Patent Publication Number: US-2023158366-A1

Title: Exercise device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a PCT application that claims the benefit of and priority to U.S. patent application Ser. No. 17/335,668, filed on Jun. 1, 2021, which is a continuation-in-part of U.S. patent application Ser. No. 17/066,467, filed on Oct. 8, 2020, the disclosures of which are all incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to exercise systems and devices including portable exercise devices that provide a resistance force or torque. 
     BACKGROUND 
     The present disclosure relates to exercise devices, such as can be used for various exercises to condition or strengthen various muscles, including the core, of a person. Exercise devices such as stationary machines, portable machines and small portable machines can be used for various exercise routines. Some exercise devices can provide a resistive force, such as through the use of springs, rubber bands, weights or gravity. Some exercise devices can be very sophisticated and provide a great deal of flexibility in performing a number of exercises, but be expensive to purchase and complicated to set-up and use. 
     One important group of muscles to exercise is frequently referred to as the “core.” This group of muscles can include muscles of an individual&#39;s torso. In various definitions, the core can include one or more of the pelvic floor muscles, transversus abdominis, multifidus, internal and external obliques, rectus abdominis, erector spinae, longissimus thoracis, diaphragm, latissimus dorsi, gluteus maximum, trapezius, and other muscles as well. Having a strong core is believed to contribute to good posture and balance as well as decreasing back and joint pain, muscle fatigue, nerve pain and injury, improve blood circulation, blood pressure, personal energy and positive emotional outlook. 
     Exercises without exercise equipment can be used to provide general exercise, but exercise equipment can provide additional benefits to an exercise routine, such as to assist in improving form, improve targeting of individual muscles or muscle groups, facilitate a different/greater range of movement during the exercise and vary the resistance during the exercise as compared to exercise without equipment. 
     One option for individuals that would like to use exercise equipment during a workout would be to join a gym. However, gym memberships can be expensive and frequenting agent can be inconvenient. Purchasing exercise equipment can expensive and the equipment can be bulky. Accordingly, there is a need for compact and inexpensive exercise equipment which can assist in providing an improved exercise experience. 
     SUMMARY 
     In a first aspect, an exercise device is provided. The exercise device comprises: a platform having a first end and a second end opposite the first end; first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; a first motor configured to apply a first torque to the first wheel where the magnitude of the first torque is related to the distance of the exercise device from a zero position and the direction of the first torque urges movement of the exercise device toward the zero position. 
     In a first embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position. 
     In a second embodiment of the first aspect, the exercise device further comprises a stabilizing wheel system comprising one or more stabilizing wheels, wherein the one or more stabilizing wheels are positioned and configured to roll across the surface and to limit rotation of the platform in relation to the first and second wheel. 
     In a third embodiment of the first aspect, the surface comprises a continuous horizontal surface extending from the first wheel to the second wheel. 
     In a fourth embodiment of the first aspect, the surface comprises a first track and a second track where the first wheel rolls on the first track and the second track rolls on the second track. 
     In a fifth embodiment of the first aspect, the exercise device further comprises a stabilizing wheel system comprising one or more stabilizing wheels, wherein the one or more stabilizing wheels are positioned and configured to roll across the surface and to limit rotation of the platform in relation to the first and second wheel, and there are two stabilizing wheels. 
     In a sixth embodiment of the first aspect, the exercise device further comprises a stabilizing wheel system comprising one or more stabilizing wheels, wherein the one or more stabilizing wheels are positioned and configured to roll across the surface and to limit rotation of the platform in relation to the first and second wheel, and the first motor is configured to apply a second torque to the second wheel, where the magnitude of the second torque is related to the distance of the exercise device from the zero position and a direction of the second torque urges movement of the exercise device toward the zero position. 
     In a seventh embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof. 
     In an eighth embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof, and the first pattern is a linear curve with constant magnitude. 
     In an ninth embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof, and the first pattern has increasing magnitude with increasing distance from the zero position. 
     In a tenth embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof, and the first pattern has decreasing magnitude with increasing distance from the zero position. 
     In an eleventh embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof, and the first pattern is a linear curve with increasing magnitude with increasing distance from the zero position. 
     In a twelfth embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof, and the first pattern has increasing then decreasing magnitude with increasing distance from zero. 
     In a thirteenth embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof, and the first pattern has decreasing then increasing magnitude with increasing distance from zero. 
     In a fourteenth embodiment of the first aspect, the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof, and the first pattern is different from the second pattern. 
     In a second aspect, a method of operating an exercise device is provided where the exercise device comprises: a platform having a first end and a second end opposite the first end; first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; a first motor configured to apply a first torque to the first wheel where the magnitude of the first torque is related to the distance of the exercise device from a zero position and the direction of the first torque urges movement of the exercise device toward the zero position, and the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position. The method comprises: the first or second motor applying a first or second torque to the first or second wheel, respectively as the exercise device is pushed across the surface away from the zero position, where the first or second torque opposes the motion of the exercise device; and the first or second motor applying a first or second torque to the first or second wheel, respectively as the exercise device is pushed across the surface toward the zero position, where the first or second anti-return force opposes the motion of the exercise device. 
     In a first embodiment of the second aspect, the first or second torque is changed to compensate for yaw of the exercise device. 
     In a second embodiment of the second aspect, the first or second torque is changed to compensate for tipping of the platform in relation to the first or second wheel. 
     In a third embodiment of the second aspect, the first or second torque is changed when the acceleration of the exercise device away from or toward the zero position exceeds a preset value. 
     In a third aspect, a method of operating an exercise device is provided where the exercise device comprises a platform having a first end and a second end opposite the first end; first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; a first motor configured to apply a first torque to the first wheel where the magnitude of the first torque is related to the distance of the exercise device from a zero position and the direction of the first torque urges movement of the exercise device toward the zero position, and the exercise device further comprises a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position, and the magnitude of the first torque follows a first pattern as the distance from the zero position increases and the magnitude of the second torque follows a second pattern as the distance from the zero position decreases, where the first and the second pattern are independently selected from: a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and combinations thereof. The method comprises selecting the first or second pattern at the start of an exercise session. 
     In a fourth aspect, an exercise system is provided. The exercise system comprising: an exercise device comprising: a platform having a first end and a second end opposite the first end; first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; a first motor configured to apply a first torque to the first wheel where the magnitude of the first torque is related to the distance of the exercise device from a zero position and the direction of the first torque urges movement of the exercise device toward the zero position; and a user interface configured to provide an indication of an exercise parameter achieved or an exercise deviation performed to a user of the exercise device. 
     In a first embodiment of the fourth aspect, the user interface provides a haptic indication to the user. 
     In a second embodiment of the fourth aspect, the user interface comprises a visual display in the exercise device. 
     In a third embodiment of the fourth aspect, the user interface comprises a visual display external to the exercise device. 
     In a fourth embodiment of the fourth aspect, the user interface comprises an audio signal. 
     In a fifth embodiment of the fourth aspect, the indication of an exercise parameter achieved comprises a display of a representation of the user&#39;s position operating the exercise device and a standard position of operation of the exercise device. 
     In a sixth embodiment of the fourth aspect, the indication of an exercise parameter achieved comprises an indication of a degree of success in achieving a standard movement form during operation of the exercise device. 
     In a fifth aspect, an exercise device is provided. The exercise device comprising: a platform having a first end and a second end opposite the first end; first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; the first wheel applies a force that resists movement of the exercise device when the exercise device is moved from a zero position where a magnitude of the force is related to the distance of the exercise device from the zero position and a direction of the force urges the device toward the zero position. 
     In a sixth aspect, an exercise device is provided, the exercise device comprising: a body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; first and second axles connected to and rotationally locked to first and second wheels, respectively, the first and second wheels able to rotate both in clockwise and counterclockwise directions in relation to the body, the first axle also connected to the body proximate the first end at a first hub and the second axle also connected to the body proximate the second end at a second hub; a first spring with a wheel end and a hub end, the first spring positioned at least partially within the first axle, with the first spring wheel end slidably connected to the first wheel at a first wheel junction, wherein the first wheel junction is configured to convey torque between the first wheel and the first spring wheel end, and the first spring hub end slidably connected to the first hub at a first hub junction, wherein the first hub junction is configured to convey torque between the first hub and the first spring hub end; and a second spring with a wheel end and a hub end, the second spring positioned at least partially within the second axle, with the second spring wheel end slidably connected to the second wheel at a second wheel junction, wherein the second wheel junction is configured to convey torque between the second wheel and the second spring wheel end, and the second spring hub end slidably connected to the second hub at a second hub junction, wherein the second hub junction is configured to convey torque between the second hub and the second spring hub end; when the first and second wheels are rotated against respective first and second spring torques, energy is stored in the first and second springs and the first and second springs apply restoring torque to the first and second wheels, respectively. 
     In a seventh aspect, an exercise device is provided, the exercise device comprising: a body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; a first axle connected to a first wheel, the first axle also connected to the body proximate the first end at a first hub; a first spring having a first spring end, the first spring positioned at least partially within the first axle, with the first spring end slidably connected to one of the first wheel and the first hub at a first junction, wherein the first junction is configured to convey torque between the one of the first hub and the first wheel and the first spring end. 
     In a eighth aspect, a method of using an exercise device is provided, the method comprising: moving an exercise device away from a person&#39;s waist while the person&#39;s feet are placed on a body of the exercise device and the first and second wheels are on a surface, wherein when the exercise device is moved away from the person&#39;s waist, the first and second wheels rotate along the surface, and torque energy is stored in the first and second springs; and moving the exercise device toward the person&#39;s waist while the person is assisted by or resists torque supplied to the first and second wheels by the first and second springs, respectively, wherein the exercise device comprising: the body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; first and second axles connected to and rotationally locked to first and second wheels, respectively, the first and second wheels able to rotate both in clockwise and counterclockwise directions in relation to the body, the first axle also connected to the body proximate the first end at a first hub and the second axle also connected to the body proximate the second end at a second hub; a first spring with a wheel end and a hub end, the first spring positioned at least partially within the first axle, with the first spring wheel end slidably connected to the first wheel at a first wheel junction, wherein the first wheel junction is configured to convey torque between the first wheel and the first spring wheel end, and the first spring hub end slidably connected to the first hub at a first hub junction, wherein the first hub junction is configured to convey torque between the first hub and the first spring hub end; and a second spring with a wheel end and a hub end, the second spring positioned at least partially within the second axle, with the second spring wheel end slidably connected to the second wheel at a second wheel junction, wherein the second wheel junction is configured to convey torque between the second wheel and the second spring wheel end, and the second spring hub end slidably connected to the second hub at a second hub junction, wherein the second hub junction is configured to convey torque between the second hub and the second spring hub end; when the first and second wheels are rotated against respective first and second spring torques, energy is stored in the first and second springs and the first and second springs apply restoring torque to the first and second wheels, respectively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows an embodiment of an exercise device. 
         FIG.  2    shows an exploded diagram of an embodiment of an exercise device. 
         FIG.  3    shows an embodiment of an exercise device. 
         FIG.  4    shows an embodiment of an exercise device. 
         FIG.  5    shows an embodiment of an end of an exercise device. 
         FIG.  6    shows an embodiment of an exercise device having two wheels. 
         FIG.  7    shows an embodiment of a wheel junction. 
         FIG.  8    shows an embodiment of a hub junction. 
         FIG.  9    shows an embodiment of a spring. 
         FIG.  10    shown an embodiment of an exercise device. 
         FIG.  11    shows an embodiment of an exercise device having a strap. 
         FIGS.  12 A-D  show an embodiment of an exercise device. 
         FIGS.  13 A-B  show an embodiment of an exercise device. 
         FIGS.  14 A-D  show an embodiment of an exercise device. 
         FIGS.  15 A-D  show an embodiment of an exercise device. 
         FIG.  16    shows a portion of an embodiment of an exercise device. 
         FIG.  17    shows a portion of an embodiment of an exercise device. 
         FIG.  18    shows a portion of an embodiment of an exercise device. 
         FIGS.  19 A-D  show an embodiment of an exercise device. 
         FIGS.  20 A-E  show an embodiment of an exercise device. 
         FIGS.  21 A-E  show an embodiment of an exercise device. 
         FIGS.  22 A-F  show an embodiment of an exercise device. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to clearly describe various specific embodiments disclosed herein. One skilled in the art, however, will understand that the presently claimed invention may be practiced without all of the specific details discussed below. In other instances, well known features have not been described so as not to obscure the invention. 
     In resistive stretching, the exercise device can provide a force to the user that resists the stretching movement performed by the user that the user must overcome to move the exercise device. In some embodiments of resistive stretching, the exercise device can provide a stabilizing force that counters the weight of the user, while imparting an additional force that the user must overcome to move the exercise device. In some embodiments, the stabilizing force can hold the exercise device in a fixed position waiting for the user to initiate movement of the exercise device. 
     In forced stretching, the exercise device can provide movement that the user can follow or resist while performing a stretching movement. In one embodiment, the exercise device moves through the exercise motion while the user follows the motion while contacting the exercise device. The exercise device can overcome a degree of resistance to movement provided by the user. In some embodiments, the degree of resistance overcome by the exercise device can be set as a preset value or can be determined by the exercise device based upon one or more exercise performance parameters and/or exercise deviation parameter, or can be determined by external direction or combination thereof. Forced stretching can be used in such situations as where a user needs help to increase the extent of motion during a stretching exercise. 
     In passive stretching, the exercise device can follow the movements of the user performing a stretching movement without significantly forcing the movement (with the user resisting) or resisting the movement by the user. In some embodiments of passive stretching, the exercise device can provide a stabilizing force that counters the weight of the user, while allowing intentional movements of the user without significantly more force applied by the exercise device than that needed to counter the force applied by the user due to the weight of the user. 
     In each form of stretching, an exercise parameter or exercise device operational parameter (such as speed, torque, force, direction, exercise performance parameter, exercise deviation parameter, etc.) can be preset or determined based upon an action of the user or by external direction. In some embodiments, an exercise parameter or exercise operational parameter can be preset with modification based upon an action of the user, by external direction, or based upon exercise history, exercise performance parameter or exercise deviation parameter. Examples can include an audible command (e.g. start, stop, faster, slower, etc.), a sound or signal from a remote control, a movement of the exercise device (such as a tilt or other manipulation of the exercise device), a pause or halt in the operation of the exercise device, an exercise deviation or series of exercise deviations, environmental sound or signal (e.g. sound or signal due to a fall, broken equipment, timer, person entering the room, person calling or crying, animal sounds (vocal or otherwise), etc.) and exercise routine related (e.g. sound or signal from a recording or video of an exercise routine, interactive exercise routine such as a part of a local or remote exercise session conducted over television, the Internet, or other transmitted/received means, including all types of exercise class or session including in-person, pre-recorded, live, “virtual”, “online”, remote, computer generated, etc.) 
     In each form of stretching, an exercise movement can be initiated or stopped or restarted or continued or returned to a starting point or zero position by any suitable method such as the user initiating or stopping motion of the exercise device, Examples can include an audible command (e.g. start, stop, faster, slower, etc.), a sound or signal from a remote control, a movement of the exercise device (such as a tilt or other manipulation of the exercise device), an exercise deviation or series of exercise deviations, environmental sound or signal (e.g. sound or signal due to a fall, broken equipment, timer, person entering the room, person calling or crying, animal sounds (vocal or otherwise), etc.) and exercise routine related (e.g. sound or signal from a recording or video of an exercise routine, interactive exercise routine such as a part of a local or remote exercise session conducted over television, the Internet, or other transmitted/received means, including all types of exercise class or session including in-person, pre-recorded, live, “virtual”, “online”, remote, computer generated, etc.) 
     In each form of stretching, the extent of movement can be a constant from repetition to repetition, or can be varied from repetition to repetition. In some embodiments, the extent of movement can be increased with successive repetitions. In some embodiments, the extent of movement can be decreased with successive repetitions. In some embodiments, in a set of repetitions, successive repetitions can be a combination of two or more of constant, increasing and decreasing distances for successive repetitions. 
     In each form of stretching, the force provided by the exercise device in the respective form of stretching can be a constant from repetition to repetition, or can be varied from repetition to repetition. In some embodiments, the force can be increased with successive repetitions. In some embodiments, the force can be decreased with successive repetitions. In some embodiments, in a set of repetitions, successive repetitions can be a combination of two or more of constant, increasing and decreasing force for successive repetitions 
     In some embodiments of each form of stretching, the exercise device can determine the extent of stretching movement the user can make or the extent of stretching movement can be controlled by the user in the user&#39;s operation of the exercise device. 
     In some embodiments, the exercise device can provide left-right direction stabilization to counter uneven force applied by the user to the exercise device. For example, if the user applies greater force to a first end (e.g. the left end) of the exercise device in comparison to second end (e.g. the right end), the exercise device can twist during operation resulting in yaw of the exercise device during operation. In one embodiment of the exercise device, the exercise device can adjust the force applied by the exercise device to counter the imbalanced left-right force applied by the user. One embodiment of countering uneven applied force can comprise applying different amounts of force on left and right wheels, such as by applying different torque at a left wheel as compared to a right wheel. In one such embodiment, a motor provides a different amount of torque to a left wheel as compared to a right wheel. Such differential torque can be applied from a common motor or by utilizing separate motors for the left wheel and the second wheel. 
     In various embodiments described herein, torque can be applied to one or more wheels. The torque can come from any number of devices, such as motor(s), spring(s), or other electrical or mechanical devices that can impart torque to the associated wheel(s). In the description provided herein, the word “motor” is used in multiple places as a shorthand way of referring to ways of applying torque to the wheel(s) and can also include other electrical torque sources and mechanical torque generating devices such as spring(s). Further, these different devices for applying torque to the wheel(s) can be used interchangeably or combined as desired. 
     Also as described herein, a battery is described and used to store energy to power a motor. However, other energy storage systems can be used, such as springs, capacitors and other electrical and mechanical energy storage devices. In the description provided herein, “battery” and “batteries” are also intended as a shorthand way of referring to these other energy storage systems and these energy storage systems can be used interchangeably or combined as desired. 
     As described herein, variation of torque applied to the wheel(s), variation of torque applied by the wheel(s), force applied by the exercise device, force applied by the wheel(s), stoppage of movement of the exercise device, variation of speed of the exercise device and variation of distance of the exercise device can be accomplished by varying the torque produced by motor(s) or by mechanical devices, such as with clutch(es), brake(s), cog(s), pawl(s), etc. 
     In the description provided herein, control of and variation of the torque applied to the wheel(s) and force produced by the exercise device are described in the context of motor(s) and varying the torque produced by the motor(s). In the description provided herein, this variation and control of torque and force, the discussion of a motor is also intended as a shorthand way of referring to control and variation of torque by way of other techniques, such as mechanical methods. 
     Further, the electrical control techniques described herein including those described as being used with motor(s) can also be integrated with and used with mechanical torque variation and with mechanical torque generation as a part of exercise devices. 
     The exercise device disclosed herein can be utilized by placing any appropriate portion of the user&#39;s body on the exercise device and following an exercise routine of moving the exercise device (or the exercise device moving the user, the user&#39;s body or portion of the user&#39;s body). Suitable portions of a user&#39;s body for placement on the exercise device can include, but is not limited to feet, hands, hips, back, butt, shoulders, arms legs, knees, elbows, chest, abdomen, and portions and combinations thereof. For convenience of description, the description herein has described the feet or hands as being used to contact the exercise device, but other portions of the user&#39;s body, such as these can be used. 
     The discussion below and in the Appendix primarily describe resistive stretching. However, forced stretching, passive stretching and strength exercises can also be performed by changing the direction and/or the magnitude of the force applied by the exercise device and are included in this disclosure. 
       FIG.  1    shows an embodiment of an exercise device  111  with two wheels  113 ,  114 . In the embodiment shown in  FIG.  1   , a platform  112  has a first wheel  113  and a second wheel  114  located at opposite ends of the platform  112 . A first motor  115  is located in functional communication with the first wheel  113  to apply torque to the first wheel  113 . In some embodiments, a second motor  116  can be located in functional communication with the second wheel  114  to apply torque to the second wheel  114 . In some embodiments, only one motor can be present to apply torque to both wheels, such as through a common shaft, a gearbox or a gearbox and clutch or a gearbox and differential arrangement. In some embodiments of a single motor configured to apply torque to the first  113  and second wheels  114 , the same torque, an approximately same torque or a different torque can be applied to both the first and second wheels. 
     Exercise devices described herein can be operated, for example by a user pushing the exercise device  111  away from a zero position, which can be the starting position for an exercise with such movement opposed by the motor(s) of the exercise device  111 , and allowing the motor(s) of the exercise device  111  to move the exercise device  111  back toward the zero position while being opposed by the user, the exercise device  111  can be operated by a user pulling the exercise device  111  away from the zero position with such movement opposed by the motor(s) of the exercise device  111 , and allowing the motor(s) of the exercise device  111  to move the exercise device  111  back toward the zero position while being opposed by the user. The amount of effort required for the pushing, pulling and opposing can be varied by the user and by adjusting the torque applied by the motor(s). 
     In some embodiments of operating the exercise device  111 , a user can place one or both hands on the platform  112 , while the user&#39;s foot or feet are placed on a surface or on a platform. A surface can be a horizontal surface, such as the floor, table, platform, etc., or a vertical surface, such as a wall, barrier, etc., inclined, and can be flat or curved. The surface can also be a combination of these types of surfaces. The user can then push the exercise device  111  away from the zero position along the surface to an extended position. While the user pushes the exercise device  111  away from the zero position, the motor (or motors) can apply a torque to the wheel or wheels associated with the motor(s) that resists the pushing by the user. In some embodiments, the torque applied by the motor(s) can be a constant or a variable as the exercise device moves away from the zero position, such as by pushing by the user. In some embodiments of a variable torque, the torque can vary in relation to the distance between the exercise device and the zero position. 
     After the exercise device reaches the extended position, the exercise device can move along the surface toward the zero position with the motor(s) applying torque to the wheel(s) that urges the exercise device toward the zero position and the user can resist the movement caused by the torque of the motor(s). In some embodiments, the torque applied by the motor(s) can be a constant or a variable as the exercise device moves toward the zero point, such as while being opposed by the user. In some embodiments of a variable torque, the torque can vary in relation to the distance between the exercise device and the zero position. 
     In some embodiments, the user can pull the exercise device  111  away from the zero position along the surface to a compressed position. While the user pulls the exercise device  111  away from the zero position, the motor (or motors) can apply a torque to the wheel or wheels associated with the motor(s) that resists the pulling by the user. In some embodiments, the torque applied by the motor(s) can be a constant or a variable as the exercise device moves away from the zero position, such as by pulling by the user. In some embodiments of a variable torque, the torque can vary in relation to the distance between the exercise device and the zero position. 
     After the exercise device reaches the compressed position, the exercise device can move toward the zero position along the surface with the motor(s) applying torque to the wheel(s) that urges the exercise device toward the zero position and the user can resist the movement caused by the torque of the motor(s). If In some embodiments, the torque applied by the motor(s) can be a constant or a variable as the exercise device moves toward the zero point, such as while being opposed by the user. In some embodiments of a variable torque, the torque can vary in relation to the distance between the exercise device and the zero position. 
     In some embodiments of an exercise routine, various combinations of the above operations can be performed. For example, the exercise device can be pushed away from the zero position, followed by a return to the zero position, which is then followed by the exercise device being pushed away from the zero position. Another example of an exercise routine can include the exercise device being pushed away from the zero position, followed by a return to the zero position, which is then followed by the exercise device being pulled away from the zero position. In additional, shortened motions of the exercise device can be utilized during a routine, such as where the exercise device returns only partway to the zero position before changing direction to move away from the zero position, or where the exercise device is moved to a different distance from the zero position with a successive repetition before moving again toward the zero position. 
       FIG.  2    shows an embodiment of an exercise device with a first wheel  113 , a second wheel  114  and two stabilizing wheels  117 . In some embodiments, only one stabilizing wheel  117  can be present. In some embodiments, more than two stabilizing wheels, such as three, four, five, six or more stabilizing wheels can be present. The stabilizing wheel(s)  117  are sized, configured and positioned to in combination with the first wheel  113  and second wheel  114  provide platform stability of the exercise device  111  by limiting or preventing rotation of the platform  112  around the first and/or second wheel  113 ,  114  of the exercise device. 
       FIG.  2    also shows a chassis  118  that can serve as a frame for attachment directly or indirectly, other parts, such as the platform  112 , first wheel  113 , second wheel  114 , first motor  115 , second motor  116 , stabilizing wheel(s)  117 , battery  119 , battery cover  120 , suspension assembly(ies)  122  and strap  123 . In some embodiments, not all of the listed parts might be present, with one or more of these parts being absent or integrated into another part. For example, one or more of the second motor, one or both stabilizing wheels, battery cover, wheel guards, strap might be absent. Further, the chassis and platform might be present as an integrated single unit, the first and or second motor can be located within respective first and second wheels or be mounted separate from the wheel and in operational communication with the respective wheel. 
       FIGS.  3  and  4    show embodiments of an exercise device  111  with a platform  112  and a strap  123 . Also shown are first wheel  113 , first motor  115 , chassis  118 , stabilizing wheel  117  and suspension assembly  122 .  FIG.  3    also shows user interface  124  with an indicator light.  FIG.  4    also shows resilient bushing  125  in the suspension assembly. 
     The suspension assembly  122  can provide resistance to tilting of the platform in relation to the surface the exercise device travels. For example, resilient elements can provide resisted flexibility over a desired range of movement for the platform. In some embodiments the resilient element can be or comprise a bushing or a spring. In some embodiments, the bushing can comprise an elastomeric or plastic material that compresses or stretches or flexes with movement of the suspension assembly. In some embodiments, the spring can be any suitable type of spring, such as one that compresses, extends or flexes, such as coil, compression, extension, torsion, constant force belleville, drawbar, volute, garter, flat, or helical springs. 
     In various embodiments of an exercise device, the torque applied to the wheels can have a pattern when viewed from the perspective of the distance from the zero point where the pattern is a constant torque or a pattern that is a variable torque over the distance of the exercise device from a zero position or over a portion of the distance of the exercise device from a zero position. In some embodiments, the torque pattern can have a portion that is constant and a portion that is variable over the distance of the exercise device from the zero point. In some embodiments of a variable torque, the torque of the pattern can be related to the distance the exercise device has been moved from the zero position. For example, in one embodiment, the torque can have a pattern where the torque increases as the distance from the zero position increases. In other embodiments, the torque can have a pattern that increases then decreases. In additional embodiments, patterns that can be used can include a linear pattern with constant magnitude, a linear pattern with increasing magnitude with increasing distance from the zero position, a linear pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with decreasing magnitude with increasing distance from the zero position, a variable pattern with increasing then decreasing magnitude with increasing distance from zero, a variable pattern with decreasing then increasing magnitude with increasing distance from zero. In some embodiments, the torque profile over the entire movement of the exercise device away from or toward the zero position can follow a single pattern or a combination of patterns described herein and can optionally include repeated patterns. 
     In some embodiments of using the exercise device, the exercise device can operated by the exercise device moving away from the zero position followed by the exercise device moving toward the zero position. In some embodiments, the moving away from the zero position can be accomplished by a user pushing the exercise device. In some embodiments, the moving away from the zero position can be accomplished by a user by a user pulling the exercise device. In various embodiments, the torque profile of the exercise device moving away from the zero position can be the same or different from the torque profile of the exercise device moving toward the zero position. 
     Resistance and Stability Corrections 
     In some embodiments, the torque profile of the exercise device can be changed in response to how the user operates the user device. In one embodiment, the torque profile can be changed based upon a characteristic of the user&#39;s operation of the exercise device. In some embodiments, the characteristic can be a speed that the user moves the exercise device at, a steadiness of speed that the user operates the exercise device, the tilt or variability of the tilt of the platform of the exercise device, the linearity of the travel of the exercise device (i.e. how well the exercise device moves in a straight line), the twisting of the exercise device during operation (“yaw”) or a combination thereof. In response to the characteristic being outside of a desired range or being higher or lower than a desired value, the torque can be increased or decreased from the profile value. 
     In one embodiment, when the speed of movement of the exercise device is higher than a preset value, the torque value can be increased or decreased to make the exercise device easier or harder to move. 
     In one embodiment, when the speed of movement of the exercise device has undesirable variations, such as when the movement includes accelerations or decelerations outside of a preset value, the torque value can be increased or decreased to make the exercise device easier or harder to move. In some embodiments, the accelerations and decelerations can be evaluated based upon the rate of acceleration (or deceleration), the duration of the acceleration (or deceleration), the frequency at which accelerations (or decelerations) occur or a combination of thereof. 
     In one embodiment, when the tilt of the platform is outside or a preset range or is greater or less than a preset value, the torque value can be increased or decreased to make the exercise device easier or harder to move. 
     In one embodiment, when the movement of the exercise device is insufficiently linear, such as when the exercise device moves to the left or the right or moves to one side and then the other in a way that exceeds a preset range or value, torque value can be increased or decreased to make the exercise device easier or harder to move. In some embodiments, the movements to the left or right or to one side and then the other can be evaluated based upon such parameters as the speed of movement to the side, the distance moved to the side, the frequency of changes of direction to the side, back to center (the desired direction of travel) or to the other side, or combinations thereof. In some embodiments, one or more of the torque value of the first and second motors can be varied in relation to one another to compensate for the movement to the side by the exercise device, such as by creating a countering torque that can steer the exercise device back to center. 
     In one embodiment, when the twisting movement or the twisting force (yaw movement or yaw force, both of which can be referred to as “yaw”) on the exercise device is outside of a preset range or greater or smaller than a preset value, the torque value can be increased or decreased to make the exercise device easier or harder to move. In some embodiments, one or more of the torque value of the first and second motors can be varied in relation to one another to compensate for the twisting force or twisting movement applied to the exercise device, such as by creating a countering torque. 
     In various embodiments, the preset values and ranges described above can be a value entered by the user for an exercise session or a stored value or range, such as a value or range that was previously stored by the user or that is downloaded or that is entered by another or provided with the exercise device. 
     Interface 
     In some embodiments of an exercise device, a user interface can be provided. In some embodiments of a user interface, the user interface can provide the user with an indication of an exercise parameter achieved or an exercise deviation performed. In some embodiments, the indication provided can include a visual display, an audio display, a haptic indication or a combination thereof. In some embodiments, data from operation of the exercise device can be collected and stored in a memory or transferred to another device, such as an internal or external interface, and the data from operation can be analyzed for performance parameters or deviations and for logging of activity using the exercise device. User interfaces can also include one or more input interfaces or input interface component, such as an input interface or input interface component which can be used with equipment, computers, phones, etc. Suitable user interface and user interface components can include switches, buttons, dials, keypads, keyboards, mice, joystick, light pen, trackball, scanner, graphic tablet, microphone, magnetic ink reader, optical character reader, barcode reader, camera, touchpad, pointing stick, etc. Interfaces can also be provided for connection to connect to a phone, computer or data store (e.g. CD, DVD, flash drive, memory usable with a computer, etc.) Connections can be accomplished via wired or wireless techniques. 
     Suitable audio displays can include tones, buzzers, clicks, music, voice or other types of sounds. In some embodiments, the audio display can provide an alert, such as for accomplishment of a task or a deviation from a task. In some embodiments, the audio display can utilize varying pitch, varying volume, a vocabulary, etc. 
     Suitable haptic indication can include indications that are felt, and can be provided as haptic feedback through the platform or another part of the exercise device that contacts the user, including but not limited to vibration, tapping, shock, thermal, etc. Haptic feedback can also be provided through external devices, such as a remote, a worn device, such as a wristband, watch, finger clip, collar, chest strap, ankle strap, phone, etc. and can include types of haptic feedback as described for feedback through the platform. 
     Suitable visual displays can include one or more lights, a screen display, a video display or other display that can display information such as numbers, words, pictures or indicators of a condition. In some embodiments, a visual display can turn on a light or change a color, or display a representation of a person performing an exercise (for example a stick representation or a camera representation showing posture or form during performance of the exercise), a meter, etc. as well as combinations thereof. In some of these embodiments, the visual display can indicate an exercise task complete, incomplete, completed correctly, completed incorrectly, a score for an accomplishment, logged activity such as a cumulated set of accomplishments (including but not limited to time exercise, number of repetitions, distance moved, and in some embodiments the cumulated set of accomplishments can be displayed per session or per a period of time.) 
     In some embodiments, the display can be located on the exercise device, such as on the platform, or the display can be located on an external device, such as a wall, a screen, a computer display, a television, a phone, a remote or other device capable of displaying parameters, indicators of condition, pictures, etc. In some embodiments, the exercise device can interface with an external device, such as a computer, phone, television, remote, etc. and the external device can collect operating data from the exercise device. 
     In some embodiments, the interface can be used as a training aid to provide feedback on the quality of the exercise performed. In some embodiments, quality of exercise parameters can include parameters such as those related to the distance the exercise device is moved in a repetition, the steadiness of the movement (such as variation in speed), straightness of movement, twisting torque applied to the exercise device, tilt of the platform, speed of the exercise device, motor torque value, etc. In some embodiments, quality of exercise parameters can include parameters related to user form, such as the position that the user assumes during the use of the exercise device (such as head position, hip position, arm position, or position of other body parts during a repetition or part of a repetition.) In some embodiments, historical results of exercise results, such as quality of exercise parameters or exercise deviations (discussed below) can be displayed during or after an exercise session. 
     In various embodiments, the exercise quality parameter can be compared to a preset value or can be compared to parameter values from other repetitions (of the user or a different user), such as successive repetitions or an averaged set of repetitions or a standard deviation of repetitions. 
     In some embodiments, an exercise deviation parameter can be displayed, logged or alerted. Exercise deviations can include parameters that indicate a deviation from a preferred or an idealized exercise repetition. In some embodiments, exercise deviations can include changes in speed, changes in linearity of movement, unbalanced forces on the left side and right side of the exercise device (e.g. torque applied to the exercise platform), tilting of the platform, user posture, user position, etc. 
     In some embodiments, the user interface can provide an indication of an exercise deviation when it occurs, such as by turning on a light, changing the color of a light, displaying a picture that shows a representation of a deviation (for example, a display of a non-linear track with or without showing a linear track), or a representation of a user (stick figure, simplified person or picture or video of a person) with an area of the user&#39;s body that is exhibiting a position or posture deviation marked. 
     Sensors 
     Various sensors can be used in conjunction with embodiments of the exercise device. Examples of sensors that can be used with an embodiment of an exercise device include sensors that can be used to determine the amount of travel of the exercise device, a direction of travel of the exercise device, a tilt of the exercise device or a part of the exercise device (such as where one portion of the exercise device or part of the exercise device moves closer to the surface across which the exercise device travels as compared to another part of the exercise device or part of the exercise device), twisting of the exercise device or part of the exercise device (such as rotation around an axis normal to the surface the exercise device travels across), contact by a user, location of contact by a user, geographic location of the exercise device, pushing force exerted by a user, torque applied by the motor, motor current, motor voltage, motor speed, amount of rotation of a motor or a wheel, wheel speed, acceleration, angular movement, temperature, time, elapsed time, global position, etc. 
     In some embodiments, a sensor to determine the amount of travel or a direction of travel of the exercise device can measure operation of one or more motors and/or wheels. In some embodiments, a sensor, such as a motor encoder, can detect the rotation of a motor or a wheel, and can be used, for example, to determine travel distance, travel speed, linearity of travel (such as by comparing the rotation of two wheels or motors), rotation of the device during operation (yaw), accelaration, smoothness of motion (lack of accelerations/decelerations during operation), commencement of an exercise routine or repetition, change of direction at maximum travel during a repetition, and stopping the exercise device such as to end an exercise routine. 
     In some embodiments, acceleration sensors, such as accelerometers, can be used to determine the same parameters as a sensor that detects the rotation of a motor or a wheel. For example, when an exercise routine begins, the accelerometer or other acceleration sensor can determine the rate of change in speed of the exercise device. This parameter combined with time can allow determination of the distance and direction of travel and speed of travel. The direct measurement of acceleration also allows determination of changes in speed, linearity of travel, acceleration, smoothness of motion, etc. In addition, acceleration sensor, such as an accelerometer, can determine twisting of the exercise device or tilting of the platform or other part of the exercise device. Accordingly, the acceleration sensor can also provide determination of yaw. 
     In some embodiments, torque can be measured directly by a torque meter (torque sensor) or implied from motor operational parameters, such as one or more of voltage, current, pulse characteristics, frequency and speed. 
     In some embodiments, one or more sensors can detect when a user places his/her hand(s) or foot/feet, knee(s), elbow(s), arm(s) or other body part on the exercise device to begin an exercise. Suitable sensors can include contact sensors, pressure sensors, proximity sensors, capacitance sensors, etc. In some embodiments, the sensor can detect where the user contacts the exercise device. In some embodiments, the location of contact can be used to identify the type of exercise to be performed. 
     In some embodiments, the exercise device can be set for a particular exercise routine among a plurality of exercise routines. In some embodiments, a selection of exercise routine can be made with the user interface. In some embodiments, the selection of a particular exercise routine can load motor parameters and a set of data or parameters to be used for comparison of the current exercise session to previous, target, idealized or model exercise session(s). 
     In some embodiments, a camera or camera system can be used in evaluating the user form or position in performing an exercise. In some embodiments, an evaluation image or data can be collected by a camera or camera system of a user performing an exercise, and then the evaluation image or data is compared to an image or image data of a comparison image or image data to identify conformities and differences between the evaluation image or data and the comparison image or data. (Conformities are areas of the images or data that correspond to one another and differences are areas where there are differences between the images or image data.) In some embodiments, the conformities or differences can relate to the position of a body part during performance of an exercise, such as head position, straightness of back, slope of back, angle of a joint, such as an elbow or shoulder, extent of movement, etc. In some comparisons, an overlaid image can be created by overlaying an evaluation image and a comparison image on one another. In some embodiments, the overlaid image can be simplified images, such as comprising a stick figure. In some embodiments, conformities or differences can be identified in a displayed image of a user, such as with marking or coloring, or other types of marks to identify the particular areas of the image. For example, an arm of the image can be displayed in a different color or be circled or marked with an arrow. In some embodiments, the image showing the conformities or differences can be an actual image of the user or a representation of the user, such as an avatar or a stick figure or another form used to represent the user and the relevant body parts of the user. In some embodiments, the comparison image can be based upon an idealized model of a user or another user or a previous image of the current user. 
     Skill Levels 
     Motor output can be varied to assist the user to achieve a constant speed, with greater or more frequent interventions to correct speed indicating a lower skill level and lesser or less frequent interventions indicating a higher skill level. Motor output can also be varied to assist the user in linearity of travel or to limit tilting or to counter twisting or yaw of the exercise device during operation. Again, greater or more frequent interventions to to correct the operation by the user indicating a lower skill level and lesser or less frequent interventions indicating a higher skill level. Occurrence of such interventions can in some embodiments be tracked over time to determine progression in skill level and can be reported to the user through the user interface or through other reporting methods. In addition, these are can in some embodiments select a skill level which changes how frequently or to what extent interventions will be made by the exercise device, such as through the motor output, to assist the user with an exercise parameter or exercise deviation. In some embodiments, a specific exercise parameter or exercise deviation can be selected for assistance through the motor output. 
     Further Discussion 
     Further discussion of exercise devices, exercise device features and exercise device operation are provided below. The embodiments and elements of the exercise device and its operation presented below can be combined with and substituted for the embodiments and elements of the exercise device of the disclosure above, and embodiments and elements of the exercise device in the disclosure above can be combined with and substituted for the embodiments and elements of the exercise device below. For example, the energy storage system and spring system described below can be interchanged or used in combination with the motor(s) and battery(ies) of the disclosure above and the motor(s) and battery(ies) of the disclosure above can be interchanged or used in combination with the energy storage system and spring system of the description below. Further the controls, switches, sensors and operation of the disclosure above can be applied to the exercise device of the description below and the controls, switches, sensors and operation of the description below can be applied to the exercise device of the disclosure above. 
     In an embodiment of an exercise device  1 , an exercise device can include a body  2  connected to a wheel  3  through a hub assembly  4  where the hub assembly is able to store torsional energy. In some embodiments, such as is shown in  FIG.  5   , the wheel  3  and hub assembly  4  can be proximate a first end of the body  2 . In some embodiments, such as is shown in  FIG.  6   , an exercise device can include first and second wheels  3  attached to body  2  through respective first and second hub assemblies  4 . In some embodiments, the first and second wheels and first and second hub assemblies  4  can be located proximate opposite ends of body  2 , as shown in  FIG.  6   . 
     The hub assembly  4  can comprise a hub  5 , axle  6  and spring  11 . In one embodiment, as shown in  FIG.  5   , the hub  5  can be connected to an axle  6  at a hub end  7  of the axle  6 , with the axle  6  extending outward from the hub  5 . External to the axle  6  are one or more bearings  8  in contact with the axle  6  and providing a rotating connection between the axle  6  and the housing  9 . Bearings  8  can be of any suitable type, such as ball, sleeve, bushing, roller, etc. The axle  6  connected to a wheel  3  at the wheel end  10  of the axle  6 . Within axle  6  is located spring  11 . Spring  11  has a hub end  12  (“spring hub end”) connected to the hub junction  13  located on the hub  5 , and a wheel end  14  (“spring wheel end”) of spring  11  connected to the wheel junction  15  located on the wheel  3 . 
     In some embodiments, one or both of the hub junction  13  and the wheel junction  15  are connected to their respective ends of spring  11  by way of sliding connections, such that wheel end  14  of spring  11  is slidably received into wheel junction  15  and/or hub end  12  of spring  11  is slidably received into hub junction  13 . In some embodiments, a hub junction  13  can be configured to transfer torque between the hub junction  13  and the spring  11 . In some embodiments, the wheel junction  15  can be configured to transfer torque between the wheel junction  15  and the spring  11 . In some embodiments, both the wheel junction  15  and the hub junction  13  can be configured to transfer torque between the spring  11  and the wheel junction  15  and the hub junction  13 . 
     Junctions 
     Junctions, such as wheel junctions and hub junctions are configured to transfer torque between the junction and the spring. In some embodiments, a junction can comprise a relief opening, such as a slot, which receives an end of the spring, such as a hub end or a spring end.  FIG.  7    shows an embodiment of a wheel junction having a slot and  FIG.  8    shows an embodiment of a hub junction having a slot. The spring end can include one or more extensions extending from the spring, such as a loop, a tab, a pin or another shape or a series of loops, tabs, pins, other shapes and combinations thereof which when inserted into the relief opening can interact with the interior surfaces of the relief opening to transfer forces therebetween such as in the form of a couple. In some embodiments, the relief opening can extend entirely across the face of the junction so as to have open ends at each edge of the junction. In some embodiments, the relief opening can extend across only a portion of the junction so as to have no open ends or only one open end at an edge of the junction. 
     In some embodiments, the relief opening can comprise two parallel faces extending into the face of the junction. In some embodiments, one or more faces of the relief opening can be curves. In some embodiments, the relief opening can have faces which are planar. In some embodiments, the junction can comprise more than one relief opening, such as where two or more relief opening cross one another or where two or more relief opening do not intersect with one another. In some embodiments, the relief opening can have a shape where the length is substantially the same as the width, such as in the shape of a square, or where the length is longer than the width, such as in the shape of a rectangle. In some embodiments, the relief opening can be in the shape of a triangle or other geometric shape where a spring end would be able to interact with wall to transfer torque. In some embodiments, the relief opening can comprise multiple openings, such as two or more holes and the spring end can comprise extensions which fit into two or more holes so as to transfer torque. In some embodiments, the two or more holes can be in the shape of circles, squares, triangles, ovals or other suitable shape, with one hole having the same or different shape from the other. 
     In some embodiments, the junction can have one or more extensions, as described above for spring end, and the spring end can include a relief opening as described above for the junctions, where the one or more extensions are slidably received into the relief openings and transfer torque. 
     In some embodiments, a wheel junction can be a part of the wheel or the wheel junction can be a separate part attached to the wheel.  FIG.  7    shows an embodiment of a replaceable wheel junction having a square shape, however different shapes can be used. In some embodiments, the replaceable wheel junction can be made to have different sizes/shapes/configurations/number of holes or slots for use with different spring ends. In some embodiments, a replaceable wheel junction can be dropped into a receptacle in the wheel or it can be a friction fit into a receptacle in the wheel or it can be attached to the wheel by other means as would be understood by those of skill in the art. 
     In some embodiments, the hub junction can be a part of the hub or the hub junction can be a separate part attached to the hub. In some embodiments, the hub junction can be replaceable having features as discussed for a replaceable wheel junction. 
     Spring Tension/Movement of the Exercise Device 
     In some embodiments, as the wheel turns in relation to the body, torsional energy will be stored in the spring  11 . Rotating the wheel further results in greater energy being stored in the spring  11 . 
     When the exercise device is placed on a surface and moved in a first direction, the wheel  3  will turn and energy can be stored in the spring  11 . The further the exercise device is moved, such as by pushing the exercise device with the wheel(s) turning as the exercise device moves across a surface, more energy can be stored in spring  11 . As energy is stored in the spring, a countering force can be present which resists further movement of the exercise device in the first direction. If the pushing force is decreased to below that of the countering force, the exercise device will move backwards counter to the first direction. In some embodiments, the exercise device can also be moved in a second direction, opposite to the first directions and the spring will store energy and apply a countering force in an opposite direction to when the exercise device is moved in the first direction. 
     Spring 
     In various embodiments, the spring  11  can be a material which is capable of storing torsional energy. In some embodiments, the spring  11  can be a coil spring, such as is shown in  FIG.  9   . In various embodiments of a coil spring, the coil spring can have different numbers of loops, the loops can be spaced close to one another, such as would be associated with a coil spring that is tightly wound, or the loops can be spaced further apart, such as would be associated with a coil spring that is more loosely wound. In various embodiments, the spring material can be thicker or thinner and of a suitable material so as to provide desirable spring force characteristics and energy storage. 
     In some embodiments, the spring  11  can have a different shape, such as being in the form of a rod, a sheet or multiple rods, or sheets or combinations thereof. 
     Spring material can be or comprise any suitable metal, such as steel, stainless steel, steel alloy, bronze, phosphor bronze, titanium, beryllium copper, or other metals and combinations thereof. Spring materials can also be or comprise polymer or elastomers. 
     In some embodiments, the spring  11  can be installed entirely within the axle  6 . In some embodiments, the spring  11  can be located partially within and partially without the axle  6 . In some embodiments, the spring  11  can be located such that at least a portion of one or both of the spring ends extend from the axle  6 . In some embodiments, the spring  11  can be located entirely within the wheel  3  where the spring  11  does not extend past the inner plane  16  and the outer plane  17  of the wheel  3 . In some embodiments, the spring  11  can be located only partially within the wheel  3 , where the spring  11  extends only partially outside of the inner plane  16  and/or the outer plane  17  of the wheel  3 . In some embodiments, the spring  11  can be located outside of the wheel  3  where the spring  11  is located entirely outside of the inner plane  16  and the outer plane  17  of the wheel  3 . 
     In some embodiments, the spring  11  can be sized such that the clearance between the spring and the axle prevents kinking of the spring when the spring is overwound. 
     In some embodiments, the spring  11  is sized such that the clearance between the spring and the axle and/or the overall length of the spring  11  relieves stress from the spring by allowing the hub and wheel ends of the spring  11  to move toward one another during an overwound condition, resulting in one of the hub and wheel ends of the spring  11  slipping out of the respective junction. 
     In some embodiments, such as shown in  FIG.  5   , the spring  11  can be can be installed or replaced, for example, by removing a spring by removing the screws  18  which attach wheel  3  to the axle  6 , removing the wheel  3 , and then pulling out the spring  11  from the interior of axle  6 ; then installing a spring by placing the spring  11  into the interior of axle  6  so as the hub end of the spring  11  aligns with and is slidably received into the hub junction such as into a slot in the hub junction; and then installing the wheel  3  by aligning the wheel junction with the wheel end of the spring  11 , slidably receiving the wheel end of the spring  11  into the wheel junction, and installing screws  18  to attach the wheel  3  to axle  6 . 
     Wheels 
     In some embodiments, the wheel can be rotationally affixed to the axle. In one embodiment, as shown in  FIG.  5   , screws  18  attach wheel  3  to axle  6 . However other types of fastening can also be used, such as bolts, clips, pins, nuts and the like. 
     In some embodiments, a body  2  can be attached to one wheel through a hub assembly  4  which can store torsional energy, as described herein. In some embodiments, a body  2  can be attached to two wheels  18  through respective hub assemblies  2 , each of which can store torsional energy as described herein. In some embodiments, a body  2  can be attached to a first wheel  3  through a hub assembly  4  which can store torsional energy as described herein and to a second wheel through other than a hub assembly  4  which can store torsional energy as described herein. In some embodiments, the exercise device  1  includes only one wheel and the wheel is connected to the body  2  through a hub assembly  4  which can store torsional energy as described herein. In one embodiment, the exercise device includes exactly two wheels  18  and both of the two wheels are connected to the body  2  through respective hub assemblies  2  which can store torsional energy as described herein. 
     In some embodiments, an exercise device  1  can have more than two wheels, such as four wheels. In some embodiments having more than two wheels, one or more or all of the wheels can be attached to the body  2  through respective hub assemblies  2  which can store torsional energy as described herein. In some embodiments with four wheels, one, two, three or four wheels can be attached to the body  2  through respective hub assemblies  2  which can store torsional energy as described herein. 
     When a wheel  3  is attached to body  2  other than through a hub assembly  4  that can store torsional energy as described herein, the wheel  3  can be attached by any suitable means such as through a fixed axle, a rotating axle, or otherwise as would be known to one of skill in the art. 
     In some embodiments, wheels of different sizes and with different surface contacting features (e.g. tread) can be used for example to accommodate different exercises, different sizes of user, different surfaces for the exercise device to move along, and the like. 
     Body 
     In some embodiments, a body can extend between two wheels. The body can be sized and configured for an individual using the exercise device to be able to place any portion of a user&#39;s anatomy that is desired and in the orientation desired. In some embodiments, the body  2  can be sized and configured for one or two feet, hands, knees, forearms or etc. on the body to use the exercise device. In some embodiments, one or two feet/hands/knees/forearms/etc. can be oriented with the feet/hands/knees/forearms oriented with the direction of movement of the body. In some embodiments, the feet/hands/knees/forearms/etc. can be oriented sideways (e.g. with toe and heel pointing at the wheels  3 ) or at an angle to the direction of movement of the body  2 . In some embodiments, the body can be sized and configured for an individual using the exercise device to be able to place only one foot, hand, knee, forearm or etc. on the body to use the exercise device. In some embodiments, the body  2  can be sized and configured for a user&#39;s back or bottom to contact the body  2  during exercise. 
     In some embodiments, the body can include recess(es) or bump(s) or combinations thereof on a surface of the body to interface with feet or hands or forearms or other portions of a user&#39;s anatomy and assist in placement of the feet/hands/knees/forearms/etc. at an appropriate location on the body.  FIG.  10    shows an embodiment of an exercise device  1  having recesses  19  in the body  2 . In some embodiments, the recesses or bumps can be achieved by curving the body  2 . 
     In some embodiments, one or more straps can be positioned on the body to be grasped by an individual while using the exercise device  1  or for the user to place hands/feet/forearms between the strap and the body while using the exercise device  1 . (See  FIG.  11   .) 
     In some embodiments, padding can be provided on the body. 
     Secondary Platform 
     In some embodiments, the exercise device can be used with a secondary platform  20  comprising a surface  21  raised off the ground as shown in  FIG.  11   . In general, the secondary platform  20  can be sized and configures to support one portion of a user&#39;s anatomy while the exercise device  1  supports and is moved by another portion of a user&#39;s anatomy. In some embodiments, the secondary platform can be sized and configured for placing one&#39;s feet thereon while one uses the exercise device with one&#39;s hands on the exercise device. In some embodiments, the secondary platform can be sized and configured for placing one&#39;s hand(s) on the secondary platform or to grasp the edge(s) of the secondary platform while one uses the exercise device with one&#39;s foot/feet on the exercise device. In some embodiments, the secondary platform can be sized and configured to support one foot of a user while the exercise device  1  supports the other foot of the user. In some embodiments, the secondary platform can be used to support one or both feet of a user while the exercise device support one or both hands of a user. 
     Operation of the Exercise Device 
     Generally, the exercise device operates by the spring(s)  11  providing a resisting force against rotation of the wheel(s) while the spring(s)  11  store torsional energy during rotation of the wheel(s)  3 , and then releasing this stored energy while providing a restoring force during rotation of the wheel(s)  3  in the opposite direction. In various embodiments, the restoring force can be a force that assists the user in the movement of the exercise device  1  or the restoring force can be a force that the user resists during movement of the exercise device  1 . 
     Exercise device  1  can be employed in exercises by a user in many ways. 
     One exemplary embodiment involves the user placing his/her hands on the body  2  with the wheels  18  resting on a surface, the user placing his/her feet on the surface with the user&#39;s body bent at the waist, and the user pushing the exercise device  1  away from the feet against spring force in the exercise device  1  and at least partially straightening the user&#39;s body. With this movement, the exercise device is moved against a resisting force provided by the spring(s)  11  while torsional energy will be stored in the spring(s)  11  of the exercise device  1 . The user can then move exercise device back toward the starting position and toward the user&#39;s feet with the spring(s)  11  of the exercise device  1  providing a restoring force which can assist the user in the movement back toward the starting position while releasing energy stored in spring(s)  11 . In a variation on this embodiment of a use, the user can place his/her hands on the surface and his/her feet on the body. In further variations on these embodiments, the starting position can be with a more straightened body, and the motion that stores torsional energy into spring  11  can be a movement that bends the body, for example, at the waist. 
     In another embodiment of an exercise with the exercise device, a user can place one foot on the exercise device and his/her other foot on the surface the exercise device is on or on a secondary platform that is placed on the surface the exercise device is on, and the feet are moved alternately away from and toward each other, with the spring(s)  11  alternately storing torsional energy while providing a resisting force and releasing energy while providing a restoring force. 
     Further Embodiments 
     The features discussed in various embodiments above can be combined with the features of various embodiments discussed below. Exercise devices, such as those discussed herein, can include a platform and one or more wheels. In embodiments that comprise two wheels, the wheels can rotate independently of one another or two or more wheels can be in locked rotation with one another. When wheels (or other parts) are in locked rotation with one another, rotation of one wheel can cause rotation of the other wheel and stopping or braking of one wheel can cause the stopping or braking of the other wheel. 
     Locked rotation can be achieved in some embodiments by using a common axle for two or more wheels, where each of the wheels rotates with the axle, rather than where at least one of the wheels rotates on the axle. 
     Locked rotation can be achieved in some embodiments by providing a shaft  55  that interacts with each of a first and a second wheel  73 ,  74  which are rotationally locked thereby. In some embodiments, the shaft  55  is not the axle for one or both of the wheels. In some embodiments, the shaft  55  is physically offset from the axle of one or both wheels. In one embodiment, the first wheel  73  rotationally interacts with a first end of the shaft  55  and the second wheel  74  rotationally interacts with a second end of the shaft  55 . The shaft  55  can have a first spur wheel or gear  85  at the first end and optionally a second spur wheel or gear  85 ′ at the second end of the shaft  55 , where the first spur wheel or gear  85  rotationally communicates with the first wheel, such as by contacting (directly or indirectly) an outer surface or an inner surface of the first wheel, and the second spur wheel or gear  85 ′ rotationally communicates with the second wheel, such as by contacting (directly or indirectly) an outer or an inner surface of the second wheel. In some embodiments, the first wheel or the second wheel can have a raised inner surface that is smooth, roughened or toothed for rotational communication with the respective first or second spur wheel or gear, such as is shown in  FIGS.  12 A- 12 D . In some embodiments, the first and second spur wheel or gears  85 ,  85 ′ can be affixed to the shaft  55  by any suitable method such as pressing, pinning, threading, adhesive, clips, retaining rings, spiral retaining rings, etc. 
     The shaft  55  can be a single piece, such as a rod or a hollow rod, or it can be a multi-part shaft. The shaft  55  can be straight or it can have bends, curves or angulations, including those formed by a gear-box or other direction changing or torque converting mechanisms. 
     In further embodiments, the exercise device  41  can include an energy storage device coupled to one or more wheels through a shaft. One such embodiment of connecting an energy storage device through a shaft  55  is shown in  FIGS.  12 A-D . In various embodiments, the energy storage system can comprise one or more springs with the energy being stored by loading the spring(s) and energy being released by unloading the spring(s). 
       FIG.  12 A  is a plan view of an embodiment of an exercise device with the exercise device  41  comprising a body  45 , the body having a top  60 , a bottom  62 , a first end  56  located at an edge of the body, a second end  58  located at an opposite edge of the body, and a first side  52  and a second side  54  extending between the first end  56  and second end  58 . As shown in  FIG.  12 B , the exercise device can comprise a first wheel assembly  64  and a second wheel assembly  66  proximate respective first and second ends  56 ,  58  of the body  45 . The first and second wheel assemblies  64 ,  66  comprise first and second wheels  73 ,  74 , respectively which are configured to roll along a surface during use of the exercise device  41 . 
       FIGS.  12 B and  12 C  show cross-sectional views of the exercise device of  FIG.  12 A  and show an embodiment of an energy storage device coupled to both of the wheels  73 ,  74  of the exercise device  41 . Although, in some embodiments, the energy storage device can be coupled to only one of the first and second wheels  73 ,  74 .  FIG.  12 D  shows an enlarged view of a portion  FIG.  12 B . In the embodiment of  FIGS.  12 B and  12 D , the energy storage device  70  stores energy in a spring  63  with the rational energy of the wheel(s) transferred through shaft  55  to compress spring  63  by movement of shuttle  57 . 
     In the embodiment of  FIG.  12 D , the first and second wheel assemblies  64 ,  66  respectively comprise a first wheel  73 , a second wheel  74  and shaft  55 , with the first wheel  73  in rotational communication with the second wheel  74  through the shaft  55 . In some embodiments, the shaft is in rotational communication with the first wheel and the second wheel where the first wheel is rotationally locked to the second wheel. In one embodiment of wheels (or other parts) being rotationally locked to one another, rotation of the first wheel  73  causes rotation of the second wheel  74  without substantial slippage the first wheel  73 . The rotational locking can be accomplished through friction or through other means, such as mechanical interference (e.g. with splines, gear teeth, non-circular shapes, etc.) The rotation can be in the same direction or a different direction, such as through the use of gears, beveled surfaces, etc. The rotation can also be at the same speed or at a different speed, such as can be accomplished through gearing, pulleys or other speed changing techniques. In some embodiments, the shaft  55  can extend through the body of the device. In some embodiments, such as is shown in  FIG.  12 D , the first and second wheel assemblies can include shaft support(s)  65  that support the shaft. In some embodiments, the first and second wheel assemblies can include bearing(s) such as sleeve bearing(s)  77  providing a rotating connection between the shaft  55  and shaft support(s)  65 . (While a sleeve bearing  77  is shown, any suitable type of bearing can be used such as sleeve bearings, bushings, roller bearings, ball bearings, etc. or no additional bearing at all, with the shaft riding on the support.) As the first wheel  73  rotates in relation to the body  45  of the exercise device, such as when the exercise device  41  is rolled across a surface, such as when using the exercise device  41  for exercise, the wheel rotates the shaft  55 , which then causes the shuttle  57  to move toward the first or second wheel  73 ,  74 , compressing the spring  63  by the shuttle.  FIGS.  13 A and  13 B  show an additional embodiment of an exercise device with a spring loaded shuttle as an energy storage device. 
     In the embodiment of  FIG.  16   , the energy storage system is a spring  63  that stores energy through rotational deflection of the spring  63  as torsional energy. In  FIG.  16   , as the wheel  73  turns, the spur wheel or gear  85  is rotated by the wheel  73 . The rotation of the spur rotates the shaft  55  which is fixed to one end of spring  63  while the opposite end of spring  63  is affixed to the body  45  or a stationary part of the wheel assembly  64 . As the shaft  55  turns, from movement of the wheel  73  from a rest position, the spring is twisted and stores energy, providing a resisting torque to further movement of the wheel  73  away from the rest position and when the wheel is moved or allowed to move back toward the rest position, the spring  63  provides a restoring force to urge the wheel back to the rest position. While the embodiment of  FIG.  16    shows the spring attached to a stationary part of the exercise device  41  at a stationary anchor  80  proximate the wheel  73  and attached to the shaft at a rotating anchor  82  distal the wheel  73 , some embodiments can have the rotating anchor  82  proximate the wheel  73  and the stationary anchor  80  distal the wheel  73 . In some embodiments, an exercise device can include an energy storage device associated with only one of the wheels of the exercise device, or can include respective energy storage devices associated with more than one wheel of the exercise device. In some embodiments, an energy storage device of  FIG.  16    can reach from a first wheel  73  to a second wheel  74  of the exercise device, or can be located between and spaced apart from one or both of the wheels. In some embodiments, an energy storage device can be deflected by movement of both wheels  73 ,  74  of the exercise device, such as where both wheels are rotationally locked to the shaft  55  and the spring is twisted by the rotation of the shaft  55 . 
     Features shown in  FIG.  16    include 1) the source of resistance being from a torsional spring located inside or under the body  45 , 2) the rotational alignment between the wheels is maintained with a matching planetary gear set and cross shaft, 3) damping can be achieved with a magnetic damper located inside the hub or friction damper, and 4) stability is maintained via a low-slug body  45 . 
       FIG.  17    shows an embodiment that is similar to that shown in  FIG.  16   , but with a spring  63  that is compressed and/or extended with a shuttle  57 , lead screw  55 ′ and lead nut  55 ″. In  FIG.  17   , as the wheel  73  turns, the inner surface  73 ′ of the wheel turns the spur wheel or gear  85 , which turns shaft  55  and lead screw  55 ′, which then turns within the lead nut  55 ″ of shuttle  57 , causing lead nut (restrained from rotating due to interaction with the underside of body  45 ) to move along lead screw  55 ′ and shaft  55 , compressing or decompressing spring  63  to apply a resistive or restoring torque to the wheel. In some embodiments there can be a plurality of energy storage devices such as that shown in  FIG.  17   , with some embodiments having a first spring associated with a first wheel  73  and a second spring associated with a second wheel  74 . In some embodiments, the first and second springs can be operated by the respective first and second wheels only and in some embodiments, the first and second springs can each be operated by one of or both of the first and second springs. 
     Features shown in  FIG.  17    include 1) the source of resistance being from a compression spring located inside or under the body  45 , 2) rotational alignment between the wheels is maintained with a matching ring gear set and cross shaft, and 3) stability is maintained via a low-slug body  45 . In one embodiment, compression springs push the lead nut  55 ″ to center from either side along the lead screw  55 ′ and the wheels turn gears to rotate shaft, which travels along length of body internal to board. 
       FIG.  18    shows an embodiment that is similar to that shown in  FIG.  16   , but with a clock spring energy storage device. In the embodiment of  FIG.  18   , a clock spring  63 ″ is located within the wheel assembly.  FIG.  18    also shows a shaft  55  with a spur wheel or gear  85  interacting with an interior surface  73 ′ of the wheel  73  or wheel assembly  64 . The shaft  55  can in some embodiments extend to a second wheel assembly (not shown) with a second spur wheel or gear interacting with an interior surface of a second wheel or the second wheel assembly. In some embodiments, the shaft can rotationally lock the first and second wheels to one another. The clock spring is functionally connected to a rotating portion of the exercise device  41 , such as the wheel  73 , and to a stationary portion of the exercise device  41 , such as a non-rotating portion of the wheel assembly  64  or the end  56 ,  58  of the body  45 . In operation, when the wheel rotates, the clock spring is torsionally deflected to load or unload the clock spring  63 ″, which applies a resistive or restoring torque to the wheel. In some embodiments there can be a clock spring energy storage device associated with only one of the wheels, where the clock spring energy storage device is operated by only one or by both wheels (such as through the shaft  55 ). In some embodiments, there can be a clock spring energy storage device associated with each of the first and second wheels, and the wheels are locked in rotation to one another or not locked in rotation to one another. In some embodiments, more than one type of energy storage device can be present within a single exercise device  41 , such as a combination of two or more of compression spring arrangement, clock work spring arrangement, torsion spring arrangement or another type of energy storage device, such as others disclosed herein. 
     Features shown in  FIG.  18    include 1) the source of resistance being an internal hub clock spring, 2) rotational alignment between the wheels is maintained with a matching planetary gear set and cross shaft, 3) damping can be achieved with a magnetic damper located inside the hub, or friction damper and 4) stability is maintained via low-slung body. 
     In some embodiments, the shaft, the shuttle, the energy storage device, the lead nut and/or the lead shaft can be located under the body  45  or within the body  45 . In some embodiments, a cover can be located under the body  45  to cover the shaft, the shuttle, the energy storage device, the lead nut and/or the lead shaft. In some embodiments, one or more access panels can be located on the body  45 , such as on the top, the underside and/or one or more sides of the body  45  to allow access to the shaft, the shuttle, the energy storage device, the lead nut and/or the lead shaft, such as for assembly, replacement, repair, adjustment, cleaning, etc. 
     Wheel Assembly 
     Exercise devices discussed herein are frequently described as having two wheels and two wheel assemblies. However, in various embodiments, the exercise device can include only one wheel and wheel assembly, or the exercise device can have two or more wheels and wheel assemblies, such as two, three, four, five, six, seven, eight or more. In embodiments with more than one wheel and wheel assembly, can include two wheels or more wheels that are rotationally locked to one another. In some embodiments, rotationally locking wheels across the width of the exercise device (e.g. a left wheel and a right wheel) can increase the linear stability of the exercise device during operation, if desired. In some embodiments, the wheels will not be rotationally locked, such as to increase the maneuverability and/or movement flexibility of the exercise device. In some embodiments one pair of wheels or two pairs of wheels can be rotationally locked. In some embodiments, more than two pairs of wheel can be rotationally locked. In some embodiments, three or four or more wheels can be rotationally locked to one another. 
     Each of the first and second wheels  73 ,  74  can be supported by one or more bearings  72  to allow the wheel to rotate in the wheel assembly. The centerline of each wheel  73 ,  74  lies within a respective wheel plane  78 . Each of the bearings can be connected to the respective wheel assembly  64 ,  66  or the body  45  of the exercise device  41  through, for example, a shaft support  65 . In some embodiments, an axle  84  can be functionally positioned between the body  45  of the exercise device  41  and the wheel  73 ,  74 . In some embodiments, an axle  84  can rotate with the wheel  73 ,  74 , such as is shown in  FIG.  16    where the axle is connected to the body  45  through a bearing  86  (a sleeve bearing is shown, but other types of bearings can also be used, such as a bushing, a roller bearing or a ball bearing), and the axle is connected to the wheel  73  through a flange. In some embodiments, such as is shown in  FIG.  12 D , a shaft support  65  can serve as an axle by acting as an interface between the inner race  68  and the body  45  of the exercise device  41 . 
     A shaft support can be or comprise a rigid material such as, for example, metal, plastic, ceramic, etc. In some embodiments, the shaft  55  and/or the shaft support(s)  65  can at least partially support the body  45  of the exercise device  41 . In some embodiments, the shaft  55  and/or the shaft support(s)  65  can fully support the body  45  of the exercise device  41 . In some embodiments, the shaft  55  can rotate in relation to the body of the device. In some embodiments, such as is shown in  FIG.  12 B , the shaft  55  can extend through first and second shaft supports  65 . 
     In some embodiments, such as is shown in  FIGS.  12 B and  12 D , a wheel assembly  64 ,  64  can include a wheel bearing  72  that supports the wheel  73 ,  74  in the wheel assembly to allow rotation of the wheel  73 ,  74  within the wheel assembly. (In the discussion provided herein, various features, elements and capabilities which can be a part of the wheels and wheel assemblies will be discussed, and the first wheel, or wheel assembly, can be the same or different from the second wheel, or wheel assembly.) Any suitable bearing can be used, such as bushing, roller bearing, ball bearing or sleeve bearing, etc. As shown in  FIG.  12 D , a ball bearing  72  is shown which comprises balls  69  located between an inner race  68  and an outer race  67 . The embodiment of  FIG.  12 D  shows shaft  55  passing through the inner race  68 , but in other embodiments, the shaft  55  can pass within the bore of the inner race  68 . In some embodiments, the shaft  55  does not pass within or through the inner race  68 . 
     In some embodiments, such as is shown in  FIG.  12 D , a wheel assembly  64 ,  66  can include an inner portion  76  covering a side surface  68 ′ of the inner race. In some embodiments, the inner portion  76  of the wheel assembly can comprise an upper inner portion  76 ′ situated above a lower inner portion  76 ″, for example, during operation. In some embodiments, the upper inner portion  76 ′ of the wheel  73  can cover the upper inner surface of the inner race  68 . In some embodiments, such as is shown in  FIG.  12 D , the lower inner portion of the wheel  73  can cover a side surface  65 ′ and an upper surface  65 ″ of the first shaft support  65 . In some embodiments, the upper surface  65 ″ of a shaft support  65  can be a surface facing toward an upward direction, for example, facing away from a floor or other surface the exercise device moves across during operation. In some embodiments, the upper surface  65 ″ of the shaft support  65  can be a planar surface. In some embodiments, the inner portion  76  of the first wheel can be or comprise plastic, metal, elastomer, wood, ceramic or other material that can act as a portion of a cover for the area of the exercise device  41 . In some embodiments, the inner portion  76  of the wheel can be referred to as a hubcap. In some embodiments, the hubcap can include an inner cap  53  and an outer cap  51 . In some embodiments, the inner cap  53  can be situated closer to the body  45  of the exercise device  41  relative to the outer cap  51 . 
     In some embodiments, the exercise device  41  can include a bearing such as a thrust bearing  75  providing a sliding connection between the spur wheel  85  and the shaft support  65 , such as is shown in  FIG.  12 D . 
     In some embodiments, the hubcap  76  can be a single unitary piece that serves as or includes the inner and outer caps  53 ,  51 . In some embodiments, only an inner cap  53  or only an outer cap  51  can be present. In some embodiments, the inner cap  53  or the outer cap  51  can comprise a plurality of pieces that when assembled in the exercise device forms the inner cap  53  or the outer cap  51  or both. 
     In some embodiments, the wheel assembly  64  can include an opening  89  into which a portion of a user&#39;s body (e.g., a user&#39;s hand or foot or a portion of a user&#39;s hand or foot or other body part) can be placed or can pass through.  FIGS.  15 A-D  shows an embodiment of an exercise device  41  with such openings. In some embodiments, a portion of the edge of the opening  89  can serve as a grip or gripping surface or handle or as a supporting surface of the body part placed within the opening such as for operation of the exercise device  41 . In some embodiments, the inner portion of the wheel assembly  64  can be rotationally affixed to the body of the device so that during operation, the inner portion of the wheel assembly  64  can move and rotate with the body  45  of the exercise device  41  while allowing an outer portion (or wheel  73 ) of the wheel assembly to rotate in relation to the body  45  of the exercise device  41 . 
     In operation, the opening  89  can be used in the operation of the exercise device  41 . In some embodiments, the handles or grips  71  can assist the user in the movement of the exercise device  41 . In some embodiments, the handles or grips  71  and/or the body of the device can be positioned below the axis of rotation of one or both of the first and second wheels  73 ,  74  to improve rotational stability of the body  45  during operation of the exercise device  41 . By positioning the handles or grips and/or the body of the device below the axis of rotation of the first and second wheels, without wishing to be limited by theory, it is believed that greater rotational stability of the body (and/or the handles or grips  71 ) is achieved due to the reduction in potential downward movement of the end  56  of the body  45  during operation of the exercise device  41  as compared to when the handles or grips and/or body of the exercise device were positioned higher in the exercise device. 
     In some embodiments, the wheel assembly  64  can be made to not include the opening  89 , such as by providing a cover or other panel or portion of the end of the body that bridges the space within the wheel. Such a configuration is shown for example in  FIGS.  19 D and  20 A . 
     In some embodiments, a portion, such as the inner portion of the wheel assembly  64 , can be rotationally affixed to the body  45  by a board support  43  extending from within the inner portion  76  of the wheel assembly  64  to within the body  45  of the exercise device  41 , while allowing the wheel  73  to rotate. 
     In some embodiments, the wheel  73  can be or comprise any material that can provide sufficient traction between the wheel and the surface the wheel rides upon, such as an elastomer, a plastic, a metal or other suitable material that provides traction and acceptable durability and acceptable sensory characteristics (sound, feel, smoothness, etc.) 
     In some embodiments, the inner race  68  and the outer race  67  can be coaxial. In some embodiments, the inner race  68 , the outer race  67 , and the wheel  73  can be coaxial. 
     In some embodiments, such as is shown in  FIGS.  12 C and  12 D , the wheel assembly  64  can further include a spur wheel  85  in rotational communication with a rotating surface of the wheel assembly  64 , such as a surface or an inner surface  73 ′ of the wheel  73 , to rotate as the wheel  73  rotates or a surface of another rotating portion of the wheel assembly, such as, for example, the outer race or a portion in contact (directly or indirectly) with the outer race. 
     In some embodiments, the spur wheel  85  can engage the rotating surface  73 ′ of the wheel  73  with a frictional contact, such as one smooth or substantially smooth wheel rolling along a surface, with sufficient friction being present to prevent undue slippage. In some embodiments, the frictional contact can allow for some slippage, for example to allow turning the exercise device  41  or for other reasons, and the slippage of the first wheel can be the same or different from the second wheel. In some embodiments, the spur wheel  85  can engage the rotating surface  73 ′ of the wheel  73  with a mechanical interaction, such as where the spur wheel is a spur gear and the rotating surface  73 ′ of the wheel  73  is a geared surface that gearingly interacts with the spur gear. 
     In some embodiments, such as is shown in  FIG.  12 D , the shaft  55  can extend through the spur wheel  85 . In some embodiments, the shaft  55  can be fastened to the spur wheel  85  by any suitable method that can hold the spur wheel  85  on the shaft  55  and prevent undesirable relative rotation of the spur wheel  85  and the shaft  55 , such as by threading, press fit, adhesive, pinning, set screw, retaining ring, lock ring, clip, splining, etc., including combinations thereof. Suitable retaining rings can include spiral retaining rings. 
     Shuttle and Shaft 
     In some embodiments, such as that shown in  FIG.  12 C , the shaft  55  can comprise a lead screw  55 ′, and the shuttle  57  can comprise a lead nut  55 ″ interfacing with the lead screw  55 ′. In  FIG.  12 C , as the wheels  73 ,  74  turn, such as by moving the exercise device  41  across a surface, the shaft  55  and lead screw  55 ′ turn. The shuttle  57  and the lead nut  55 ″ can be prevented from rotating due to interference from the underside of the body  45  or due to interference from tracking devices affixed to the underside of the body or affixed to the wheel assembl(ies), and move along the lead screw  55 ′ and shaft  55  toward the first wheel assembly  64  or the second wheel assembly  66 , loading first spring  63  and/or second spring  63 ′. In some embodiments, there can be protrusions extending from the body  45  or one or more recesses in the body  45  that assist in preventing rotation of the shuttle  57 . In some embodiments, such as that shown in  FIG.  12 C , the exercise device  41  can comprise a shuttle track  61  extending along a direction generally parallel to the shaft  55 , the shuttle track  61  slidably interacting with the shuttle  57  and preventing rotation of the shuttle  57  during operation. The exercise device  41  can comprise a shuttle roller shaft  59  extending through the shuttle and affixed to the shuttle  57  by way of, for example, a pin such as spring pin  83  (or by any other suitable means.) In some embodiments, the spring pin  83  can prevent the shuttle roller shaft  59  from abutting a protrusion extending from the body  45  or from the shuttle track  61 . The exercise device can comprise bearings such as roller bearings  87  on the shuttle roller shaft  59  and providing sliding contact between the shuttle roller shaft  59  and the shuttle track  61 . In some embodiments the roller bearings  87  can be affixed to the shutter roller shaft  59  by retaining rings  79  (or by other suitable methods) disposed one or both ends of the shuttle roller shaft  59 . In some embodiments, the first and/or second spring  63 ,  63 ′ can be affixed at one end to the shuttle and/or at the second end to, for example, the body  45  or the wheel assembly  64 , movement of the shuttle away from the end of one spring will load the spring by extending the spring, while loading the other spring by compression. (If only one spring is present, the spring will extend or compress depending upon the direction of travel of the shuttle  57 .) If the spring is not affixed at both ends, then movement away from the spring will not result in loading of the spring by extension, but will result in loading of the other spring, if present, by compression. If the first end of the spring is not affixed to the shuttle or the second end of the spring is not affixed, for example to the body  45  or the wheel assembly, movement of the shuttle away from the second end of the spring will not load the spring, but movement of the shuttle away from the second end of the spring will load the other spring by compression. The loading of the first and/or the second spring  63 ,  63 ′ then creates a torque at the first and second wheels  73 ,  74  resisting the movement of the exercise device when the exercise device is moved away from a rest position (or assisting movement of the exercise device when the exercise device is moved toward the rest position.) When the force applied to the exercise device by a user is reduced sufficiently, the restoring torque applied to the wheels  73 ,  74  by the first and second spring  63 ,  63 ′ allows for the first and second wheels  73 ,  74  to turn, such as by moving the exercise device  41  across a surface back to the original position. 
     The thread of the lead screw and lead nut can be of any suitable type, such as square, triangular, trapezoidal, ACME, buttress, round, etc. 
     In some embodiments, the lead screw and the shaft can be separate parts. In some such embodiments, the lead screw can be turned by a mechanism that is turned by the shaft or a rotating part of the wheel assembly. 
     Springs 
     In various embodiments, one, two or more springs can be used to store energy. In some embodiments, such as is shown in  FIG.  12 B , a spring  63 ,  63 ′ can be positioned between an end  56 ,  58  of the body  45  and the shuttle  57  or lead nut  55 ″. In some embodiments, a first spring  63  can be positioned between the first end  56  of the body  45  and the shuttle  57  or lead nut  55 ″ and a second spring  63 ′ can be positioned between the second end  58  of the body  45  and the shuttle  57  or lead nut  55 ″. In some embodiments, two or more springs can be located on the same side of the shuttle  57  or lead nut  55 ″, with zero, one or more than one springs on the other side of the shuttle  57  or lead nut  55 ″. In some embodiments, the number of springs on one side of the shuttle or lead nut can be the same or different from the number on the other side of the shuttle or lead nut. In some embodiments, the amount of energy stored in spring(s) on one side of the shuttle or lead nut can be the same or different from the amount of energy stored in spring(s) on the other side of the shuttle or lead nut. In some embodiments, the spring can be concentric with the shaft or lead screw. In some embodiments, the spring can be coaxial with the shaft and/or the lead screw. In some embodiments, the spring is not coaxial with the lead screw. In some embodiments, the spring is not concentric with the lead screw. In some embodiments, the spring can be wound around the shaft. 
     Springs that can be utilized for energy storage in the exercise device can be of any type suitable for being deflected by a force and can include coil springs, torsion springs, clock springs, bands, bars, levers, tension, compression, flat, serpentine cantilever, helical, leaf, volute, V, etc. The spring can be made from any suitable material that can deflect under force and at least partially return to its original shape when the force is removed. Suitable materials include metals, plastics, elastomers, etc. 
     Asymetric Load and Preload 
     In some embodiments, energy device(s) can provide different resistive forces (and restorative forces) for rotation of the wheel(s) in a first direction as compared to a second direction. Such a configuration can provide an exercise device that provides two levels of resistive force difficulty depending upon which direction the exercise device is rolled. For example, a user can roll the device across a surface and experience a first range of resistive force for the movement, and then turn the exercise device around (rotate the device such that a wheel that was on the left side of the exercise device is now on the right side), and experience a second range of resistive force for the same movement. In some embodiments, the first range of resistive force can be higher than the second range of resistive force or can be lower. In some embodiments, a rate of change in the resistive force with displacement can be higher in first range of resistive force than the second range of resistive force or lower. 
     In some embodiments, an asymmetric force can be achieved by using different springs (or other energy storage devices) with different resistance force characteristics (e.g. spring constant, pressure chamber size, pressure chamber preload, spring preload, charger characteristics, motor characteristics, etc.) for movement in each direction, such as by utilizing a first spring (or other energy storage device) for loading in a first wheel rotation direction and a second spring (or other energy storage device for loading in a second wheel direction. Using the example of a compression spring, a spring on one side of the shuttle is loaded by wheel rotation in a first direction and a spring on the other side of the shuttle is loaded by wheel rotation in a second direction. Similar arrangements can be configured for other types of springs and other energy storage devices disclosed herein. 
     In some embodiments, an energy storage device can configured to have a preload where the energy storage device can provide a higher initial force for movement from the rest position or for a higher restoring force at the end of the shuttle&#39;s or wheel&#39;s travel back to the rest position. For example, by way of explanation, preloading a compression spring moves the spring to a point on the force-displacement graph where the displacement is not zero, and there for the force of the spring is higher than when displacement is zero. In some embodiments, additional features can be provided in the exercise device, to reduce the felt force of the energy storage system or to restrict the movement of the energy storage system. In some embodiments, a stop can be provided such that the spring or other energy storage device component does not push on the shuttle or wheel or exercise device at or near the rest position. In some embodiments, a friction surface can be provided proximate to the rest position that resists movement of the spring (or other energy storage device component) when the shuttle or wheel or exercise device is at or near the rest position. With the use of a friction surface, the friction surface can also act to increase the resistive force for movement from the rest position. In some embodiments, more than one feature can be used to resist movement or reduce felt force, such as for example using both a stop and a friction surface. 
     Rest Position 
     The exercise device can be present in a rest position where the energy storing device is not exerting a net torque to the wheel(s). In some embodiments, the energy storage device(s) (such as spring(s), pressure chamber(s), electrical storage unit(s), etc.) will not be loaded in the rest position. In some embodiments, the energy storage device(s) can be loaded while in the rest position, such as with springs, by placing one or more of the springs under tension or compression or otherwise deflecting the spring(s), yet still providing no net torque to the wheel(s). In some embodiments, this rest position can be accomplished by loading more than one energy storage device where the energy storage devices counter each other. In some embodiments one or more energy storage devices can be preloaded, but also be provided with a stop (physical or electrical) to reduce or prevent the exercise device from acting on or pushing the shuttle or wheel when the shuttle is in the rest position. In some embodiments, the use of a preload can result in a higher initial resistive force when the exercise device is initially moved from the rest position and/or provide a higher restoring force at or near the point where the exercise device returns to the rest position than if preloading were not used. 
     Energy Storage Device 
     The energy storage device used in an exercise device  41  can be any suitable device that can store energy from resisted motion (such as from pushing a device that resists motion) and then release the stored energy at a later time (such as by rotating the wheels of the exercise device to move the exercise device toward a rest position or a starting position.) As discussed herein, an energy storage device can be based on springs, with the springs being loaded and unloaded. In some embodiments, the energy storage device can utilize energy storage based upon another phenomena, such as pressure or volume, and in some embodiments, the pressure or volume of a gas. In some such embodiments, as a wheel turns, a pressure chamber linked to the wheel can increase in pressure when the energy storage device is loading energy and can decrease in pressure when the energy storage device is unloading energy. In some embodiments, the chamber can be linked through a shaft to the movement of the wheel, for example with rotation of the shaft, such as a shaft linked to a wheel through a spur gear or wheel as in  FIG.  12 B,  13 A,  14 B,  16 ,  17  or  18   . 
     In some embodiments energy storage device can include a piston and chamber configured to change the pressure within the chamber by increasing the pressure when loading the energy storage device and decreasing the pressure in the chamber when unloading the energy storage device. In some embodiments, decreasing the pressure in the chamber can load the energy storage device and increasing the pressure in the chamber can unload the energy storage device. In some embodiments, the piston can be in communication with the shuttle  57  or lead nut  55 ″ or the body  45 . In some embodiments, the chamber can be in communication with the shuttle  57  or the lead nut  55 ″ or the body  45 . In some embodiments, the pressure in the chamber can be at or near atmospheric pressure when the exercise device is in the rest position. In some embodiments, the pressure in the chamber can be at a pressure above atmospheric pressure when the exercise device is in the rest position. 
     In some embodiments, the shuttle  57  or lead nut  55 ″ can be moved along the lead screw  55 ′ to change a pressure in the chamber. In some embodiments, the piston can be moved along an inside of the chamber to change the pressure in the chamber. The pressure in the chamber can be above atmospheric pressure, at atmospheric pressure or below atmospheric pressure. 
     In some embodiments, changing the pressure in the chamber can change the torque to the first and second wheels. For example, increasing or decreasing the pressure in the chamber can increase or decrease the torque to the first and/or second wheels  73 ,  74 . In some embodiments, the pressure in the chamber can apply a load to the piston, thereby applying a load to the shuttle or lead nut so that the lead nut applies a torque to the lead screw, or the pressure in the chamber can apply a load to the chamber, thereby applying a load to the shuttle or lead nut. 
     In some embodiments, the energy storage device can store electrical energy. In some embodiments, the energy storage device can include the use of a battery and/or the use of a capacitor and/or other device that can hold an electrical charge. In some embodiments energy from movement of one or more of the wheels of the exercise platform can be stored and then released to assist movement of the platform in a return direction or to provide a force tending to move the platform in a return direction, but which can be resisted by the user of the platform. In some embodiments an electrical storage medium, such as a battery or a capacitor, etc., can be used to store the energy. In some embodiments, additional features can include suitable devices (not all might be present in any particular embodiment) such as a motor, charger (e.g. generator), a piezoelectric device and the like to convert the movement of the wheel into electrical energy and to convert electrical energy back into movement and to convert stored electrical energy into movement, along with levers, wheels, shafts, clutches, pawls, anchor points, bands, gears and the like so as to transfer at least a portion of the energy of the movement of the wheels to the motor, generator, piezoelectric device, etc. where the movement is converted into electrical energy and stored in the battery and/or capacitor, and then to transfer the movement of the motor, generator, piezoelectric device from the stored electrical energy back to the wheels in the form of rotation or torque. 
     In some embodiments, a charger can be a generator or alternator that converts rotational energy into electrical energy through the use of magnetic interaction. In some embodiments, a charger can be a device based upon the piezoelectric effect, such as a piezoelectric charger. In some embodiments, the motor can be a linear movement motor, a rotary motion motor, a piezoelectric motor, or other suitable device to convert electric energy into movement through, for example voltage, potential and/or current. 
     In some embodiments, the energy can be stored in the form of thermal energy, such as through the use of a thermoelectric device where the rotation of the wheel is used to generate electrical energy, such as with a charger, which is then used to heat or cool a thermal storage device (e.g. heat sink, etc.) upon movement of the wheel away from a rest position, and causing a resistive torque to be applied to the wheel. Upon movement of the wheel toward the rest position, the thermal electric device then utilizes the heat or cooling stored in the thermal storage device to convert thermal energy into electrical energy to turn a motor to apply torque to the wheel and urge the wheel toward the rest position. 
     Variable Torque 
     In some embodiments, if the torque to the lead screw is changed, the torque to the shaft can be changed. In some embodiments, if the torque to the shaft is changed, the torque to the first and second wheels can be changed, for example, if changing the torque to the shaft changes the torque to the first and second spur wheels. In some embodiments, the energy storage device can provide a constant torque or approximately constant torque to the first and or second wheel, such as by use of a constant spring or a spring arrangement that provides a constant load throughout the deflection of the spring. 
     Brake 
     In some embodiments, the exercise device can further include an optional brake to inhibit movement of at least one of the first and second wheels  73 ,  74 . In some embodiments, this brake can provide a form of resistance to movement of the exercise device  41  in addition to the resistance provided by the energy storage system. In some embodiments, the brake can be configured to reduce an angular acceleration or angular velocity of the first and second wheels during operation. Suitable braking systems can include those that convert one form of energy to another, such as those based upon movement of air (e.g. fans) or those based on magnetic forces (e.g. eddy current devices), or viscous flow (e.g. hydraulic systems), etc. In some embodiments, the brake can be operationally connected to one or more of the wheels or to an axle or shaft extending from a wheel. 
     In some embodiments, such as is shown in  FIG.  16   , an optional eddy current brake can be located in the exercise device. In the embodiment of  FIG.  16   , the eddy current brake comprises a magnet  99  and a conductor  101 . In some embodiments, the locations of the magnet  99  and conductor  101  shown in  FIG.  16    can be reversed. In some embodiments, the magnet can be a series of magnets and the conductor can be a series of conductors. In some embodiments, the magnet and the conductor can be separately attached to a rotating part and a second rotating part or a stationary part of the exercise device  41 , so as to have relative motion between the magnet and the conductor. In some embodiments, the rotating part can be a wheel or a shaft (either shaft  55  or another shaft that rotates with one of the wheels), a second rotating part can be a shaft (either shaft  55  or another shaft), and the stationary part can be a part of the wheel assembly, a part of the body  45  or the wheel assembly  64  of the exercise device. 
     In some embodiments, more than one brake can be present and in some particular embodiments, more than one eddy current brake can be present. 
     Double Shaft Embodiment 
       FIGS.  14 A and  14 B  show an embodiment utilizing a double shaft arrangement of the exercise device  41 . In  FIG.  14 A , the shaft  55  is rotationally locked to the first and second wheels  73 ,  74 . The shuttle  57  comprises two end blocks  91  positioned on or adjacent the shaft  55 . A second shaft  105  runs from one of the end blocks  91  to the second end block  91 . Connecting the end blocks  91  is a gear mount  93 . The gear mount has a series of transfer gears attached thereto to transfer rotational motion of the shaft  55  to a second shaft  105 . The second shaft  105  can comprise a second shaft lead screw  55 ′. A lead nut  55 ″ can be located, for example, in a transfer gear  95 , the gear mount  93  and one or both end blocks  91 . 
     The set of transfer gears can be a set of two gears or a set of more than two gears, with a first gear  95  located on the shaft and a second gear  95  located on the second shaft  105 . In some embodiments, the first gear  95  can be mounted onto the shaft  55  by any suitable means such that the first gear  95  will rotate with the shaft  55 . In some embodiments, the first gear  95  can be allowed to slide longitudinally along the shaft  55 . The first gear  95  can also rotate in relation to the gear mount  93 . 
     In some embodiments, the second gear  95  will include or will turn a second lead nut  55 ″ which in turn moves the second shaft  105  toward one of the first and second wheels  73 ,  74  or the other. With this arrangement of the second gear  95  and the lead nut, the movement of the second shaft  105  moves the end blocks  91  toward the first wheel  73  or the first wheel  73  or the second wheel  74 , loading or unloading the first and second springs  63 ,  63 ′ (or just one spring if only one spring is present.) 
     In some embodiments employing a different operational sequence, rotation of the second gear  95  will rotate the second shaft  105 , with one or both end blocks including a lead nut  55 ″, and the lead nut moving the end block(s)  91  along the second shaft  105  and thereby loading or unloading the first and second springs  63 ,  63 ′ (or just one spring if only one spring is present.) 
     Also shown in  FIGS.  14 A and  14 B  is a bumper  97  to act as a stop for the travel of the end blocks in relation to the transfer gears and gear mount. 
     As discussed in other embodiments, the first and second springs  63 ,  63 ′ can be affixed at one end, both ends or no ends. The springs can be loaded by compression or by extension. When an end of the spring is affixed, it can be affixed as described herein, such as to the wheel assembly, to the body, to the end block or to the lead nut. 
     Gears 
     The gears used herein can utilized any appropriate type and shape of tooth suitable for the service for which they are employed. For example, the spur gears can be straight-cut or helical or any other relevant tooth shape or cut to work in the service they are provided for and to interface with the gears that they are paired with. 
     Strap 
     The exercise device  41  can also have a strap  49  extending along the body  45 . The strap  49  can be sized and configured to provide a handhold or foothold or can act as a retainer for a hand, foot or other body part, such as by allowing a person using the exercise device  41  to locate one or more hands, feet or other parts under the strap to help maintain contact with the exercise device  41  during use. In some embodiments, the strap  49  can be affixed to the exercise device, such as by having a first strap end  103  and a second strap end  104  attached to respective first and second ends  56 ,  58  of the body  45  or affixed to the body proximate the respective first and second ends of the body  45 . 
     Body and Wheel Assembly Further Embodiments 
       FIGS.  14 A-D ,  19 A-D,  20 A-E,  21 A-E and  22 A-F show further designs of the exercise device. In various embodiments, one or both of the wheels or wheel assemblies shown in  FIGS.  15 A-D ,  19 A-D,  20 A-E,  21 A-E and  22 A-F can be used with other embodiments of an exercise device of  FIGS.  15 A-D ,  19 A-D,  20 A-E,  21 A-E and  22 A-F or disclosed elsewhere herein. In various embodiments, the body of an exercise device of  FIGS.  15 A-D ,  19 A-D,  20 A-E,  21 A-E and  22 A-F can be used with other embodiments of an exercise device of  FIGS.  15 A-D ,  19 A-D,  20 A-E,  21 A-E and  22 A-F or disclosed elsewhere herein. In various embodiments, the strap or other features described herein can be combined with an exercise device of  FIGS.  15 A-D ,  19 A-D,  20 A-E,  21 A-E and  22 A-F. 
       FIGS.  20 E and  21 E  show embodiments with round raised hubcaps  22 , soft curves of the body  45  and a padded “touch” area of the body  45 .  FIG.  22 E  shows an open wheel  23  with an indentation to complete the circle  24  with a rounded tire  25  and body  45  with board with molded curves. 
     Having now described the invention in accordance with the requirements of the patent statutes, those skilled in this art will understand how to make changes and modifications to the present invention to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention as disclosed herein. 
     The foregoing Detailed Description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the invention to the precise form(s) described, but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. Applicant has made this disclosure with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the invention be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the Claims. Use of language such as “approximately”, “somewhat”, “about”, “nearly” and other terms of degree that appear within this disclosure are intended to be interpreted as a person of skill in the art would understand the language based upon the context, with a further understanding that if the context provides insufficient guidance, a tolerance of 20% should be applied. Use of the word “or” should be understood to also include the meaning “and”, except where the context indicates otherwise. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the Claims. 
     All elements, parts and steps described herein are preferably included. It is to be understood that any of these elements, parts and steps may be replaced by other elements, parts and steps or deleted altogether as will be obvious to those skilled in the art. 
     Broadly, this writing discloses at least the following: an exercise device is described. An exercise device can include a platform having a first end and a second end opposite the first end; first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; a first motor configured to apply a first torque to the first wheel where the magnitude of the first torque is related to the distance of the exercise device from a zero position and the direction of the first torque urges movement of the exercise device toward the zero position; versions of exercise devices are also described with more wheels and more motors. An exercise device can also include a body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; one or more wheels; and an energy storage device applying resistive and restoring force to the wheel; optionally, a shaft can be present that rotationally locks two or more of the wheels. 
     Concepts 
     Concept 1. An exercise device comprising: 
     a body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; 
     first and second axles connected to and rotationally locked to first and second wheels, respectively, the first and second wheels able to rotate both in clockwise and counterclockwise directions in relation to the body, the first axle also connected to the body proximate the first end at a first hub and the second axle also connected to the body proximate the second end at a second hub; 
     a first spring with a wheel end and a hub end, the first spring positioned at least partially within the first axle, with
         the first spring wheel end slidably connected to the first wheel at a first wheel junction, wherein the first wheel junction is configured to convey torque between the first wheel and the first spring wheel end, and   the first spring hub end slidably connected to the first hub at a first hub junction, wherein the first hub junction is configured to convey torque between the first hub and the first spring hub end; and       

     a second spring with a wheel end and a hub end, the second spring positioned at least partially within the second axle, with
         the second spring wheel end slidably connected to the second wheel at a second wheel junction, wherein the second wheel junction is configured to convey torque between the second wheel and the second spring wheel end, and   the second spring hub end slidably connected to the second hub at a second hub junction, wherein the second hub junction is configured to convey torque between the second hub and the second spring hub end;       

     when the first and second wheels are rotated against respective first and second spring torques, energy is stored in the first and second springs and the first and second springs apply restoring torque to the first and second wheels, respectively. 
     Concept 2. An exercise device comprising: 
     a body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; 
     a first axle connected to a first wheel, the first axle also connected to the body proximate the first end at a first hub; 
     a first spring having a first spring end, the first spring positioned at least partially within the first axle, with the first spring end slidably connected to one of the first wheel and the first hub at a first junction, wherein the first junction is configured to convey torque between the one of the first hub and the first wheel and the first spring end. 
     Concept 3. The exercise device of Concept 2, wherein the first spring comprises a second spring end opposite the first spring end, and the first spring end is slidably connected to one of the first hub and first wheel and the second spring end is slidably connected to the other of the first hub and first wheel at a second junction, wherein the second junction is configured to transfer torque between the other of the first hub and the first wheel and the second spring end.
 
Concept 4. The exercise device of Concept 2, wherein the first junction is a slot configured to receive the first spring end.
 
Concept 5. The exercise device of Concept 3, wherein the second junction is a slot configured to receive the second spring end.
 
Concept 6. The exercise device of Concept 2, wherein the first axle is rotationally locked to the first wheel.
 
Concept 7. The exercise device of Concept 2, wherein the first spring is contained entirely within the first axle.
 
Concept 8. The exercise device of Concept 2, wherein the body is sized and configured for two feet to be placed upon the body and for the feet to push the body; and
 
     the first wheel has a neutral position wherein the first spring does not apply torque to the first wheel, and when the first wheel is rotated away from the neutral position, energy is stored in the first spring and the first spring applies a restoring torque to the first wheel. 
     Concept 9. The exercise device of Concept 3, wherein the wheel comprises a spring cover and the junction or the second junction is located in the spring cover.
 
Concept 10. The exercise device of Concept 2, further comprising:
 
     a second wheel, a second axle and a second spring; 
     wherein the second axle is connected to the second wheel, the second axle is also connected to the body proximate the second end of the body at a second hub; 
     the second spring having a first spring end, the second spring positioned at least partially within the second axle, with the first spring end of the second spring slidably connected to one of the second wheel and the second hub at a third junction, wherein the third junction is configured to convey torque between the one of the second hub and the second wheel and the first spring end of the second spring. 
     Concept 11. The exercise device of Concept 10, wherein: 
     the second spring further comprises a second spring end opposite the first spring end of the second spring; and 
     the second spring end of the second spring is slidably connected to the other of the second wheel and the second hub at a fourth junction, wherein the fourth junction is configured to convey torque between the other of the second hub and the second wheel and the second spring end. 
     Concept 12. The exercise device of Concept 2, wherein the first spring is located above the body when the body top is facing up.
 
Concept 13. The exercise device of Concept 2, wherein the first spring is located below the body when the body top is facing up.
 
Concept 14. The exercise device of Concept 2, wherein the first spring is located at least partially within the first wheel.
 
Concept 15. The exercise device of Concept 2, wherein the first spring is located entirely within the first wheel.
 
Concept 16. The exercise device of Concept 2, wherein the first spring is a coil spring.
 
Concept 17. A method of using the exercise device of Concept 1 comprising:
 
     moving the exercise device away from a person&#39;s waist while the person&#39;s feet are placed on the body of the exercise device and the first and second wheels are on a surface, wherein when the exercise device is moved away from the person&#39;s waist, the first and second wheels rotate along the surface, and torque energy is stored in the first and second springs; and 
     moving the exercise device toward the person&#39;s waist while the person is assisted by or resists torque supplied to the first and second wheels by the first and second springs, respectively. 
     Concept 18. An exercise device comprising: 
     a body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; 
     first and second axles connected to and rotationally locked to first and second wheels, respectively, the first and second wheels able to rotate both in clockwise and counterclockwise directions in relation to the body, the first axle also connected to the body proximate the first end at a first hub and the second axle also connected to the body proximate the second end at a second hub; 
     a first spring with a wheel end and a hub end, the first spring positioned at least partially within the first axle, with
         the first spring wheel end slidably connected to the first wheel at a first wheel junction, wherein the first wheel junction is configured to convey torque between the first wheel and the first spring wheel end, and   the first spring hub end slidably connected to the first hub at a first hub junction, wherein the first hub junction is configured to convey torque between the first hub and the first spring hub end; and       

     a second spring with a wheel end and a hub end, the second spring positioned at least partially within the second axle, with
         the second spring wheel end slidably connected to the second wheel at a second wheel junction, wherein the second wheel junction is configured to convey torque between the second wheel and the second spring wheel end, and   the second spring hub end slidably connected to the second hub at a second hub junction, wherein the second hub junction is configured to convey torque between the second hub and the second spring hub end;   when the first and second wheels are rotated against respective first and second spring torques, energy is stored in the first and second springs and the first and second springs apply restoring torque to the first and second wheels, respectively.
 
Concept 19. An exercise device comprising:
       

     a body, the body having a top, a bottom, a first end located at one edge of the body, a second end located at an opposite end of the body, and first and second sides extending between the first and second ends; 
     a first axle connected to a first wheel, the first axle also connected to the body proximate the first end at a first hub; 
     a first spring having a first spring end, the first spring positioned at least partially within the first axle, with the first spring end slidably connected to one of the first wheel and the first hub at a first junction, wherein the first junction is configured to convey torque between the one of the first hub and the first wheel and the first spring end. 
     Concept 20. The exercise device of Concept 19, wherein the first spring comprises a second spring end opposite the first spring end, and the first spring end is slidably connected to one of the first hub and first wheel and the second spring end is slidably connected to the other of the first hub and first wheel at a second junction, wherein the second junction is configured to transfer torque between the other of the first hub and the first wheel and the second spring end.
 
Concept 21. The exercise device of Concept 19 or 20, wherein the first junction is a slot configured to receive the first spring end.
 
Concept 22. The exercise device of any one of Concepts 20-21, wherein the second junction is a slot configured to receive the second spring end.
 
Concept 23. The exercise device of any one of Concepts 19-22, wherein the first axle is rotationally locked to the first wheel.
 
Concept 24. The exercise device of any one of Concepts 19-23, wherein the first spring is contained entirely within the first axle.
 
Concept 25. The exercise device of any one of Concepts 19-24, wherein the body is sized and configured for two feet to be placed upon the body and for the feet to push the body; and
 
     the first wheel has a neutral position wherein the first spring does not apply torque to the first wheel, and when the first wheel is rotated away from the neutral position, energy is stored in the first spring and the first spring applies a restoring torque to the first wheel. 
     Concept 26. The exercise device of Concept 19 or 20, wherein the first wheel comprises a spring cover and the first junction or the second junction is located in the spring cover.
 
Concept 27. The exercise device of any one of Concepts 19-26, wherein the first spring is located above the body when the body top is facing up.
 
Concept 28. The exercise device of any one of Concepts 19-27, wherein the first spring is located below the body when the body top is facing up.
 
Concept 29. The exercise device of any one of Concepts 19-28, wherein the first spring is located at least partially within the first wheel.
 
Concept 30. The exercise device of any one of Concepts 19-29, wherein the first spring is located entirely within the first wheel.
 
Concept 31. The exercise device of any one of Concepts 19-30, wherein the first spring is a coil spring.
 
Concept 32. The exercise device of any one of Concepts 19-31-14, further comprising:
 
     a second wheel, a second axle and a second spring; 
     wherein the second axle is connected to the second wheel, the second axle is also connected to the body proximate the second end of the body at a second hub; 
     the second spring having a first spring end, the second spring positioned at least partially within the second axle, with the first spring end of the second spring slidably connected to one of the second wheel and the second hub at a third junction, wherein the third junction is configured to convey torque between the one of the second hub and the second wheel and the first spring end of the second spring. 
     Concept 33. The exercise device of Concept 32, wherein: 
     the second spring further comprises a second spring end opposite the first spring end of the second spring; and 
     the second spring end of the second spring is slidably connected to the other of the second wheel and the second hub at a fourth junction, wherein the fourth junction is configured to convey torque between the other of the second hub and the second wheel and the second spring end. 
     Concept 34. A method of using the exercise device of Concept 18 comprising: 
     moving the exercise device away from a person&#39;s waist while the person&#39;s feet are placed on the body of the exercise device and the first and second wheels are on a surface, wherein when the exercise device is moved away from the person&#39;s waist, the first and second wheels rotate along the surface, and torque energy is stored in the first and second springs; and 
     moving the exercise device toward the person&#39;s waist while the person is assisted by or resists torque supplied to the first and second wheels by the first and second springs, respectively 
     Concept 35. An exercise device comprising: 
     a body, the body having a top, a bottom, a first end located at an edge of the body, a second end located at an opposite edge of the body, and first and second sides extending between the first and second ends; 
     a first wheel assembly comprising a first wheel, the first wheel assembly connected to the body proximate the first end; 
     a second wheel assembly comprising a second wheel, the second wheel assembly connected t the body proximate the second end; 
     a shaft in rotational communication with the first wheel and the second wheel, the shaft rotationally locked to the first wheel; 
     a shuttle configured to move along the shaft upon rotation of the first or second wheel; 
     a first spring, wherein the exercise device is configured for the first spring to be loaded and unloaded by the moving of the shuttle along the shaft 
     wherein when the first wheel is rotated in relation to the body from a rest position, the shaft rotates, moving the shuttle which loads the first spring which applies a resisting torque to the first wheel, and when the first wheel is moved or allowed to move back to the rest position, the spring applies a restoring torque to the wheel through the shuttle and the shaft to urge the wheel toward the rest position. 
     Concept 36. The exercise device of Concept 35, wherein the first wheel, the second wheel and the shaft are rotationally locked to one another.
 
Concept 37. The exercise device of Concept 35, wherein the shaft comprises a lead screw and the shuttle comprises a lead screw nut in threaded communication with the lead screw.
 
Concept 38. The exercise device of Concept 35, wherein the spring is a coil spring and the shaft passes through the coil spring, with coils of the coil spring encircling the shaft.
 
Concept 39. The exercise device of Concept 37, wherein the coil spring is located between the shuttle and the first wheel or the second wheel.
 
Concept 40. The exercise device of Concept 35, further comprising a second spring, the exercise device is configured for the second spring to be loaded and unloaded by the moving of the shuttle along the shaft.
 
Concept 41. The exercise device of Concept 40, wherein as the first spring is loaded, the second spring is unloaded.
 
Concept 42. The exercise device of Concept 40, wherein the first spring is a coil spring and the shaft passes through the coil spring, with the coils of the coil spring encircling the shaft, and the second spring is a coil spring, with the coils of the coil spring encircling the shaft, and during operation, the first spring is loaded by compression and the second spring is loaded by extension.
 
Concept 43. The exercise device of Concept 36, further comprising:
 
     a first spur wheel rotationally locked to the shaft and in rotational communication with a surface of the first wheel; and 
     a second spur wheel rotationally locked to the shaft and in rotational communication with a surface of the second wheel. 
     Concept 44. The exercise device of Concept 43, wherein the first and second spur wheels are spur gears and the inner surfaces of the first and second wheels have geared surfaces that engage the first and second spur gears, respectively.
 
Concept 45. The exercise device of Concept 35, further comprising first and second hand grips, wherein each of the first and second hand grips is located adjacent to the respective first and second ends of the body and allow a hand of a user to pass through a wheel plane of the respective first or second wheel while the hand of the user grips the exercise device.
 
Concept 46. The exercise device of Concept 35, wherein the first and second wheel assemblies further comprise first and second axles, respectively, and the first axle is connected to and rotationally locked to the first wheel and the second axle is connected to and rotationally locked to the second wheel.
 
Concept 47. The exercise device of Concept 35, wherein a wheel assembly further comprises an eddy current brake positioned within the first wheel assembly, wherein the eddy current brake is configured to reduce the rotational speed of the first wheel during operation.
 
Concept 48. The exercise device of Concept 47, wherein the eddy current brake comprises a magnet and a conductor,
 
     wherein
         the magnet rotates as the first wheel rotates, and the magnet and the conductor rotate in relation to one another during operation and the conductor is optionally affixed to a non-rotating part of the exercise device; or   the conductor rotates as the first wheel rotates, and the magnet and the conductor rotate in relation to one another during operation and the conductor is optionally affixed to a non-rotating part of the exercise device.
 
Concept 49. The exercise device of Concept 48, wherein the conductor comprises metallic material.
 
Concept 50. The exercise device of Concept 35, wherein the shaft does not comprise the first axle or the shaft does not comprise the first and second axle.
 
Concept 51. The exercise device of Concept 35, wherein the shuttle comprises a second shaft, first and second end blocks, a gear mount and first and second transfer gears, wherein
       

     each of the first and second end blocks move along the shaft and are rotatingly anchored to the second shaft,
         the gear mount is located between the first and second end blocks,   the first transfer gear is mounted to the gear mount and is rotationally locked with the shaft while engaging the second transfer gear which is mounted to the slider, and   i) the second shaft comprises a lead screw with the second gear having a corresponding lead nut, and upon rotation of the shaft, the first transfer gear rotates the second transfer gear which then moves the second shaft and the end blocks toward the first end of the body or the second end of the body, loading or unloading the first spring,   or   ii) the second shaft is comprises a lead screw and is rotationally locked to the second gear and upon rotation of the shaft,   the first transfer gear rotates the second transfer gear which then rotates the shaft the second shaft first and second lead nuts located in the first and second end blocks cause the first and second end blocks to move toward the first end of the body or the second end of the body, loading or unloading the first spring.
 
Concept 52. The device of Concept 46, wherein the shaft is physically offset from the first axle.
 
Concept 53. The device of Concept 46, wherein the shaft is physically offset from the first and second axles.
 
Concept 54. An exercise device comprising:
       

     a body, the body having a top, a bottom, a first end located at an edge of the body, a second end located at an opposite edge of the body, and first and second sides extending between the first and second ends; 
     a first wheel assembly comprising a first wheel, the first wheel assembly connected to the body proximate the first end; 
     a second wheel assembly comprising a second wheel, the second wheel assembly connected to the body proximate the second end; 
     a shaft in rotational communication with the first wheel and the second wheel, the shaft rotationally locked to the first wheel; 
     a first spring, wherein the exercise device is configured for the first spring to be loaded and unloaded by the rotation of the shaft, 
     wherein when the first wheel is rotated in relation to the body from a rest position, the shaft rotates and torsionally deflecting an end of the spring which loads the spring which applies a resisting torque to the first wheel, and when the first wheel is moved or allowed to move back to the rest position, the spring applies a restoring torque to the wheel through the shaft to urge the wheel toward the rest position. 
     Concept 55. An exercise device comprising: 
     a body, the body having a top, a bottom, a first end located at an edge of the body, a second end located at an opposite edge of the body, and first and second sides extending between the first and second ends; 
     a first wheel assembly comprising a first wheel, the first wheel assembly connected to the body proximate the first end; 
     a second wheel assembly comprising a second wheel, the second wheel assembly connected to the body proximate the second end; 
     a shaft in rotational communication with the first wheel and the second wheel, the shaft rotationally locked to the first wheel; 
     an energy storage device, comprising a gas in a chamber, wherein the exercise device is configured for the energy storage device to be loaded and unloaded by the rotation of the shaft, wherein when the first wheel is rotated in relation to the body from a rest position, the shaft rotates and increases a pressure within the chamber which applies a resisting torque to the first wheel through the shaft, and when the first wheel is moved or allowed to move back to the rest position, the pressure within the chamber applies a restoring torque to the wheel through the shaft to urge the wheel toward the rest position. 
     Concept 56. An exercise device comprising: 
     a body, the body having a top, a bottom, a first end located at an edge of the body, a second end located at an opposite edge of the body, and first and second sides extending between the first and second ends; 
     a first wheel assembly comprising a first wheel, the first wheel assembly connected to the body proximate the first end; 
     a second wheel assembly comprising a second wheel, the second wheel assembly connected to the body proximate the second end; 
     a shaft in rotational communication with the first wheel and the second wheel, the shaft rotationally locked to the first wheel; 
     an energy storage device, comprising a battery or a capacitor, wherein the exercise device is configured for the energy storage device to be loaded and unloaded by the rotation of the shaft, wherein when the first wheel is rotated in relation to the body from a rest position, the shaft rotates and 
     operates a charger, the charger increasing the electrical energy stored in the battery or capacitor, which in turn runs a motor that acts on the first wheel to apply a resisting torque to the first wheel through the shaft, and when the first wheel is moved or allowed to move back to the rest position, the motor a restoring torque to the wheel through the shaft to urge the wheel toward the rest position. 
     Concept 57. The exercise device of Concept 56, wherein the charger is a generator.
 
Concept 58. An exercise device comprising:
 
     a platform having a first end and a second end opposite the first end; 
     first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; 
     a first motor is configured to apply a first torque to the first wheel where the magnitude of the first torque is related to the distance of the exercise device from a zero position and a direction of the first torque urges the exercise device toward the zero position. 
     Concept 59. The exercise device of Concept 58, further comprising a second motor configured to apply a second torque to the second wheel where a magnitude of the second torque is related to the distance of the exercise device from the zero position and the direction of the second torque urges movement of the exercise device toward the zero position.
 
Concept 60. The exercise device of Concept 58, further comprising a stabilizing wheel system comprising one or more stabilizing wheels, wherein the one or more stabilizing wheels are positioned and configured to roll across the surface and to limit rotation of the platform in relation to the first and second wheel.
 
Concept 61. The exercise device of Concept 58 wherein the surface comprises a continuous horizontal surface extending from the first wheel to the second wheel.
 
Concept 62. The exercise device of Concept 58, wherein the surface comprises a first track and a second track where the first wheel rolls on the first track and the second track rolls on the second track.
 
Concept 63. The exercise device of Concept 60, wherein there are two stabilizing wheels.
 
Concept 64. The exercise device of Concept 60, wherein the first motor is configured to apply a second torque to the second wheel, where the magnitude of the second torque is related to the distance of the exercise device from the zero position and a direction of the second torque urges movement of the exercise device toward the zero position.
 
Concept 65. The exercise device of Concept 59 wherein the magnitude of the first torque follows a first pattern as the distance from the zero point increases and the magnitude of the second torque follows a second pattern as the distance from the zero point decreases, where the first and the second pattern are independently selected from:
 
     a linear pattern with constant magnitude, 
     a linear pattern with increasing magnitude with increasing distance from the zero position, 
     a linear pattern with decreasing magnitude with increasing distance from the zero position, 
     a variable pattern with increasing magnitude with increasing distance from the zero position, 
     a variable pattern with decreasing magnitude with increasing distance from the zero position, 
     a variable pattern with decreasing magnitude with increasing distance from the zero position, 
     a variable pattern with increasing then decreasing magnitude with increasing distance from zero, 
     a variable pattern with decreasing then increasing magnitude with increasing distance from zero, and 
     combinations thereof. 
     Concept 66. The exercise device of Concept 65, wherein the first pattern is a linear curve with constant magnitude.
 
Concept 67. The exercise device of Concept 65, wherein the first pattern has increasing magnitude with increasing distance from the zero position.
 
Concept 68. The exercise device of Concept 65, wherein the first pattern has decreasing magnitude with increasing distance from the zero position.
 
Concept 69. The exercise device of Concept 65, wherein the first pattern is a linear curve with increasing magnitude with increasing distance from the zero position.
 
Concept 70. The exercise device of Concept 65, wherein the first pattern has increasing then decreasing magnitude with increasing distance from zero.
 
Concept 71. The exercise device of Concept 65, wherein the first pattern has decreasing then increasing magnitude with increasing distance from zero.
 
Concept 72. The exercise device of Concept 65, wherein the first pattern is different from the second pattern.
 
Concept 73. A method of operating the exercise device of Concept 59 comprising:
 
     the first or second motor applying a first or second torque to the first or second wheel, respectively as the exercise device is pushed across the surface away from the zero position, where the first or second torque opposes the motion of the exercise device; and 
     the first or second motor applying a first or second torque to the first or second wheel, respectively as the exercise device is pushed across the surface toward the zero position, where the first or second anti-return force opposes the motion of the exercise device. 
     Concept 74. The method of Concept 73, wherein, the first or second torque is changed to compensate for yaw of the exercise device.
 
Concept 75. The method of Concept 73, wherein the first or second torque is changed to compensate for tipping of the platform in relation to the first or second wheel.
 
Concept 76. The method of operating the exercise device of Concept 65, wherein the first or second pattern is selected at the start of an exercise session.
 
Concept 77. The method of operating the exercise device of Concept 73, wherein the first or second torque is changed when the acceleration of the exercise device away from or toward the zero position exceeds a preset value.
 
Concept 78. An exercise system comprising:
 
     the exercise device of Concept 58; and 
     a user interface configured to provide an indication of an exercise parameter achieved or an exercise deviation performed to a user of the exercise device. 
     Concept 79. The exercise system of Concept 78, wherein the user interface provides a haptic indication to the user.
 
Concept 80. The exercise system of Concept 78, wherein the user interface comprises a visual display in the exercise device.
 
Concept 81. The exercise system of Concept 78, wherein the user interface comprises a visual display external to the exercise device.
 
Concept 82. The exercise system of Concept 78, wherein the user interface comprises an audio signal.
 
Concept 83. The exercise system of Concept 78, wherein the indication of an exercise parameter achieved comprises a display of a representation of the user&#39;s position operating the exercise device and a standard position of operation of the exercise device.
 
Concept 84. The exercise system of Concept 78, wherein the indication of an exercise parameter achieved comprises an indication of a degree of success in achieving a standard movement form during operation of the exercise device.
 
Concept 85. An exercise device comprising:
 
     a platform having a first end and a second end opposite the first end; 
     first and second wheels, wherein the first wheel is positioned proximate the first end and the second wheel is positioned proximate the second end and the first and second wheels are configured to roll across a surface as the exercise device is displaced along the surface; 
     the first wheel applies a force that resists movement of the exercise device when the exercise device is moved from a zero position where a magnitude of the force is related to the distance of the exercise device from the zero position and a direction of the force urges the device toward the zero position.