Abstract:
A leg press exercise apparatus with composite motion movement combining a moving actuating member and a moving user support, the leg press having a support member, a frame on which the user support is located, the frame being pivotally connected to the support member, a truck in slidable engagement with the support member and the frame, an actuating member on which a push plate is located, the actuating member being pivotally connected to the support member and operatively connected to the truck, the actuating member being adapted to move between a first position and a second position, and a linking mechanism operatively connecting the actuating member the truck, wherein, when the user pushes the actuating member between the first position and the second position, the truck moves along rails on the support member, forcing the frame to pivot relative to the support member and causing the user to actuate a resistance weight, thus exercising certain of the user&#39;s muscles.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field. 
     This invention relates to the general technical field of exercise equipment and machines and to the more specific technical field of mechanically operated resistance exercise machines designed to strengthen certain leg muscles and muscle groups. 
     2. Prior Art. 
     Exercise equipment and machines are available in various configurations and for various purposes. Generally, exercise equipment and machines can be categorized into three broad categories: free weights, mechanically operated resistance machines, and electrically operated resistance machines. Mechanically operated resistance machines can be subcategorized into three broad categories: stack weight resistance operated, free weight resistance operated, and alternative resistance operated. Mechanically operated resistance machines are available for exercising and strengthening various individual muscles, muscle groups and combinations of muscle groups. 
     Exercise equipment and machines for exercising and strengthening the leg muscles commonly are called leg presses. There are two typical types of leg presses. The first typical leg press has a push plate that can move relative to a frame supporting a stationary seat or other user supporting means. The second typical leg press has a seat or other user supporting means that can move relative to a frame supporting a stationary push plate. Both types of leg presses can operate using a weight stack, free weights, user body weight or other resistance means to supply the desired amount of resistance for exercising the desired leg muscle or muscles. 
     In the first typical leg press, when the user pushes the push plate forward, the plate either travels on a linear path or, if hinged or pivoted, an arcuate path. Both linear and arcuate paths can induce incorrect biomechanical movement of the user&#39;s muscular-skeletal system, thereby causing undesirable stress in various areas of the user&#39;s body. In the second typical leg press, when the user pushes against the push plate, the seat or other user supporting means travels in a linear path. As already discussed, such a linear path can induce incorrect biomechanical movement of the user&#39;s body, resulting in undesirable stress in various areas of the user&#39;s body. 
     U.S. Pat. No. 4,149,714 to Lambert, Jr. discloses a seated weight lifting leg press exercise machine having a moving push plate and a stationary seat. Lambert &#39;714 is a typical example of a mechanical leg press using weight stacks. The user sits on the seat, bends his knees and places his feet on the push plate, and pushes the push plate by straightening his legs. The push plate travels in an arcuate path and is mechanically connected to a weight stack that can be adjusted to a desired weight. A variable radius cam causes the resistance from the weights to increase during the latter phase of the exercise. 
     U.S. Pat. No. 4,828,254 to Maag discloses a crank and slider/four-bar variable resistance carriage-type leg press machine having a stationary push plate and a moving seat. Maag &#39;254 is an atypical example of a mechanical leg press using free weights. The user stands on the push plate, bends her knees and places her back against a pad and her shoulders against shoulder pads, and pushes the shoulder pads by straightening her legs. The shoulder pads travel in a linear direction and are mechanically connected to a weight bar that can carry a desired amount of weight. A four-bar linkage causes the resistance from the weights to change during the course of the exercise. 
     U.S. Pat. No. 5,106,080 to Jones discloses a leg press exercise machine having a stationary seat and two moving push plates, one for each leg. Jones &#39;080 is a typical example of a mechanical leg press using free weights. The user sits on the seat, bends his knees and places each of his feet on one of the push plates, and pushes each push plate by straightening his respective legs. The push plates travel in arcuate paths and each comprise a weight bar that can carry a desired amount of weight. Separate push plates allow independent exercise of each leg. 
     U.S. Pat. No. 5,366,432 to Habing et al. discloses a leg press having a stationary seat and a moving push plate. Habing &#39;432 is a typical example of a mechanical leg press using a weight stack. The user sits on the seat, bends her knees and places her feet on the push plate, and pushes the push plate by straightening her legs. The push plate travels in a linear path and is mechanically connected to a weight stack that can be adjusted to a desired weight. A pulley and cable system causes the resistance from the weights to change during the course of the exercise. 
     U.S. Pat. No. 5,484,365 to Jones et al. discloses a leg press exercise machine having a stationary seat and a moving push plate. Jones &#39;365 is another typical example of a mechanical leg press using a weight stack. The user sits on the seat, bends his knees and places his feet on the push plate, and pushes the push plate by straightening his legs. The push plate travels in an arcuate path and is mechanically connected to a weight stack that can be adjusted to a desired weight. A parallel link system, a pair of weight stacks and a counterweight cause the need for overhead connections between the push plate and the weight stack and eliminate the slack inherent in cable systems. 
     U.S. Pat. No. 5,554,086 to Habing et al. discloses a leg press exercise apparatus having a stationary push plate and a moving seat. Habing &#39;086 is an atypical example of a mechanical leg press using a weight stack. The user sits on the seat, bends her knees and places her feet on the push plate, and pushes the seat by straightening her legs. The seat travels in an arcuate direction and is mechanically connected to a weight stack that can be adjusted to a desired weight. The Habing &#39;086 device is intended to be an add-on feature for a multi-station exercise machine. 
     U.S. Pat. No. 5,616,107 to Simonson discloses a method and apparatus for leg press exercise with counterbalance having a stationary seat and a moving push plate. Simonson &#39;107 is another typical example of a mechanical leg press using a weight stack. The user sits on the seat, bends his knees and places his feet on the push plate, and pushes the push plate by straightening his legs. The push plate travels in an arcuate path and is mechanically connected to a weight stack that can be adjusted to a desired weight. A counterweight counterbalances the inherent resistance of the leg press machine over the range of the exercise. 
     U.S. Pat. No. 5,795,270 to Woods et al. discloses a semi-recumbent arm and leg press and aerobic exercise apparatus having a stationary seat and a moving push plate. Woods &#39;270 is an atypical example of a mechanical press using air resistance. The user sits on the seat, bends her knees and places her feet on the push plate, and pushes the push plate by straightening her legs. Air resistance means are mechanically coupled to the push plate and are actuated by pushing the push plate. The user continuously pushes and releases the push plate, achieving both leg press and aerobic exercise. A similar mechanism also is included for exercising the upper body. 
     The previously described art comprises a general cross-section of the leg press art as it is today. As can be seen, individual apparatuses have either a stationary seat and a moving push plate or a moving seat and a stationary push plate, but not a combination. Further, individual apparatuses have either a linear travel path or an arcuate travel path, but not a combination or a path that more closely resembles the actual biomechanical path of the human body in motion. Individual apparatuses also either use weight stacks, free weights, user body weight or air resistance, or other single resistance mechanisms, and only a small number of apparatuses combine weight stacks or free weights with the user&#39;s body weight. 
     Thus it can be seen that a leg press exercise machine comprising a combination moving seat and moving push plate, an improved travel path more closely resembling the actual biomechanical path of the human leg in motion, and a combination resistance using weight stacks or free weights and the user&#39;s body weight would be useful, novel and not obvious, and a significant improvement over the prior art. It is to such leg press exercise machine that the current invention is directed. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a leg press that comprises a composite motion movement in which both the user support and the actuating member move. In the preferred embodiment, the leg press comprises both a moving user support and a moving actuating member. The user support, in this instance a backrest, is mounted on a frame that is pivotally connected to a support member and that rides upon a truck. The actuating member also is pivotally connected to the support member via a support bar that also is mechanically coupled to the truck. The truck rides upon rails that are an integral part of the support member. The frame further may comprise or may be mechanically coupled to a supplemental weight resistance means. 
     According to a preferred embodiment of the invention, the user support has a supine orientation and is located on the top side of the frame. The user support further comprises shoulder pads and hand grips at the head end that the user engages when operating the machine. The frame is pivotally coupled to the support member at the foot end. The frame pivots generally upward and downward in an arcuate path relative to the support member. Running along the length of the bottom side of the frame is one or more rail for engaging the truck. The shoulder pads and hand grips can be adjustable relative to the user support based on the size of the user. Supplemental weight resistance means can be coupled to the frame preferably at the head end. 
     The actuating member is located proximal to the foot end of the frame and is pivotally coupled to the support member. Typically, the actuating member is coupled to the support member at a location proximal to where the frame is coupled to the support member. The actuating member further comprises a push plate and a support bar for supporting the push plate on the support member and for operatively coupling the actuating member to the truck. The actuating member pivots generally horizontally in an arcuate path relative to the support member. The push plate can be adjustable relative to the support bar based on the size of the user. 
     The support member is a generally H-shaped component that lays flat on the floor or other supporting surface. The frame and actuating member are pivotally connected on or near a first side of the H. Both sides of the H provide stability for the machine. One or more rail for carrying the truck is or is located along a portion of the center portion of the H. 
     The truck is located between the frame and the support member and is slidably connected to both via the rails. The truck is a hinged component comprising a top portion pivotally hinged to a bottom portion. Top bearings located on the top portion of the truck cooperate with the rail or rails running along the bottom side of the frame, and bottom bearings located on the bottom portion of the truck cooperate with the rail or rails running along the center portion of the support member. The truck slides generally linearly along the rail or rails running along the center portion of the support member. The truck also is separately connected to the frame via a belt that travels through a pulley connected to the support bar of the actuating member. 
     In operation, the user lies supine on the user support, bends his or her knees to the proper angle and places his or her feet on the push plate. The push plate is adjusted up or down on the support bar to the proper height so that the user&#39;s feet are at an acceptable position on the push plate. The angle of the push plate also can be adjusted relative to the support bar. The shoulder pads can be adjusted forward or backward relative to the user support to the proper position to snugly engage the user&#39;s shoulders. The user then initiates the exercise motion by straightening his or her legs, forcing the push plate away from the user and the frame. 
     The exercise motion causes several actions. Pushing the push plate causes the actuating member to pivot about the connection between the support bar and the support member and to be forced away from the frame. The movement of the actuating member also moves the pulley, which is attached to the support bar, and acts upon the belt connecting the truck to the frame and traveling through the pulley. The truck is pulled along the rail or rails running along the center portion of the support member in the same general direction as the movement of the actuating member. The movement of the truck acts like a wedge between the frame and the support member and forces the frame to pivot about the connection between the frame and the support member, and the head end of the frame moves upwards and away from the support member. The hinge between the top portion of the truck and the bottom portion of the truck allows the top bearings to maintain smooth contact with the rail or rails running along the bottom side of the frame, and allows the bottom bearings to maintain smooth contact with the rail or rails running along the center portion of the support member. 
     Weight resistance is provided by the weight of the user, the weight of the frame and the weight of any supplemental resistance weights attached to the machine. The machine is capable of at least two separate exercise regimens. First, the user can exercise the upper leg muscles by repetitiously straightening the legs, forcing the actuating member from a first position proximal to the user to a second position distal from the user, and then bending the legs, allowing the actuating member to return from the second position to the first position. Second, the user can exercise the calf muscles by straightening the legs, forcing the actuating member from a first position proximal to the user to a second position distal from the user, holding the actuating member at the second position, and then repetitiously contracting and releasing the calf muscles thus pushing the actuating member an additional distance distal from the user. 
     The combined motion of the frame and the actuating member alters the biomechanical movement of the user&#39;s body to a composite motion somewhere between linear and a true arc, more closely resembling the accurate biomechanical motion of the human body. Additionally, this composite motion has the added advantage of helping the user&#39;s feet maintain continuous and more even contact with the push plate, rather than causing the user&#39;s feet to rotate forcing the balls of the feet or heels of the feet to have more or less contact with the push plate as in much of the prior art, thus reducing the overall stress to individual parts of the user&#39;s feet. Further, this composite motion has the added advantage of helping the user&#39;s back maintain continuous and more even contact with the user support, rather than causing the user&#39;s back to arch away from the user support as in much of the prior art, thus reducing the overall stress to individual parts of the user&#39;s back. 
     Thus, it is an object of the present invention to provide a leg press that allows the user to exercise certain muscles in a more biomechanically correct manner. 
     It is another object of the present invention to provide a leg press that efficiently exercises certain muscles. 
     It is another object of the present invention to provide a leg press that causes a reduced amount of stress on certain parts of the user&#39;s body that are not the primary focus of the exercise. 
     These objects, and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art when the following detailed description of the preferred embodiments is read in conjunction with the appended figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the leg press exercise machine shown in accordance with a preferred embodiment of the present invention at the first position of the exercise movement. 
     FIG. 2 is a side view of the leg press exercise machine shown in FIG. 1 at the second position of the exercise movement. 
     FIG. 3 is a side view of the support truck of the leg press exercise machine shown in FIG. 1 at the first position of the exercise movement. 
     FIG. 4 is a side view of the support truck of the leg press exercise machine shown in FIG. 1 at the second position of the exercise movement. 
     FIG. 5 is a top view of the support truck of the leg press exercise machine shown in FIG.  1 . 
     FIG. 6 is a front view of the leg press exercise machine shown in FIG.  1 . 
     FIG. 7 is a rear view of the leg press exercise machine shown in FIG.  1 . 
     FIG. 8 is a view of the drive mechanism for the leg press exercise machine shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1 through 8, in which like reference numerals represent like components throughout the several views, a leg press exercise machine  10  according to the preferred embodiment is shown. Machine  10  comprises both moving user support  20  and moving actuating member  14 . User support  20  is mounted on frame  12  that is pivotally connected to support member  16  and that rides upon truck  18 . Actuating member  14  also is pivotally connected to support member  16  via support bar  24  that also is mechanically coupled to truck  18 . Truck  18  rides upon base rails  70  that are an integral part of support member  16 . Frame  12  further may comprise or may be mechanically coupled to a supplemental weight resistance means  28 . FIGS. 1 and 2 show a side view of machine  10 , which comprises frame  12 , actuating member  14 , support member  16  and truck  18 . 
     Referring now to FIGS. 1 and 2, frame  12  is a generally hollow box-like structure comprising top side  30 , bottom side,  32 , left side  34 , right side  36 , head end  38  and foot end  40 . Frame  12  preferably is made of a number of heavy duty steel tubing sections  42  welded or bolted together to form the desired structure. Panels  44  can be inserted between adjacent sections  42  to form the respective sides. User support  20  is located on top side  30  and has a supine orientation. User support  20  further comprises shoulder pads  46  and hand grips  48  at the head end  38  that the user engages when operating the machine  10 . Shoulder pads  46  and hand grips  48  can be adjustable relative to user support  20  based on the size of the user. 
     Frame  12  is pivotally coupled to support member  16  at foot end  40  using frame rods  50  journaled into frame bearings  52 . As shown in FIGS. 1 and 2, the sections  42  making up bottom side  32  preferably are elongated in the direction of foot end  40 . As shown in more detail in FIG. 6, elongated sections  56  provide the pivotal connection between frame  12  and support member  16  using frame rods  50  and frame bearings  52 . Frame  12  pivots generally upward and downward relative to support member  16  from a first position shown in FIG. 1 to a second position shown in FIG.  2 . Frame  12  travels in arcuate path F about the centerline between frame bearings  52 . 
     Running along the length of bottom side  32  of frame  12  are frame rails  54  for engaging truck  18 . Rails  54  preferably are elongated steel cylinders securely attached to bottom side  32 . If two rails  54  are used, one rail  54  is located on bottom side  32  proximal to left side  34 , and another rail  54  is located on bottom side  32  proximal to right side  36 . As shown in more detail in FIG. 7, rails  54  are generally coextensive with the length of bottom side  32 . 
     Supplemental weight resistance means  28  can be coupled to frame  12  preferably at head end  38 . As shown in FIGS. 1 and 2, supplemental weight resistance means  28  can be free weight support rods  58  extending outwardly from head end  38 . Alternatively, free weight support rods  58  may extend outwardly from left side and right side instead of or in addition to from head end  38 . Although two free weight support rods  58  are shown, the number of free weight support rods is variable. There are many alternatives for supplemental weight resistance means  28  including linkages to weight stacks (not shown), air resistance devices (not shown), elastomeric or tension devices (not shown), compression devices (not shown), gas cylinders (not shown), and hydraulic cylinders (not shown). 
     Actuating member  14  is located proximal to foot end  40  of frame  12  and is pivotally coupled to support member  16 . Preferably, actuating member  14  is coupled to support member  16  at a location proximal to where frame  12  is coupled to support member  16 . Actuating member  14  comprises push plate  22  and support bar  24  for supporting push plate  22  on support member  16  and for coupling actuating member  14  to truck  18 . Actuating member  14  pivots generally horizontally in arcuate path P relative to support member  16 . Push plate  22  can be adjustable relative to support bar  24  based on the size of the user. As shown in FIGS. 1 and 2, support bar  24  preferably is an angled component in the preferred embodiment. This is for practical purposes in that the angle allows more range of motion for the exercise and properly positions the user&#39;s feet on the push plate  22  relative to the user&#39;s position on the user support  20 . Additionally, the angle in support bar  24  can provide additional room between frame  12  and actuating member  14  to accommodate both the user&#39;s legs and the pulley system described later. Alternatively, support bar  24  can be straight or curved. 
     Actuating member  14  is pivotally coupled to support member  16  using member rods  60  journaled into member bearings  62 . As shown in more detail in FIG. 6, the lower end of support bar  24  provides the pivotal connection between actuating member  14  and support member  16  using member rods  60  and member bearings  62 . Actuating member  14  pivots relative to support member  16  from a first position shown in FIG. 1 to a second position shown in FIG.  2 . Actuating member  14  travels in arcuate path P about the centerline between member bearings  62 . 
     Support member  16  is a generally H-shaped component that lays flat on the floor or other supporting surface. Frame  12  and actuating member  14  are pivotally connected on or near a first side  64  of support member  16 . Both first side  64  and second side  66  of support member  16  provide stability for the machine  10 . One or more base rail  70  for carrying truck  18  is or is located along a portion of the center portion  68  of support member  16 . As shown in more detail in FIG. 7, base rail extends generally along the length of center portion  68  of support member  16 . 
     As shown in more detail in FIG. 6, in the preferred embodiment, frame bearings  52  and member bearings  62  are mounted on first side  64  of support member  16 . Also in the preferred embodiment, the centerlines of frame bearings  52  and member bearings  62  are collinear, allowing both frame  12  and actuating member  14  to pivot about the same axis. Support member  16  also may have extension  72  extending from first side  64  collinearly with center portion  68 . As an alternative, member bearings  62  may be located on extension  72 . In this situation, the centerlines of frame bearings  52  and member bearings  62  are not collinear, and frame  12  and actuating member  14  do not pivot about the same axis. Additionally, extension  72  can comprise actuating member stop  74  for delineating the farthest extent actuating member  14  may travel. 
     Truck  18  is located between frame  12  and support member  16  and is slidably connected to frame  12  by frame rails  54  and to support member  16  by base rail  70 . As shown in more detail in FIGS. 3 through 5, truck  18  is a hinged component comprising a top portion  76  pivotally hinged to a bottom portion  78 . Frame or top bearings  80  located on top portion  76  of truck  18  cooperate with frame rails  54  running along bottom side  32  of frame  12 , and base or bottom bearings  82  located on bottom portion  78  of truck  18  cooperate with base rail  70  running along center portion  68  of support member  16 . Truck  18  slides generally linearly along path T along base rail  70  from a first position as shown in FIGS. 1 and 3 to a second position as shown in FIGS. 2 and 4. Truck  18  also is separately connected to frame  12  by belt  84  that travels through pulley  86  connected to support bar  24  of actuating member  14 . 
     As truck  18  is pulled along path T by the movement of actuating member  14 , truck  18  acts analogously to a wedge between frame  12  and support member  16 . When pressure is applied to push plate  22 , truck  18  is pulled by actuating member  14  from the first position shown in FIGS. 1 and 3 to the second position shown in FIGS. 2 and 4 forcing frame  12  to pivot upwards along path F. When pressure is released from push plate  22 , truck  18  is forced by the weight of frame  12 , as well as the weight of the user and any resistance weights coupled with frame  12 , from the second position shown in FIGS. 2 and 4 to the first position shown in FIGS. 1 and 3. As frame  12  pivots relative to support member  16 , the angle a between frame  12  and support member  16  changes. Hinge  88  allows top portion  76  to rotate relative to bottom portion  78  as truck  18  moves from the first position to the second position such that the angle between top portion  76  and bottom portion  78  matches angle a. 
     Truck  18  is operatively coupled to actuating member  14 . Although truck  18  can be operatively coupled directly to actuating member  14 , it is preferred that truck  18  be coupled directly to frame  12  and coupled indirectly to actuating member  14 . The preferred coupling mechanism is shown in more detail in FIGS. 5,  6  and  8 . A first end of belt  84  is securely attached to truck  18 , preferably with a first clamp  90 . Belt  84  then passes over pulley  86  that is mounted on actuating member  14 , preferably on support bar  24 . A second end of belt  84  is securely attached to frame  12 , preferably with a second clamp  92 . Pressure on actuating member  14  away from frame  12  causes tension in belt  84 , pulling truck  18  along path T towards actuating member  14 . Additionally, pressure on actuating member  14  away from frame  12  causes tension in belt  84 , pulling frame  12 . The combined pulling of truck  18  and frame  12  causes frame  12  to rotate about path F. Although a belt and pulley linking mechanism is described as the preferred embodiment, alternatives are suitable. For example, the belt can be of any known structure, such as steel cables, wound cables, wire, polymer tows, carbon fiber, tension devices, bar linkages, and elastomers. Likewise, the pulley can be any direction changing device, such as gears, Teflon® or other slippery material rods, and elbow-shaped components. Both clamps  90 ,  92  can be pivotally connected to truck  18  and actuating member  14 , respectively, such that as machine  10  moves through its range of motion, belt  84  and clamps  90 ,  92  can pivot, reducing stress on belt  84 . 
     In operation, the user lies supine on the user support  20 , bends his or her knees to the proper angle and places his or her feet on push plate  22 . Push plate  22 , if adjustable, can be adjusted up or down on support bar  24  to the proper height and/or angled forward or backward relative to support bar  24 , so that the user&#39;s feet are at an acceptable position on push plate  22 . Shoulder pads  46  and hand grips  48  can be adjusted forward or backward relative to user support  20  to the proper position to snugly engage the user&#39;s shoulders. The user then initiates the exercise motion by straightening his or her legs, forcing push plate  22 , and thus actuating member  14 , from the first position proximal to the user and frame  12  to the second position distal from the user and frame  12 . 
     The exercise motion causes several actions. Pushing push plate  22  causes actuating member  14  to pivot about the connection between support bar  24  and support member  16  and to be forced away from frame  12 . The movement of actuating member  14  also moves pulley  86 , which is attached to support bar  24 , and acts upon belt  84  connecting truck  18  to frame  12  and traveling through pulley  86 . Truck  18  is pulled along the base rail  70  running along center portion  68  of support member  16  in the same general direction T as the movement P of actuating member  14 . The movement T of truck  18  acts analogously to a wedge between frame  12  and support member  16  and forces frame  12  to pivot about the connection between frame  12  and support member  16 , and head end  38  of frame  12  moves upwards and away from support member  16  along path F. Further, because belt  84  preferably is connected to frame  12 , the action of pushing actuating member  14  assists in causing frame  12  to travel in arcuate path F. Hinge  88  between top portion  76  of truck  18  and bottom portion  78  of truck  18  allows top bearings  80  to maintain smooth contact with frame rails  54  running along bottom side  32  of frame  12 , and allows bottom bearings  82  to maintain smooth contact with the base rail  70  running along center portion  68  of support member  16 . 
     Various supplemental weight resistance means  28  can be used to provide resistance weight for the machine  10 . If the user so chooses, the user does not have to add any supplemental weight resistance means  28  to the machine  10  and in this situation the resistive force will be the weight of frame  12  and the weight of the user. The user can place free weights on free weight support rods  58  to increase the resistive force. In an alternative embodiment, a weight stack or other supplemental weight resistance means  28  is attached to the machine  10 , by cables, linkages or other coupling means (not shown). 
     An optional locking mechanism (not shown) can be included on machine  10 . Preferably, locking mechanism holds machine at an intermediate position between the first position as shown in FIG.  1  and the second position as shown in FIG.  2 . Such a locking mechanism is for convenience reasons. By holding machine  10  in an intermediate position, ingress and egress to machine by the user is simplified, adding to the convenience of machine. 
     The combined motion, or composite motion movement, of user support  20  and actuating member  14  alters the biomechanical movement of the user&#39;s body to a composite motion somewhere between linear and a true arc, more closely resembling the accurate biomechanical motion of the human body. Additionally, this composite motion has the added advantage of helping the user&#39;s feet maintain continuous and more even contact with push plate  22 , rather than causing the user&#39;s feet to rotate forcing the balls of the feet or heels of the feet to have more or less contact with push plate  22 , thus reducing the overall stress to individual parts of the user&#39;s feet. Further, this composite motion has the added advantage of helping the user&#39;s back maintain continuous and more even contact with user support  20 , rather than causing the user&#39;s back to arch away from user support  20 , thus reducing the overall stress to individual parts of the user&#39;s back. 
     While the invention has been described in connection with certain preferred embodiments, it is not intended to limit the spirit or scope of the invention to the particular forms set forth, but is intended to cover such alternatives, modifications, and equivalents as may be included within the true spirit and scope of the invention as defined by the appended claims.