided such that a portion of the rigidity lowering portions 32 extends
over the lateral midfoot region 22. Further, the plurality of rigidity lowering portions
32 are formed so as to be located on the first region 26, the second region 28, and
the third region 30 of the external torsional resistance expected region 24, respectively.
Even when the rigidity lowering portions 32 are provided in the external torsional
resistance expected region 24 as described above, the rigidity lowering portions 32
may be provided so as to extend outside the external torsional resistance expected
region 24.
(Second Embodiment)
[0065] Fig. 17 is a bottom view showing a sole 10 according to a second embodiment. Fig.
18A is a side view of the sole 10 viewed from the medial side in the foot width direction,
and Fig. 18B is a side view of the sole 10 viewed from the lateral side in the foot
width direction.
[0066] The sole 10 according to the second embodiment has a longitudinal groove portion
36 extending in the foot longitudinal direction X in addition to a plurality of medial
transverse groove portions 34. The longitudinal groove portion 36 is open on the ground
contact surface 10e of the sole 10. The longitudinal groove portion 36 is connected
to the end portion on the lateral side in the foot width direction of each of the
plurality of medial transverse groove portions 34. The longitudinal groove portion
36 according to the present embodiment is provided so as to fit in an medial midfoot
region 20 and is not provided in a lateral midfoot region 22.
[0067] The longitudinal groove portion 36 according to the present embodiment has a heel
side portion 36b provided on the heel side of an intermediate portion 36a in the foot
longitudinal direction X thereof and a toe side portion 36c provided on the toe side
of the intermediate portion 36b. The intermediate portion 36a of the longitudinal
groove portion 36 according to the present embodiment is provided so as to form a
convex shape toward the lateral side in the foot width direction. The heel side portion
36b is provided being inclined with respect to the foot longitudinal axis so as to
become closer to the medial edge 10c of the sole 10 toward the heel side of the sole
10. The distal end portion of the heel side portion 36b connects with the medial edge
10c of the sole 10. The toe side portion 36c is provided being inclined with respect
to the foot longitudinal axis so as to become closer to the medial edge 10c of the
sole 10 toward the toe side of the sole 10. The distal end portion of the toe side
portion 36c connects with the medial edge 10c of the sole 10. The longitudinal groove
portion 36 is provided such that a part of the range thereof that extends from the
intermediate portion 36a to the heel side overlaps with a line u.
[0068] A plurality of island-like regions 38 surrounded by the plurality of medial transverse
groove portions 34, the longitudinal groove portion 36, and the medial edge 10c of
the sole 10 are formed in the medial midfoot region 20 of the sole 10. The island-like
regions 38 are separated from the other region including the lateral midfoot region
22 of the sole 10 by a groove portion including the longitudinal groove portion 36.
The "groove portion including the longitudinal groove portion 36" in the present embodiment
refers to only the longitudinal groove portion 36. If the longitudinal groove portion
36 does not connect with the medial edge 10c of the sole 10, the medial transverse
groove portion 34 closest to the toes or the heel is also included. It can be considered
that the island-like regions 38 are separated from the region including the lateral
midfoot region 22 by the groove portion including the longitudinal groove portion
described above.
[0069] Thereby, when the medial midfoot region 20 is attempted to be bent and deformed at
a part where the plurality of medial transverse groove portions 34 are formed, the
deformation of the plurality of medial transverse groove portions 34 is prevented
from influencing the lateral midfoot region 22 side of the longitudinal groove portion
36. Therefore, it becomes easier to design such that the bending rigidity of the medial
midfoot region 20 and the bending rigidity of the lateral midfoot region 22 are different
from each other.
[0070] The groove width of the longitudinal groove portion 36 is set to be larger than the
respective groove widths of the medial transverse groove portions 34. The medial transverse
groove portion 34 that connects with the end portion of the longitudinal groove portion
36 and is the closest to the toes is also set to be larger than the respective groove
widths of the other medial transverse groove portions 34.
[0071] A plurality of second transverse groove portions 42 are formed in a forefoot portion
12 and a midfoot portion 14 of the sole 10 according to the second embodiment. The
plurality of second transverse groove portions 42 are provided at intervals in the
leg longitudinal direction Lx. Some second transverse groove portions 42 of the plurality
of second transverse groove portions 42 are provided so as to reach the medial edge
10c from the lateral edge 10d of the sole 10. The other second transverse groove portions
42 of the plurality of second transverse groove portions 42 are provided so as to
extend toward the medial edge 10c from the lateral edge 10d of the sole 10. The respective
end portions of the other second transverse groove portions 42 are provided at intermediate
positions in the foot width direction of the sole 10. Any of the second transverse
groove portions 42 is provided on the toe side of the above-described line y.
[0072] Fig. 19A is a bottom view of a sole 10 according to a second exemplary variation.
Fig. 19B is a bottom view of a sole 10 according to a third exemplary variation. Fig.
19C is a bottom view of a sole 10 according to a fourth exemplary variation. Regarding
the longitudinal groove portion 36 in the example of Fig. 17, an example has been
explained where both end portions of the longitudinal groove portion 36 connect with
the medial edge 10c of the sole 10. Both end portions of the longitudinal groove portion
36 according to the present example are provided at locations away from the medial
edge 10c of the sole 10 in the foot width direction. In the longitudinal groove portion
36 according to the present example, the end portions of the medial transverse groove
portions 34 and the end portions of the longitudinal groove portion 36 are connected
so as to form corner portions with the medial transverse groove portions 34. In addition
to this, the end portions of the longitudinal groove portion 36 may be provided so
as to end without connecting with other groove portions.
[0073] Fig. 19A shows an example where a single longitudinal groove portion 36 is provided,
and Fig. 19B shows an example where a plurality of longitudinal groove portions 36-A
and 36-B (hereinafter, generically referred to as longitudinal groove portions 36).
The plurality of longitudinal groove portions 36-A and 36-B include a first longitudinal
groove portion 36-A on the lateral side in the foot width direction and a second longitudinal
groove portion 36-B on the medial side in the foot width direction. The first longitudinal
groove portion 36-A is provided so as to connect with end portions of the plurality
of medial transverse groove portions 34. The second longitudinal groove portion 36-B
is provided so as to connect with intermediate portions of the plurality of medial
transverse groove portions 34 such that the second longitudinal groove portion 36-B
intersect with the intermediate portions in a T-shape or X-shape.
[0074] Figs. 19A and 19B show examples where the respective longitudinal groove portions
36 are provided so as to extend in a linear manner along the respective lines s, and
in Fig. 19C shows an example where the longitudinal groove portion 36 is provided
so as to extend in a linear manner along the line u. The expression "linear" means
a shape looking like a straight line and does not mean a strictly linear shape in
a geometrical manner. An extending direction Pb in which the linear longitudinal groove
portion 36 extends from the toe side to the heel side as described above is set to
have, for example, an angle formed by the direction axis thereof with respect to the
line s of from 0 to 15 degrees.
(Third Embodiment)
[0075] Fig. 20 is a side view of a shoe bottom 50 according to a third embodiment as viewed
from the same viewpoint as that of Fig. 15. In the above-described embodiment, an
example has been explained where a sole 10 has only a midsole 56; however, the sole
10 may have an outer sole 58 as well.
[0076] The outer sole 58 is disposed below the midsole 56 and is attached to the lower surface
of the midsole 56 by adhesion or the like. The ground contact surface 10e of the sole
10 is formed by the lower surface of the outer sole 58. The outer sole 58 mainly has
a role of securing grip performance against the road surface. The outer sole 58 is
formed using, for example, a non-foam or foam rubber, or the like. The midsole 56
is formed to be thicker than the outer sole 58 from the viewpoint of playing the role
of alleviating the impact of the landing. Further, since the outer sole 58 plays a
role of securing the grip performance, the outer sole 58 may have hardness that is
larger than that of the midsole 56. The medial transverse groove portions 34 according
to the present embodiment are formed within a range that does not reach the midsole
56 from the ground contact surface 10e of the outer sole 58.
(Fourth Embodiment)
[0077] Fig. 21 is a side view of a shoe bottom 50 according to a fourth embodiment as viewed
from the same viewpoint as that of Fig. 15. Different from the example of Fig. 20,
medial transverse groove portions 34 according to the present example are formed within
a range that reaches a midsole 56 from the ground contact surface 10e of an outer
sole 58.
[0078] As described, a sole 10 may have either one or both of the midsole 56 and the outer
sole 58. For example, although not shown in the figure, the sole 10 may have only
the outer sole 58.
[0079] Described above is a detailed explanation of the embodiments of the present invention.
All of the above-described embodiments merely show specific examples for carrying
out the present invention. The details of the embodiments do not limit the technical
scope of the present invention, and many design changes such as change, addition,
deletion, etc., of constituent elements may be made without departing from the spirit
of the invention as defined by the claims. In the above-described embodiments, such
details that are changeable in a design manner are explained with notations of "according
to the embodiment", "in the embodiment", etc.; however, it does not mean that design
changes are not allowed for features without such notations. Further, hatching applied
to cross sections of the drawings does not limit the material of an object with the
hatching.
[0080] The expression "foot longitudinal direction Lx" may be defined as a direction along
a straight line connecting the toe side end portion of the second toe to the rearmost
end portion (calcaneus tuberosity) of the calcaneus of the wearer's foot, which is
assumed to be on the sole 10 by design.
[0081] As the sole center line s, a straight line extending along the foot longitudinal
direction Y, which divides the full width Lb of the sole 10 into 1:1, may be used.
From another viewpoint, a straight line along the foot longitudinal direction Y may
be used by which the full width Lb of the sole 10 is divided from 1:1 to 3.7:3.2 from
the medial side in the foot width direction to the lateral side in the foot width
direction.
[0082] For example, the midsole 56 may be formed by stacking two or more parts having different
material properties in the vertical direction or arranging the parts in the foot longitudinal
direction.
[DESCRIPTION OF THE REFERENCE NUMERALS]
[0083] 10 sole, 10c medial edge, 10d lateral edge, 10e ground contact surface, 14 midfoot
portion, 16 rearfoot portion, 16a toe side end portion, 16b heel side end portion,
16c continuous surface, 20 medial midfoot region, 22 lateral midfoot region, 24 external
torsional resistance expected region, 26 first region, 28second region, 30 third region,
32 rigidity lowering portion, 34 medial transverse groove portion, 36 longitudinal
groove portion, 44 lateral transverse groove portion, 50 shoe bottom, 52 shoe, 56
midsole, 58 outer sole
[INDUSTRIAL APPLICABILITY]
[0084] The present invention relates to shoe bottoms of shoes.
1. A shoe bottom comprising a sole,
wherein when a midfoot portion of the sole is divided by a predetermined sole center
line into an medial midfoot region and a lateral midfoot region one on each side in
the foot width direction, the sole has a rigidity lowering portion that is provided
in the medial midfoot region, and
wherein, in such a manner that the bending rigidity of the medial midfoot region around
a foot width direction axis becomes smaller than that of the lateral midfoot region,
the rigidity lowering portion in the medial midfoot region reduces the bending rigidity
of the medial midfoot region due to another factor other than the shape of an medial
edge and the shape of a lateral edge of the sole in a planar view.
2. The shoe bottom according to claim 1, wherein a continuous surface that is continuous
in the foot longitudinal direction from a toe side end portion to a heel side end
portion of a rearfoot portion of the sole is formed on a ground contact surface of
the sole.
3. The shoe bottom according to claim 1 or 2, wherein a lateral transverse groove portion
that is open on the ground contact surface of the sole and that extends from the lateral
edge in the foot width direction is not formed in a range in the foot longitudinal
direction where the rigidity lowering portion is provided and in a range in the foot
longitudinal direction located on the heel side of the range.
4. The shoe bottom according to any one of claims 1 through 3, wherein the rigidity lowering
portion is open on the ground contact surface of the sole and serves as an medial
transverse groove portion that extends in the foot width direction from the medial
edge.
5. The shoe bottom according to any one of claims 1 through 4,
wherein the sole has either one or both of a midsole and an outer sole, and wherein
a reinforcing member is not attached to the midfoot portion of the sole.
6. The shoe bottom according to any one of claims 1 through 5,
wherein on the sole,
a plurality of medial transverse groove portions are formed that are open on a ground
contact surface of the sole and extend in the foot width direction from the medial
edge, and
a longitudinal groove portion is formed that is open on the ground contact surface
of the sole, extends in the foot longitudinal direction, and connects with respective
end portions of the plurality of medial transverse groove portions in the foot width
direction.
7. The shoe bottom according to any one of claims 1 through 6,
wherein in a planar view of the sole, given that
straight lines along the foot width direction that divide the full length La of the
sole in the foot longitudinal direction into 1.5:1.0:1.1 from the toe side to the
heel side are defined as lines p and q, respectively,
a straight line along the foot longitudinal direction that divides the full width
Lb of the sole into 1.2:1.0 from the medial side to the lateral side in the foot width
direction is defined as a line s, which serves as the sole center line,
being viewed from a point o1, which is the intersection point of the line p and the
line s, a straight line obtained by rotating the line p by 13 degrees around the point
o1 in an outward direction that rotates the toe side outward in the foot width direction,
is defined as a line t,
a straight line obtained by rotating the line s by 8 degrees around the point o1 in
the outward direction viewed from the point o1 is defined as a line u, being viewed
from a point o2, which is the intersection point of the line u and the line q, a straight
line obtained by rotating the line q by 5 degrees around the point o2 in the outward
direction is defined as a line v,
a region surrounded by the line t, the line u, the line v, and the medial edge is
defined as a first region, and
a region formed of the first region is defined as an external torsional resistance
expected region,
a rigidity lowering portion is provided in the external torsional resistance expected
region.
8. The shoe bottom according to any one of claims 1 through 6,
wherein in a planar view of the sole, given that
straight lines along the foot width direction that divide the full length La of the
sole in the foot longitudinal direction into 1.5:1.0:0.2:0.9 from the toe side to
the heel side are defined as lines p, q, and r, respectively,
a straight line along the foot longitudinal direction that divides the full width
Lb of the sole into 1.2:1.0 from the medial side to the lateral side in the foot width
direction is defined as a line s, which serves as the sole center line,
being viewed from a point o1, which is the intersection point of the line p and the
line s, a straight line obtained by rotating the line p by 13 degrees around the point
o1 in an outward direction that rotates the toe side outward in the foot width direction,
is defined as a line t,
a straight line obtained by rotating the line s by 8 degrees around the point o1 in
the outward direction viewed from the point o1 is defined as a line u, being viewed
from a point o2, which is the intersection point of the line u and the line q, a straight
line obtained by rotating the line q by 5 degrees around the point o2 in the outward
direction is defined as a line v, being viewed from a point P, which is the intersection
point of the line r and the line u, a straight line obtained by rotating the line
r by 4 degrees around the point P in the outward direction is defined as a line w,
a straight line connecting a point o5, which is the intersection point of the medial
edge and the line w, and the point o2 is defined as a line x,
a region surrounded by the line t, the line u, the line v, and the medial edge is
defined as a first region,
a region surrounded by the line v, the line x, and the medial edge is defined as a
second region, and
a region formed of the first region and the second region is defined as an external
torsional resistance expected region,
a rigidity lowering portion is provided in the external torsional resistance expected
region.
9. The shoe bottom according to any one of claims 1 through 6,
wherein in a planar view of the sole, given that
straight lines along the foot width direction that divide the full length La of the
sole in the foot longitudinal direction into 1.5:1.0:0.2:0.9 from the toe side to
the heel side are defined as lines p, q, and r, respectively,
a straight line along the foot longitudinal direction that divides the full width
Lb of the sole into 1.2:1.0 from the medial side to the lateral side in the foot width
direction is defined as a line s, which serves as the sole center line,
being viewed from a point o1, which is the intersection point of the line p and the
line s, a straight line obtained by rotating the line p by 13 degrees around the point
o1 in an outward direction that rotates the toe side outward in the foot width direction,
is defined as a line t,
a straight line obtained by rotating the line s by 8 degrees around the point o1 in
the outward direction viewed from the point o1 is defined as a line u, being viewed
from a point o2, which is the intersection point of the line u and the line q, a straight
line obtained by rotating the line q by 5 degrees around the point o2 in the outward
direction is defined as a line v, being viewed from a point P, which is the intersection
point of the line r and the line u, a straight line obtained by rotating the line
r by 4 degrees around the point P in the outward direction is defined as a line w,
a straight line connecting a point o5, which is the intersection point of the medial
edge and the line w, and the point o2 is defined as a line x,
a region surrounded by the line t, the line u, the line v, and the medial edge is
defined as a first region,
a region surrounded by the line v, the line x, and the medial edge is defined as a
second region,
a region surrounded by the line s, the line u, the line x, and the line w is defined
as a third region, and
a region formed of the first region, the second region, and the third region is defined
as an external torsional resistance expected region,
a rigidity lowering portion is provided in the external torsional resistance region.
10. The shoe bottom according to any one of claims 1 through 9, wherein the factor is
any one or a combination of two of a recessed portion that is open on the ground contact
surface of the sole and the elongation characteristic of a material constituting the
sole.
11. A shoe comprising the shoe bottom according to any one of claim 1 through 10.