US20020020078A1

US20020020078A1 - Boot with anti-vibration bottom assembly

Info

Publication number: US20020020078A1
Application number: US09/516,933
Authority: US
Inventors: Bernard Bressoux; Frederic Cretinon; Jean-Marie Begey
Original assignee: Salomon SAS
Current assignee: Salomon SAS
Priority date: 1999-03-02
Filing date: 2000-03-01
Publication date: 2002-02-21
Also published as: EP1033088A1; JP2000253903A; FR2790371A1; FR2790371B1; CN1267491A

Abstract

A boot having a structure for the treatment of the micro-vibrations that can occur between the bottom assembly and the upper of the latter by resonance effect on impact with the ground. A thin elastic membrane with a Shore A hardness of about 20-30 is positioned between the core layer of the bottom assembly and the upper to serve as a dynamic screen with respect to the micro-vibrations. The invention is particularly adapted to the design of sports boot, such as walking shoes and/or running shoes.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a boot whose upper is mounted on a multi-layered bottom assembly having a wearable layer on which an intermediate layer, or “core layer,” having predetermined characteristics of rigidity in torsion and bending, is directly fixed. More particularly, the invention relates to an intercalary layer which makes it possible to dampen the shocks between the upper and the “core layer.”

2. Description of Background and Relevant Information

Boots of the aforementioned type are known, for example, from the published patent applications EP 0 887 027, EP 0 748 596, WO 96/04811, as well as from patent document EP 0 548 475. In these boots, the bottom assembly, as opposed to the upper, includes all of the elements that constitute the bottom of the boot and are positioned between the foot and the ground.

According to these documents, the bottom assembly of the boot has a plurality of layers, including a wearable layer adapted to come into contact with the ground, and on which an intermediate layer, or “core layer,” provided with characteristics of torsional rigidity and bending and forming the bottom of these boots, is directly fixed. Complementarily, an upper layer, referred to as the comfort layer, is placed on the core layer and it functions to dampen the shocks upon each impact of the bottom assembly on the ground, and especially during the passive phase of the foot movement in which the vertical component of the ground reaction forces can reach values that are equal to several times the user's body weight, during a very brief period of time on the order of 20-30 milliseconds.

For these reasons, the upper comfort layer of these boots, and the generality of known sports boots, except those adapted for sprinting, is characterized by a substantial thickness that is measured in multiple millimeters, and by its ability to deform elastically, especially to compress itself. Thus, the constituent material of the comfort layer is generally characterized by a Shore A hardness that is almost always greater than 35. The treatment of the shock from the impact is therefore generally achieved due to the resistance and great elastic deformation capacity of this comfort layer which, in fact, offers a certain braking distance to bring the foot vertical positioning speed, which is on the order of 1 meter/second, to zero. Moreover, since the comfort layer is inserted between the foot and the core layer, risks of interference of this core layer with comfort are avoided, which is not the case with most bottom assemblies where the comfort layer is located between the wearable layer and the core layer.

More specifically, the boots described in the documents EP 0 548 475, EP 0 887 027, and WO 96/04811 include bottom assemblies that successively have a wearable layer, a core layer, and a shock-absorbing comfort layer over almost the entire zone corresponding to the plantar surface with, at least for the shock-absorbing comfort layer, a decreasing variation in thickness from the heel to the tip of the bottom assembly. On the other hand, according to the document EP 0 748 596, the shock-absorbing comfort layer is limited to the heel zone and is housed in a recess provided in the core layer.

These different arrangements and distributions of the shock-absorbing layer between the heel and the tip of the bottom assembly aim at providing a shock absorption, through elastic deformation, localized only in the areas where the shocks resulting from the contact with the ground are the most intense and the most frequent. Thus, a reliable support and a certain stability over the largest possible surface of the bottom assembly are preserved, which is favorable to the support of the foot during movement thereof, especially when shock absorption ceases during the propulsion phase.

By way of example, these multi-layered bottom assemblies having a variable distribution of the comfort layer, in correspondence with the plantar surface zone are capable of providing, through elastic deformation of a certain amplitude of their comfort layer, a dampening of the intensity of the shocks transmitted to the foot on impact, which is on the order of 30-50% at the heel, which satisfies the notion of comfort, and on the order of 10% on the tip of the bottom assembly, which satisfies the notion of performance-efficiency. In fact, these bottom assemblies have a resonance frequency that can vary between the heel and forefoot zones, as a function of the most frequent localization of the most intense shocks.

The aforementioned multi-layered bottom assemblies are therefore generally satisfactory for the shock treatment, because they offer a good compromise which provides comfort, load distribution and stability during propulsion.

However, due precisely to the variation in their resonance frequency, from the heel to the forefoot, they are capable of amplifying an impulse, such as a shock applied to a given area, instead of absorbing it, if that impulse biases them at a frequency that is close to their resonance frequency in that area. A direct consequence from this type of vibrating phenomena is the propagation of shockwaves in the user's foot and the occurrence of micro-vibrations in the foot/boot interface, especially on impact of the heel on the ground at the end of the braking course, and during the propulsion phase at the forefoot beneath the metatarsal heads where pressure increases substantially.

To dampen these vibrating phenomena that disturb the proprioceptive system of the boot user and cause micro-traumas, additional shock-absorbing elements are often introduced into the boot a posteriori, and are arranged between its bottom assembly and the user's foot. By way of example, one can cite the internal soles and heel pieces that are often commercially available as boot accessories for treating “the shockwave.” In any event, insofar as these soles and heel pieces are satisfactory in the shock wave treatment, they have proven to be a hybrid solution. Indeed, on the one hand, they modify the initial fitting volume of the boot, as well as the foot seating, particularly in the rear-to-front direction, especially with respect to the heel pieces, and, on the other hand, they provide the boot with a heterogeneous character.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the various disadvantages of the aforementioned boots for the shockwave treatment, and especially to absorb the micro-vibrations that can occur by resonance effect, while retaining the advantages provided by the multi-layered bottom assemblies in which the core layer is fixed directly on the wearable layer.

To this end, a particular object of the invention is precisely not to substantially increase the thickness of the bottom assembly, despite the use, in the foot/bottom assembly interface, of a shock-absorbing layer adapted to serve as a dynamic screen, due to its “elastic deformation” capacity, for the micro-vibrations which are characterized by a very quick periodical displacement of very small amplitude, and which can occur by resonance effect during the shock from the impact, especially when shock absorption ceases.

Another object is to respect the natural foot movement, such that this shock-absorbing layer does not require any substantial expenditure of supplemental energy to deform the bottom assembly when the user's foot bends, during the propulsion phase in the area of the forefoot, for example, and does not alter the stability.

Yet another object of the invention is to propose a homogeneous multi-layered bottom assembly structure which, provided with a layer for absorbing the micro-vibrations, can be variable in order to meet the various needs for shock absorption in amplitude and frequency, according to the intended use of the boot, for example, a foot-race, walking, hiking, team sports such as soccer, rugby, etc. In this sense, the dampening of the micro-vibrations is generally treated between the bottom assembly and the boot upper, or only over a predetermined area of the bottom assembly.

To achieve these objects, the boot, whose upper is mounted on a multi-layered bottom assembly having a wearable sole on which a core layer is fixed directly, includes a specific shock-absorbing layer for treating the micro-vibrations, in the form of a thin elastic membrane with a thickness of less than 2 millimeters, fixed on the core layer so as to function between the latter and the boot upper. This thin shock-absorbing layer or elastic membrane includes a visco-elastic material having a Shore A hardness on the order of 20-30, such that, due to its elastic deformation properties, it behaves in the manner of a dynamic screen that is particularly well adapted for dampening the micro-vibrations that are characterized by a displacement of very small amplitude and a high frequency. This integration of the elastic membrane into the multi-layered bottom assembly allows a homogeneous construction of the latter and, thus, of the boot, without causing much harm to the stability, since it only slightly increases the thickness of the bottom assembly, and therefore the relative height of the plantar surface relative to the ground.

According to an interesting embodiment, the shock-absorbing layer constituted by the elastic membrane has, on the side facing the core layer, a discontinuous surface having a multitude of points of contact that are determined by the intersecting points of a multitude of cavities open on the side facing the core layer. In this way, a portion of the energy is further dissipated-absorbed by the elastic membrane, perpendicular to the micro-vibrations.

According to one embodiment, the boot, whose bottom assembly is provided with an elastic membrane for absorbing the micro-vibrations fixed directly on the core layer, and a core layer is obtained, in the heel zone, with a vertical extension that rises along at least a portion of the boot upper, such extension forming the stiffener thereof. Advantageously, the shock-absorbing elastic membrane which is fixed on the core layer, in this example of construction, is provided to extend over the entire internal surface of the stiffener in a manner so as to be inserted completely between the upper and the core layer. The shock-absorbing elastic membrane can be associated with the core layer, fixed directly on the wearable layer, over the entire zone corresponding to the plantar surface, or only over a more restricted zone such as that of the heel or forefoot.

More specifically, according to the intended use of the boot, such as hiking, for example, the multi-layered structure of the bottom assembly can have an elastic membrane for dampening the micro-vibrations only in the forefoot zone, and a shock-absorbing layer at the heel that can be deformed-compressed over a certain distance to bring the foot vertical positioning speed to zero by dampening the intensity of the shock from the impact to the maximum. Thus designed, the boot provides the user, on the one hand, with good shock absorption at the heel, which is absolutely necessary when walking down a slope, for example, and, on the other hand, an excellent support without micro-vibrations beneath the forefoot, which contributes to stability and efficiency.

According to an advantageous embodiment of such a boot, the core layer is divided, in the heel zone and from a common attachment point located in the vicinity of the forefoot zone, into two elastic blades that are spaced apart in the direction of the bottom assembly thickness.

These two elastic blades extending from the core layer thus constitute either a shock-absorbing structure complementary to the shock-absorbing comfort layer, or a shock-absorbing structure capable of replacing this shock-absorbing layer. Preferably, an elastically deformable material is inserted between the two elastic blades of the core layer so as to provide the bottom assembly with a more homogeneous configuration and/or to increase the resistance to deformation provided by the blades.

Furthermore, according to an alternative embodiment of the core layer, the latter is obtained with at least one lateral and vertical extension which rises in the direction of the instep girth where it is connected to a device for tightening and holding the foot, this extension thereby constituting the equivalent of a tightening flap. The foot is therefore flattened against the elastic membrane that is fixed on the core layer, by direct action on the tightening flap coming from the core layer, which prevents any loss of the tightening force through the upper. The solution, which includes providing the core layer with two lateral and vertical extensions each rising along a side of the boot upper, in the direction of the instep girth where they are mutually connected to the tightening device, is preferred. Indeed, it provides a better foot retention, a more energetic tightening, and more stability, because the tightening force on the user's foot is symmetrically recovered with respect to the longitudinal axis of the bottom assembly and beginning at the core layer.

According to another embodiment of the invention, a shock-absorbing layer is fixed on the elastic membrane which is thus “sandwiched” between this comfort layer and the core layer. In such a structure of the multi-layered bottom assembly, the following can be successively identified, from the ground toward the user's foot:

a wearable layer that has predetermined properties of flexibility, adherence, and abrasion resistance capable of allowing good foot movement, good grip on the ground, as well as good wear resistance;

a core layer which, arranged directly on the wearable layer, has controlled properties of torsional rigidity and bending in order to simultaneously ensure the distribution of the shocks recorded by the wearable layer and their transfer toward the foot, while allowing good movement of the latter;

an elastic membrane which, contiguous to the core layer, is provided with dimensional and mechanical characteristics such as thinness, of less than 2 millimeters, combined with a high elasticity and a low Shore A hardness, on the order of 20-30, in order to dampen the micro-vibrations that are characterized by a displacement of very small amplitude and a high frequency; and

a shock-absorbing comfort layer which, arranged on the elastic membrane, has a thickness that is measured in multiple millimeters, on the one hand, and an elastically compressible constituent material having a Shore A hardness at least equal to 35, on the other hand. The object of the comfort layer is to provide, by deforming itself, a certain braking distance used to bring the vertical foot positioning speed to zero on impact, or a zero value, simultaneously with a maximum dampening of the intensity of the shock from the impact.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood from the following description, with reference to the annexed schematic drawings illustrating, by way of examples, how the invention can be embodied, and in which: [0029]
FIG. 1 is an exploded view of a boot consistent with the invention according to one embodiment; [0030]
FIG. 2 shows a second embodiment of the boot of FIG. 1; [0031]
FIGS. 3, 4 and [0032] 5 show improvements provided in the area of the bottom assembly of the boot;
FIG. 6 shows the bottom assembly of the boot in a transverse cross-sectional view along the line VI-VI of FIG. 4 according to an alternative embodiment of the invention; [0033]
FIG. 7 is a view similar to that of FIG. 6 showing another embodiment of the bottom assembly; and [0034]
FIG. 8 schematically shows an enlarged cross-sectional view of a surface detail of a layer for dampening the micro-vibrations.[0035]

DETAILED DESCRIPTION OF THE INVENTION

The sport boot [0036] 1, shown in an exploded view in FIG. 1, has a multi-layered bottom assembly designated in its entirety by the reference numeral 2, on which is mounted an upper 3 having, in a known manner, an opening 4 that allows the passage of the user's foot, not shown. A tightening device 5, of the lacing type, for example, ensures the closure and retention of the boot on the foot.
The [0037] multi-layered bottom assembly 2 is obtained according to a stratified structure composed of a plurality of layers respectively fulfilling distinct functions. More specifically, the bottom assembly 2, in this first example of construction according to the invention, is made of three successive layers 6, 7, and 8 distributed in the following manner:
a [0038] wearable layer 6 that has predetermined properties of flexibility, adherence, and abrasion resistance capable of allowing good foot movement, good grip on the ground, as well as good wear resistance;
a [0039] core layer 7 arranged directly on the wearable layer 6, and which has controlled properties of stiffness in torsion and bending in order to simultaneously ensure the distribution of the shocks recorded by the wearable layer 6 and their transfer toward the foot, without disturbing the movement of the latter. The object of the core layer is also to improve the adherence effect by constituting a carcass that prevents the overall deformation of the contact layer, in the manner of a radial carcass of an automobile tire, and allows the use of softer, and therefore more adherent, rubbers; and a shock-absorbing layer 8 in the form of an elastic membrane having, on the one hand, by a thinness of less than 2 millimeters, and, on the other hand, by a high elasticity procured by the visco-elastic material of which it is made, and which has a Shore A hardness in the range of about 20-30. This elastic membrane 8 is furthermore directly fixed on the core layer 7 so as to be inserted between the latter and the upper 3 of the boot.
These characteristics and arrangement of the [0040] elastic membrane 8 in the multi-layered bottom assembly 2 make it possible to treat the micro-vibrations that can occur by resonance effect, which are especially characterized by their small amplitude.
In fact, the [0041] elastic membrane 8 behaves in the manner of a dynamic screen between the core layer 7 and the upper 3 of the boot 1 due to its flexibility and elasticity. Moreover, in view of its thinness and, therefore, its small working amplitude in the direction of its thickness, the stability is practically not altered neither during the shock from the impact, nor when taking support during the propulsion phase.
As illustrated in this example of reconstruction shown in FIG. 1, the [0042] core layer 7 and the elastic membrane 8 extend over the zone of the bottom assembly 2, which corresponds substantially to the entire zone of the plantar surface of the user's foot, not shown.
Other constructions respecting the same arrangement of the [0043] various layers 6, 7, and 8 are also contemplated according to the invention.
Thus, the [0044] core layer 7 and elastic membrane 8, for example, can extend over the zone of the bottom assembly 2 corresponding only to the zone of the forefoot 10 or to the zone of the heel 11.
Furthermore, the [0045] wearable layer 6 can be made of a single element, as shown, or of a plurality of elements, such as a heel 12 independent of the anterior sole portion 13. The wearable layer 6 can also be made of a multitude of spikes or studs 14 independent of one another and attached directly to the core layer 7 by any known method, such as adhesion, welding, overmolding, mechanical assembly, etc.
According to a second embodiment of the [0046] boot 21, shown in FIG. 2, the core layer 27 of the multi-layered bottom assembly 20 includes, in the zone of the heel 11, a vertical extension 17 that rises along a portion 3 a of the upper 3 of the boot 21. This vertical extension 17 is obtained all in one piece with the core layer 27, and therefore has, among others, stiffness properties that are similar to those of the latter. Consequently, it advantageously constitutes the rear reinforcement, i.e., the stiffener, of the boot 21. In this example of construction, the elastic membrane 28 is preferably also obtained with a vertical extension 28 a corresponding to the vertical extension 17 of the core layer 27; thus, it is completely inserted between the portion 3 a of the upper 3 of the boot 21 and the core layer 27, while providing, in addition to the dampening of the micro-vibrations between the bottom assembly 20 and the upper 3, a dampening of the micro-vibrations that can occur in the very wall of the upper 3.
Depending on the intended use of the [0047] boot 21, the dampening of the micro-vibrations might be desired only in a demarcated zone of the core layer 27. Thus, the core layer 27 can extend, for example, over the entire zone corresponding to the plantar surface, whereas the elastic membrane 8 only covers the zone 10 corresponding to the forefoot, or only the zone 11 corresponding to the heel.
As disclosed previously, the use of an [0048] elastic membrane 8, 28, fixed directly on the core layer 7, 27 makes it possible, among others (FIGS. 1 and 2), to keep the stability unchanged on impact and/or when taking support. However, due to the fact that the upper 3 of the boot 1, 21 is assembled to the bottom assembly 2, 20, either through a lasting allowance surface (not shown), or via an insole, a loss of the sensations coming from the ground to the user's foot can occur via the upper 3 of the boot 1, 21, in spite of the thinness of the elastic membrane 8. In this case, the foot is capable of moving relative to the bottom assembly 2, 20. Consequently, a portion of the advantages provided by the particular structure of the bottom assembly 2, 20 with its elastic membrane 8, 28, is then lost. To prevent this type of drawback, an advantageous solution, shown in FIG. 3, consists of recovering the tightening force directly from the core layer 7 of the bottom assembly 2. To this end, the core layer 7 is provided with two lateral and vertical extensions 18 which each rise along a side of the upper 3 of the boot 31, in the direction of the instep girth, where they are connected to the tightening device 5.
In such a construction, the user's foot is therefore flattened against the [0049] elastic membrane 8 by direct action on the extensions 18 coming from the core layer 7, which constitute the equivalent of tightening flaps. Therefore, there is no loss of the tightening force through the upper 3 of the boot 31. In addition, due to the tightening symmetry, the stability provided by the bottom assembly 2 is entirely recovered on the user's foot.
An embodiment with a [0050] single lateral extension 18 can be envisioned, especially if a lateral direction of the tightening force is preferred, as the case may be in cross-country boots, for example.
Still according to the invention, as shown in FIGS. 4 and 5, the [0051] boot 31, in view of a predetermined use such as hiking, for example, can have a multi-layered bottom assembly 32 with an elastic membrane 8 for dampening the micro-vibrations only in the zone of the forefoot 10, and a shock-absorbing layer 35 in the zone of the heel 11 adapted to bring the vertical foot positioning speed to zero on impact, with a maximum dampening of the shock intensity. This multi-layered bottom assembly 32 therefore includes two distinct structures:
at the [0052] forefoot 10, a wearable layer 36, a core layer 37, and an elastic membrane 8; and
at the [0053] heel 11, a wearable layer 36 and a shock-absorbing layer 35 including elastic portions 37 a and 37 b of the core layer 37 with a shock-absorbing structure 35 a.
More specifically, the shock-absorbing [0054] layer 35 of the bottom assembly 32 provided at the heel 11 includes the core layer 37 which, in this area, is divided into two elastic blades 37 a and 37 b spaced apart along the thickness of the bottom assembly 32. As is particularly visible in FIG. 5, these elastic blades 37 a and 37 b come from the core layer 37, beginning at a common attachment point located in the vicinity of the zone of the forefoot, approximately at a right angle with the arch of the foot, for example. Thus designed, the two elastic blades 37 a and 37 b of the core layer 37 can provide, by deforming during bending, a shock absorption of a certain amplitude when they are subject to a shock from the impact in the zone of the heel 11. The shock-absorbing means 35 a inserted between the blades 37 a and 37 b must be provided to be made of an elastically deformable material which allows bending of the latter. To this end, the shock-absorbing structure 35 a can, for example, be made out of a very low density micro-cellular material only having a “filling” role to provide the bottom assembly with a homogeneous configuration. The constituent micro-cellular material of the shock-absorbing structure 35 a can also be selected with higher densities in order to very substantially increase the resistance to deformation provided by the blades 37 a and 37 b.
It can be envisioned that an [0055] elastic membrane 8 can be included in the bottom assembly 32 of the heel 11. Furthermore, the structure of the bottom assembly 32 at the heel 11 can also be obtained at the forefoot 10.
In another example of construction, which can be envisioned as a function of the properties of stiffness in torsion and bending of the [0056] core layer 37, the elastic blades 37 a and 37 b constitute, alone, a shock-absorbing structure which replaces a shock-absorbing comfort layer of a conventional type, due to the fact that they have a great elastic deformation capacity and a certain stiffness.
According to a preferred embodiment, shown in FIG. 5, the [0057] elastic blade 37 b directed toward the ground is in the form of a horseshoe, and the elastic blade 37 a directed toward the heel of the user's foot is in the form of a tongue whose contour fits within that of the blade 37 b. This structure provides an optimized support for the heel of the user's foot, because the heel support point, which is central, is located in correspondence with the tongue-shaped elastic blade 37 a. Moreover, the horseshoe shape imparted to the elastic blade 37 b, outside of the projection of the blade 37 a, constitutes an excellent support base for the heel central support, because it defines a support surface extending markedly outside of this heel central support, and because it makes it possible to recover the forces via the core layer 37, directly in the area of the wearable sole 36, therefore closest to the ground. The stability is therefore preserved and the grip to the ground is optimized.
This structure of the [0058] core layer 37 can be associated with lateral extensions 18 for tightening and holding the foot, such as described with reference to FIG. 3.
These different embodiments of the invention that have just been described with reference to FIGS. [0059] 1-5 can be provided with shock-absorbing comfort layers of a conventional type, i.e., having a great elastic deformation capacity associated with a certain stiffness. For example, this shock-absorbing layer can be made out of an elastically compressible material having a Shore A hardness at least equal to 35, and having a thickness that is measured in several millimeters.
Thus, in the example shown in FIG. 6, a shock-absorbing [0060] comfort layer 45 is fixed on the elastic membrane 8, 28 that is sandwiched between this comfort layer 45 and the core layer 7, 27, 37, the upper 3 of the boot being assembled to the bottom assembly 2, 20, 32 through a lasting allowance surface or layer 3 b directly in contact with the elastic membrane 8.
In the example that follows with reference to FIG. 7, the shock-absorbing [0061] comfort layer 55 is mounted in the same manner as in the construction of FIG. 6, but the upper 3 of the boot is assembled to the bottom assembly 2, 20, 32, via this shock-absorbing comfort layer 55, starting from a lasting allowance layer 3 b.
According to an improvement, illustrated in FIG. 8 which shows an enlarged partial cross-section of a [0062] bottom assembly 2, 20, 32, the elastic membrane 8 has, on the side directed toward the core layer 7, 27, 37, a discontinued surface including a multitude of contact points 41 that are determined by the intersecting points of a multitude of cavities 42 open on that side.
This arrangement makes it possible to dissipate-absorb a portion of the energy, perpendicular to the micro-vibrations. [0063]
Finally, the [0064] core layer 7, 27, 37 of the multi-layered bottom assemblies 2, 20, 32 can also be designed from particular constituent materials, in order to have predetermined controlled properties of stiffness in torsion and bending. For example, the core layer 7, 27, 37 can be a composite made, at least partially, of a material of mineral origin in the form of unidirectional fibers or woven fibers.
The instant application is based upon the French patent application No. 99.02806, filed on Mar. 2, 1999, the disclosure of which is hereby expressly incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. §119. [0065]

Claims

What is claimed is:

1. A boot comprising:

an upper mounted on a multi-layered bottom assembly;

a wearable layer and a core layer directly fixed on said wearable layer;

a shock-absorbing layer in the form of a thin elastic membrane, having a thickness of less than about two millimeters, is fixed on said core layer to treat the micro-vibrations that can occur by resonance effect during impact shocks.

2. A boot according to claim 1, wherein the elastic membrane is made out of a visco-elastic material having a Shore A hardness of about 20-30.

3. A boot according to claim 1, wherein the core layer and the elastic membrane extend over the zone of the bottom assembly corresponding substantially to a zone of the forefoot.

4. A boot according to claim 1, wherein the core layer and the elastic membrane extend over a zone of the bottom assembly corresponding substantially to a zone of the heel.

5. A boot according to claim 1, wherein the core layer and the elastic membrane extend over a zone of the bottom assembly corresponding substantially to an entire zone of the plantar surface.

6. A boot according to claim 4, wherein the core layer comprises, in a zone of the heel, a vertical extension which rises at least along a portion of the upper of the boot, said extension constituting the stiffener of the boot.

7. A boot according to claim 6, wherein the elastic membrane extends over the entire internal surface of the stiffener.

8. A boot according to claim 1, wherein the core layer of the bottom assembly extends over the entirety of a zone of the plantar surface, said elastic membrane only extending over a zone corresponding to the forefoot.

9. A boot according to claim 1, wherein the core layer of the bottom assembly extends over the entirety of a zone of the plantar surface, said elastic membrane only extending over a zone corresponding to the heel.

10. A boot according to claim 1, wherein the core layer of the bottom assembly comprises one lateral and vertical extension which rises along a side of the upper of the boot, in the direction of the instep girth where said extension is connected to a tightening device, thus constituting the equivalent of a tightening flap.

11. A boot according to claim 1, wherein the core layer of the bottom assembly comprises two lateral and vertical extensions which each rise along a side of the upper of the boot, in the direction of the instep girth where said extensions are connected, between them, to a tightening device, said extensions thus constituting the equivalent of two tightening flaps.

12. A boot according to claim 4, wherein the core layer is divided, along the thickness of the bottom assembly and in the zone of the heel, starting from a common attachment point located in the vicinity of a zone of the forefoot, into two elastic blades which are spaced apart by a certain value.

13. A boot according to claim 12, wherein a shock-absorbing structure made of an elastically deformable material is positioned between the two elastic blades of the core layer.

14. A boot according to claim 1, wherein a shock-absorbing comfort layer, made of an elastically compressible material with a Shore A hardness at least equal to about 35 and having a thickness of multiple millimeters, is fixed on the elastic membrane, said comfort layer adapted to provide a certain braking distance used to reduce the foot positioning speed down to a zero value, simultaneously with a maximum dampening of the intensity of the shock from the impact, due to its characteristics of compressibility and elastic resistance.

15. A boot according to claim 8, wherein a shock-absorbing comfort layer, made of an elastically compressible material with a Shore A hardness at least equal to about 35 and having a thickness of multiple millimeters, is fixed directly on the core layer, outside of a zone covered by the elastic membrane.

16. A boot according to claim 1, wherein the core layer is a composite made, partially, of a material of mineral origin in the form of unidirectional fibers.

17. A boot according to claim 1, wherein the core layer is a composite made, partially, of a material of mineral origin in the form of woven fibers.

18. A boot according to claim 1, wherein the elastic membrane has, on the side directed toward the core layer, a discontinued surface constituted by a multitude of contact points that are determined by the intersecting points of a multitude of cavities open on said side.