Abstract:
A reinforcement for a boot, in particular a sports boot, more particularly a cross-country ski boot. The boot reinforcement makes it possible to improve the torsional stiffness, efficiency, durability, lightness, cost, foot protection, and industrial workability. To achieve this goal, the boot reinforcement according to the invention includes a front zone A from the front end up to the beginning of the plantar arch, a median zone B corresponding to the plantar arch, a rear zone C. The reinforcement includes, at least in the zones B and C, at least one “sandwich” structure constituted by at least one core inserted between at least two layers, and, in the zone A, it is flexible in a substantially longitudinal direction and torsionally stiff. The layers of the sandwich structure are made of composite, carbon fibers/polymeric resin, whereas the core of this sandwich structure is made of synthetic foam, wood or honeycomb. Each zone A, B, C has a longitudinal flexural strength RfA, RfB, RfC, such that RfA&lt;RfB≦RfC. The invention also relates to a sports boot including such a reinforcement.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon French Patent Application No. 01 04799, filed Apr. 9, 2001, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. §119. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of boots, in particular sports boots, and more particularly sports boots adapted to cooperate with a sports apparatus, such as a cross-country ski, an in-line roller skate, a snow shoe, etc., along a movement in which, the tip of the boot being affixed to the apparatus, the heel can be displaced between a position supported on the apparatus and a position raised in relation to the apparatus. 
     2. Description of Background and Relevant Information 
     The aforementioned foot movement is that which is found in particular in cross-country skiing involving the evolutional techniques referred to as the “alternate step” or “skating step.” These evolutional modes also exist for sports apparatuses such as roller skis, or roller skates. 
     The essential qualities desired for the boots adapted to this type of movement are rigidity in the transverse direction (high torsional stiffness), combined with a longitudinal flexibility, especially in the metatarsophalangeal zone (low longitudinal stiffness). 
     SUMMARY OF THE INVENTION 
     The present invention thus relates more specifically to a reinforcement intended to improve the aforementioned mechanical properties. 
     Such a reinforcement is advantageously adapted to be a constituent element of the lower portion of the boot, in particular a sports boot, for example a cross-country ski boot. By way of example, such a lower portion conventionally includes an outer sole adapted to cooperate with the sports apparatus, a lasting insole, and an inner sole. This lower portion is assembled with the upper portion of the boot which includes a vamp, and possibly an upper. The lower edge of the vamp is generally sewn and/or cemented and/or welded to the outer sole, as well as to the lasting sole. There are other lasting methods, especially using the so-called “strobel” technique. 
     It is indeed important that the boots, in particular sports boots, and more particularly cross-country ski boots, be torsionally rigid or stiff in relation to the longitudinal axis of the boot. This guarantees a good stability of the boot, especially in cross-country skiing, where the boot cooperates with the ski, this torsional stiffness making it possible to ensure that the ski is optimally guided by the boot. Generally speaking, the torsional stiffness of a boot makes it possible to guarantee that the sports apparatus to which it is attached is properly guided. 
     Furthermore, flexibility of the boot sole in the longitudinal direction is desired for walking and running, and it proves indispensable in the case of a sports boot cooperating with an apparatus, such as a cross-country ski, for example, to which it is fixed only by its front end, especially when moving with the “alternate step”. The foot and the boot must be capable of rolling and unrolling easily and in harmony relative to the fixed front tip of the boot. 
     The boot and the upper and lower portions (bottom assembly) of the boot are subject to bending during almost the entire sporting activity. In practice and in the context of the present disclosure, bending is referred to as that which occurs in the movement in the area of the metatarsophalangeal joint. In its design, the boot must fully respect the positioning of this joint which forms an angle of about 71/72° with the inner tangent to the foot, and which is located along this same tangent at about 73/74% of the total length of the foot. 
     To promote bending, reinforcements incorporated into the upper portion (upper/vamp) or in the lower portion (bottom assembly of the boot) are conventionally used. 
     In addition to the mechanical characteristics of torsional stiffness and longitudinal bending flexibility along the metatarsophalangeal axis, other parameters must be taken into consideration, including lightness, cost, industrial workability, etc. 
     With respect to the bottom assembly reinforcements, which are those aimed at more specifically in the present invention, there are numerous prior technical propositions which, to date, have not been entirely satisfactory. 
     U.S. Pat. No. 5,406,723 relates to a cycling shoe sole provided with a multilayered structure. The latter is supposed to provide the cycling shoe with sufficient longitudinal rigidity so that it can withstand the bending force which is exerted on the shoe sole during pedaling, while meeting a particularly important lightness requirement to alleviate the exhaustion of the cyclist. The multilayered structure of the shoe sole is constituted by a core made of polyurethane foam inserted between two sheets each constituted of a plurality of composite layers based on glass or carbon fibers embedded in a cross-linked polymer resin (phenol resin). It is clear that such a sandwich reinforcement of a cycling shoe outsole has a torsional stiffness such that it virtually prevents any longitudinal bending movement. In fact, this is precisely what is desired. Consequently, such a reinforcement is really unsuited for boots adapted to enable a rolling/unrolling movement of the boot. 
     The document EP 0 931 470 describes a sports footwear including a stiffening element incorporated into the lower part (sole unit of the footwear). This stiffening element is an insole or outsole, or a sandwich-type support including a layer  15  made of expanded plastic foam (light wood, vertical plastic cylinders, or a cellular material), this layer being inserted between two layers  13  and  14  based on polymer (nylon, polyurethane, polypropylene), resin or a composite material including synthetic resins in which carbon, aramid, or glass fibers are included. The rigidity of the layers  13  and  14  is higher than that of the layer  15 . The thickness of the latter is greater than that of the layers  13  and  14 . It appears from FIG.  5  and the specification, column 3, lines 41-53, of the document EP 0 931 470 that the stiffening element can include portions of variable cross-section and different flexibilities, having a greater longitudinal flexibility at the forefoot, in particular. However, such a sole construction remains essentially rigid and is not suited for sports requiring an unrolling movement of the foot as do cross-country skiing, racing, etc. In fact, the document EP 0 931 470 essentially aims at an application to boots having a rigid sole, such as cycling shoes, mountain boots, etc. 
     French Patent No. 2 600 868 (based upon Application NO. 86 10130) relates to a cross-country ski boot sole, torsionally stiff and flexible in the longitudinal direction. This sole includes a reinforcement located at least in the metatarsophalangeal zone and corresponding to a lasting sole constituted by a composite sheet (glass, carbon or aramid fibers embedded in epoxy or polyester resins). This composite sheet has the characteristic of having fibers that are oriented in two or three directions relative to the longitudinal axis of the sole (multidirectional cloth). This is supposed to make it possible to obtain the desired longitudinal, transverse and torsional stiffnesses. This reinforcement does not involve a sandwich structure. Furthermore, this shoe sole remains perfectible with respect to the transverse rigidity, therefore the steering of the ski, the flexibility, durability, lightness, efficiency, uniformity, and sensitivity of the rolling/unrolling movement, as well as protection of the foot during bendings. 
     French Patent Application No. 2 682 011 (based upon Application No. 91 12376) relates to a cross-country ski boot whose torsional strength and longitudinal flexibility in the metatarsophalangeal zone are improved, and which includes an outer sole covered with a lasting insole, defining therebetween a peripheral assembly zone referred to as the lasting allowance, which makes it possible to affix the upper and the vamp to the lower portion of the boot. The outer sole has torsional strength properties and it is jointly mounted with the lasting insole made of a material that is flexible in bending (rubber) in a zone corresponding to the front portion of the foot. Furthermore, the lasting insole is made of leather or cellulose fibers in its front end zone corresponding to the zone of the finger bones, whereas the rear portion is made of cardboard, for example. 
     A sandwich structure is not used in the bottom assembly according to FR 2 682 011, and it has proven that the torsional strength, and therefore the control of the ski, remain perfectible. 
     Furthermore, this boot could also be improved with respect to optimizing its efficiency, which results from the spring power in this zone of the metatarsophalangeal bending axis zone. 
     Finally, the materials used in the lasting insole of this boot do not have all of the guarantees desired in terms of stability of the mechanical properties over time. 
     Therefore, it must be noted that the prior technical propositions are not entirely satisfactory, or are unsuited to resolving the technical problem(s) including:
         increasing the torsional stiffness so as to improve the steering and control of the sports apparatus, while optimizing the bending ability in the metatarsophalangeal zone, so as to enable a uniform and flexible rolling/unrolling movement of the boot, and to further make it possible to perceive the reactions of the sports apparatus and of the ground, and therefore to proportion the forces;   improving the efficiency of the boot by optimizing the spring power in the metatarsophalangeal zone, without negatively affecting the flexibility of the torsional stiffness;   using materials that meet the aforementioned specific mechanical specifications, and are capable of conserving those properties or qualities, and therefore the subsequent behaviors, over an extended period of time (slow degradation-increased durability);   further reducing the weight of the boot;   protecting the foot during bendings by minimizing the compressive stresses to which the foot is subject;   maintaining the cost within acceptable limits;   developing a reinforcement that is industrially easy to manufacture.       

     One of the objects of the present invention is to provide a reinforcement for a boot, in particular a sports boot (e.g., for cross-country skiing), which procures significant improvements with respect to the aforementioned technical specifications. 
     Another object of the invention is to propose a reinforcement for a cross-country ski boot that makes it possible to improve the ski steering efficiency, durability, flexibility, savings in weight, cost, foot protection, industrial workability. 
     Another object of the present invention is to provide a boot, especially a sports boot, and more specifically a cross-country ski boot, having a reinforcement in the bottom assembly that is capable of meeting the aforementioned specifications at best. 
     These objects, among others, are achieved by the present invention which relates primarily to a reinforcement for a boot, in particular a sports boot, of the type adapted to cooperate with a sports apparatus along a movement in which, the tip of the boot being affixed to the sports apparatus, the heel can be displaced between a position supported on the sports apparatus and a position raised relative to the sports apparatus, this reinforcement:
         extending over at least a portion of a front zone A, located on both sides of the metatarsophalangeal joint, from the front end up to the beginning of the plantar arch, over at least a portion of a median zone B corresponding to the plantar arch and over at least a portion of a rear zone C corresponding to the heel and starting from the end of the plantar arch and ending at the rear end;   being adapted to improve the longitudinal flexibility of the zone A, on the one hand, and the torsional rigidity at least of the zone A, on the other hand, wherein:
           it includes, at least in the zones B and C at least one “sandwich” structure constituted by at least one core inserted between at least two layers; and   in the zone A, it is flexible in a substantially longitudinal direction and torsionally stiff.   
               

     According to the invention, the choice of a material having a sandwich structure at least in the rear zone C corresponding to the heel and in the zone B corresponding to the plantar arch contributes to obtaining the desired results in terms of longitudinal flexibility and torsional stiffness in the metatarsophalangeal front zone A. The same is true with respect to the efficiency of the boot (spring power in the zone A), steering of the ski, durability, lightness, ease and precision of the rolling/unrolling movement of the foot and of the boot, as well as protection of the foot during bendings. 
     The present invention also relates to a boot, in particular a sports boots, and more particularly a cross-country ski boot, including the reinforcement such as defined in the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be better understood from the following description of a non-limiting example of a preferred embodiment of the reinforcement and boot considered. 
       This description is provided with reference to the annexed drawings, in which: 
         FIG. 1  is a perspective view of a cross-country ski boot, according to the invention, which is reversibly fixed to a cross-country ski by its front tip and raised relative to the cross-country ski along a flexional rolling movement; 
         FIG. 2  is a transverse cross-sectional view of the boot and ski shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of the inner sole of the boot shown in  FIGS. 1 and 3 ; 
         FIGS. 4A and 4B  show a bottom view and a side view, respectively, of the outer sole of the boot shown in  FIGS. 1 and 2 ; 
         FIGS. 5A and 5B  show a bottom view and a side view, respectively, of the lasting insole appearing in  FIG. 2 ; 
         FIG. 6  schematically shows a longitudinal cross-sectional view of a first embodiment of the reinforcement according to the invention; 
         FIG. 7  schematically shows a longitudinal cross-sectional view of a second embodiment of the reinforcement according to the invention; 
         FIG. 8  schematically shows a longitudinal cross-sectional view of a third embodiment of the reinforcement according to the invention; 
         FIG. 9  schematically shows a longitudinal cross-sectional view of a fourth embodiment of the reinforcement according to the invention; 
         FIG. 10  schematically shows a longitudinal cross-sectional view of a fifth embodiment of the reinforcement according to the invention; 
         FIG. 11  is a bottom view of a lasting insole similar to that shown in  FIG. 5A , with a partial tear in the front zone A, of a first example of manufacture of the fibrous web of the reinforcement according to the invention; 
         FIG. 12  is a bottom view of a lasting insole similar to that shown in  FIG. 5A , with a partial tear in the front zone A, of a second example of manufacture of the fibrous web of the reinforcement according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention relates to a reinforcement for a boot, for example a cross-country ski boot, designated by the reference numeral  1  in the drawings. This cross-country ski boot is removably fixed at its front tip to a cross-country ski  2  equipped with a binding  3 . The lower leg, including the foot and ankle positioned in the boot  1 , is schematically illustrated in FIG.  1  and are designated by the common reference numeral  4 . The boot  1  includes an outer sole  5  and a vamp/upper  6 . In  FIG. 1 , the boot  1  is shown in the raised position of the heel relative to the ski  2 . 
       FIG. 2  shows the boot  1  in a position supported on the upper surface of the cross-country ski  2 . As seen in  FIGS. 1 ,  2  and  4 A, the outer sole  5  of the boot  1  has a longitudinal groove  7  adapted to cooperate with a guiding rib  8  affixed to the upper surface of the ski  2 . The groove  7  and rib  8  have complementary transverse trapezoidal cross sections. The guiding groove  7  of the outer sole  5  is partially defined by two parallel side bars  18  having, in their front portion, transverse recesses  19  adapted to improve the bending flexibility of the sole without compromising its torsional rigidity (FIG.  4 A). 
     The boot  1  and foot  4  move from the unrolled position supported on the ski of  FIG. 2  to the rolled (raised) position of  FIG. 1 , by bending about the metatarsophalangeal bending axis shown in FIG.  11  and designated by the reference character α. 
     As seen in  FIG. 2 , the lower portion or bottom assembly of the boot  1  includes the outer sole  5  on which rests the lasting insole  9  overlaid by an inner sole  10 , and affixed to the upper portion of the boot constituted by the vamp/upper  6  by means of an assembly by sewing and/or welding and/or cementing of the lower edge of the vamp  6  which, in this case, is inserted between the lasting insole  9  and the outer sole  5 . 
     According to the invention, the reinforcement is integrated into, or made unitary with, at least one of the constituent elements  5 ,  9 ,  10  of the lower portion of the boot  1 , namely:
         an inner sole  10 , shown in  FIGS. 2 and 3 ;   a lasting insole  9 , shown in  FIGS. 2 ,  5 A and  5 B; and   an outer sole  5  shown in  FIGS. 2 ,  4 A and  4 B.       

     According to an alternative embodiment, the reinforcement integrally or unitarily constitutes one of the constituent elements  5 ,  9 ,  10 . 
     The boot reinforcement considered here is schematically divided into three zones with reference to the anatomy of the foot, namely:
         the front zone A extending on both sides of the metatarsophalangeal bending axis α as shown in FIG.  11  and corresponding to the positioning of the metatarsophalangeal joint, which forms an angle of about 71/72° with the inner tangent T to the foot, and which is located along this same tangent at about 73/74% of the total length of the foot from the rear end P;   the median zone B extending from the rear limit L A  of the zone A corresponding to the front of the plantar arch up to the rear of the plantar arch;   the rear zone C extending from the rear limit L B  of the zone B up to the end of the heel.       

       FIG. 5B  schematically shows the foot  4  in dotted lines, and the zones A, B, C are defined with reference to the foot anatomy. 
     The reinforcement according to the invention can be divided into three zones A, B, C indicated in  FIGS. 3 ,  4 A,  4 B  5 A,  5 B. 
     The same is true with respect to  FIGS. 6-10 , which schematically show five different embodiments of the reinforcement according to the invention, and which show the sandwich structure specific to the zones B and C, and possibly A. 
     This sandwich structure includes two layers, namely, an upper layer  11  and a lower layer  13  between which a core  12  is positioned. The type of materials constituting the layers  11  and  13  and the core  12  in the five embodiments of  FIGS. 6-9  is described hereinafter. 
     According to an advantageous characteristic of the invention, the boot reinforcement to which it relates can be characterized by the longitudinal flexural strengths RfA, RfB, RfC of the zones A, B, C. 
     Thus, according to a preferred arrangement of the invention, each zone A, B, C has a longitudinal flexural strength RfA, RfB, RfC, such that:
 
RfA&lt;RfB≦RfC.
 
     Yet more preferably:
         the zone A has a front-to-rear constant or progressive stiffness RfA;   the zone B has a front-to-rear constant or progressive stiffness RfB;   the zone C has a front-to-rear constant or progressive stiffness RfC;       

     According to a first embodiment of the reinforcement shown in FIG.  6 :
 
RfA&lt;RfB≦RfC
 
with front-to-rear progressive RfA, RfB, RfC.
 
     According to a second embodiment of the reinforcement shown in FIG.  7 :
 
RfA&lt;RfB≦RfC, with:
         constant RfA   front-to-rear progressive RfB   front-to-rear progressive RfC.       

     In this second embodiment of the reinforcement, two areas of different stiffnesses are provided, namely, the area of minimum stiffness corresponding to the zone A, and an area of progressive stiffness corresponding to the zones B and C. 
     According to a third embodiment of the reinforcement according to the invention, shown in FIG.  8 :
 
RfA&lt;RfB≦RfC, with:
         constant RfA   front-to-rear progressive RfB   constant RfC.       

       FIG. 9  shows a fourth embodiment in which the sandwich structure extends over the three zones A, B, C, with characteristics of longitudinal flexural strength such as:
         constant RfA   front-to-rear progressive RfB and RfC.       
       FIG. 10  corresponds to a fifth embodiment in which the sandwich structure extends over the three zones A, B, C, and in which, as for the third embodiment of  FIG. 8 , the characteristics of longitudinal flexural strength are as follows:
 RfA&lt;RfB≦RfC, with:         constant RfA   front-to-rear progressive RfB   constant RfC.       
     The control of the longitudinal flexural strength of the zones A, B, C of the reinforcement is obtained by playing with the type of materials constituting the layers  11  and  13  and the core  12  of the sandwich structure. This longitudinal flexural strength can also be varied by playing with the thickness by progressively varying this stiffness of the reinforcement in the zones A, B, C, as shown in  FIGS. 6-10 . 
     According to various alternative embodiments of the examples of  FIGS. 6-10 , the possible variations in thickness of the reinforcement according to the invention are not linear, knowing that it is preferable not to have any sudden break in slope at the connecting lines, between the zones A and B (rear limit L A  of the zone A), on the one hand, and between the zones B and C (rear limit L B  of the zone B). 
     With respect to the type of materials used to make the reinforcement, and more particularly its sandwich structure, it must be noted that one, preferably both, of the layers  11 ,  13 , of this sandwich structure is(are) made of a composite material based on woven or non-woven fibers included in a matrix. 
     These fibers are preferably selected from the group including: carbon fibers, glass fibers, metallic fibers, natural or synthetic textile fibers, and their mixtures; the carbon and glass fibers being particularly preferred. 
     The material constituting the matrix is preferably selected from the group including: epoxy, polyester or phenolic resins; thermoplastics—advantageously polyamides, polyurethanes, polyolefins—and their mixtures. 
     Examples of fibers that can be used in the manufacture of the composite layers  11 ,  13  of the reinforcement according to the invention, include fibers listed in the Table below, which also indicates the type of weaving webs ( 15 ,  16 ,  15 ′,  16 ′) used, as well as the mechanical properties of these networks or fibrous webs. 
                                                 Stress at break   Modulus greater       Fibers   Weaving   greater than   than                   Glass   UD   700 MPa   25000 MPa       Glass   Multidirectional   350 MPa   12000 MPa       Carbon   UD   1500 MPa    70000 MPa       Carbon   Multidirectional   700 MPa   35000 MPa                    
In this Table, UD signifies unidirectional.
 
     Advantageously, the core of the sandwich structure is made of synthetic foams (preferably polyurethane, poly(meth)acrylic, polyvinyl chloride), wood or honeycomb. 
     In the case of a first embodiment shown in  FIG. 6 , the zone A has a variable stiffness. This corresponds to the first embodiment shown in FIG.  6 . 
     In the first, fourth, and fifth embodiments ( FIGS. 6 ,  9 ,  10 ), the sandwich structure extends into all of the zones A, B, C, whereas it only occupies the zones B and C in the second and third embodiments shown in  FIGS. 7 and 8 . 
     The preferred embodiment of the reinforcement according to the invention could be the third embodiment described hereinabove, in which the zone A with minimum RfA stiffness has a minimum constant thickness and conjugates the maximum torsional strength with a low flexural strength. 
     In all of the embodiments defined hereinabove by way of examples, the median zone B is a zone of evolutional stiffness, variable thickness, and makes it possible to connect the two end zones A and C by providing the progressive stiffness to the reinforcement and to the boot. 
     The rear zone C has a maximum torsional and flexural strength and (preferably) has constant thickness and stacking characteristics. 
     According to alternative embodiments, each zone A, B, C can include one or several sub-zones having longitudinal flexural strengths that are:
         identical to or different from one another; and   constant or evolutional for each sub-zone considered.       

     As seen in  FIGS. 7 and 8  corresponding to the second and third embodiments of the reinforcement according to the invention, the zone A with minimum stiffness RfA does not have any sandwich structure and includes at least one of the two layers  11 ,  13  of the zones B and C in their continuity, and possibly at least another additional layer, not shown in the drawings. 
     In the second embodiment of  FIG. 7 , the zone A of the reinforcement is constituted by the extension of the upper layer  11  of the sandwich structure of the zones B and C, attached to the lower layer  13  of this same sandwich structure. 
     In  FIG. 8 , third embodiment, the zone A of the reinforcement is simply constituted by the extension of the lower layer  13  of the sandwich structure of the zones B and C. In this embodiment, the upper layer  11  of the sandwich structure of the zones B and C is extended by a portion  11 A up to the zone A for a preferably partial covering with the layer  13  in the zone A, in order to ensure the resistance of the reinforcement in the zone contiguous to the limit between A and B. 
       FIGS. 11 and 12  show two methods of manufacturing the reinforcement according to the invention, in particular when it corresponds to the lasting insole  9 . These  FIGS. 11 and 12  partially show the composite structure of the layers  11  or  13  of the sandwich structure. The fibers  14  of the composite layer(s)  11  or  13  of the sandwich structure are arranged in one or several webs  15  and  16  (FIG.  11 ),  15 ′,  16 ′ ( FIG. 12 ) of parallel fibers  14 , the web(s)  15 ,  16 ,  15 ′,  16 ′ being oriented in one or several directions (uni-directional UD or multi-directional orientation). 
     In the two methods of manufacturing the layers, shown in  FIGS. 11 and 12 , the reinforcement includes two webs ( 15  and  16 ), ( 15 ′ and  16 ′) of parallel fibers  14 , these webs being oriented along different directions. 
     According to a preferred characteristic of the invention, these two webs ( 15 ,  16 ) and ( 15 ′,  16 ′) of parallel fibers  14  are symmetrical relative to an axis, the latter preferably being the longitudinal median axis β ( FIG. 12 ) of the reinforcement  9 , or the axis δ ( FIG. 11 ) perpendicular to the metatarsophalangeal bending axis α, which forms an angle of about 19°+/−5° relative to the longitudinal median axis β. 
     Advantageously, the angle between the two webs ( 15 ,  16 ) and ( 15 ′,  16 ′) of parallel fibers  14  is about 90°+/−10°. 
     Preferably, each web  15 ,  16 ,  15 ′,  16 ′ is constituted by a fiber cloth. 
     According to an alternative embodiment, the reinforcement of the invention is an insert  17  that is duplicate molded, or fixed in any other manner, in at least one of the constituent elements  5 ,  9 ,  10  of the lower portion of the boot, this element being preferably selected from the group including the inner sole  10 , lasting insole  9 , outer sole  5 ; the outer sole  5  being more particularly preferred. 
       FIGS. 4A and 4B  show this advantageous alternative embodiment of the invention. The sole  5  includes a duplicate molded insert  17  forming the reinforcement according to the invention. 
     Advantageously, this insert has a composite structure, of the type described, for example, in the five embodiments of  FIGS. 7-10 . 
     According to another alternative embodiment of the outer sole  5  of  FIG. 4A , the duplicate molded insert  17  can be made apparent at one or several locations of the lower surface of this outer sole  5 . The insert  17  can also extend over part or all of the bottom assembly surface. 
     According to the invention, it can be envisioned to use special composite sandwich materials for the manufacture of the reinforcement according to the invention. Thus, this reinforcement can be at least partially constituted by one or several micro-sandwich composite sheets each having a thickness less than or equal to 3 millimeters, and including a composite core inserted between at least two composite layers, the mechanical strength and cost per mass unit of the core being less than those of at least one of the layers. 
     The conventional techniques for producing composites are used to manufacture the reinforcements according to the invention. 
     Thus, the polymeric foams that can constitute the cores of the sandwich structures are obtained by machining or by injection, for example. 
     The composite layers of the sandwich structures are obtained by pressure polymerization techniques. 
     The assembly of the various composite layers and of the core(s), whether made of foam or composite, is carried out by superimposition and pressuring (pressure on the order of 2-10 bars at temperatures of about 100-180° C.). 
     Gluing and heat sealing techniques can also be used. 
     According to another one of these aspects, the present invention also relates to a boot, in particular a sports boot, more particularly a cross-country ski boot ( FIGS. 1 and 2 ) characterized in that it includes at least one reinforcement  5 ,  9 ,  10 ,  17  according to the invention, as described hereinabove. 
     This boot and reinforcement improve the spring power in the metatarsophalangeal journal zone, therefore the efficiency of the boot. 
     Optimizing the flexibility in bending and torsional stiffness makes it possible to significantly improve the control and steering of the ski. 
     The materials used are lightweight and maintain their properties over a very long period of time. They impart a behavior on the boot, especially the cross-country ski boot, such that the rolling/unrolling movements are much more uniform and provide the athletes with better sensations. 
     Finally, the reinforcement according to the invention offers a good foot protection during bending, for it reduces the compressive stresses.