WO2010082132A1 - Back and thigh exercise apparatus - Google Patents

Abstract

An exercise method and system are provided. The exercise system includes a saddle (1) and extensible legs (23). The saddle is connected to the extensible legs. Each extensible leg is connected at one end to the saddle at a pivot point (21), and at another end to a set of wheels (22). A rebounding mechanism (4) is connected between the extensible legs. A position-limit mechanism (51) is connected between the extensible legs.

Description

BACK AND THIGH EXERCISE APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of: China- mainland Design Application Serial No. 200930003209.3, filed on January 19, 2009, China-mainland Utility Patent Application No. 200920008410.5, filed on March 6, 2009, and U.S. Provisional Patent Application Serial No. 61/159,741, filed on March 12, 2009, which all are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The present invention relates generally to exercise devices, and in particular to a back and thigh exercise apparatus .

Background Information

[0003] Toning and strengthening the back, abdomen and leg muscles is important in maintaining proper posture and a healthy body. An effective way of toning and strengthening such muscles involves performing squat motions as shown by example in Fig. 1. However, the body weight is only supported by the legs while the individual raises and lowers the upper torso during up/down squatting motions. Specifically, the majority of weight of the individual must be supported by the lower back and knee joints. This leads to lower back and knee pain after repeated squats.

BRIEF SUMMARY OF THE INVENTION

[0004] One embodiment of the present invention provides a horse-riding apparatus comprising a saddle, left and right support legs that are pin-jointed to the bottom of the saddle. The two support legs include pulleys at the lower portion, which can directly couple with the ground. A synchronizing mechanism and a rebounding mechanism respectively and automatically control the opening and closing of the two legs. A position-limit mechanism includes a wire rope and two fixing blocks between the two support legs that limit their opening. The two ends of the wire rope are fixed on the two fixing blocks, while the fixing blocks are fixed at the middle part of the two support legs.

[0005] In one implementation, the fixing blocks of the position-limit mechanism are equipped with several fixing holes, on which the ends of the wire rope are fixed with pins. The synchronizing mechanism comprises two synchronizing teeth gearing into each other that are fixed on a pin joint shaft at an upper portion of the left and right support legs. The rebounding mechanism comprises a rubber tension board, the two ends of which are fixed at a middle portion of the right and left legs through torsional springs. The rebounding mechanism comprises a spring or spring rope fixed at the middle portion of the right and left legs. The right and left legs comprise an extensible structure.

[0006] The above-described embodiment comprises two synchronizing support legs under the saddle and two pulleys at the lower portion of the support legs. Therefore, this implementation of an exercise apparatus may ensure physical training of leg muscles while a user is riding and pressing the saddle, as like riding a horse, with his/her legs on the ground. Additionally, one implementation includes rebounding and position-limit mechanisms between the two support legs, which can respectively rebound the apparatus automatically and limit its maximum opening, which provides additional safety in use. The apparatus comprises a simple mechanism and is convenient to operate. One implementation is easy to fold by closing the two support legs inwardly. The support legs are also adjustable, so they can be shortened to reduce the machine's size, which is helpful for transport and storage .

[0007] Another embodiment provides an exercise apparatus comprising a seat supported by two tubes, each tube is connected at one end to the seat at a pivot point, and at another end to a wheel that can roll on a surface. The apparatus further includes an elastic member connecting the tubes along the length of the tubes. Application of downward pressure on the seat due to a user' s body weight on the seat causes the tubes to pivot and rotate apart as the wheels roll on the surface, stretching the elastic member. Upon removal of the downward force, contraction of the elastic member causes the tubes to rotate back together and raise the seat.

[0008] These and other features, aspects and advantages of the present invention will become understood with reference to the following description and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a fuller understanding of the nature and advantages of the invention, as well as a preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings, in which:

[0010] Fig. 1 shows an individual performing squats without an exercise apparatus;

[0011] Fig. 2 shows a perspective view of an exercise apparatus according to an embodiment of the invention;

[0012] Fig. 3 shows a side view of the embodiment illustrated in Fig. 2;

[0013] Fig. 4 shows a sectional view of the embodiment illustrated in Fig. 1;

[0014] Fig. 5 shows a side view of the embodiment illustrated in Fig. 1 in use at a first position;

[0015] Fig. 6 shows a side view of the embodiment illustrated in Fig. 1 in use at a second position; [0016] Fig. 7 shows a perspective view of an exercise apparatus according to another embodiment of the invention;

[0017] Fig. 8 shows an exploded view of the exercise apparatus illustrated in Fig. 7 ;

[0018] Fig. 9 shows a perspective view of the exercise apparatus illustrated in Fig. 7 as viewed looking up towards the seat;

[0019] Fig. 10 shows a perspective view of the exercise apparatus illustrated in Fig. 7 while assembling the tubes and extension legs;

[0020] Fig. 11 shows a perspective view of the exercise apparatus illustrated in Fig. 7 while assembling the elastic members (rubber bands) ;

[0021] Fig. 12 shows a perspective view of the exercise apparatus illustrated in Fig. 7 while further assembling the elastic members (rubber bands) and a stopper;

[0022] Figs. 13 and 14 show views of the exercise apparatus illustrated in Fig. 7 while assembling an optional display monitor; [0023] Fig. 15 shows a perspective view of the exercise apparatus illustrated in Fig. 7 while assembling the seat;

[0024] Figs. 16-19 show an individual using the exercise apparatus illustrated in Fig. 7 in performing squats; and

[0025] Fig. 20 shows side views of the exercise apparatus with the stopper of Fig. 12 attached in different positions on the tubes to control the maximum separation distance between the tubes as the user weighs down on the seat.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The following description is made for the purpose of illustrating the general principles of the invention and is not meant to limit the inventive concepts described herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.

[0027] The description may disclose several preferred embodiments for a back and thigh exercise apparatus. While the following description will be described in terms of such languages for clarity and placing the invention in context, it should be kept in mind that the teachings herein may have broad application to all types of systems, devices and applications .

[0028] In one embodiment, the present invention provides an exercise apparatus comprising a seat supported by two telescopic tube members adjustable in length, each tube member connected at one end to the seat at a pivot point, and at another end to a wheel that can roll on a surface.

[0029] The apparatus further includes an elastic member connecting the tubes along the length of the tubes. Application of downward pressure on the seat due to a user' s body weight on the seat causes the tubes to pivot and rotate apart as the wheels roll on the surface, stretching the elastic member. Upon removal of the downward force, contraction of the elastic member causes the tubes to rotate back together and raise the seat.

[0030] Figs. 2, 3 and 4 show an operating example for an exercise machine 100 according to one embodiment of the invention. The "horse-riding" exercise machine 100 of this utility model mainly includes saddle 1, right and left support legs 2, synchronizing mechanism 3, rebounding mechanism 4 and position-limit mechanism 51.

[0031] In one embodiment of the invention, the top of the right and left support legs 2 is pin-jointed at the bottom of the saddle 1; below the right and left support legs 2 are pulleys/wheels 22 that may be directly in contact with the ground. In order to be suitable for people of different heights, the right and left support legs 2 are designed to be telescopically extensible, thus to have the function of being flexibly adjusted as desired. The right and left support legs 2 comprise the upper support tube 23 and the lower support tube 24. On the side walls of the upper and lower support tubes 23, 24, there are several positioning holes 25. Tiny snaps 26, which can be fixed into the positioning holes 25, are positioned between the walls of the upper and lower support tubes 23, 24 so as to fix the two tubes 23, 24 in relation to one another. Such mechanism provides positioning structure for telescoping tubes 23, 24.

[0032] In one embodiment of the invention, the structure of the synchronizing mechanisms 3 enables the right and left support legs 2 to open or close synchronously. In this operational example, each synchronizing mechanism 3 comprises synchronizing teeth on a pin joint shaft 21 at an upper part of the right and left support legs 2, wherein two sets of synchronizing teeth of the synchronizing mechanisms 3 gear into each other. This synchronizing structure enables the right and left support legs 2 to open or close synchronously, preventing desynchronization of the two support legs.

[0033] The rebounding mechanism 4 enables an opened right and left support legs 2 to close (move back towards each other) automatically. In this operational example, the rebounding mechanism 4 comprises a rubber tension element/board, the two ends of which are fixed at the middle part of the right and left support legs 2 with couplers, such as torsional springs 6, which can prevent damage to the rebounding mechanism in operation. The rebounding mechanism may be a spring, spring rope, stretchable device, etc.

[0034] The position-limit mechanism 51 is used to limit the opening angle of the right and left support legs 2. In this operational example, the position-limit mechanism includes limiting wire rope 51 and two fixing blocks 52. The two ends of the wire rope 51 are fixed on the fixing blocks 52, which are attached along the length of the right and left support legs 2. On the fixing blocks 52, there are several fixing holes 53, on which the wire ropes 51 may be attached using pins 54 (fixing the rope 51 between different holes 53 on the respective legs, allows varying the range of maximum opening angle of the legs 2) .

[0035] While using the exercise machine 100, the user sits on the saddle 1 putting his/her feet on the ground, then he/she presses the saddle 1 by allowing his weight to bear on the saddle 1, causing the right and left support legs 2 open by moving apart from each other, as shown by example in Fig. 5. The synchronizing teeth 3 enable the two support legs 2 to move (open/close) synchronously, and the tension board 4 resists an applied force (i.e., weight of the user) that causes the legs 2 to open apart. The synchronizing teeth 3 may also prevent the right and left support legs 2 stretching outwardly to strengthen the effects of exercise. Then, the user stands on his/her feet (essentially removing most/all of his weight from the saddle 1), wherein the right and left support legs 2 close automatically with the restoring/contracting force of the tension board 4. Meanwhile, the saddle 1 rises. Repeating the above actions, the user is able to exercise his/her leg muscles.

[0036] Without the position-limit mechanism 51, the right and left support legs 2 would possibly be allowed to remain in a flat state, as shown in Fig. 6, when the user presses down on the saddle. Then, as the tension board 4 is almost parallel to the right and left support legs 2, its restoring force is minimized. According to one or more embodiments of the invention, the position-limit mechanism 51 limits the maximum opening angle of the right and left support legs 2. When the position-limit wire rope 51 is fixed at different positioning holes 52 on the positioning blocks, the maximum opening of right and left support legs 2 is adjustable and the user may adjust the exercise machine 100 to different strength levels through the adjustment. [0037] Fig. 7 shows another example implementation of the exercise apparatus, according to the invention. The apparatus 700 includes multiple component parts as shown by the exploded view in Fig. 8. For ease of description, Table 1 below provides a list of example component parts of the apparatus along with component reference numbers (NO.), the name of each component part, and the quantity (Qty) of each component part. Table 1 further provides example dimensional specification for certain component parts. The structural supporting parts of the apparatus may be made of metals, metal alloys, etc. The example components are also useful for the embodiment of the invention shown in Fig. 2.

Table 1 - Component List

(Φ meaning diameter, φ meaning spherical diameter) The following list further elaborates on the function of the various components in Table 1 above:

Component 801: Screws used for fixing the seat and foot tube plastic cover;

Component 802: Foot tube covers for making the outlook more beautiful;

Component 804: Spring part of pop-pin system which works combined with Component 805;

Component 807: Pin for stopper which is part of stopper system and works with Component 810;

Component 811: Axle bushing to fix the leg tubes;

Component 813: Seat cover for making the outlook more beautiful;

Component 815: Nut for fixing the Component 818;

Component 817: Nut for fixing the Component 818, but with a different shape as Component 815;

Component 818: Steel part of seat for holding the seat;

Component 820: Bushing fixing the wheel;

Component 826: Sticker for display; and

Component 829: Magnet working with a sensor 827 and a monitor 828 to display exercise related information.

[0038] Figs. 9-12 show assembly of the exercise apparatus using the component parts. As shown in Fig. 9, bolts 815 are used to affix the handle 821 to the seat 823. As shown in Fig. 10, pop pin 805 is released, and bottom leg extension tubes 803 are placed into upper leg tube 806 (left) and upper leg tube 812 (right) , with the height selected for the best fit to an individual. Then, as shown in Fig. 11, resistive (elastic) rubber band 808 is installed between the tubes 806, 812, using pinch clips 809. The assembled apparatus is as shown in Fig . 7.

[0039] Fig. 12 shows adjustment of the stopper 810 (e.g., fixed length cable) . The stopper 810 may have six adjustment options as: connect A-C, A-D, A-E, B-C, B-D, or B-E. In the example shown in Fig. 12, the stopper 810 is connected between hole D on tube 806 and hole B on tube 812.

[0040] As the user places his weight on the seat 816, the upper part of tubes 806 and 812 pivoting about bolts 814

(Fig. 8), the lower parts of the tubes 806 and 812 move apart rolling on wheels 824 (essentially along dashed curve 831, Fig. 12) . The rubber band 808 is stretched out (along dashed line 832) until the stopper 810 is extended to its maximum length between the tubes 806 and 812 (the stopper has a fixed length and will not stretch beyond the fixed length) . At that point, the lower part of the tubes 806 and 812 (i.e., legs 803) cannot move further apart since the stopper 810 is at its maximum length. In the embodiments shown in Figs. 7- 12, the stopper 810 is similar or the same as the position- limit mechanism 51 shown in Figs. 2-6; the rubber band 808 is similar or the same as the rebounding mechanism 4 shown in Figs. 2-6; and the synchronizing mechanisms 3 are attached similarly or attached in a same way to each of the upper leg tube 806 and the upper leg tube 812, therefore further description of the details of the stopper 810, the rubber band 808, and the synchronizing teeth are not included in reference to Figs. 7-12.

[0041] As shown in Fig. 12, as the user lowers to a squat position, stretching of the elastic rubber band 808 helps reduce loading on the back and knees of the user. When the user begins to rise up, the rubber band 808 contracts, helping the user rise up with reduced loading on the lower back and knees.

[0042] When the stopper 810 is connected between holes A and C, the rubber band 808 may experience maximum stretching before the tubes 806 and 812 are stopped from moving further apart by the stopper 810. When the stopper 810 is connected between holes B and E, the rubber band 808 may experience minimum stretching before the tubes 806 and 812 are stopped from moving further apart by the stopper 810. [0043] Figs. 13-14 show an optional display monitor assembly by releasing the handle 821, placing the display monitor 828 in an opening in the handle 821 (top drawing in Fig. 13), and fixing the monitor in the opening within the handle 821 (bottom drawing in Fig. 13) . The display monitor 828 may display exercise related information such as physical condition of the individual and/or the apparatus, via sensor 827. Fig. 14 shows the handle 821 attached under the seat 823. Fig. 15 shows attaching the handle 821 to the seat 823 using nuts 815 and flat washers 816.

[0044] Figs. 16-19 show example uses of the exercise apparatus according to an embodiment of the invention. As shown in Fig. 16, initially the user adjusts height of the seat 823 according to the height of the user's hips for a comfortable level.

[0045] Then, as shown in Fig. 17, the user positions the seat 823 between the legs and grabs the seat 823 with both inner thighs (the user may also grab the handles 821 by hand) .

[0046] Then, as shown in Fig. 18, the user places his body weight on the seat 823, squats down as indicated by vertical down arrow, causing the tubes 803 at bottom of tubes 806, 812 to rotate apart along the horizontal arrows while rolling on the wheels 824. The squatting motion causes stretching of the rubber band 808. Stretching of the rubber band 808 helps support the user's weight.

[0047] Then as shown in Fig. 19, the user rises up as indicated by the vertical up arrow, wherein contracting action of the rubber band 808 causes the tubes 803 at bottom of tubes 806, 812 to rotate together along the horizontal arrows. The contracting action of the rubber band 808 further helps the user rise up.

[0048] When squatting, the user may gently squat down, wherein the body weight on the seat is partially supported/distributed by stretching resistance of bands 808 and with the four wheels 824.

[0049] Upon rising up, the contracting action of the rubber band 808 helps raise the user. As such, the exercise device helps reduce pressure on the lower back and knee joints of the user. The user then may perform repeated squats with reduced pressure on the lower back and knee j oints . [0050] Fig. 20 shows six side views of the exercise apparatus with the stopper 810 attached in different positions on the tubes 806, 812 to control the maximum separation angle between the tubes 806, 812 as the user weighs down on the seat. Specifically, Fig. 12 shows holes A, B on tube 812 and, holes C, D, E on tube 806. The stopper 810 may be attached at one end to holes A or B, and at another end to holes C, D or E.

[0051] For example, in Fig. 20: A-C means that the stopper 810 is connected between hole A on tube 812 and hole C on tube 806, allowing maximum separation angle of 121 degrees for a minimum seat distance to floor of 380 millimeters; A-D means that the stopper 810 is connected between hole A on tube 812 and hole D on tube 806 allowing maximum separation angle of 113 degrees for a minimum seat distance to floor of 414 millimeters; A-E means that the stopper 810 is connected between hole A on tube 812 and hole E on tube 806 allowing maximum separation angle of 105 degrees for a minimum seat distance to floor of 446 millimeters; B-C means that the stopper 810 is connected between hole B on tube 812 and hole C on tube 806 allowing maximum separation angle of 98 degrees for a minimum seat distance to floor of 473 millimeters; B-D means that the stopper 810 is connected between hole B on tube 812 and hole D on tube 806 allowing maximum separation angle of 91 degrees for a minimum seat distance to floor of 498 millimeters; B-E means that the stopper 810 is connected between hole B on tube 812 and hole E on tube 806 allowing maximum separation angle of 85 degrees for a minimum seat distance to floor of 521 millimeters. The A-C attachment for stopper 810 allows greatest separation between tubes 806, 812, and the B-E attachment for stopper 810 allows least separation between tubes 806, 812, under the weight of the user on the seat.

[0052] While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art .

[0053] Reference in the specification to "an embodiment," "one embodiment, " "some embodiments, " or "other embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments. The various appearances of "an embodiment," "one embodiment, " or "some embodiments" are not necessarily all referring to the same embodiments. If the specification states a component, feature, structure, or characteristic "may, " "might, " or "could" be included, that particular component, feature, structure, or characteristic is not required to be included. If the specification refers to "a" or "an" element, that does not mean there is only one of the element. If the specification refer to "an additional" element, that does not preclude there being more than one of the additional element.

[0054] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in any claims are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

What is claimed is:

1. An exercise apparatus comprising: a seat (823) ; a first telescopic tube member (803, 806) and a second telescopic tube member (803, 812), the first and second telescopic tube members each adjustable in length, wherein the seat is supported by the first and second telescopic tube members, each of the first and second telescopic tube members connected at one end to the seat at a pivot point, and at another end to a wheel (824) that can roll on a surface; an elastic device (808) connected between the first and second telescopic tube members; and a non-elastic stopper (810) connected between the first and second telescopic tube members.

2. The exercise apparatus of claim 1, further comprising: a first synchronizing gear device (3) coupled to the pivot point of the first telescopic tube member (803, (806); and a second synchronizing gear device (3) coupled to the pivot point of the second telescopic tube member (803, 812), wherein the first synchronizing gear device and the second synchronizing gear device fit into each other to synchronize movement of the first telescopic tube member with the second telescopic tube member.

3. The exercise apparatus of claim 1, wherein the elastic device (808) comprises a rubber tension board, wherein a first end of the rubber tension board is coupled to a middle portion of the first telescopic tube member via a first torsional spring (809) and a second end of the rubber tension board is coupled to a middle portion of the second telescopic tube member via a second torsional spring (809) .

4. The exercise apparatus of claim 1, wherein the elastic device (808) comprises a spring device, wherein a first end of the spring device is coupled to a middle portion of the first telescopic tube member via a first torsional spring (809) and a second end of the spring device is coupled to a middle portion of the second telescopic tube member via a second torsional spring (809) .

5. The exercise apparatus of claim 1, wherein the non- elastic stopper (810) is coupled to a first fixing block (52) coupled to the first telescopic tube member, and a second fixing block (52) coupled to the second telescopic tube member .

6. The exercise apparatus of claim 5, wherein the first fixing block (52) and the second fixing block (52) each comprising plurality of fixing holes (53), on which ends of the non-elastic stopper (810) are fixed.

7. The exercise apparatus of claim 6, wherein an opening angle between the first telescopic tube member (803, 806) and the second telescopic tube member (803, 812) is adjusted based on a selection of fixing holes (53) for attaching the ends of the non-elastic stopper (810) .

8. The exercise apparatus of claim 1, further comprising: a monitor (828) coupled to the seat (823), wherein the monitor is configured to display exercise related information .

9. An exercise system comprising: a saddle (1) ; a first extensible leg (23) and a second extensible leg (23) , wherein the saddle is coupled to the first and second extensible legs, and each of the first and second extensible legs is coupled at one end to the saddle at a pivot point (21), and at another end to a set of wheels (22); a rebounding mechanism (4) coupled between the first and second extensible legs; and a position-limit mechanism (51) coupled between the first and second extensible legs.

10. The exercise system of claim 9, further comprising: a monitor (828) coupled to the saddle, wherein the monitor is configured to display exercise related information .

11. The exercise system of claim 9, further comprising: a first synchronizing gear device (3) coupled to the pivot point (21) of the first extensible leg (23); and a second synchronizing gear device (3) coupled to the pivot point (21) of the second extensible leg (23), wherein the first synchronizing gear device and the second synchronizing gear device couple with each other to synchronize movement of the first extensible leg with the second extensible leg.

12. The exercise system of claim 9, wherein the rebounding mechanism (4) comprises a stretchable device, wherein a first end of the stretchable device is coupled to a portion of the first extensible leg via a first coupler (6) and a second end of the stretchable device is coupled to a portion of the second extensible leg via a second coupler (6) .

13. The exercise system of claim 9, wherein the stretchable device (4) comprises a spring device.

14. The exercise system of claim 9, wherein the position- limit mechanism (51) is made of a non-elastic member and coupled to a first fixing block (52) coupled to the first extensible leg (23), and a second fixing block (52) coupled to the second extensible leg (23) .

15. The exercise system of claim 14, wherein the first fixing block (52) and the second fixing block (52) each comprising plurality of fixing holes (53) , on which ends of the non-elastic member (51) are fixed.

16. The exercise system of claim 15, wherein an opening angle between the first extensible leg (23) and the second extensible leg (23) is adjusted based on a selection of fixing holes (53) for attaching the ends of the non-elastic member (51) .

17. A method of exercising comprising: selecting a length of a first leg and a second leg of a horse-riding exercise machine; adding a force from body weight to a seat of the horse- riding machine for causing the first leg and the second leg to spread apart to a limit angle to lower the seat towards a surface, wherein a position-limit mechanism limits the angle that the first and second legs can be spread apart; and reducing the force to the seat with assistance of a rebounding mechanism coupled between the first and second legs for causing the first leg and the second leg to move towards one another to raise the seat from the surface.

18. The method of claim 17, further comprising: selecting a coupling position on the first leg and the second leg for coupling the position-limit mechanism, wherein the coupling position is configured for adjusting the limit angle .

19. The method of claim 17, further comprising: grasping a handle coupled to an exercise monitor, wherein the exercise monitor is configured to display exercise information.

20. The method of claim 17, wherein the horse-riding exercise machine comprises: a seat (823) ; a first telescopic tube member (803, 806) and a second telescopic tube member (803, 812), the first and second telescopic tube members each adjustable in length, wherein the seat is supported by the first and second telescopic tube members, each of the first and second telescopic tube members connected at one end to the seat at a pivot point, and at another end to a wheel (824) that can roll on a surface; an elastic device (808) connected between the first and second telescopic tube members; and a non-elastic stopper (810) connected between the first and second telescopic tube members.