WO2010094861A1

WO2010094861A1 - Board for practicing acrobatic jumps on a trampoline

Info

Publication number: WO2010094861A1
Application number: PCT/FR2010/000138
Authority: WO
Inventors: Thomas Harding; Nadia Oudot; Alain Zanco
Original assignee: Sinaxis
Priority date: 2009-02-20
Filing date: 2010-02-18
Publication date: 2010-08-26
Also published as: FR2942413A1; EP2398643A1

Abstract

The invention relates to a board (2) for training in acrobatic board sports on a springing surface, such as a trampoline, said board (2) including a multilayer core (5) containing: two layers of solid wood with a thickness of less than 3 mm each; a layer of resin inserted between the layers of wood; and two layers of a composite material, including a polymer matrix laden with strengthening fibres, arranged on either side of the wooden layers.

Description

PLATE FOR THE PRACTICE OF ACROBATIC JUMPING ON TRAMPOLINE

The invention relates to boardsports, and more specifically to the training in boardsports, including: skiing, surfing, snowboarding, skateboarding, wakeboarding, etc. More specifically, the invention relates to a board for training in such sports, in which aerobatic jumps aerials are performed. Sliding sports are old. The first clubs appeared skiers in Norway during the second half of the 19th ^century, but the invention of the ski is impossible to date as it is old and appears to have utility functions in cold countries well before rejoicing crowds Downhill amateurs then become a winter Olympic discipline in several events: downhill, slalom, moguls, long jump, acrobatic jump, etc.

Surfing find meanwhile its origins in the 15th ^century in Hawaii, although the first testimonies reported by James Cook date from the 18th ^century, long before Duke Kahanamoku contributes to the global democratization of the sport in the early 20 ^th century . Snowboarding dates back to the 1920s, but its real explosion dates from the mid-1990s, with the adoption of the sport by some of the big names in skateboarding and the escalation of the technical prowess inspired by it.

On the other hand, the invention of skateboarding is dated more precisely in the early 1970s. It is commonly accepted that this sport would have appeared on the initiative of surfers who would have had the idea, to train on hard surface, of equip wheels with profiled boards like surfboards. If the initial movements were limited to ripples in empty pools ("bowls"), some athletes had the idea of a practice playing with elements of urban architecture, giving birth in the early 1980s to a new discipline called "Street", while, marginally, more radical sportsmen indulged in freestyle that, thanks to the invention of the jump on flat surface ("ollie"), contributed to a remarkable technical and demographic boom of the street. At the same time, a vertical practice of skateboarding developed to give birth to the discipline of the ramp. The stylistic orientations of the street, with the adoption by the practitioners of figures derived from freestyle: flips (rotations of the board around a horizontal axis), 180 °, 360 ° (rotation of the board and skater around a vertical axis), grabs (holding the board with the hand), shaped the practice of snowboarding since the mid-1990s, while ramp techniques gave birth, on snow, to the discipline of the half pipe - today hui - transpose, snowboarding on the feet, a part of the aerial tricks practiced on a ramp in a half-tube of snow.

As for wakeboarding, it is initially a variant of water skiing inspired by modern snowboarding: the board incorporates the essential characteristics (dimensional relationships, spacing of the feet, orientation of the bindings, perpendicular to the main axis and to the direction of displacement) ; the figures made (jumps, rotations, grabs) are similar.

Thanks to their popularity, these sports have seen the number of their followers grow exponentially, while manufacturers have offered boards increasingly powerful and resistant, adapted to the most daring acrobatics and increasing demands of athletes, justified by the more and more technical nature of disciplines, as we have just recalled.

Ski and snowboard boards, in particular, must be sufficiently torsionally rigid to have good cornering responsiveness, while having a relative flexibility in bending to adapt to the terrain and absorb some of the shocks to receiving jumps. whose amplitude frequently reaches several meters.

Planks are thus generally formed from a rigid core, composed of several layers around a central layer of wood. Document DE 196 04 016 shows an example of a snowboard comprising a solid wood core covered on both sides with a layer of resin reinforced with fibers for example glass. The documents US Pat. No. 3,844,576, US Pat. No. 5,238,260 and EP 0 492 498 describe skis whose core comprises several wooden boards juxtaposed and assembled for example with glue or resin, making it possible to increase the flexibility of the core. A layer of composite material applied to the wood layer helps to stiffen the whole.

Other documents such as FR 2 830 200 and US 2008/0220276 describe boards whose core comprises plywood. The practice of snow sports, especially snow sports, is usually seasonal, and with the exception of athletes who are fortunate enough to travel the world in search of snow-capped peaks or high waves, common practitioners must frequently give up their sport. exercise for part of the year, or resolve to practice room.

Thus, while in the rainy season the skaters invade some sheltered skateparks, offering conditions close to the urban reality thanks to their relief reproducing the architecture of the cities (steps, stepped sides, stair railings), skiers and snowboarders wishing to practice acrobatic jumping can fall back on the practice on trampoline, which in recent years has experienced remarkable growth and is probably one of the most promising new sports practices.

A trampoline usually includes a frame mounted on feet (and thus raised above the ground). An elastic fabric, generally woven of nylon threads, is stretched between the frame uprights by means of springs. The practitioner, board (s) with the feet, uses the impulses of the trampoline to carry out in the air the figures of his choice (rotations, saltos, etc.). Under current conditions, this training is not without danger, and many injuries are reported, not only because of a lack of practice or physical fitness, but also because of inadequate equipment. Indeed, most practitioners use their usual gliding equipment, which is quite inappropriate for trampoline training.

Firstly, the gliding boards are too long and too rigid to adapt properly to the deformations of the trampoline.

Secondly, the boards have a weight too high for a stationary practice, this weight increasing the inertia of the sport-board couple and thus limiting the amplitude of the movements. Thirdly, the presence of metal edges, useful on snow, damages the trampoline cloth and can cause deep cuts to practitioners during bad receptions. In fact, athletes tend to neglect the wearing of protections (reinforced fabric pants, gloves, helmets) which, in the field, are de rigueur.

The need was therefore urgent to have boards specifically adapted to practice on trampoline and, by improving the quality of indoor training, ultimately secure the practice in the field. Some solutions have been proposed, still few to date.

The documents US 2005/0017463, US 2005/0001392, US 2002/0077222 and US 6,195,558 are based on the principle of a flexible board, for example foam, to which are added fasteners for the feet.

The document FR 2 860 984 describes another example of a trampoline board, which seems technically more accomplished. The board has a frame in tubular structure. Plates placed inside the frame allow to mount fixings. The frame rails are bent to define a curvature on the board. The board is made by assembling a succession of wooden slats, according to a determined radius of curvature. Other materials such as composite materials can be used.

FR 2,831,452 discloses a board in which a wooden core is covered with two layers of fiberglass, woven unidirectionally, arranged on both sides of the core and laminated with an epoxy resin. The upper side is provided with a non-slip layer, and the underside is varnished to make it smooth. These boards did not have the hoped success. If the safety aspect has progressed, however, the excessive flexibility of these boards results, according to some athletes, a lack of nervousness (in English "pop") detrimental to the amplitude and accuracy of acrobatics, as well as stability during the impulse phase on the trampoline. Also, the equipment currently available on the market does not seem to allow athletes to find on trampoline sensations close to those felt on the ground, or to perform acrobatics that can be reproduced later, the season came .

The invention aims to propose a solution to overcome these difficulties.

A first object of the invention is to provide a trampoline board for performing figures in the air. A second object of the invention is to provide a trampoline board flexible enough to accompany the trampoline bending during pulses and sufficiently nervous to improve the accuracy of acrobatics performed in the air.

A third object of the invention is to provide a board for trampoline capable of restoring the sensations experienced on the gliding boards during jumps, including the pulse and reception.

A fourth object of the invention is to provide a board for training jumps limiting the risk of injury to the user.

To this end, the invention proposes, in the first place, a board for training in acrobatic gliding sports on a spring surface, such as a trampoline, this board comprising a multilayer core including: two layers of solid wood; a thickness of less than 3 mm each, a resin layer interposed between the wood layers, - two layers of a composite material comprising a polymer matrix loaded with reinforcing fibers, arranged on either side of the wood layers.

Each layer of wood preferably has a thickness of between 1 mm and 2 mm, for example approximately 1.5 mm.

The essence of wood is selected from the group consisting of ash, poplar, maple; the fibers of the wood layers are preferably oriented along a main axis of the board. Furthermore, according to a preferred embodiment, the reinforcing fibers (such as glass or carbon fibers) are offset angularly with respect to a main axis of the board; they may be crossed, a portion of the fibers being for example angularly offset by an angle of approximately 36 ° with respect to the main axis of the board while the other part is oriented symmetrically with respect to the axis.

A protective foam sheath can at least partially wrap the core. The invention proposes, secondly, a method of manufacturing such a board, the method comprising the following steps:

unwinding a log of wood to obtain a wood sheet having an upper face and a lower face;

- cutting in the sheet of two adjacent wooden boards in the direction of the fibers;

- Assembling the two wooden plates so that their fibers are parallel, their respective lower faces are opposite and the direction of their respective fibers are opposite. The assembly of the wood plates preferably comprises a laminating operation by means of an epoxy resin.

The invention proposes, thirdly, a board for the practice of jumping on a spring surface such as trampoline, this board having a flexibility of between 12 and 26 mm. According to various embodiments, the flexibility can be between 18 and 26 mm, and for example between 20 and 26 mm. - or between 12 and 18 mm, and for example between 12 and 16 mm.

Other objects and advantages of the invention will become apparent in the light of the description given hereinafter with reference to the appended drawings in which:

- Figure 1 is a perspective view of a board for training sports acrobatic gliding, snowboard type comprising a multilayer core partially coated with a sheath, and two fasteners for the feet mounted on the core; Figure 2 is a detail sectional view of Figure 1 showing the slice the core of the board; Figure 3 is a view similar to Figure 1, showing a pair of boards for training in sports freestyle skiing, ski type; each ski comprises a multilayer core partially coated with a sheath, and a fixation for a foot mounted on each core; Figure 4 is a perspective view of a multilayer core for a board as shown in Figures 1 and 3; - Figure 5 is a cross-sectional exploded view of the core of Figure 4; Figure 6 is a schematic diagram illustrating the deformation of the board on a trampoline; Fig. 7 is a diagram illustrating a test protocol for measuring the flexibility of the board; Figure 8 is a perspective view illustrating the manufacture of wood plates of the multilayer core from the unwinding of a log; Figure 9 is a perspective view illustrating a step of the assembly of wood plates; Figure 10 is a side view of the plates of Figure 9; Figure 11 is a top plan view showing a composite layer of a board according to the invention. In Figures 1 and 3 are shown boards 1, 2 for training sports gliding on a spring surface. In Figure 1 is shown a board 1 of the snowboard type, provided with two fasteners 3 spaced apart to receive the sportsman's feet substantially perpendicular to the major axis 4 of the board (main axis). In Figure 4 is shown a pair of boards 2 ski type, each provided with a single attachment 3 provided to receive a foot parallel to the main axis of the ski.

By "spring surface" is meant here any elastic surface capable of resuming almost instantaneously its original shape when deformed, so as to provide a pulse substantially perpendicular to the surface. Typically, this spring surface is the stretched canvas of a trampoline. The board 1, 2 comprises a multilayer core 5 partially coated with a foam sheath 6. The core 5 has an oblong shape extending along an axis coinciding with the main axis 4 of the board 1, 2. It has two parallel lateral edges 7, 8 and has two symmetrical rounded ends 9, 10 opposite each other. In the example shown, the core 5 is plane, including at its ends 9 and 10, but one could, alternatively, imagine ends 9, 10 inclined, like spatulas of a ski or skateboard .

The structure of the core 5 is furthermore symmetrical with respect to a central plane and comprises at least five superimposed layers, namely:

Two layers 11 of solid wood;

A central layer of resin interposed between the layers of wood; Two outer layers 13a and 13b of composite material, covering the wood layers.

Each layer 11 of wood is made of a plate 14 of solid wood. The wood species used is preferably ash, poplar or maple, recognized for good compromise between hardness (synonymous with longevity) and flexibility (ability to deform elastically). However, any other wood species with similar mechanical characteristics could be selected.

In order to give the core 5 (and thus the board 1, 2) the desired flexibility (see below), each layer 11 of wood has a thickness of less than 3 mm. In practice, the thickness of each layer 1 1 of wood is preferably between 1 mm and 2 mm. According to a preferred embodiment, this thickness is equal to approximately 1.5 mm.

As will be seen below in more detail, each plate 14 of wood is cut so that its main axis (axis of greater length) extends along the tracheids (longitudinal fibers of the trunk of the tree in which the board is cut out). This orientation of the fibers makes it possible to give the plate 14 good elasticity in flexion. By definition, the composite material used for producing the outer layers 13a, 13b comprises a matrix 15, for example of polymer type, loaded with reinforcing fibers 16. The matrix 15 is, for example, epoxy resin. As for the fibers 16, it is preferably glass fibers or carbon. These two fibers can be combined or superimposed. According to a preferred embodiment, the outer layers 13a, 13b comprise glass fibers 16, applied to the wood layers in the manner of a fabric. These fibers 16 are not (at least not all) applied in the axis of the board 1, 2, but are angularly shifted (at least a part of them) relative to it, it is that is to say that the oriented fibers 16 form with the axis 4 of the board 1, 2 a predetermined angle α (Figure 11). In addition, the fibers 16 are preferably crossed, a portion of the fibers 16 (for example half of them), forming weft yarns 17, being angularly offset according to the predetermined angle α with respect to the axis 4 main part of the board 1, 2, while the other part, forming 18 son of warp, is oriented symmetrically with respect to the axis 4. The angle α of the fibers 16 is preferably between 20 ° and 40 °. According to a preferred embodiment, the angle α of the fibers 16 is approximately 36 ° with respect to the main axis 4 of the plate 1, 2. This arrangement of the reinforcing fibers 16, and in particular the preferred angle of 36 °, contributes to the flexibility characteristics of the board 1, 2 in bending, and torsional stiffness.

The grammage of the glass fiber fabric 16 used is preferably between 550 and 800 g. m ^"2. According to a preferred embodiment, the basis weight is 700 g. ^{m" 2} approximately.

Alternatively, for a carbon fiber fabric 16, a grammage of between 220 and 500 g will be retained. m ^"2 , and for example about 400 g, m ^'2 .

The thickness of the outer layers 13a, 13b is preferably between 0.2 mm and 0.8 mm. According to a preferred embodiment, this thickness is equal to about 0.55 mm.

The resin used for the central layer 12, intended to allow a solid assembly of the layers 11 of wood, is for example epoxy. According to one embodiment, its thickness is between 0.1 mm and 0.5 mm, and preferably about 0.2 mm (in the present description, the term "about" means that tolerance of ± 10% is applied to the indicated dimensions). As a variant, the central resin layer 12 has a greater thickness, between 0.5 mm and 1 mm, and is reinforced with a middle layer of composite material (such as fiberglass or carbon fiber) having a thickness of between 0.1 and 0.2 mm and a fiber orientation similar to that of the outer layers 13a, 13b. This variant is essentially intended to stiffen the boards 2 ski type, which given their smaller width have equal structure flexibility greater than that of the board 1 type snowboard.

In addition, a decorative layer may be applied to the upper outer layer 13a. This layer may be in the form of a varnish applied by brush or spray, or a film. An additional layer of transparent or translucent finish preferably comes to cover the upper outer layer 13a of the core 5, trapping the decorative layer so that it protects against external aggressions (scratches, blows, etc.). This topcoat is for example made of polyamide and has a thickness of about 0.3 mm. Neither the decorative layer nor the topcoat affect the mechanical properties of the core 5.

To reduce the risk of injury by contact with the board, the core S is partially coated with a sheath 6. As shown in Figure 1, the sheath completely covers only one of the outer layers 13a, 13b - so-called layer 13b external outer opposed to the upper outer layer 13a - the slice 19 of the core 5, as well as the periphery of the upper outer layer 13a.

The sheath 6 is made of a high density foam, for example polyethylene or polyurethane. Its thickness, on the side of the lower outer layer 13b and around the wafer 19, is preferably between 20 mm and 40 mm. This thickness is lower on the side of the upper outer layer 13a, where it is between 5 mm and 20 mm. The foam strip covering the upper outer layer 13a has a width of between 10 mm and 50 mm. The core 5 thus structured gives the board 1, 2 mechanical characteristics particularly interesting for practice on a surface 20 spring such as a trampoline.

With regard to the external dimensions, the core 5 of the snowboard 1 has a length (measured between the ends) of between 80 cm and 120 cm, and preferably of about 95 cm, and a width (measured between the side edges) between 20 cm and 30 cm, and preferably about 25 cm. The core 5 of the skis 2 has a similar length, between 80 cm and 120 cm and preferably about 95 cm and a width between 10 and 15 cm, and preferably about 12 cm.

It should be noted that the stresses undergone by the board 1, 2 are mainly caused by bending deformation along its main axis 4 (that is to say a deformation bending the board 1, 2 in a plane containing its main and perpendicular axis 4). to the surfaces of the outer layers 13a, 13b) when, under the weight of the user, the board 1, 2 flexes in the hollow of the surface 20 of the trampoline. The deformation d of the board 1, 2 (measured independently of the depression of the board 1, 2 in the trampoline) is maximum at the moment of the impulse, when the web 20 of the trampoline is at its lowest point Pb; it is at this moment that the board 1, 2, which marries the surface 20 of the fabric, has its smallest radius of curvature (FIG. 6).

The board 1, 2 is also subjected to stresses due to a secondary bending deformation perpendicular to the main axis 4 (that is to say a deformation bending the board 1, 2 in a transverse plane, perpendicular to its main axis 4 ), because of the unequal nature with which the weight of the user applies in the width of the board 1, 2, as well as torsional stresses due to possible tilting of the feet of the user from before back. These transverse bending and torsion constraints are, however, negligible with respect to the bending stresses along the main axis of the plate 1, 2. They do not affect the performance of the board 1, 2, which can be characterized. by the flexibility of the latter according to its main axis 4.

The objectives are: • sufficient flexibility to accompany the fabric without breaking the board 1, 2 to a sufficiently low point Pb, thus maximizing the impulse,

• On the contrary, sufficient rigidity to give the board 1, 2 after the impulse a nervousness close to the classic boards and to allow on trampoline most of the acrobatic figures usually performed in the field. The elasticity of the board 1, 2, that is to say its capacity to resume its initial shape without rupture, can be tested in situ, directly on trampoline. By convention, it is decreed that the elasticity is satisfactory when the board remains in its elastic deformation range when used on a trampoline STAR® range, marketed by the company KANGUI, having a frame of dimensions 3.8 x 2 , 5 m, with a canvas of 3 x 1, 80 m for a maximum user weight of 140 kg.

Moreover, a characteristic parameter of the inherent flexibility of the plate 1, 2 is defined arbitrarily, that is to say its capacity to deform under the application of an external constraint. By convention, this parameter is termed "flexibility", measured by means of a predetermined test protocol, which will now be described with reference to FIG. 7.

The impact of the sheath on the performance of the board being negligible, the measurement is performed directly on the core 5, a length of 95 cm. The core 5 is positioned horizontally flat, symmetrically, resting on two transverse linear supports 21 spaced a distance D of 52 cm. The ends of the core 5 therefore extend cantilevered beyond the linear supports 21. A static load C of 20 kg is applied to the center of the core 5, which generates at this point a force directed vertically downwards by a value of about 200 N. Under the effect of this load, the core 5 flexes and curves between the linear supports 21. The flexibility of the core 5 (or of the plate 1, 2) is called the maximum arrow f of the core 5, equal to the distance, measured on the axis of application of the force, separating the two places from the intersection point of the axis of application of the force with the upper surface of the core 5, the first in the absence of effort, the second when the effort is applied. The value of the flexibility is given in mm.

Note that the flexibility thus measured provides a static characterization of the flexibility of the core 5, while the performance of the board 1, 2 is dynamically appreciated (that is to say that the load actually applied to the board - resulting from the weight of the user - varies over time, as the board sinks into the trampoline cloth, to reach a maximum at the lower Pb points during the impulse). However, tests carried out in situ under the conditions of normal use have shown that the perception by the athletes of the performance of the boards 1, 2 tested can be directly correlated to the flexibility measured under the static conditions described above. On the basis of criteria of subjective appreciation on the part of the sportsmen, one can limit the flexibility of the nucleus between:

• a useful minimum, below which the board 1, 2 is certainly very nervous, for the benefit of its pop, that is to say its own rebound capacity, but has a rigidity such as the impulse it can benefit on the trampoline is limited, the height of jumps then proving insufficient to allow the execution of a large number of figures; and

• a useful maximum, beyond which the board 1, 2 proves too flexible, the important impulse that it authorizes being counterbalanced by an insufficient nervousness, to the detriment of the pop and the speed of execution of the figures. The compromise appears satisfactory when the flexibility of the board 1, 2 is between 12 mm and 26 mm. In this range, board 1, 2 is sufficiently flexible to allow substantial deformation of the trampoline web (benefiting the momentum) while being rigid enough to contribute significantly to pop. The sensations felt during acrobatic jumps on trampoline are then close to those felt in the field under normal conditions of gliding. Whatever the season, users can train effectively in their sport. For confirmed practitioners, looking for a board 1, 2 nerve, the flexibility is advantageously between 12 and 18 mm, or even between 12 and 16 mm.

Such values can be obtained without modifying the thickness of the board 1, 2 but by using carbon fiber instead of fiberglass in the outer layers of the core.

For beginners, who are looking for a board 1, 2 more flexible, it will retain flexibility values between 18 mm and 22 mm, or between 18 mm and 20 mm. We have seen that the core 5 is coated with a foam sheath 6.

This is not only to protect the user from the blows that the board could inflict on poor jumps or falls poorly received, but also to preserve the web 20 of the trampoline of any cuts. In order to extend the life of the board 1, 2, and in particular of the sheath 6, it will be moreover advantageous to provide the edge of the core 5 with a protective bead, for example an elastomer such as rubber, preserving the foam shear forces generated by possible movement of the core 5 relative to the sheath 6. Described below the method of manufacture of the board.

The wood plates 14 are cut from a wood sheet obtained by tangential slicing or unwinding of a log 22, in which the wood fibers extend along the longitudinal axis of the ball 22. The slicing of the ball 22 and the cutting of the plates 14 are illustrated together in Figure 8, which illustrates a log 22 of wood being peeled. The ball 22 is driven in a rotational movement, while a knife 23 pressed against the ball 22 forms a wooden sheet, of width equal to the longitudinal dimension of the ball 22 and whose thickness corresponds to the thickness desired layers 11 of wood of the core 5.

An opposite bottom face 24 and an opposing top face 25 are arbitrarily defined on the thus unwound sheet. The upper face corresponds for example to the face initially turned towards the inside of the ball. In this case, the upper face is concave, the lower face 24 being convex. Two plates 14 of wood for the same core 5 are then cut on the thus unwound sheet, so that the wood fibers extend along a main axis 4 of each plate and that the plates 14 are adjacent, their axes 4 the main

The two plates 14 are then assembled by being superimposed (FIG. 9), their axes 4 kept parallel, so that their respective lower faces 24 are opposite each other (in other words, the plates are back-to-back). ) and that their fibers are of opposite directions (in other words, the plates are head-to-tail, the plates 14 having undergone relative to each other a rotation of 180 ° with respect to a central axis perpendicular to their faces).

This arrangement of the plates 14, which have thus undergone a double reversal with respect to each other, aims at canceling the deviation, with respect to the main axis, from the natural direction of preferential deformation of the wood and conferring on the core 5 a symmetrical mechanical behavior with respect to a plane containing its main axis and perpendicular to its faces.

Once the plates 14 thus arranged, they are pressed against each other (this pressure is shown in Figure 10 by the two pairs of antagonistic arrows) with the interposition of a layer 12 of resin. The plates 14 can be kept in press for a certain time, necessary for the drying of the resin and the flatness of the assembly. The layers 13a, 13b of composite are then applied on both sides of the wood plates 14. For this purpose, we first apply a layer of resin, then apply a fiber fabric (glass or carbon) respecting the angular constraints indicated above (Figure 1 1). Then the fabric is covered with a new layer of resin so as to embed the fibers in a resin matrix. A hardener may be associated with the resin.

The assembly is then baked to allow the resin to harden.

Optionally, one or more decorative layers are affixed, then a topcoat is applied to protect them. A bead can be added on the edge of the core 5 thus obtained, in order to avoid any sharp edge. Then the core 5 is threaded into its sheath 6. Alternatively, the sheath 6 can be made by injection into a mold in which the core had previously been introduced. Fixings 3 are mounted on the core (before or after the addition of the sheath), by screwing, gluing or riveting.

Claims

1. Board (1, 2) for training in acrobatic gliding sports on a spring-loaded surface (20), such as a trampoline, this board (1, 2) comprising a multilayer core (5), characterized in that the core (5) comprises: two layers (11) of solid wood with a thickness of less than 3 mm each, a layer (12) of resin interposed between the layers of wood, - two layers (13a, 13b) of a material composite comprising a polymer matrix (15) loaded with reinforcing fibers (16) arranged on either side of the layers (11) of wood.

2. Board (1, 2) according to claim 1, wherein each layer (11) of wood has a thickness of between 1 mm and 2 mm.

3. Board (1, 2) according to claim 2, wherein each layer (11) of wood has a thickness of about 1.5 mm.

4. Board (1, 2) according to one of claims 1 to 3, wherein the wood species is selected from the group consisting of ash, poplar, maple.

5. Board (1, 2) according to one of claims 1 to 4, wherein the fibers of the layers (11) of wood are oriented along a main axis (4) of the board.

6. Board (1, 2) according to one of claims 1 to 5, wherein the reinforcing fibers (16) are offset angularly with respect to a main axis (4) of the board (1, 2).

7. Board (1, 2) according to claim 6, wherein the reinforcing fibers (16) are crossed.

8. Plank (1, 2) according to claim 7, wherein a portion of the fibers (16, 17) is angularly offset by an angle of 36 ° relative to the axis (4) of the main board (1). , 2), the other part (16, 18) being oriented symmetrically with respect to the axis (4).

9. Board (1, 2) according to one of claims 1 to 8, wherein the fibers (16) of reinforcement are glass or carbon fibers.

10. Board (1, 2) according to one of claims 1 to 9, which comprises a sheath (6) foam at least partially enveloping the core (5).

11. Board (1, 2) for practicing jumps on a surface (20) spring such as trampoline, the board (1, 2) being characterized in that it has a flexibility of between 12 and 26 mm.

12. The board (1, 2) according to claim 11, which has a flexibility of between 18 and 26 mm, and preferably between 20 and 26 mm.

13. The board (1, 2) according to claim 11, which has a flexibility of between 12 and 18 mm, and more precisely between 12 and 16 mm.

14. A method of manufacturing a board (1, 2) according to one of claims 1 to 10, comprising the following steps: - unwinding a log (22) of wood for obtaining a wood sheet having an upper face (25) and a lower face (24);

- cutting in the sheet of two adjacent plates (14) of wood in the direction of the fibers; - Assembling the two plates (14) of wood so that their fibers are parallel, their respective lower faces (25) are vis-à-vis and the direction of their respective fibers are opposite.

15. The method of claim 14 wherein the assembly of the wood plates (14) comprises a laminating operation by means of an epoxy resin.