Patent Publication Number: US-2013231226-A1

Title: Exercise device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 11/692,270 filed Mar. 28, 2007, now U.S. Pat. No. 8,425,385, entitled RESISTANCE THERAPY, which is a continuation of U.S. application Ser. No. 11/101,942 filed Apr. 8, 2005, now U.S. Pat. No. 7,207,930, entitled EXERCISE DEVICE, each of which are herein incorporated by reference in their entirety. 
    
    
     FIELD 
     The invention relates to an exercise system and method utilizing expandable bladders to provide resistive forces to the muscles being exercised. 
     BACKGROUND 
     Exercise has long been known to be beneficial for people of all ages. In the past, many people were able to exercise simply by carrying out routine daily tasks that previously were labor intensive. The modern age, however, has succeeded in eliminating many “inconveniences” of life that involved physical exertion, and consequently there has been an increasing need for people to find other ways to exercise in order to achieve better health. 
     Today, a wide variety of exercise equipment is available for helping people achieve better health. Some devices and equipment help people achieve a cardiovascular workout, while other devices and equipment allow people to focus on muscle toning, strengthening, and development. Devices and equipment designed for muscle strength and development typically involve a muscle or muscle group applying a force in opposition to a resisting mechanical force generated by the exercise device. Thus, current devices and equipment can be highly specialized for the development of a particular muscle or muscle group. 
     While the ability to focus on a particular muscle or muscle group is beneficial, this specialization often neglects to allow for development of complementary muscle groups. Complimentary muscle groups include muscles that allow a person to move a part of their body and then return it to an original position. One example of complimentary muscle groups are biceps and triceps, which allow a person to bend their arm and then extend it again. Typically, exercise equipment that specializes in developing bicep muscles are not targeted for developing triceps without either modification of the equipment, repositioning of the exerciser, or both. Free weights useful for developing biceps, for example, may be too heavy for tricep development and would require an exerciser to choose which muscle group to develop during any set of exercises. As a result of this specialization, often people need to use multiple devices or complex exercise systems in order to strengthen or develop these complementary muscle groups. 
     Some exercise equipment requires a relatively uniform amount of exertion throughout the entire range of motion. Free weights, for example, provide the same weight resistance regardless of how far they have been lifted. Other exercise machines provide for variable resistance over the range of motion in which they are used. For example, some exercise machines simulating bench presses of weights may use camming mechanisms to vary the mechanical advantage given by the machine to the exerciser as the bar or grip is moved by the exerciser&#39;s arm extension. Thus, as an exerciser exerts a force to move the bar or grip, the machine can be designed to become progressively more difficult or more easy to move. Likewise, the use of a spring in an exercise device can result in requiring progressively increasing forces in order to further compress the device. 
     While such devices have been effective in some ways, they also suffer from disadvantages. Such machines tend to be large, being of high weight and requiring a large amount of space. These machines may also be difficult to use, requiring not only weight adjustment, but also adjusting the position of the user. 
     Another problem with such devices, or the use of conventional weights, is one of safety and convenience. If an exerciser lifts free weights connected to a bar, for example, relaxation of the muscles exercised during lifting may cause the weights to fall and injure the exerciser. Thus, it is difficult for a person exercising by such methods to safely stop in the middle of an exercise stroke, as the weights must be returned to a resting position. 
     SUMMARY 
     The present invention provides a system and method of exercise utilizing expandable bladders. One or more of the bladders may define a reservoir that holds a fluid that can be at least partially transferred from one chamber or bladder to another. Alternatively, one or more of the expandable bladders may have compressible fluid or gasses inside that, when compressed, provide resistance to exercise the user&#39;s muscles. 
     One potential benefit of the devices of the present invention is that they may be small in size. In addition, some embodiments of the invention do not require heavy weights in order to achieve adequate resistance for muscle development. These features of the present invention may be implemented in a manner that also allows the devices to be easily transported or conveniently stored when not in use. Alternatively, the entire device, or just the patient contacting portion, can be made as a single-use disposable device. This minimizes, if not eliminates, the risk of disease transmission. Regardless of whether disposable or reusable, the size of devices according to the present invention allows use in a confined space, like an airplane, or other locations where the use of traditional exercise equipment would not be feasible. 
     Additionally, it is believed that several embodiments of the present invention also are safer to operate than some current exercise equipment. In this regard, the present invention can be used for low-impact work outs. Such work outs are particularly useful for disabled individuals, such as a stroke patient, partially bed ridden patients, or patients recovering (or as part of a post-operative therapy program) from surgery. Another application of the present invention is to build bone mass, for example, to delay the progression of osteoporosis. 
     One embodiment of the present invention involves a series of fluidly connected expandable bladders to provide resistive forces to the muscles being exercised. Two or more bladders may be connected, for instance by apertures or tubes that allow air or other fluid to be transferred therethrough. In this embodiment, the system includes a first bladder having a first stiffness and a second bladder having a second stiffness, wherein the second stiffness is greater than the first stiffness. 
     As a result, it is possible to achieve different levels of resistance from the exercise device in this embodiment depending upon which portion is being utilized or compressed. In particular, a first force is needed to compress the first bladder in order to force air or other fluid into the second bladder, while a second, different force is needed to compress the second bladder in order to force air or other fluid into the first bladder. The bladders may be configured or oriented so that compression of a first bladder helps a user develop a first muscle group, while compression of the second bladder helps develop a second muscle group. Preferably the second muscle group is complementary to the first group. 
     Upon removal of the compressive force, the expanded bladder compresses or returns toward its original shape by forcing some of the fluid back to the other bladder until reaching an equilibrium condition. The tube or aperture providing fluid communication between two or more expandable bladders also may be configured to partially restrict flow from one bladder to another. This may extend the time needed for the bladders to return to an equilibrium state. Restriction of flow between two or more bladders can be achieved, for instance, simply by providing a small aperture that allows for a more gradual transfer of fluid or gas from one bladder to another. 
     Alternatively, the aperture or tube may be formed from elastic material so that flow therethrough is substantially or fully restricted until the pressure gradient exceeds a desired level. In this configuration, a person using the device would need to impart a first force in order to displace some or all of the fluid or gas in a bladder, and then would need to impart a second, potentially smaller force in order to maintain equilibrium of the compressed device. As the force applied is reduced, pressure in the expanded bladder may cause the aperture to expand or open to allow the air or fluid to return to the previously compressed bladder. 
     In yet another alternative embodiment, the bladders need not be in fluid communication with each other. Instead, the bladders may be capable of surrounding a compressible gas, such as air, so that resistance by each bladder is achieved either by the compression of the gas, the resilient expansion of the bladder material, or both. 
     The bladder system can be incorporated into an exercise device or machine to work any muscle group, including, arm, leg, chest, back, shoulder, abdominal, or neck muscles. As mentioned above, and discussed more fully below, the system also may be useful in allowing complimentary muscle groups to be exercised. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  depicts a bladder exercise system of the present invention; 
         FIG. 2  depicts the bladder exercise system of  FIG. 1  with an additional restrictive band disposed around a bladder; 
         FIG. 3  depicts the bladder exercise system of  FIG. 1  acted upon by a compressive force; 
         FIG. 4  depicts the bladder exercise system of  FIG. 1  including a control valve: 
         FIG. 5  depicts the bladder exercise system or  FIG. 1  including a fill valve; 
         FIG. 6  illustrates an alternative embodiment where one or more bladders may be selective removed from the exercise system; 
         FIG. 7  depicts a bladder exercise system of the present invention including multiple serially linked bladders; 
         FIG. 8  depicts a bladder exercise system of the present invention including multiple linked bladders; 
         FIG. 9  depicts an exercise system including multiple bladder exercise systems; 
         FIG. 10  depicting an bladder exercise system including accordion bladders; 
         FIG. 11  depicts an alternative bladder exercise system of the present invention; 
         FIG. 12  depicts the accordion bladder system of  FIG. 11  in a first position; 
         FIG. 13  depicts the accordion bladder system of  FIG. 11  in a second position; 
         FIG. 14  is a schematic representation of exercising opposing muscles on a limb; 
         FIGS. 15A-B  are schematic representations of a first embodiment for exercising agonist and antagonist muscles of opposite limbs; 
         FIGS. 16A-B  are schematic representations of a second embodiment for exercising agonist and antagonist muscles of opposite limbs; 
         FIGS. 17A-B  are schematic representations of exercising the same muscles on opposite limbs; 
         FIG. 18  depicts a cuff bladder exercise system of the present invention; 
         FIG. 19  depicts a sectional view of the cuff bladder exercise system of  FIG. 18 ; 
         FIG. 20  depicts the cuff bladder exercise system of  FIG. 19  in use during a bicep exercise; 
         FIG. 21  depicts the cuff bladder exercise system of  FIG. 19  in use during an abdominal exercise; 
         FIG. 22  depicts an adjustable cuff bladder exercise system of the present invention; 
         FIG. 23  depicts the cuff bladder exercise system of  FIG. 19  including multiple serial bladders; and 
         FIG. 24  depicts the cuff bladder exercise system of  FIG. 19  including multiple stacked bladders. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a system and method of exercise utilizing expandable bladders. The bladder system can be a stand-alone exercise device or alternatively may be incorporated into another device or machine to work muscles for arms, legs, chest, back, shoulder, abdomen, or the neck. 
     Referring now to the drawing figures,  FIG. 1  illustrates one embodiment of a bladder system  10  of the present invention that uses a plurality of fluidly connected bladders to provide resistive forces to the muscles being exercised. The bladder system  10  includes first and second bladders  12  and  14  in fluid communication with each other, such as through a tube  16 . Alternatively, portions of the expandable bladders may be disposed adjacent to each other to define one or more apertures through which a fluid may travel. Unless indicated otherwise herein, the term “fluid” may include air or other gases in addition to liquids. 
     Returning once again to the embodiment of  FIG. 1 , a compressible or non-compressible fluid  18  is disposed within the bladders  12  and  14 , such that a compression of one of the bladders  12  or  14  forces the fluid  18  through the tube  16  into the opposite bladder  12  or  14 . It is also contemplated by the present invention that a malleable foam, gelatin, or other similar material can be placed in either or both of bladders  12  and  14 . Such a material could occupy all or part of the volume of the bladder(s) and could be used either with or without the fluid. 
     The size, shape, construction, physical or material properties, and composition of the expandable bladders may be varied according to a desired use or performance of the exercise device. For example, while the bladders  12  and  14  shown in  FIG. 1  are substantially similar in size and shape, one bladder may be configured to be substantially larger than the other. For instance, one bladder may have a volume of about 1.5 times or greater the volume of the other bladder under similar conditions of fluid pressure. Alternatively, the difference in volume of one bladder may be about 2 times or greater than the volume of another bladder, or may even differ by more than 4 times the volume of the other. 
     Providing a difference in bladder volumes is one way to achieve a different level of resistance that can be created when exerting pressure on the device during exercise. For instance, it is believed that the amount of exertion required to compress the smaller bladder, or to displace fluid from the smaller bladder into the larger one, will be less than the amount of exertion that may be required to compress the larger bladder a similar amount, or to displace a similar amount of fluid from the larger bladder into the smaller one. 
     Without being bound to any particular theory, it is believed that the reason for this difference in required exertion to displace similar amounts of fluid is that the relative increase in volumes required to accommodate the increase in fluid will be different. In other words, the smaller bladder will need to expand more than the larger bladder for a given amount of additional fluid, and therefore it will provide greater resistance to expansion. Thus, the resulting difference in resistance that can be achieved may be tailored to provide different workout levels from the same device. This feature may be beneficial when one muscle group is capable of exerting greater force than a complimentary muscle group. 
     Likewise, the shapes of the bladders may be designed to provide different amounts of resistance to a given increase of fluid or pressure. For example, while the shapes of the bladders shown in  FIG. 1  are generally rounded or perhaps spherical, it is also possible that one or more of the bladders may be oblong in shape. As the pressure or fluid level increases, the mid-section of the oblong shape initially may expand more readily. The bladders may have other shapes as well, such as a pancake shape, an accordion shape, a belt or tubular shape, or the like. 
     The construction of the bladders also may be varied to provide different levels of resistance. For instance, the wall thickness of one bladder may be greater than the wall thickness of another bladder. In one embodiment, the wall thickness of one bladder is about 1.25 times or greater than the wall thickness of a second bladder. Greater differences in wall thickness may be used to provide even greater differences in resistance. For example, in one embodiment the wall thickness of one bladder may be about 2 times or greater, or even about 3 times or greater, than the wall thickness of a second bladder. U.S. Pat. No. 5,033,457, the contents of which are expressly incorporated by reference herein, also discloses other manners in which bladders can be provided to have different resistances or flexibilities. 
     Once the potential value of utilizing different bladder wall thicknesses for the present invention is understood from the discussion above, skilled artisans would appreciate that there can be several ways that these different wall thicknesses can be achieved. For instance, a bladder may be formed of multiple layers, or plies, of material. Thus, in an embodiment where one bladder wall thickness is about 2 times or greater than another bladder wall thickness, the first bladder may be formed by forming an additional layer of material over a first layer. The use of multi-ply constructions also allows the material and/or physical properties of one ply or layer to differ from the properties of another layer. 
     In another embodiment, the walls of the bladders may be constructed to include reinforcing fibers. The material used to form the reinforcing fibers may have a different modulus of elasticity (E) than that of the material used to form the bladders. The difference in modulus of elasticity may be used to provide even greater differences in resistance between the bladders. For example, in one embodiment the wall of one bladder include fibers having a modulus of elasticity of about 2 times or greater, or even about 3 times or greater, than the modulus of elasticity of a second bladder. 
     In another alternative embodiment, a second layer of material formed around a bladder need not fully cover the first layer. As shown in  FIG. 2 , for example, a second layer may form a restrictive band  18  around only a portion or region of a bladder  12 . The restrictive band  18  may be designed to be removable and interchangeable with one or more other restrictive bands having varying degrees of resistance. Additionally, the bands may be configured to fit over more than one expandable bladder. In this manner, a user of the device may further customize the degree of resistance of one or more expandable bladders by selecting from a plurality of bands. 
     The physical properties of the materials used to form an exercise device of the present invention also may be selected to provide a desired level of resistance. For example, the modulus of elasticity E of material used to form one bladder may be about 1.25 times greater or more than the modulus of elasticity of material used to form another bladder. Once again, the difference in modulus of elasticity may be even more pronounced, such as by 1.5 times or more, or by 2 times or more, depending on the degree of different resistance that is desired. 
     Likewise, the elasticity of one expandable bladder may be greater than the elasticity of another expandable bladder to provide different resistance. For example, the elasticity of material used to form a first bladder wall may be about 1.5 times or greater than the elasticity of a material used to form a second bladder wall. In other embodiments, this difference may be about 3 times greater, or even about 5 times greater. 
     It is believed that many different materials may be used to make devices of the present invention. By way of illustration, components of the present invention may be formed from urethanes, natural or synthetic rubbers, or the like. Preferably, the materials used to form the expandable bladders are elastomeric material that can stretch or expand and then substantially return to its original shape once pressure is released. 
     Additionally, the components of the present invention may be formed from a biodegradable material. It is contemplated that the present invention may be provided as a disposable exercise device. As a disposable device, the present invention could have a limited useful life, after which the device is easily disposed and reclaimed. 
     It should be understood that any selection of potential variations described above may be used either in combination with other variations or on its own. Thus, it is not necessary that any embodiment of this invention utilizes every variation to create a difference in resistance. In fact, many of the design elements described above may be “neutralized” from creating a noticeable difference in resistance between two expandable bladders. This can be achieved by making the design factor substantially the same for one bladder as another (e.g., bladder wall thickness, shape, and size may be relatively the same while other design elements are varied). In addition, in some instances it may be desirable for the design and performance of one bladder to be substantially the same as another expandable bladder. 
     Another way to express the differences in resistive forces that may result from design variations between expandable bladders is by stiffness or by effective spring constant of each bladder. For example, regardless of how the variations are achieved, it is preferred that one expandable bladder has an effective spring constant k 1  that is different from the effective spring constant k 2  of a second expandable bladder. Hooke&#39;s Law defines a spring constant k as the ratio of an applied static force to the linear displacement of a spring. Regardless of how the differences are characterized (e.g., resistance level, stiffness, effective spring constant, etc.), it is preferred that the differences are at least about 10 percent or greater, and more preferably the bladder designs result in a difference of about 25 percent or more. In some cases, a more pronounced difference may be desired, such as differing by about 50 percent or more, or even by about 100 percent or more (i.e., one bladder requires twice as much force to be exerted on it in order to achieve the same effect). 
       FIG. 3  illustrates the effect of exerting a compressive force F 1  on the first bladder  12  of one embodiment of the invention. The compressive force F 1  causes the fluid from the first bladder  12  to travel through tube  16  and into the second bladder  14 . In response to the additional fluid, the second bladder  14  may expand to accommodate the additional volume. Alternatively, the fluid in the first and second bladders may be compressible gas, such as air or nitrogen. Thus, some embodiments of the invention may utilize a compressible fluid and one or more relatively non-expandable bladders so that exertion of a compressive force F 1  may reduce the internal volume of one or more bladders. 
     Returning to the embodiment shown in  FIG. 3 , upon removal of the compressive force F 1 , the second bladder  14  contracts and eventually may return to approximate its initial shape and size. The higher pressure exerted by either the expanded wall of the second bladder, the compressed of gas inside the bladder, or both, results in the contraction of the second bladder  14  and expansion of the first bladder  12 . In turn, this causes fluid from the second bladder  14  to travel into the first bladder  12  as the device returns to an equilibrium position. 
     The bladder system  10  of the present invention provides a resistance profile R to the compressive force F 1 . Initially, to force fluid from the first bladder  12  into the second bladder  14  the compressive force F 1  exerted by a user must be equal to or greater than a threshold force TF. The threshold force TF is the force required to initiate expansion of the second bladder  14 . This relationship is more likely to be observed where the fluid is liquid or relatively incompressible, but may be less likely observed if the fluid itself can be compressed. In cases where compressible fluid is present, the fluid may initially compress until reaching a level of pressure that meets or exceeds the threshold force of the second bladder. In general, the threshold force TF may be dependent on the elasticity or effective spring constant k of the second bladder  14 . Thus, a low elasticity or high effective spring constant k 2  will likely result in a higher threshold force TF, while a high elasticity or low stiffness k 2  is likely to result in a lower threshold force TF needed before the second bladder expands. 
     Upon exceeding the threshold force TF, the second bladder  14  will begin to expand, still providing a resistance against the compressive force F 1 . The resistance profile R can be a uniform resistance, where the stiffness k 2  and/or size of the second bladder  14  are selected to provide a relatively uniform resistance. Alternatively, the stiffness k 2  and/or size of the second bladder  14  may be selected to provide an increasing or decreasing resistance profile R. 
     Additionally, the tube  16  or aperture between two bladders may also be configured to resist the compressive force F 1 . For example, the diameter of the tube  18  can be selected to restrict the rate at which fluid can be transferred from one bladder to another. Whereas a relatively large diameter tube  16  may impart only negligible restriction on fluid flow, a small cross-sectional area and longer length connection between two bladders may significantly increases pressure losses during transfer of fluid from one location to another. 
     One feature that can be obtained by utilizing a connection that at least partially restricts fluid flow is that sudden relaxation of muscles by the exerciser need not result in the device suddenly and immediately returning to its original shape. Instead, there may be a more gradual return to equilibrium. For instance, in one embodiment, restricted fluid flow that results from full removal of compressive force may result in the delaying the return to initial shape of the device by about 0.25 seconds or more. In other embodiments, the restriction in fluid flow results in an even greater delay, such as about 0.5 seconds or more, about 1 second or more, or even about 5 seconds or more. These delays can be used to help ensure safe operation of the device. In addition the ability to control the rate at which fluid flows through the tube  16  or aperture also may be beneficial in customizing the resistance that a user will experience from the device during a workout. 
     The viscosity of the fluid  18  also may be used to control the resistance of the exercise device. The fluid viscosity is selected to provide a specific maximum flow rate through the tube  16 . A more viscous fluid will have a decreased flow rate, providing a greater resistance. A less viscous fluid will have an increased flow rate, providing a decreased resistance. The benefits that may be obtained from selecting viscosity of the fluid to achieve a desired maximum flow rate are similar to the benefits described above for restricting fluid flow by choosing an appropriate cross-sectional area for the aperture or tube  16  connecting two bladders. 
     Referring to  FIG. 4 , the fluid connection between two bladders may be configured so that the connection has a variable cross-section through which fluid may flow. That is, the size of opening between two bladders may be changed to control the rate at which fluid flows between them. As illustrated in  FIG. 4 , one way the cross-section may be varied is by operation of a valve  20  or similar device capable of selectively changing the size of the opening between the two devices. The valve  20  may be manually controlled or adjusted or alternatively may be operatively connected to an automated control system. In addition, the fluid connection  16  between bladders may be expandable. Thus, the connection may initially be small, or perhaps even substantially closed, but can expand in response to an increased pressure differential from one side of the connection to the other. 
     Thus, the bladder system  10  may include a control valve for regulating the diameter of tube  16  or flow of the fluid. In a fully open position, the tube  16  has a maximum diameter allowing for a maximum flow rate of the fluid  18 . In a closed position, the control valve  20  minimizes the diameter of the tube  16 , resulting in a minimum flow rate of the fluid through the tube  16 . In one embodiment, the valve may be fully closed to substantially restrict or prevent any fluid flow. An exemplary control valve  20  includes a housing positioned about the tube  16 . A threaded member may then be screwed into a threaded orifice in the housing. Rotation of the threaded member gradually causes the cross section of the tube  16  to be restricted or decreased. A knob may be provided on the threaded member to allow for easier manual adjustment. 
     Referring to  FIG. 5 , one or more bladders may include a mechanism for controlling or adjusting the fluid pressure in the bladder system  10 . In the illustrated embodiment, the control mechanism may be one or more fill valves  22 . Skilled artisans would appreciate that a great variety of fill valves may be used, some non-limiting examples of which include screw caps, interference fit plugs (such as, for example, may be found on beach balls, or the like), or needle valves (such as found on sporting equipment), and the like. 
     A pressure gauge, transducer, or other similar means may be used in conjunction with the fill valve  22  to determine the fluid pressure in the bladder system  10 . To increase the resistance to the compressive force F 1 , fluid is added, through the fill valve  22 , into the bladder system  10 . The fluid may be pumped or injected into the bladder system  10  from a pressurized container, being added until the desired fluid pressure is present in the bladder system  10 . To decrease the resistance to the compressive force F 1 , fluid may be evacuated from the bladder system  10 . 
     The fill valve  22  may be opened, allowing some or substantially all of the pressurized fluid to exit the bladder system  10 . Providing a fill valve not only allows fluid to be added or removed from the bladder system  10  in order to increase or decrease fluid pressure in a bladder, but also the valve may be useful in allowing for a substantial amount of the fluid to be removed in order to more conveniently store or transport the exercise device. 
     In an alternative embodiment, one or more of the bladders of the exercise device  10  may be removed from the fluid connection to another bladder. As shown in  FIG. 6 , one or more bladders may be selectively connected to or removed from the fluid connection  16 . This configuration not only allows for adjustment of fluid levels and convenient storage and transport of the exercise device, but also allows different bladders having different properties to be used interchangeable on the device. In one embodiment, the exercise device comprises a plurality of interchangeable bladders where the resistance of at least one bladder differs from another bladder by about 10 percent or more, and more preferably differs in resistance by about 20 percent or more. An interchangeable bladder may be secured to a fluid connector  16  with clamps, by interference fit, or in any other suitable manner. 
     Preferably, the exercise device  10  has sufficient structural integrity to permit a wide range of initial fluid pressure (i.e., the internal pressure of the system without application of a compressive force F 1 ) without experiencing significant pressure loss over time. For purposes of this application, significant pressure loss is defined as the device losing more than 25 percent of its pressure over a 24-hour period of non-use. In some embodiments, it may be desirable for the device to be capable of withstanding an initial fluid pressure of at least about 50 psi without significant pressure loss, and more preferably can hold at least about 100 psi. It should be understood, however, that the device may be subjected to significantly greater pressures when subjected to compressive forces. 
     In the above examples, the exercise system  10  has been depicted as having a pair of bladders  12  and  14 . However, it is contemplated the bladder system  10  can include multiple fluidly connected bladders. For example, the exercise system  10  may have 3 or more bladders, or even 5 or more bladders. Providing a combination of bladders may be beneficial, for instance, when the range of body motion involved in the exercise is long. For instance, stomach, arm, or leg exercises may involve body motion over a sufficiently large area to warrant use of more than just two bladders. In addition, providing more bladders may allow for greater variation of resistance over the range of motion. 
     A non-limiting example of the use of 3 or more bladders in an exercise device  10  is illustrated in  FIG. 7 . As shown, the bladder system  10  may include multiple bladders serially connected. As generally shown in  FIG. 7 , a first bladder  30  may be fluidly connected, via first tube  32 , to a second bladder  34 . Second bladder  34  may then be fluidly connected, via second tube  36 , to a third bladder  38 . Optionally, the third bladder  38  also may be fluidly connected to a fourth bladder  38  via third tube  40 . As a compressive force F 1  is applied to the first bladder  30 , the fluid is compressed into the second, third, and fourth bladders  34 ,  38 , and  42 , providing a resistance to the compressive force F 1 . 
     The stiffness of the second, third, and fourth bladders  34 ,  38 , and  42  may be selected to provide a prescribed resistance profile R to the compressive force. For example, each the second, third, and fourth bladders  34 ,  38 , and  42  can have the same stiffness k. Alternatively, each of the second, third, and fourth bladders  34 ,  38 , and  42  can have different stiffnesses. The different stiffnesses are selected and arranged to provide the resistance profile R. 
     Likewise, flow rates between the bladders also may be varied to achieve a desired resistance profile R. The bladders  30 ,  34 ,  38 , and  42  are serially connected with tubes  32 ,  36 , and  40 . As described above, the tubes  32 ,  36 , and  40  provide a specific flow rate therethrough and can be used to adjust resistance the compressive force F 1 . The tube diameters are selected to provide a prescribed resistance profile R to the compressive force F 1  and may be adjustable in the manner described above. A larger tube diameter will have an increased flow rate, providing a lesser resistance. A decreased tube diameter while provide a decreased flow rate, providing an increased resistance. Each of the tubes  32 ,  36 , and  40  can have the same tube diameter, providing a uniform flow rated through each of the tubes. Alternatively each of the tubes  32 ,  36 , and  40  can have different tube diameters, wherein the tube diameters are selected and arranged to provide the resistance profile R. 
     As discussed above, the sizes and arrangement of the bladders  30 ,  34 ,  38 , and  42  can be selected to provide a prescribed resistance profile R to the compressive force F 1 . Referring to  FIG. 7B , the bladders  34 ,  38 , and  42  are arranged in a decreasing size arrangement. Alternatively, as shown in  FIG. 7C , the bladders  34 ,  38 , and  42  are arranged in an increasing size arrangement. 
     The above-described elements may be used individually or in combination to design a bladder system  10  to provide a specific resistance profile R. 
     It is not necessary for every bladder of the exercise system  10  to be linked or connected serially with the others. Referring to  FIG. 8 , the exercise system  10  may include a central bladder  12  with multiple secondary bladders attached thereto. Each of the secondary bladders may be fluidly connected to the central bladder  50  with tubes or apertures in the manner already described above. In some embodiments, only a portion of the secondary bladders may be in fluid communication with the central bladder. Thus, some secondary bladders may be self contained in order to provide some cushioning or stabilization for the user. As a compressive force F 1  is applied to the central bladder  12 , the fluid is compressed into fluidly connected secondary bladders providing a resistance to the compressive force F 1 . 
     As discussed above, each of the bladders in any embodiment may be sized or otherwise designed to have a desired stiffness in order to provide a specific resistance profile R in response to a compressive force F 1 . Likewise any other design parameter discussed above also may be used with the embodiments illustrated in  FIGS. 7 and 8 . 
     In the above examples, the exercise systems  10  have been described as being a single collection of bladders. However, it is contemplated that multiple bladder systems  10  can be used in combination to provide a selected resistance profile R to the compressive force F 1 . Referring to  FIG. 9 , a pair of bladder systems  70  and  72  are used in combination to provide a effective resistance profile R for the overall combination. Each of the bladders systems  70  and  72  can have the same or different individual R 1  and R 2  resistance profiles. The individual resistance profiles R 1  and R 2  are selected to provide the effective resistance profile R of the combined systems  70  and  72 . 
     Other bladder configurations also may be used with the present invention. For instance, one or more of the bladders may be formed from an inelastic (non-elastomeric) material so that it does not expand significantly when subjected to increased pressure during normal operation of the device. This type of bladder may be useful with compressible fluid or may also be used as an overflow reservoir. In addition, one or more bladders may have a pleated or accordion construction as illustrated in  FIG. 10 . 
     Referring to  FIG. 11 , the bladder system  100  also may include a vent port  104 , such that when a compressive force is applied to the bladder  102  air is evacuated from the bladder  102  through the vent port  104 . Upon removal of the compressive force, the bladder  102  reverts to its original form, drawing air in through the vent port  104 . 
     Bladder  102  provides a resistance to the compressive force, wherein the resistance is dependent on the material properties of the bladder  102 . The higher stiffness k of the bladder  102  results in the higher resistive force. The lower stiffness k of the bladder  102  results in the lower resistive force. 
     The vent port  104  may also be utilized to provide resistance to the compressive force F 1 . The diameter of the vent port  104  is selected to provide a specific flow rate of the fluid  108  from the bladder  102  through the vent port  104 . A larger vent port  104  diameter will have an increased flow rate, providing a lesser resistance. A smaller tube diameter vent port  104  will have a decreased flow rate providing an increased resistance. 
     The bladder system  102  of the present invention provides a resistance profile R to the compressive force F 1 . Initially, to force the fluid from the bladder  102  through the vent port  104  the compressive force F 1  must be equal to or greater than a threshold force TF. The threshold force TF is the force required to initiate expansion of the bladder  102 . The threshold force TF is dependent on the stiffness k of the bladder  102 , and the characteristic of the vent port  104 . Upon removal of the compressive force, the bladder expands drawing air into the bladder  102  through the vent port  104 . 
     The bladder system  102  may include a control valve  106  for regulating the diameter of vent port  104  and/or the flow rate of the fluid. In a fully open position, the vent port  104  has a maximum diameter allowing for a maximum flow rate of the fluid, providing a minimum resistance. In a closed position, the control valve  106  minimizes the diameter of the vent port  104 , resulting in a minimum flow rate of the fluid through the vent port  104 , providing a maximum resistance. Exemplary control valves are discussed above with respect to  FIGS. 4 and 5 . 
     Referring to  FIGS. 12 and 13 , the bladder  108  is an accordion bladder, providing first and second resistances. When a compressive force F C  is applied to the accordion bladder  108 , air is evacuated from the bladder  108  through the vent port  110 , providing the first resistance. When an expansive force F E  is applied to the accordion bladder  108 , air is drawn into the bladder  108  through the vent port  110 , providing the second resistance. Both the first and second resistances are dependent upon the stiffness of the bladder  108  and the configuration on the vent port  110 . 
     The first and second resistances can be used to exercise opposing muscle. Referring to  FIG. 14 , a schematic of a leg extension/hamstring exercise machine is shown. When a leg L is moved into an extended position, the quadriceps leg muscles are contracted. Similarly, when the leg L is moved into a flexed position, the hamstring muscles are contracted. The accordion bladder  108  of the present invention can be positioned in a leg machine, such that the bladder  108  provides a resistance to both flexion and extension of the leg. For example, the bladder  108  is positioned in the leg machine such that when the leg is flexed, a compressive force F C  is applied to the bladder (see also  FIG. 12 ). The bladder  108  provides a first resistance, resisting the compressive force F C . When the leg is extended, an expansive force F E  is applied to the bladder  108  (see also  FIG. 13 ). The bladder  108  provides a second resistance, resisting the expansive force F E . The first and second resistances exercise the hamstring and quadriceps muscles. It is contemplated that the bladder can be used as a stand alone device or incorporated into an exercise machine systematically exercising opposing muscles groups, such as, chest/upper back, abdominal/lower back, quadriceps/hamstring, biceps/triceps, etc. 
     Referring to  FIG. 15A , the bladder system  10  of the present invention can be positioned in a leg machine, such that the bladders  12  and  14  provide forces to agonist and antagonist muscles of opposite legs. An agonist muscle is a muscle that contracts when another muscle relaxes and an antagonist muscle is a muscle that relaxes when another muscle contracts. For example, when performing a leg extension exercise, the quadriceps muscle (the agonist muscle) contracts and the hamstring (the antagonist muscle) relaxes when the leg is extended. 
     In an exemplary embodiment, the bladder  12  is positioned in the leg machine such that when a first leg L 1  is extended from an initial position, a first force F 1  is applied to the bladder  12 . The bladder  12  provides a first resistance R 1  to the quadricep muscle (agonist muscle) resisting the extension of the first leg L 1 . Simultaneously and in response to the first force F 1 , the fluid from bladder  12  is forced through the tube  16  into bladder  14 , expanding bladder  14 . The expansion of bladder  14  provides a second force F 2  to the second leg L 2 , tending to force the second leg L 2  into the extending position. The hamstring muscle (antagonist muscle) of the second leg L 2  provides a second resistance R 2  resisting the second force F 2 , moving the second leg L 2  into flexion. In this manner the quadriceps muscle of the first leg L 1  and the hamstring muscle of the second leg L 2  are simultaneously exercised. 
     In the above described motion, the first and second bladders  12  and  14  provide positive exertions to the quadricep muscle of the first leg L 1  and the hamstring muscle of the second leg L 2 . Upon completion of the motion, the first force F 1  is released, wherein, similar to free weights, the bladder system  10  tends to conform back to the equilibrium position, initial position. As such, the bladders  12  and  14  provide forces to the first and second legs as the fluid in the bladders  12  and  14  moves to the equilibrium position. The resistance of these forces provides a negative exertion on the quadricep muscle of the first leg L 1  and the hamstring muscle of the second leg L 2  as the first and second legs L 1  and L 2  move to the initial position. 
     Referring to  FIG. 15B , the bladder system  10  of the present invention can be positioned in a leg machine such that as first leg L 1  is flexed, a first force F 1  is applied to the bladder  12 . The bladder  12  provides a first resistance R 1  to the hamstring muscle, agonist muscle, resisting the flexion of the first leg L 1 . Simultaneously and in response to the first force F 1 , the fluid from bladder  12  is forced through the tube  16  into bladder  14 , expanding bladder  14 . The expansion of bladder  14  provides a second force F 2  to the second leg L 2 , tending to force the second leg L 2  into the flexed position. The quadricep muscle, antagonist muscle, of the second leg L 2  provides a second resistance R 2  resisting the second force F 2 , moving the second leg L 2  into an extended position. In this manner the hamstring muscle of the first leg L 1  and the quadricep muscle of the second leg L 2  are simultaneously exercised. As with the previous embodiment, the bladders  12  and  14  can likewise provide negative exertions on the hamstring muscle of the first leg L 1  and the quadricep muscle of the second leg L 2  as the first and second legs L 1  and L 2  move to the initial position. 
     Referring to  FIG. 16A , the bladder system  10  of the present invention can be positioned in a leg machine, such that the bladders  12  and  14  provide forces to agonist and antagonist muscles of opposite legs, wherein the legs move in the same direction. The bladder  12  is positioned in the leg machine such that when a first leg L 1  is extended from an initial position a first force F 1  is applied to the bladder  12 . The bladder  12  provides a first resistance R 1  to the quadricep muscle resisting the extension of the first leg L 1 . Simultaneously and in response to the first force F 1 , the fluid from bladder  12  is forced through the tube  16  into bladder  14 , expanding bladder  14 . The expansion of bladder  14  provides a second force F 2  to the second leg L 2 , forcing the second leg L 2  into the extending position. The hamstring muscle of the second leg L 2  provides a second resistance R 2  resisting the second force F 2 . In this manner the quadriceps muscle of the first leg L 1  is provided with a positive exertion and the hamstring muscle of the second leg L 2  is provided with a negative exertion. 
     Upon completion of the motion, both the first and second legs L 1  and L 2  are in the extended position. Referring to  FIG. 16B , the second leg L 2  is then flexed, applying a third force F 3  to the bladder  14 . The bladder  14  provides a third resistance R 3  to the hamstring muscle resisting the flexion of the second leg L 2 . Simultaneously and in response to the third force F 3 , the fluid from bladder  14  is forced through the tube  16  into bladder  12 , expanding bladder  12 . The expansion of bladder  12  provides a fourth force F 4  to the first leg L 1 , forcing the first leg L 1  into the flexed position. The quadricep muscle of the first leg L 1  provides a fourth resistance R 4  resisting the fourth force F 4 . The first and second legs L 1  and L 2  are moved into the flexed position, initial position. In this manner, the hamstring muscle of the second leg L 2  is provided with a positive exertion and the quadricep muscle of the first leg L 1  is provided with a negative exertion. 
     It is contemplated that the bladder  10 ,  102 , or  108  can be used as a stand alone device or incorporated into an exercise machine systematically exercising agonist and antagonist muscle groups of opposing limbs, such as, quadriceps/hamstring, biceps/triceps, etc. It is further contemplated that regardless of the specific application, the device can include a tracking mechanism, such as a radio frequency identification (RFID) tag. One use for such a tracking mechanism would to be monitor patient compliance. In this regard, U.S. Patent Publication No. 2004/0215111, the contents of which are incorporated by reference herein, discloses a monitoring system and method that can be used with the present invention. 
     The bladder system of the present invention can be positioned on an exercise machine to provide a positive exertion to a first muscle and a negative exertion to a second muscle, wherein the first and second muscles include identical muscle on opposite limbs. Referring to  FIG. 17A , the bladder system  10  of the present invention is positioned on a preacher curl machine. The bladder  12  is positioned in the curl machine such that when a first arm A 1  is flexed from an initial position a first force F 1  is applied to the bladder  12 . The bladder  12  provides a first resistance R 1  to the bicep muscle, resisting the flexion of the first arm A 1 . Simultaneously and in response to the first force F 1 , the fluid from bladder  12  is forced through the tube  16  into bladder  14 , expanding bladder  14 . The expansion of bladder  14  provides a second force F 2  to the second arm A 2 , forcing the second arm A 2  into the extending position. The bicep muscle of the second arm A 2  provides a second resistance R 2  resisting the second force F 2 . In this manner the bicep muscle of the first arm A 1  is provided with an positive exertion and the bicep muscle of the second arm A 2  is provided with a negative exertion. 
     Referring to  FIG. 17B , upon completion of the motion, the first arm A 1  is in the flexed position and the second arm A 2  is in the extended position. The second arm A 2  is then flexed, applying the first force F 1  to the bladder  14 . The bladder  14  provides the first resistance R 1  to the bicep muscle, resisting the flexion of the second arm L 1 . Simultaneously and in response to the first force F 1 , the fluid from bladder  14  is forced through the tube  16  into bladder  12 , expanding bladder  12 . The expansion of bladder  12  provides the second force F 1  to the first arm A 1 , forcing the first arm A 1  into the extended position. The bicep muscle of the first arm A 1  provides the second resistance R 2  resisting the second force F 2 . The second arm A 2  is moved into the flexed position and the first arm A 1  is moved into the extended position. In this manner the bicep muscle of the second arm A 2  is provided with a positive exertion and the bicep muscle of the first arm A 1  is provided with a negative exertion. 
     It is contemplated that the bladder  10 ,  102 , or  108  can be used as a stand alone device or incorporated into an exercise machine systematically exercising identical muscle groups of opposing limbs, such as, providing a positive exercise to the muscle of the first limb and a negative exercise to the same muscle of the second limb. It is further contemplated that regardless of the specific application, the device can include a tracking mechanism, such as a radio frequency identification (RFID) tag. One use for such a tracking mechanism would to be monitor patient compliance. In this regard, the previously incorporated by reference U.S. Patent Publication No. 2004/0215111 can be used with the present invention. 
     Referring to  FIGS. 18 and 19 , there is shown a cuff exercise system  120  of the present invention. The cuff  120  includes an annular ring  122  defining an annular bladder  124 . The annular bladder  124  includes a compressible or non-compressible fluid  126  enclosed therein. The annular ring  122  is made of an elastic material have a stiffness k R . The stiffness k R  is selected to provide the desired resistance profile to the muscle or muscle group being exercised. 
     In use, the annular ring  122  is positioned about a muscle or muscle group. The contraction of the muscle pushes against the annular ring  122 , causing a compression of the fluid  126  and corresponding expansion of the annular ring  122 . The stiffness k R  of the annular ring  122  resists the expansion of the annular ring  122 , imparting a compressive force about the muscles. As a result, the muscles  128  must provide an expansive force to overcome the compressive force of the annular ring  122 . 
     Referring to  FIG. 20 , the annular ring  122  may be positioned about a bicep muscle  128 . When the arm  130  is flexed, the bicep muscle  128  provides a pulling force to lift the weight  132 , resulting in a contraction of the bicep muscle  128 . The contracting bicep muscle  128  expands, pushing against the annular ring  122 , causing a compression of the fluid  126  and corresponding expansion of the annular ring  122 . The stiffness k R  of the annular ring  122  resists the expansion of the annular ring  122 , imparting a compressive force about the bicep muscle  128 . As a result, the bicep muscle  128  must not only provide the pulling force to lift the weight  132 , but also an expansive force to overcome the compressive force of the annular ring  122 . 
     When lowering the weight, the bicep  128  provides a pulling force to controllable lower the weight  132 . The compressive force applied by the annular ring  122  tends to increase the rate at which the weight  132  is lowered. In order to maintain a controlled lowering rate, the bicep  128  must provide an expansive force to overcome the compressive force of the annular ring  122 . 
     The cuff  120  may include a mechanism for controlling the fluid pressure in the annular ring  122 . The control mechanism may include a fill valve positioned annular ring  122 . Fluid  126  is added or removed from the annular ring  122 , increasing or decreasing the fluid pressure therein. The fluid can progressively added to removed from the annular ring  122  during the exercise to control the resistance profile. 
     Referring to  FIG. 21 , the cuff  120  can be positioned about any muscle group, such as, abdominal/lower back, chest/upper back, quadriceps/hamstring, biceps/triceps, etc. 
     Referring to  FIG. 22 , the cuff  120  may be configured with attachments that allow the cuff to be adjustably fitted about the muscle group. For example, the cuff  120  may have first and second end portions  134  and  136  each including fastener members  138  and  140 , to securely fit the cuff  120  about the muscle. The fastener members  138  and  140  are adjustable members, allowing the cuff  120  to be securely, snugly, fitted about the muscle. For example, the fastener members  138  and  140  are hook-and-loop type fasteners, or could involve a plurality of snaps, zippers or other fasteners. 
     Referring to  FIG. 23 , the cuff  120  includes a plurality of bladder members  144  positioned serially within the annular ring  122 . Each of the bladder member  144  includes a compressible or non-compressible fluid  126  enclosed therein and are made of elastic materials have a stiffness k R . The stiffness k R  of each of the bladder members  144  is selected to provide the desired resistance profile to the muscle or muscle group being exercised. Each of the bladder members  144  can have the same stiffness k R  or a different stiffness k R , depending on the desired resistance profile. Each of the adjacent bladder members  144  can be fluidly connected with tube member  146 . As described above, the tube members  146  may also be used to control the resistance profile. 
     Referring to  FIG. 24 , the cuff  120  includes a plurality of bladder members  148  positioned in a stacking arrangement within the annular ring  122 . Each of the bladder members  148  includes a compressible or non-compressible fluid  126  enclosed therein and are made of elastic materials have a stiffness k R . The stiffnesses k R  of each of the bladder members  148  are selected to provide the desired resistance profile to the muscle or muscle group being exercised. Each of the bladder members  148  can have the same stiffness k R  or a different stiffness k R , depending on the desired resistance profile. Each of the adjacent bladder members  148  can be fluidly connected with tube member  150 . As described above, the tube member  150  may also be used to control the resistance profile. 
     In another embodiment, the bladder system of the present invention includes so-called “smart materials”. For example, the walls of the bladders may be constructed to include reinforcing fibers made of a shape memory alloy. A shape memory alloy possesses the properties of returning to an original shape after having been subjected to some form of deformation. The shape memory alloy returns to the original shape with the application of an energy to heat the alloy to a temperature above a transformation temperature. In an exemplary use, the shape memory alloy is provided in the cuff exercise system  120  of  FIGS. 18 and 19 . 
     As previously disclosed, the cuff exercise system  120  includes an annular ring  122  defining an annular bladder  124 . The annular ring  122  is positioned about a muscle or muscle group. The contraction of the muscle pushes against the annular ring  122 , causing a compression of the fluid  126  and corresponding expansion of the annular ring  122 . The stiffness k R  of the annular ring  122  resists the expansion of the annular ring  122 , imparting a compressive force about the muscles. As a result, the muscles  128  must provide an expansive force to overcome the compressive force of the annular ring  122 . 
     The inclusion of the shape memory alloy in the annular bladder  124  allows for a controlled application of the compressive force about the muscle. An application of an energy to the shape memory alloy, increasing the temperature of the shape memory alloy to the transition temperature, results in the shape memory alloy reverting to the original shape. The original shape of the shape memory alloy is designed to increase the stiffness k R  of the annular bladder  124 , further increasing the resistance to the expansion of the annular ring  122  and imparting an increased compressive force about the muscles. 
     It is contemplated that the annular bladder  124  can include a number of different shape memory alloys, each having a different transition temperature. The differing transition temperatures permit the shape memory alloys to be sequentially activated to increase the compressive force about the muscle. 
     The bladder system of the present invention can include an electro-rheological (ER) fluid. An ER fluid is a fluid which changes its physical properties in the presence of an electric field. For example, the application of an electric field increases the viscosity of the ER fluid, which if desired, can ultimate change from a liquid to a solid. 
     Referring again to  FIG. 1 , the bladder system  10  of the present invention uses a plurality of fluidly connected bladders to provide resistive forces to the muscles being exercised. The bladder system  10  includes first and second bladders  12  and  14  in fluid communication with each other, such as through a tube  16 . 
     An ER fluid  18  is disposed within the bladders  12  and  14 , such that a compression of one of the bladders  12  or  14  forces the ER fluid  18  through the tube  16  into the opposite bladder  12  or  14 . The viscosity of the ER fluid  18  is used to control the resistance of the exercise device. The viscosity of the ER fluid  18  is selected to provide a specific maximum flow rate through the tube  16  without the presence of the electric field. The application of the electric field increases the viscosity of the ER fluid  18 , decreasing the flow rate and providing a greater resistance. As the intensity of the electric field is increased, the viscosity of the ER fluid is similarly increased, increasing the resistance. 
     The smart materials of the above embodiments may be used individually or in combination to provide a bladder system having an increased range of useful resistance. Additionally, while having been described on specific embodiment of the present invention, this is for exemplary purposes only and it is contemplated that the smart materials can be similarly incorporated into other embodiments of the present invention. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.