Abstract:
A collapsible exercise machine for strengthening the core muscles (transverse abdominal, internal obliques, external obliques, rectus abdominis, and erector spinae) includes a frame mounted on a base on which a user sits and manipulates an upstanding lever arm. A seat is convertible between two differently-angled positions for back extension or abdominal exercises. The lever arm rotates a curved tube having a plurality of force adjustment holes. The tube passes through a frame at the upper end of a gas spring, and engaging an adjustment pin on the frame with different adjustment holes changes the amount of resistance. The entire frame above the base can be vertically adjusted to accommodate different sizes of user without altering the relative position between the seat (and user&#39;s hips) and the axis of rotation of the lever arm thus not affecting/changing the designated resistance between users of different heights (resistance is affected when the lever arm is lengthened). The connection between the frame and the base enables the unit to be collapsed to a profile small enough to fit under a bed.

Description:
RELATED APPLICATION 
       [0001]    The present application is a continuation of U.S. application Ser. No. 14/229,772, filed Mar. 28, 2014, which claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/806,319, filed Mar. 28, 2013. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to a collapsible resistance-based machine for exercising the core muscles of the body. 
       BACKGROUND OF THE INVENTION 
       [0003]    With widespread awareness of its significant health benefits, regular exercise including progressive resistance strength training has become a matter of high priority to many members of the general public. Progressive resistance strength training is a type of strength training that uses free weights, exercise weight stack machines, compressed air (pneumatics), hydraulic resistance, elastic/rubber bands and gas springs as resistance to strengthen muscles. The key to this type of exercise is adjusting the resistance as the person progresses. A major obstacle faced by most in following a progressive resistance strength training program is the lack of readily accessible equipment that enable them to exercise different portions of the body at home. Ideally, an in-home gym facility is equipped with various exercise machines and implements for exercising different portions of the body but most do not. 
         [0004]    The most difficult and overlooked muscles to exercise at home with progressive resistance are the muscles of the core (transverse abdominal, internal obliques, external obliques, rectus abdominis and erector spinae). These muscles are antagonistic in that they oppose the movement of one another. Proper strength and tone of each muscle group is important for proper posture, reduction of back injuries and physical health. Despite the importance of the abdominal, and lower back muscles, these muscles tend to be forgotten in most home exercise gyms. Consequently, there is a need for a core exercise machine that uses progressive resistance, is compact, portable, affordable, and easy to use. 
         [0005]    Versatile machines that are reconfigurable to enable various exercises do exist. Those machines, however, typically include complex arrangements of mechanical parts and require complicated series of adjustments to reconfigure the machine for different exercises. Where such complexity is not present, the machines are either undesirably limiting in the number of different exercises that may be performed on them, don&#39;t allow for any significant resistance, don&#39;t offer a wide range of resistance or are physically of such substantial mass and dimensional extent that they may be fully utilized only in certain wide-open areas of a given home, and are hardly movable, let alone portable. Preferably, an in-home machine with such versatility offers a broad range of progressive resistance, is safe, easy to use, affordable, light weight, and collapsible for storage. 
         [0006]    Known exercise machines provide weights or a reaction force as a source of resistance (weights are heavy and expensive). Rubber elements used as stretchable resistance bands have been widely used to oppose motion of certain mechanisms in an exercise machine (the problem with a stretchable band is that the resistance greatly increases as the band stretches and they tend to dry out and break). Gas springs are known as well which have a piston/cylinder arrangement. Gas inside the cylinder flows through or around the piston from one side to the other as it moves back and forth in various designs; usually the piston has one or more holes or valves in it. The whole cylinder is completely sealed, and when the piston rod is inside the cylinder, it takes up room that the gas previously occupied. In other words, when a gas spring is fully pushed in, the gas inside compresses by an amount equal to the volume of the piston rod. Furthermore, the net force on the piston is out of the cylinder because the piston rod within the cylinder takes up space and thus there is a pressure differential across the piston. For instance, a gas spring in U.S. Patent Publication No. 2005/0101464 provides a resistance force which increases somewhat during compression. Typically, Nitrogen is the working gas inside the gas spring. 
         [0007]    Despite numerous exercise machines on the market, there remains a need for a portable machine that works the core muscles of the body, that can supply similar resistance to weights yet be safer, portable, moveable, affordable, and which can easily be adjusted for different exercises and users. 
       SUMMARY OF THE INVENTION 
       [0008]    The present application provides an exercise machine for strengthening the core muscles of the body, which consists mostly of the abdominal (transverse abdominal, internal obliques, external obliques, and rectus abdominis) and erector spinae muscles of the back. The machine has a relatively elongated base, and is shaped like an upside down “T” (with the base as the top of the “T”). The machine is collapsible for storage under a bed and shipping. The angle of the top vertical bar can be adjusted forward and backward by the user. The top vertical bar can be adjusted to different angles to target the various muscles of the core, to safely limit flexion or extension if needed to avoid discomfort, and it allows for a slimmer profile when collapsing the unit so that it can be stored under a bed or shipped. The top vertical bar can also be adjusted to properly isolate the desired muscles for a given exercise or limit range of motion to avoid a painful position for the user. The height of the vertical bar can be adjusted to the height of the user&#39;s torso. There may also be a foot rest so that the height can be adjusted to match the user&#39;s leg length. 
         [0009]    In accordance with one preferred embodiment, an exercise machine comprises a base having at least one upstanding leg at the top of which is a housing within which a horizontal bar rotates, the housing having a seat firmly mounted thereon such a user can sit on the seat with his or her legs on the ground or on the base. An upstanding lever arm attaches to an end of the horizontal bar displaced from the housing and terminates in a horizontal force application bar. A user sitting in the seat can manipulate the force application bar and rotate the horizontal bar within the housing. A source of adjustable resistance is coupled to rotation of the horizontal bar, and an adjustable indexing device connects to the upstanding lever arm for changing the rotational orientation of the lever arm relative to the horizontal bar. Preferably, the leg and lever arm may be rotated with respect to the base to allow them to lie substantially flat. 
         [0010]    Another exercise machine in accordance with the application includes a base having at least one upstanding leg at the top of which is a housing within which a horizontal bar rotates. The housing has a seat firmly mounted thereon such a user can sit on the seat with his or her legs on the ground or on the base. An upstanding lever arm attaches to an end of the horizontal bar displaced from the housing terminates in a horizontal force application bar. A user sitting in the seat can manipulate the force application bar and rotate the horizontal bar within the housing. A source of adjustable resistance is coupled to rotation of the horizontal bar. A height adjustment mechanism between the at least one upstanding leg and the base permits the upstanding leg to be raised relative to the base and changes the height of the seat without altering the spacing between the seat and the axis of rotation of the horizontal bar. Preferably, the leg and lever arm may be rotated with respect to the base to allow them to lie substantially flat. By not having to raise the seat height for taller users the hips can be maintained close to the C/L of rotation of the lever arm thus mimicking the body&#39;s natural biomechanics which improves safety and isolates the desired muscle groups. In addition, by raising the vertical bar to adjust the height it minimizes the amount you have to raise the lever arm for taller users, which would otherwise lessen the overall resistance. 
         [0011]    A further exemplary exercise machine again has at least one upstanding leg at the top of which is a housing within which a horizontal bar rotates. The housing has a seat firmly mounted thereon such a user can sit on the seat with his or her legs on the ground or on the base. An upstanding lever arm attaches to an end of the horizontal bar displaced from the housing terminates in a horizontal force application bar. A user sitting in the seat can manipulate the force application bar and rotate the horizontal bar within the housing. A source of adjustable resistance is coupled to rotation of the horizontal bar, wherein the seat position can be changed relative to the upstanding leg, and wherein in one position the seat is horizontal and positioned for a user to perform abdominal exercises, and wherein in the other position the seat is angled from the horizontal in position for a user to perform back extension exercises. Preferably, the leg and lever arm may be rotated with respect to the base to allow them to lie substantially flat. The seat preferably has two downwardly extending tubes, wherein the seat position can be changed by engaging one or the other of the downwardly extending tubes with an upstanding post on the housing. 
         [0012]    A still further collapsible exercise machine has at least one upstanding leg at the top of which is a housing within which a horizontal bar rotates. The housing has a seat firmly mounted thereon such a user can sit on the seat with his or her legs on the ground or on the base. An upstanding lever arm attaches to an end of the horizontal bar displaced from the housing terminates in a horizontal force application bar. A source of adjustable resistance couples to rotation of the horizontal bar, and connections between the components of the exercise machine which permit it to be collapsed down to a maximum height of 8 inches. 
         [0013]    Another exercise machine has at least one upstanding leg at the top of which is a housing within which a horizontal bar rotates. The housing has a seat firmly mounted thereon such a user can sit on the seat with his or her legs on the ground or on the base. An upstanding lever arm attaches to an end of the horizontal bar displaced from the housing terminates in a horizontal force application bar. A gas spring connects between a fixed point on the upstanding leg and a force adjustment bar extending from the horizontal bar. The position of an upper end of the gas spring is adjustable along the force adjustment bar, wherein the progressivity of the gas spring is 1.1 or less. Preferably, the leg and lever arm may be rotated with respect to the base to allow them to lie substantially flat. 
         [0014]    The machine uses a gas (nitrogen) spring for a constant and consistent resistance force throughout the entire range of motion that is similar to a weight machine. The resistance is variable. The amount of resistance can be adjusted by changing the angle of the gas spring along an arc. If the user sits in one direction on the machine the abdominal muscles can be strengthened and if the user turns around in the other direction the lower back muscles are strengthened. The resistance is easy to switch single-handedly from 10 pounds to 130 pounds, for example, without getting off the machine and having to move dangerous weight plates. 
         [0015]    When strengthening the abdominal muscles the user sits so that the arc is between the users legs. The square mounting tube on the bottom of the seat for the abdominals is used. In this position the seat is horizontal and a majority of the seat (e.g., approximately 8″, and the seat is 12″ long) is in front of the central axis of the lever arm. The user sits so that their hips are in front of the central axis. 
         [0016]    When strengthening the muscles of the lower back the user sits so that the arc is behind them. The square mounting tube on the bottom of the seat for the lower back is used. In this position the seat is tilted forward at an angle and a majority of the seat is behind the central axis of the lever arm. The user sits so that their hips are in line with the central axis. The seat is moved from the position in which the abdominals are exercised so that the hips are in line with the central axis. 
         [0017]    There is a seat belt attached to the undersurface of the seat to stabilize the thighs and isolate the lower back and abdominal muscles. There are foot rests in front and back of the machine to lock the feet into position. The resistance can be switched single-handedly without getting off the machine and having to move dangerous weight plates. 
         [0018]    The exemplary machine provides a portable clinic grade therapeutic exercise device that can be used in a small clinic and also at home. The machine provides progressive resistance training to the abdominal and erector spinae muscles through a gas spring. 
         [0019]    The present application provides an advantage over weight stack machines: With weight stack machines momentum and gravity cause sudden acceleration in the load being placed on the joints. This application is safer because it provides a consistent resistance at different speeds without causing unnecessary loading due to gravity and momentum, the machine is space saving, and whereas weights are heavy and noisy, the present machine is relatively lightweight and quiet. 
         [0020]    The present application provides an advantage over bands: There is a more linear resistance, a variable resistance, and the machine is safer (bands get dry and crack then suddenly break). Plus, bands only provide consistent resistance in a limited range of motion. 
         [0021]    The present application provides an advantage over hydraulic resistance machines in which one can only push or pull so you are not getting the full concentric/eccentric contraction which is essential in strength training. 
         [0022]    The present application also provides an advantage over compressed air (pneumatics) which are expensive, need an air compressor, heavy, not portable and take up a lot more space. 
         [0023]    The present application, which uses a custom made gas spring also provides an advantage over other gas springs, which don&#39;t have a very linear compression factor (the extended force vs. the compressed force) and they have a much lower cycle ability (cycles/minute). 
         [0024]    A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Features and advantages of the present invention will become appreciated and become better understood with reference to the specification, claims, and appended drawings wherein: 
           [0026]      FIG. 1  is a perspective view of an exemplary core exercise machine of the present application, while  FIG. 1A  is an isolated view of a central horizontal bar thereof; 
           [0027]      FIG. 2  is an end elevational view of the exercise machine of  FIG. 1 ; 
           [0028]      FIGS. 3A and 3B  are side elevational views of the exercise machine with a user shown operating the machine in two different modes; 
           [0029]      FIGS. 4A and 4B  are enlarged elevational views looking from the side opposite that in  FIGS. 3A and 3B  and showing two different seat positions for the two different modes, while  FIG. 4C  shows the seat isolated and the angles of two lower mounting tubes; 
           [0030]      FIG. 5  shows the exemplary exercise machine partly collapsed, and  FIG. 6  shows the exercise machine fully collapsed; 
           [0031]      FIGS. 7A and 7B  are assembled and exploded views, respectively, of a lower height adjustment configuration; 
           [0032]      FIGS. 8A and 8B  are perspective and side elevational views, respectively, of an alternative exercise machine similar to that shown in  FIGS. 1-7  and illustrating the gas spring attached to an adjustment bar so as to produce relatively high force resistance; 
           [0033]      FIGS. 9A and 9B  again illustrate the alternative exercise machine with the gas spring attached so as to produce relatively high force resistance and a lever arm rotated to a different angle for a different exercise; 
           [0034]      FIGS. 10A and 10B  again show the alternative exercise machine with the gas spring attached so as to produce relatively low force resistance; 
           [0035]      FIGS. 11A and 11B  show the alternative exercise machine with the gas spring attached to produce relatively low force resistance and the lever arm rotated to a nearly horizontal position; 
           [0036]      FIGS. 12A and 12B  are perspective views of a still further alternative collapsible exercise machine in accordance with the present invention wherein the seat and lever arm are supported by multiple legs; 
           [0037]      FIGS. 13A-13D  are orthogonal views of the multi-leg exercise machine of  FIGS. 12A and 12B ; 
           [0038]      FIGS. 14A-14C  are side elevational views of the multi-leg exercise machine showing three steps preliminary to collapse thereof; 
           [0039]      FIGS. 15A and 15B  are perspective and elevational views of the multi-leg exercise machine after rotation of a lever arm indexing plate preparatory to collapse; 
           [0040]      FIGS. 16A and 16B  are perspective and elevational views of the multi-leg exercise machine in a state of partial collapse; and 
           [0041]      FIGS. 17A-17C  are several views of the fully collapsed multi-leg exercise machine. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]      FIG. 1  illustrates an exemplary exercise machine  20  of the present application that includes an upper frame having a generally vertical leg  22  supported on and by a horizontal H-shaped base  24 . The base  24  comprises a central longitudinal bar  26  welded at both ends to first and second lateral bars  28 ,  30 . At least one of the lateral bars  28  includes rubber end caps  32  to prevent movement on solid floors, while the other lateral bar  30  desirably has a pair of wheels  34  mounted on each end so that the entire machine  20  can be easily moved. 
         [0043]    With reference also to  FIGS. 1A and 2 , the upper frame of the exercise machine  20  features a cylindrical horizontal bar  40  attached at the top of the vertical leg  22  and extending laterally therefrom in one direction. An adjustable lever arm  42  extends upward and comprises a lower section  43  fixed to the horizontal bar  40  and an extendable section  44  movable therein. Preferably, the lever arm  42  and extendable section  44  are square tubes with the latter having a series of spaced holes  46  that can be registered with a spring-loaded length adjustment pin  48  that passes in through a single hole formed in the lever arm  42 . A horizontal force application bar  50  preferably covered with a foam pad  52  attaches firmly to the top of the extendable section  44  and extends laterally back over the horizontal bar  40 , preferably as far as the vertical leg  22 . As shown by the movement arrows  54  in  FIG. 1 , a user can rotate the force application bar  50  and lever arm  42  about an axis centered along the horizontal bar  40 . The center line C/L of the horizontal bar  40  defines the axis of rotation of the lever arm  42 . 
         [0044]      FIG. 1A  isolates the horizontal bar  40  so as to explain the manner in which the force application bar  50  and lever arm  42  rotate about a horizontal axis through the top of the vertical leg  22 . First of all, a short tubular fixed housing  60  rigidly attaches (e.g., by welds) at the top of the vertical leg  22  and contains therein bearings or plastic washers that enable rotation of an elongated metal inner sleeve within the horizontal bar  40 . Although not shown, the relatively large inner sleeve extends horizontally from one end of the fixed housing  60  through the bearings or plastic washers to the opposite end of the horizontal bar  40 , with the elongated structure being secured by end bolts  62 . A rotatable tubular central section  64  is rotationally fixed with respect to the inner shaft, as is a short tubular force transmission collar  66  between the central section  64  and the fixed housing  60 . The fixed housing  60  and force transmission collar  66  are independent of one another; the housing  60  does not rotate while the force transmission collar  66  does. A wedge-shaped indexing plate  68  fixed rotationally with respect to the central section  64  extends in a radial plane outward therefrom and includes a plurality of adjustment holes  70  formed in an arc oriented about the center line CL. A tubular end section  72  of the horizontal bar  40  is journaled for rotation about the inner shaft but can be fixed with respect thereto by engaging an adjustment pin  74  spring-mounted on a flange  76  with one of the adjustment holes  70  in the indexing plate  68 . That is, the entire structure of the horizontal bar  40  rotates within the fixed housing  60  with the angle of the lever arm  42  relative to the central section  64  being adjustable by virtue of the pin  74  and holes  70 . 
         [0045]    With the reference still to  FIGS. 1 and 1A , an upstanding flange  80  welded to the force transmission collar  66  provides a fastening point for an elongated curved tubular bar  82 . The bar  82  has a series of evenly spaced force adjustment holes  84  on an upper generatrix. The bar  82  passes through a bracket  86  mounted on the top end of a rod  88 . As seen best in  FIG. 4A , the rod  88  extends downward into a cylinder  90  which is pivotally mounted toward its lower end on a bracket  92  fixed to a lower end of the vertical leg  22 . In a preferred embodiment, the rod  88  is desirably positioned below the cylinder  90  so that the internal seal around the rod stays lubricated, such as seen in the alternative embodiment of  FIGS. 8-11 . 
         [0046]    Again with reference to  FIG. 1 , the upper end of the rod  88  can be fixed with respect to a position along the curved bar  82  by engaging a spring-loaded adjustment pin  94  mounted in the bracket  86  in one of the adjustment holes  84 . The rod  88  and cylinder  90  preferably comprise a nitrogen gas spring  95 , although other force resistance devices can be utilized. A gas spring supplies a constant force resembling weights. Indeed, the preferred gas spring  95  has a relatively low progressivity of 6-11%, preferably 7-8%, which means that if you start out at 100 lbs of resistance, as the gas spring compresses the resistance goes up to 106-108 lbs of force. Such a gas spring is available from Taizhou Xinda Gas Spring Co., Ltd, although other suppliers are available. Most stock springs have a progressivity of between 20-40%. It should be understood, however, that various features of the exercise machine  20  described herein are useful with a conventional gas spring, or even without including a gas spring, and therefore a spring resistance device or other such mechanism can be substituted. 
         [0047]    Also, none of the previous stock gas springs are made for using at more than 6 cycles per minute, while the gas springs disclosed herein can be used up to 18-20 cycles per minute due to the quality of the seals. 
         [0048]    When the user rotates the horizontal bar  40 , including the force transmission collar  66  and flange  80  as seen in  FIG. 1A , the curved bar  82  rotates as well, which alternately moves the rod  88  in and out of the cylinder  90 . As explained above, a gas spring  95  provides resistance to movement of the rod  88  in both directions. The user can adjust the resistance significantly (e.g., 10 lbs to about 130 lbs) for use depending on which one of the adjustment holes  84  the adjustment pin  94  engages. That is, the change in lever arm distance from moving the bracket  86  along the curved bar  82  changes the resistance. Generally speaking, the lower down on the curved bar  82  that the upper end of the rod  88  engages the greater the resistance to rotation of the lever arm  42 . Vice versa, moving the adjustment pin  94  up on the curved bar  82  toward the centerline C/L reduces the resistance. Optionally, a second gas spring in parallel with or in place of the first may be added to supply more resistance. 
         [0049]      FIGS. 3A and 3B  show the exercise machine  20  with a user operating the machine in two different training modes—back extension (erector spinae muscles) and flexion (abdominal muscles). For strengthening the oblique muscles the positioning is the same as in  FIG. 3B  for the rectus abdominus, but the user turns his/her body at an angle between 0-90 degrees. The user switches between the two primary modes of operation by moving a seat  100  into two different positions over the fixed housing  60  in order to displace the axis of rotation of the user&#39;s hips in relationship to the machine&#39;s axis of rotation.  FIGS. 3A and 3B  indicate the different centers of hip rotation, the former essentially directly above the centerline C/L of the horizontal bar  40  and the latter shifted horizontally to one side. This conversion enables a more biomechanically correct position when strengthening the abdominal and erector spinae muscles. Although not shown in  FIGS. 3A and 3B , a seat belt  101  ( FIG. 2 ) fixed under the seat  100  may be provided and utilized in either exercise mode to help isolate the targeted muscles and prevent the recruitment of undesired muscles. 
         [0050]      FIG. 1A  and also  FIGS. 4A and 4B  (looking from the direction opposite to  FIGS. 3A and 3B ) show a short square post  102  welded to the fixed housing  60  at a slight angle to the vertical, preferably between about 5-15°, and more preferably about 8°.  FIG. 4C  shows the seat  100  isolated and two square mounting tubes  104 ,  106  projecting downward therefrom at angles from the vertical, α and β, which are preferably the same (α=β). In  FIGS. 3A and 4A  a first mounting tube  106  engages the square post  102  such that the seat  100  assumes an angle θ with the horizontal, which is preferred for the back extension exercises. The angle θ is desirably between about 15-20°, and more preferably is about 16°. Conversely, as seen in  FIGS. 3B and 4B , the second mounting tube  104  engages the square post  102 . In this configuration, the seat  100  is horizontal, or within about 5° of horizontal, which is preferred for the abdominal exercises. Therefore, the angle β is approximately the same as the angle at which the square post  102  extends up, which is between about 5-15°, and more preferably about 8°. Also, the angle α plus the angle at which the square post  102  extends upward (preferably about 8°) together make up the angle θ that the seat makes in the back extension position. Therefore, since in the preferred embodiment the angles α=β, and β is preferably about 8°, in a preferred embodiment the angle θ equals about 16°. 
         [0051]      FIG. 5  shows the exemplary exercise machine  20  partly collapsed, and  FIG. 6  shows the exercise machine fully collapsed. Collapsed, the exercise machine  20  will be no more than 8″ tall and preferably 7″ or less, and thus will be able to fit under most beds. The lever arm  42  can be rotated to lie substantially horizontally by disengaging the spring-mounted adjustment pin  74  from the adjustment holes  70  in the indexing plate  68 . Also, the gas spring  95  can be pivoted down to horizontal about its lower pivot point by disengaging the spring-loaded adjustment pin  94  in the bracket  86  from the adjustment holes  84  in the curved bar  82 . Collapse of the upper components of the machine  20  over the base  24  is explained below. 
         [0052]    Advantageously, the exercise machine  20  can be adjusted to the leg height of the user to allow for optimum biomechanics and reduce the risk of injury.  FIGS. 7A and 7B  are assembled and exploded views, respectively, of a lower height adjustment assembly. The vertical leg  22  is supported on and by the central longitudinal bar  26  of the base  24 . An upwardly-opening square hole  110  is formed in the middle of the bar  26  into which fits a reduced-size lower end section  112  of the vertical leg  22 . The end section  112  has a reduced size relative to the rest of the leg  22  and passes through a height adjustment collar  114  positioned just above the bar  26 . The end section  112  has a series of vertically-spaced holes  116  that register with a single hole  118  in the collar  114  such that a pin  120  can fix their relative positions. Removing the pin  120  and shifting the vertical leg  22  up or down enables adjustment of the height of the components of the machine  20  above the base  24 . This enables adjustment of the height of the seat  100  for different sizes of users, and also maintains the relative position between the seat  100  and the centerline C/L of the horizontal bar  40 , which allows for optimum biomechanics, as seen in  FIG. 2 . This enables height adjustment without lengthening the lever arm and altering the resistance profile. Desirably, the height of the upper frame can be adjusted at least about 2 inches, and more preferably between 2-4 inches. 
         [0053]    For the purpose of collapsing the machine  20 , the vertical leg  22  is easily disengaged from the base  24  by virtue of the adjustment collar  114 . More specifically, the collar  114  has a pair of longitudinal flanges  122  spaced apart about the same lateral width as the lower base bar  26 , and flanking the same. Holes  123  in the flanges  122  line up with holes  124  in the bar  26 , and pins  126  extend through both flanges and the bar to secure the collar  114  in place. During collapse of the machine  20 , the pin  126  closest to the square hole  110  is removed allowing the upper structure to rotate about the other pin, as seen in  FIG. 5 . Eventually, the vertical leg  22  rotates to lie substantially horizontally over the lower bar  26 , as seen in  FIG. 6 . A small bumper or spacer  128  attaches to the leg  22  and extends horizontally in the direction opposite the gas spring mechanism. The spacer  128  contacts the base bar  26  when the machine collapses and the distance the spacer juts out from the leg  22  is sufficient to prevent contact between components of the horizontal bar  40  and the base  24 , as well as maintaining the generally horizontal low-profile orientation of the leg  22  when collapsed down. The spacer  128  is desirably elastomeric to reduce the noise when collapsing the structure and also to prevent marring the base bar  26 . 
         [0054]    Once the vertical leg  22  lies substantially horizontally over the lower bar  26 , the lever arm  42  rotates to lie substantially horizontally as well, as does the gas spring  95 , as shown.  FIG. 2  illustrates how these components are offset laterally from one another so as to avoid interfering with their respective collapse. The seat belts  101  may be used to wrap around the entire structure to hold the components generally together, or a separate band or strap may be provided for this purpose. 
         [0055]      FIGS. 8-11  schematically illustrate an alternative collapsible exercise machine  220  similar to that shown in  FIGS. 1-7 , but with several small differences. The exercise machine  220  again features an upper frame having a generally vertical leg  222  supported on and by a horizontal H-shaped base  224 . The upper frame includes an adjustable lever arm  242  that is mounted to rotate with a horizontal bar (not shown) as described above. The angle of the lever arm  242  can be adjusted by moving a pin  244  between an array of holes  246  provided in an indexing plate  248  (see  FIG. 8B ). A horizontal force application bar  250  preferably covered with a foam pad  252  attaches firmly to the top of the lever arm  242  and extends laterally back over the horizontal bar and over a seat  254 , preferably as far as the vertical leg  222 . As with the first embodiment, a user can rotate the force application bar  250  and lever arm  242  about an axis centered along the horizontal bar. The center line C/L of the horizontal bar  240  defines the axis of rotation of the lever arm  242 . 
         [0056]    The lever arm  242  is rotationally fixed with respect to a force adjustment bar  260  that depends downward below the seat  254  having a plurality of adjustment holes along its length. An upper end of a gas spring  262  fastens to one of the adjusted holes using a pin or nut and bolt  264 . A lower end of the gas spring  262  is pivotally connected via a pin or nut and bolt  266  to an upstanding post  268  on the base  224 . It can thus be seen the rotation of the lever arm  242  causes rotation of the force adjustment bar  260 , and the amount of resistance force imparted by the gas spring  262  depends on where the spring is connected along the bar. 
         [0057]      FIGS. 8A and 8B  illustrate the gas spring  262  attached to the distal end of the adjustment bar  260  so as to produce relatively high force resistance. Furthermore, the pin  244  is placed in one of the holes  246  in the indexing plate  248  so as to maximize the angle between the lever arm  242  and the force adjustment bar  260 . The lever arm  242  is adjusted to an obtuse angle  270  from the horizontal, so the user can sit on the seat  254  and perform back extension (erector spinae muscles) or flexion (abdominal muscles) exercises.  FIGS. 9A and 9B  illustrate the same configuration after the lever arm  242  is rotated to an acute angle  272 , thus fully compressing the gas spring  262 . The reader will understand that repositioning the lever arm  242  in a clockwise direction relative to the indexing plate  248  will increase the user&#39;s leverage and reduce the amount of force needed to rotate the lever arm  242 . Likewise, moving the upper end of the gas spring  262  along the adjustment bar  260  toward its axis of rotation (the same as the center line C/L) will reduce the moment arm and increase leverage. 
         [0058]      FIGS. 10A and 10B  again show the alternative exercise machine  220  with the gas spring  262  attached so as to produce greater leverage and relatively low force resistance. More particularly, the upper end of the gas spring  262  pivotally attaches to a hole in the force adjustment bar  260  closest to its axis of rotation. Also, the pin  244  has been moved clockwise along the holes in the indexing plate  248  to reduce the angle between the lever arm  242  and adjustment bar  260 . The lever arm  242  is shown at an obtuse angle  274  to the horizontal in  FIG. 11A . After clockwise rotation of the lever arm as seen in  FIG. 11B , the gas spring  262  is compressed, though not as far as in  FIGS. 9A and 9B . 
         [0059]      FIGS. 12-17  illustrate an alternative exercise machine  300  which is a plurality of support legs, in contrast to the single generally vertical leg  22  extending up from the base  24  in the earlier embodiments. Not only will multiple legs increase stability, but as will be shown the exercise machine  300  can easily collapse. Several features described above with regard to the first embodiment are not shown in the alternative exercise machine  300  for clarity, though such features could easily be included. 
         [0060]      FIGS. 12A and 12B  are perspective views of the exercise machine  300  wherein a seat  302  and lever arm  304  are supported by multiple legs  306 ,  308  over a base  310 . The base  310  includes a generally U-shaped member and two of the support legs  306  are pivotally mounted outside of the free ends thereof. The other two support legs  308  are pivotally mounted inside of the U-shaped base  310  and approximately halfway to the closed end thereof. As seen also in  FIGS. 13A-13D , upper ends of the legs  306 ,  308  are pivotally mounted to a generally square frame  312  under the seat  302 . Although not shown, the rotational position of each of the legs  306 ,  308  may be locked with respect to both the base  310  and the frame  312  via locking pins or the like. In the configuration of  FIGS. 12-13 , the legs  306 ,  308  are locked at 90° with respect to both the base  310  and the frame  312  such that the exercise machine  300  is in its upright and functional configuration. 
         [0061]    The lever arm  304  rotates as described earlier about a horizontal bar (not shown) mounted under one end of the seat  302 . The angle of the lever arm  304  with respect to the horizontal bar may be altered by moving a pin  320  within an array of holes in an indexing plate  322 . As seen best in  FIG. 13A , a force adjustment bar  324  depends down from the horizontal bar and has a series of holes therein. An upper end of a gas spring  326  pivotally attaches to one of the holes using a pin or nut and bolt combination. A lower end of the gas spring  326  pivotally attaches to a lower front corner of the base  310 , such as via a pivot rod  328  as seen in  FIGS. 12A and 12B . Aside from the multiple legs  306 ,  308 , the exercise machine  300  functions much like the earlier embodiment, wherein the amount of force may be adjusted as well as the angle of the lever arm  304 . 
         [0062]      FIG. 14A  illustrates an exemplary height H from the ground to the seat  302 . In a preferred embodiment, the height H is between 18-22 inches (45-56 cm), more preferably about 20 inches (50 cm). The length L of the frame  310  is between about 30-36 inches (76-91 cm), and more preferably about 34 inches (86 cm). 
         [0063]      FIGS. 14B-14C  are side elevational views of the multi-leg exercise machine  300  showing three steps preliminary to collapse thereof. First, the lever arm  304  is decoupled from the force resistance assembly by removing the pin  320  from the indexing plate  322 , as seen in  FIG. 14B . The lower end of the gas spring  326  is then detached from its pivot rod  328  ( FIG. 12A ) and both the lever arm  304  and gas spring are aligned horizontally, as in  FIG. 14C . Note the force adjustment bar  324  projecting out from under the seat  302 . 
         [0064]    Next, as seen in  FIGS. 15A and 15B , the force adjustment bar  324  is rotated about 180° underneath the seat  302 . By virtue of the fixed nature of the force assembly, this also rotates the indexing plate  322  from above to below the lever arm  304 .  FIG. 15B  shows an exemplary dimension of the height h from the top of the seat  302  to the lower edge of the indexing plate  322 . As will be seen, this height h defines the height to which the exercise machine  300  can be collapsed, and is desirably less than 8 inches (20 cm), and more preferably less than 7 inches (18 cm). In one embodiment, the height h is about 6.25 inches (16 cm). 
         [0065]      FIGS. 16A and 16B  are perspective and elevational views of the multi-leg exercise machine  300  in a state of partial collapse. The pivot points at the top and bottom of each leg  306 ,  308  are unlocked to enable this collapse. The outer legs  306  fold down on the outside of the frame  310 , and the inner legs  308  fold down on the inside thereof. 
         [0066]    Finally,  FIGS. 17A-17C  show the fully collapsed multi-leg exercise machine  300 . Again, by virtue of the laterally offset positions of the various components, as seen in  FIG. 13C and 13D , they all fold down to lie in essentially the same plane. A strap or bag may be provided to prevent the assembly from opening up, or the locking mechanism at the top and bottom of each leg  306 ,  308  may also secure them in their collapsed configuration. 
         [0067]    Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the scope of the invention, as hereinafter claimed.