referring to fig1 and 2 , the illustrated device has a support platform 10 with a circular outline , although other outlines are contemplated ( elliptical , polygonal , etc .). platform 10 can be made of wood , plastic , metal , or other materials . a flexible sheet - like member in the form of an elastomeric sheet 12 is shown secured to the edge of platform 10 . the edge of sheet - like member 12 is attached with an airtight seal to platform 10 by glueing , by clamps , or by other sealing means . sheet - like member 12 can be made of any one of a variety of materials , including natural and synthetic rubbers , plastics , etc . also , in some embodiments sheet - like member 12 may be a laminate having an outer surface that is more durable and skid resistant . sheet - like member 12 may be formed by blow molding or otherwise to have a natural hemispherical shape . this hemispherical shape preferably has a diameter of 18 to 36 inches ( 46 to 91 cm ), although other dimensions are contemplated . it will be appreciated , however , that under normal use , and when loaded , the sheet - like member 12 will have a profile that is more complex than a hemisphere . in other embodiments , sheet - like member 12 may start as a flat circular sheet that distends when inflated into a dome ( taking essentially a hemispherical shape when unloaded ). a valve means 14 is mounted in a center hole in platform 10 . the valve means 14 may be a rubber bushing covered on its inside with a flexible flap that acts as a check valve . valves of this type are used to inflate basketballs , footballs , etc . if the device need only be inflated to a relatively low pressure , a tube with a stopper can permit a user to blow into the tube to inflate the device , as is done with inflatable beach balls , and the like . various other types of valves can be used in different embodiments , depending upon the desired pressure , pumping method , etc . also , valve 14 can be located on alternate positions on platform 10 , or on various positions on sheet - like member 12 . referring to fig1 and 3 , a circular deck 16 is shown as an element attached to the underside of platform 10 by means of screws 18 , although other types of fasteners may be used instead . the edge of sheet - like member 12 is shown sandwiched between platform 10 and underlying deck 16 . the seal at the edge of sheet - like member 12 can be enhanced by using an appropriate glue , caulk , gasket compound , or other sealing material . the hole holding valve means 14 is aligned with hole 20 in underlying deck 16 , although such alignment is unnecessary , and in some embodiments a number of spaced holes may be used instead . platform 10 and deck 16 may be made of different materials , so that the outer surface may be flexible and skid proof , while the inside deck may be rigid and able to bear heavy loads . in still other embodiments , underlying deck 16 may be replaced with a hoop or other annular structure to simply concentrate on its function of acting as an affixing means for sealing sheet - like member 12 to platform 10 . the edge of platform 10 is fitted with an annular bead 22 . bead 22 may be secured by glueing or by various fasteners . also , bead 22 may have a variety of shapes . bead 22 can be formed of a length of extruded rubber or plastic that is closed into a loop . alternatively , bead 22 may be initially molded as an annulus . preferably , the top of bead 22 rises above the surface of platform 10 to provide a small barrier that tends to keep a user &# 39 ; s feet on the platform . also in preferred embodiments , bead 22 may be relatively soft material that prevents injury caused by the user accidentally kicking or otherwise colliding with the edge of platform 10 . referring to fig4 alternate platform 10 ′ is similar to the previously described platform , but with a peripheral recess 24 . an annular bead 26 is shown fitted in recess 24 , while sandwiched between them is previously mentioned sheet - like member 12 . as before , bead 26 may be a molded annulus or may be formed from a length of extruded material that is closed into a loop . alternatively , the edge of sheet - like member 12 may be sealed into recess 24 before molding bead 26 in situ . bead 26 has an outside surface that is coplanar with the outside surface of platform 10 ′ to facilitate situations where the device is placed with platform 10 ′ down , for certain exercises to be described presently . referring to fig5 previously mentioned deck 16 is shown attached by means of screws 18 to alternate platform 10 ″. also as before , sheet - like member 12 is sandwiched between elements 10 ″ and 16 . platform 10 ″ has an integral edge 28 that is rolled . platform 10 ″ maybe shaped by molding , stamping , bending , etc . referring to fig6 an alternate platform 10 ′″ is generally rectangular with rounded corners . platform 10 ′″ to be dimensioned to simulate the general size and feel of a skate board or snowboard . here , two inflatable domes 30 are sealed to the underside of platform 10 ′″ using structure and techniques similar to that previously described . the domes 30 are arranged so that the platform 10 ′″ can roll ( rotation about a longitudinal axis ) fairly easily , but cannot pitch unless the user places significant weight at the front or back of the platform 10 ′″. to facilitate an understanding of the principles associated with the foregoing apparatus , the use of the device of fig1 will be briefly described . the user will initially inflate the device by inserting a pump needle through valve means 14 . the sheet - like member 12 will be inflated and will distend accordingly . with a modest level of inflation , sheet - like member 12 will take the hemispherical shape 12 a shown in fig2 when unloaded ( that is , when suspended so that the sheet - like member 12 does not touch the ground ). the foregoing device may be used with the platform 10 resting on the ground as shown in fig7 a . here , a person p stands on sheet - like member 12 , working to maintain balance . for an especially challenging session , a person can stand on one foot . the difficulty can be further increased if the person to p rolls or tilts the head , with or without the eyes closed . another , surprisingly challenging session can consist of simply kneeling on the sheet - like member 12 . this effort can be reduced for a novice by getting down on all fours and then working to maintain balance . the person p may mount sheet - like member 12 in order to receive various benefits . the user may perform an exercise in order to improve the user &# 39 ; s sense of balance . in some cases , the user may suffer from a disability that affects coordination and balance . therefore , the device can be used to improve motor skills and balance as a form of therapy . in other cases , an athlete may wish to improve balance for any one of a number of sports requiring a refined sense of balance . alternatively , the user may stand on member 12 simply to exercise his or her muscles . of course , some users will stand on member 12 simply for enjoyment . the amount of exercise sustained by mounting the device can be substantial . the person maintaining balance will normally be required to make many rapid and urgent posture adjustments by exerting a wide range of muscles . moreover , this effort takes place with a sense of stimulation and excitement that makes the effort challenging and interesting . thus , the user can quickly reach a high level of exertion without the usual sense of tedium or labor . as the user &# 39 ; s balance , coordination , and endurance improve , the user may wish to increase the level of difficulty . accordingly , the pressure within the device can be decreased by venting valve means 14 . this reduced pressure leads to less sure footing and increased effort to maintain balance . alternatively , the pressure can be increased to accommodate an especially difficult routine , or to accommodate a user that is tired or less experienced . this increased pressure corresponds to more stability , since the sheet - like member 12 is less able to shift underneath the user . an advantage with the foregoing pressure adjustment is that the user can continuously and finely adjust the pressure and the level of difficulty to suit his or her personal needs . because the device can be adjusted to become relatively stable , the user can readily perform ordinary exercises . for example , the user can squat , or stretch and stand on his or her toes as an exercise . such exercises provide the dual benefit of conditioning muscles , while simultaneously training a person to maintain balance . other exercises are contemplated , such as leg kicks , knee lifts , etc . a person p can also sit on sheet - like member 12 as shown in fig7 b to perform situps . here , the user can decrease the level of difficulty by shifting forward to reduce the amount of upper body weight that is cantilevered out past the device . an additional advantage is that sheet - like member 12 can conform to the user &# 39 ; s body and support the lower back as the user leans back . decreasing the pressure within sheet - like member 12 can increase the amount of lower back support under such circumstances . various other exercises can be performed on the inverted device . as shown in fig7 c , person p can perform lunges . in fact , many of the exercises that are performed in step aerobics classes can be performed with the presently disclosed device . one advantage with this mode of use is that the exercise is very low impact , since sheet - like member 12 acts like a cushion . again , the pressure behind sheet - like member 12 can be adjusted to change the level of difficulty . also , the cushioning effect of sheet - like member 12 can make the exercises low impact , which is very important in step aerobics in order to avoid the joint injury that commonly occur with long - term use . the foregoing device need not be used with the platform down , but may be inverted at shown in fig7 d . because the device is inherently less stable when inverted as in fig7 d , the user will receive a more vigorous experience , which may be appropriate for athletic training . when placed on the ground ( level g 1 of fig2 ) in order to support a person as shown in fig7 d , sheet - like member 12 will become more squat and take the outline 12 a shown in phantom in fig2 . this is a relatively stable condition and the user can maintain balance while standing on platform 10 without too much difficulty . pressure can then be increased by reattaching a pump to valve means 14 . sheet - like member 12 may then be pressurized to distend further and take the outline 12 b shown in phantom in fig2 when placed on the ground at level g 2 . outline 12 b is closer to hemispherical and will make the platform 10 less stable . if the device is built sufficiently strong to sustain a very high pressure , sheet - like member 12 can distend to the almost precisely hemispherical shape shown in full line in fig2 . this represents the highest level of difficulty , requiring a high level of skill and endurance . obviously , many modifications and variations of the present invention are possible in light of the above teachings . it is therefore to be understood that within the scope of the appended claims , the invention may be practiced otherwise than as specifically described .
an inflatable device can be used for physical therapy , conditioning or training . the device has a support platform and a flexible member . the flexible member is affixed to , and has a bowl - shaped distention projecting from , one side of the platform . this flexible member is inflatable to a pressure for supporting a person . the device is inflated before placing at least some of the weight of a person on the device . when the person wishes to later change the characteristics of the device , the pressure in the inflatable device can be changed to change its stability .