Abstract:
An exercise device for simulation of the action familiar to “tire flipping” is provided, having a base frame with a rail, a carriage including a pair of supports and a guide arm coupled to the base frame and the carriage. The guide arm allows guided rotational displacement of the carriage relative to the base frame with the carriage also being supported by at least one support received by the rail of the base frame at all time. One or more weight horns may be used to add additional mass to the carriage. A brake may be used to control the downward movement of the carriage after the carriage is actuated over vertical by a user or a lift that is “missed” causing the carriage to be safely lowered to a starting position.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to exercise devices and, more particularly, to exercise devices adapted to simulate rotational displacement of a vehicle tire or similar object. 
     BACKGROUND OF THE INVENTION 
     Physical exercise has become a valuable part of everyday life. This is especially true regarding athletics. Athletes are constantly looking for an edge in an increasingly competitive environment. Success on the playing field or court may mean an athletic scholarship resulting in a paid college education or a career in the professional ranks. Training techniques may be inspired by different activities. Once such activity is the “Strong Man” competitions. In these, a variety of functional strength movements are used to test the strength and muscular endurance of athletes. One example is “tire flipping”. This involves a large truck or tractor tire and a wide open space such as a parking lot or field. The athlete flips the tire by picking up one end of the tire rotating, it to be positioned on the tread and then flipping it over back to the ground. 
     As primitive an activity as this may sound, it has many advantages. Tires can weigh as much as 1000 pounds, so with a heavy tire, flipping is no trivial task. The movement starts with a driving dead lift from at or near ground level. As the tire is rotated up, the center of gravity of the tire moves closer to the pivot (ground contact positioned away from the user) thereby reducing the load on the athlete. This corresponds to the biomechanics of the athlete as the end movement is a combination bench press/military press where the athlete is less strong compared to the initial part of the lift. Movement from the ground to a throwing movement with the entire body extended follows the body&#39;s strength capacity and therefore may be an extremely effective exercise. 
     One of the disadvantages with the current technology is that the tire must be used outdoors, so weather may be an issue. Tire flipping is not conducive to use in a weight room setting due to space and safety issues of a heavy tire being thrown around. The tire weight is also a disadvantage. The process of progressive resistance is difficult to achieve with a tire as it is very difficult to add or subtract weight from a tire. If multiple tires are used, this adds to the storage space required. For desirable incremental loading of 10-20 pounds where a range of 500 to 1000 pound tires were used, the strength and conditioning coach would need to store and maintain up to 50 different weight tires. This makes tire flipping as a mode of highly efficient training impractical, if not impossible, for most individuals and institutions. 
     It should, therefore, be appreciated that there is a need for an exercise device that simulates the action of tire flipping and can be safely used in a confined environment such as a weight room and may alter the resistance of the device. The present invention fulfills this need and others. 
     SUMMARY OF THE INVENTION 
     The present invention provides an exercise device incorporating a base frame including a rail, a carriage including a pair of non-collinear supports moveably mounted to the carriage and a guide arm coupled to the base frame and the carriage enabling rotational displacement of the carriage relative to the base frame with at least one support received by the rail at all time. The supports may include wheels, bearings or rollers or any other structure capable of displacement under load bearing conditions. 
     In an embodiment of the invention, the carriage may include one or more weight horns adapted to receive weight plates. Two non-collinear weight horns may be used that are equally spaced from the center of mass of the carriage. The weight horns may be spaced such that with evenly distributed mass added to the carriage, the mass moment of inertia of the carriage and added mass is approximately equal to that of a tire or represented by the equation:
 
M/2*(L/2−5) 2 +(L/2) 2  
 
     where “M” is the combined mass of the carriage with the added mass, and “L” is the length from a support to an end of the carriage. It may be the spacing of the horns would be between twenty-four and forty-six inches and more specifically between thirty-two and thirty-four inches apart for the mass moment of inertia of the system to approximate that as noted above. 
     A brake, such as a hydraulic damper may be coupled to the guide arm and supported by the base frame thereby enabling controlled downward movement of the guide arm and carriage relative to the base frame. The brake may be coupled to the base frame or coupled to a brake arm that is movably mounted to the base frame. A spring may be used to bias the brake to a position where the guide arm is elevated relative to the base frame. 
     A rear fit brake may be used to control the rotation of the carriage. The rear lift brake may be coupled to a rear portion of the base frame and adapted to engage a support on the carriage prior to contact with the rail of the base frame. Another system may be used to control the rotation of the carriage including a support gate with an ear moveably coupled to the base frame and adjacent to the rail. The ear in a first position restricts vertical displacement of the support on the carriage and in a second position the ear enables vertical displacement of the support and therefore the carriage. 
     An exemplary method for exercising according to the invention, for use with an exercise device as disclosed herein, includes the steps of a user grasping the first end of the carriage, lifting the first end of the carriage and displacing the carriage to past the vertical position and allowing the carriage to be guided by the rail and guide arm to present a second end of the carriage to the user. 
     For purposes of summarizing the invention and the advantages achieved over the prior art, certain advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such advantages can be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention can be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following description of the preferred embodiments and drawings, the invention not being limited to any particular preferred embodiment(s) disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which: 
         FIG. 1  is an isometric view of an exercise device incorporating a guided rotational capability in accordance with the present invention. 
         FIG. 2  is an isometric view of the device of  FIG. 1  in a partially actuated position. 
         FIG. 3  is an isometric view of the device of  FIG. 1  with the carriage in an elevated position, past that shown in  FIG. 2 . 
         FIG. 4  is an isometric view of the device of  FIG. 1  with the carriage rotated past that of  FIG. 3 . 
         FIG. 5  is an isometric view of the device of  FIG. 1  with the carriage back to a starting position. 
         FIG. 6  is an isometric view of an exercise device incorporating a guided rotational capacity in accordance with the present invention with a raised rear lift used to prevent over rotation of the carriage. 
         FIG. 7  is an isometric view of the exercise device of  FIG. 6  with a lowered rear lift used to prevent over rotating of the carriage. 
         FIG. 8  is an isometric view of an exercise device incorporating a guided rotational capability in accordance with the present invention and a support gate to prevent over rotation of the carriage. 
         FIG. 9  is a cut away, detail of the front section showing the support gate, the detail cut across line  9 - 9  in  FIG. 8 . 
         FIG. 10  is a side view of the action of the support gate as the support roller on the carriage approaches the gate. 
         FIG. 11  is a side view of the action of the support gate as the support roller contacts and displaces the gate. 
         FIG. 12  is a side view of the action of the support gate as the support roller passes through the gate letting it fall into its relaxed position. 
         FIG. 13  is a side view of the action of the support gate as the support roller and carriage are allowed vertical movement. 
         FIG. 14  is an isometric view of an exercise device incorporating a guided rotational capability in accordance with the present invention and including a brake arm coupled to the base frame. 
         FIG. 15  is a detailed view of the brake arm shown in  FIG. 14  and cut along line  15 - 15 . 
         FIG. 16  is a partial view of the exercise device of  FIG. 14  showing the brake arm elevated off the stop on the base frame. 
         FIG. 17  is a schematic view of a simulation of a tire showing the Prior Art. 
         FIG. 18  is a top view of a carriage of the invention with weight plates received thereon illustrating a dimensional relationship relative to the Prior Art. 
         FIG. 19  is a graph depicting a calculated relationship between a distance between the weight horns and the length of an exercise device in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the illustrative drawings, and particularly to  FIG. 1 , there is shown an exercise device  40  adapted to simulate rotation or “flipping” of a tire or similar object. In this figure the device  40  is as it would be positioned ready to be used. A base frame  42  includes two rails  44 , one on each side of the base frame  42 . A single rail  44  in the center of the base frame could be used, but for illustrative purposes, a two rail  44  design is shown throughout this disclosure. The rails  44  have a hollow interior  46  to allow a support  48  mounted on a carriage  50  to be received therein. In this embodiment the supports  48  are shown as rollers or wheels rotatably mounted to the carriage  50 . This is only one embodiment of the supports  48  and may be comprised of any number of components such as wheels, bearings and rollers capable of supporting the carriage  50 , as will be further illustrated. The carriage  50  may also include a lifting platform  52  on each end, suitable for grasping and pushing against to move the carriage  50  relative to the base frame  42 . Weight horns  54  may also be added to the carriage  50  to facilitate adding mass to the carriage  50 . 
     A guide arm  56  may have a first end pivotally coupled to the base frame  42  at a first axis  58  and a second end pivotally coupled to the carriage  50  at a second axis  60 . The second axis  60  may be positioned at or near the center of mass of the carriage  50 . A brake  62  may be used to slow the decent of carriage  50  relative to the base frame  42 , as will be explained in more detail later in the disclosure. The brake  62  may take any number of forms. Here, a hydraulic damper or any cylinder capable of offering a resistance to compression is an example of what may be used. In this embodiment, the brake  62  has a cylinder end that may be pivotally coupled to the base frame  42  at a cylinder axis  64  and a rod end which may be pivotally coupled to each guide arm  56  at a rod axis  66 . If a compression only hydraulic damper is used for each brake  62 , the brake  62  will extend with minimal resistance as the guide arms  56  are elevated. As the guide arms  56  are allowed to lower, the brakes  62  limit the velocity as the guide arms  56  and carriage  50  and allow them to safely lower into the position shown. 
     With reference to  FIG. 2 , the device of  FIG. 1  is shown with the addition of weight plates  68  positioned on the weight horns  54  and the carriage  50  raised as it would be during use. Spring clips  69  or any other removable lock may be used to secure the weight plates  68  on the weight horns  54 . To move the carriage  50 , a user may stand on the platform  70  of the base frame  42  and grasp the lifting platform  52  or the lifting handle  72  of the carriage  50  and pull upward. The guide arms  56  may provide an arcuate or alternate path of travel for the center of the carriage  50 . The supports  48  at the rear of the device  40  are drawn forward, toward the user and guided by the rails  44 . The weight plates  68  offer additional resistance to the user and the addition of removal of weight plates  68  allows the device  40  to be easily customized for any strength or condition of athlete. If the user “misses” a lift, and thereby drops the carriage  50 , the brakes  62  will provide a controlled decent of the guide arms  56  and the carriage  50  coupled to the guide arms  56 , thereby greatly reducing the chances of injury to the athlete. 
     In this form of the invention and throughout the disclosure the guide arms  56  are shown to be pivotally coupled to the base frame  42 . The purpose of the guide arms  56  is to guide the movement of the carriage  50  as it is lifted from the base frame  42 . An alternative would be a linear or curvilinear track coupled to the base frame  42  and a roller or other guide member received therein and mounted to the carriage  50  at or near the second axis  60  of the carriage  50 . The guide arms  56  pivotally coupled to the base frame  42  and the carriage  50  is considered a preferable design and is shown throughout this disclosure, but it is understood that a suitable alternative system could be produced in the manner described. 
     With reference to  FIGS. 3-5  and starting with  FIG. 3 , the carriage  50  is now elevated to a substantially vertical position relative to the base frame  42 , the displacement of the carriage  50  is illustrated by the arrow  74 . At this point the user may still be standing on the platform  70  of the base frame  42  with their hands pushing against the lifting platform  52 . The user may explosively “throw” the carriage  50  away from their body by rapidly extending their arms and legs. The guide arms  56  are elevated to their highest position relative to the base frame  42  and the brakes  62  are likewise extended. The result of this action by the user is illustrated in  FIG. 4 . The arrow  76  depicts the rotation of the carriage  50  relative to the base frame  42 . The guide arms  56  allow a controlled and guided lowering or descent of the carriage  50  with the assistance of the brakes  62 . The supports  48  nearest the platform  70  (and user thereon) are supported within the hollow interior  46  of the rails  44 . During this phase, the user recovers and prepares for the next lift as the lifting platform  52  that was opposite the lifter, travels to a position in preparation to now be lifted. This is shown in  FIG. 5 , where the guided rotation of the carriage  50  provides the lifting platform  52  to again be positioned adjacent to the platform  70  and therefore the user, the carriage  50  is ready to be lifted again. 
     In the event that one weight horn  54  is loaded with more weight plates  68  than the other weight horn  54  an “over rotation” condition may exist. This is when the weight horn  54  farthest away from the platform  70  is loaded heavier than the weight horn  54  closer to the platform  70  while the carriage  50  is descending to the base frame  42 . This condition is illustrated in  FIG. 6 . A total of four weight plates  68  on the weight horn  54  positioned away from the platform  70  and only two weight plates  68  are on the weight horn  54  nearest the platform  70 . The load of the carriage  50  with the added weight plates  68  are again supported by the brakes  62  and the guide arms  56  are rotatably coupled to the carriage  50  at the center of mass of the unloaded carriage  50 . Any off balanced mass creates an eccentric load, which is countered by a reaction force of the rails  44  against the supports  48  which are closest to the platform  70 . 
     The rails  44  may include a front void  78  to allow the supports  48  to exit the rails  44  when lifted by the user. Also, a rear void  80  may be added to the rails  44  to allow a descending support  48  access to be received by the rail  44 . The existence of the front void  78  in the conditions shown in  FIG. 6  presents an issue to be addressed. The greater mass due to the four weight plates  68  away from the platform  70  means the supports  48  near the platform  70  will be contacting the upper flange of the rail  44  as opposed to the lower flange in order to counteract the moment caused by the eccentric load in the carriage  50 . When the support  48  approaches the front void  78  in this situation, the carriage  50  would possibly abruptly rotate up, in the direction of a user positioned on the platform  70 . As the brake  62  lowered the carriage  50  it would eventually right itself but any sudden movement toward a user may be a potential for concern. 
     Two solutions to this have been developed and are shown here. The first is shown in  FIG. 6  and  FIG. 7  as a rear lift brake  82 , one on each side of the base frame  42 . In this embodiment the rear lift brake  82  is comprised of an arm  84  with an arm catch  86  on one end. The arm catch  86  may be positioned so as to receive the elevated supports  48  as the front supports  48  approach the front void  78 . The arm  84  may be movably mounted on the base frame  42  so as to allow the carriage  50  to be smoothly lowered to a resting position with the rear supports  48  received in the respective rails  44  as is shown in  FIG. 7  and illustrated by the arrow  88 . The resistance to downward movement and therefore the offset to the rotation of the carriage  50  may be provided by the shock absorber  90  with one end mounted to the arm  84  or arm catch  86  of the rear lift brake  82  and the other end of the shock absorber  90  mounted to the base frame  42 . A spring or other method of storing energy may be used to extend the shock  90  and therefore the rear lift brake  82 , as the support  48  moves off the arm catch  86  when the carriage is again lifted by the user. This spring may be enclosed within the shock absorber  90 , as illustrated here, or it may be an element external to the structure of the shock absorber  90 . This will cause the rear lift brake  82  to extend to the position shown in  FIG. 6  ready to receive the carriage  50  on the next repetition. 
     With reference to  FIGS. 8-13 , another embodiment of the invention with features intended to offset “over rotation” of the carriage  50  is presented. In  FIG. 8  the device  40  is shown again in a “resting” state ready for a user to begin a movement by lifting the carriage  50 . The weight horn  54  in the rear (away from the platform  70 ) has again been loaded with more weight plates  68  than is loaded on the front weight horn  54  to again illustrate the “over rotation” condition that would have been evident just prior to contact of the supports  48  positioned away from the platform  70  with the rails  44  of the base frame  42 . In  FIG. 9  a cut away is shown along line  9 - 9  in  FIG. 8  showing a front support  48  positioned in the rail  44  adjacent to the front void  78 . For illustrative purposes, the frame of the carriage  50  has been removed in  FIG. 9  with the front axle  92  remaining. In  FIG. 9  a support gate  94  is shown. The gate  94  may include an ear  96  movably coupled to the base frame  42  and as illustrated here pivotally mounted to the rail  44  about axis  98 . An embodiment of the support gate  94  is sequentially shown in operation in  FIGS. 10-13 . 
     In  FIG. 10  a partial view of a front portion of the carriage  50  including a support  48  is shown as the support  48  is moving along the rail  44  toward the front of the device  40  ( FIG. 8 ) and the support gate  94 . This movement is illustrated by the arrows  100 . As previously disclosed, this direction of movement of the support  48  happens as the rear of the carriage  50  is descending toward the rail  44  so as to be readied for the next lift. In this position, the support  48  has not yet contacted the ear  96  of the support gate  94 . As such, the ear  96  is positioned in its resting position with the ear  96  extending into the hollow interior  46  of the rail  44 . As shown in  FIG. 8 , the weight horn  54  at the rear of the carriage  50  has received more weight plates  68  than the front weight horns  54 , thus producing a condition for “over rotation” of the carriage  50  as the support  48  reaches the front void  78  in the rail  44 . As such, in  FIG. 10  the support  48  is shown to be contacting the upper flange  102  of the rail  44 . 
     As the support  48  moves further forward, as would happen as the carriage  50  continues to drop down, the support  48  may contact and displace the ear  96  of the support gate  94  up until the ear  96  hits an ear stop  104 . This may substantially align the lower surface of the ear  96  with the upper edge  102  of the rail  44 . This, in essence, temporarily extends the upper flange  102  of the rail  44  and temporarily reduces the size of the front void  78 . 
     In  FIG. 12 , the support  48  is shown to continue to move in the direction of the arrow  100 . Movement may continue to where the carriage  50  would be in a resting position to where the support  48  at the rear of the device  40  is also seated in the rail (as in  FIG. 8 ). At this point,  FIG. 12  illustrates the support  48  passing by the ear  96  of the support gate  94  so as to allow the ear  96  to fall back into the hollow interior  46  of the rail  44  as shown by arrow  106 . This provides a sufficient gap as the original front void  78  dimensions have been restored and the support  48  is now able to be vertically displaced for another repetition, as depicted by the vertical arrow  108 . 
     The object of the disclosed invention includes advantages of increasing muscular strength, muscular endurance and a great deal of caloric expenditure to assist in achieving desired body composition due in part to the massive amount of calories that can be expended from doing a great deal of work in every repetition. In addition, muscular power is a highly sought after physical quality in virtually every functional activity as well as on the field of play. To train for maximal physical power, speed of movement under load is necessary. Weight lifting, or Olympic lifting has been a standard used to develop muscular power. For this, the weighted bar is literally “thrown” up by the lifter and then caught. The catching and recovering for the next lift, or phase of lift, can be an area of injury to the athlete. The present invention eliminates the catch phase by the addition of the brake  62  and therefore reduces the likelihood of training injuries. 
     In order to optimize the physiological training effect, it may be desirable for the device  40  to allow for rapid vertical movements. The brake  62 , when mounted directly to the base frame  42  as previously disclosed, may offer some resistance to movement as the brake  62  is being extended. This drag may throw off the athlete&#39;s “feel” during a lift. The mass moment of inertia of the carriage  50  may exactly equal that of a tire of a specific weight and size but if the brake  62  adds additional resistance to oppose vertical movement, it could cause a lifter to miss a lift or simply restrict higher velocity vertical movements associated with power training. 
     To address the high velocity movement potential, a brake arm  110  is illustrated in  FIGS. 14-16 . In  FIG. 14  the device  40  is in a resting position, the carriage  50  ready to be vertically displaced for the next lift. A cut-away along line  15 - 15  of  FIG. 14  shows more detail of this embodiment of the brake arm  110  and associated components with the brake arm  110  in a lowered or resting position. In this position, the brake  62  functions similarly to that previously disclosed. As the guide arm  56  lowers, the brake  62  resists the downward movement. In this embodiment of the invention, if the guide arm  56  is displaced up faster than the brake  62  will allow, the brake arm  110  may be allowed to move relative to the base frame  42  as is shown in  FIG. 16 . This may be accomplished by the brake arm  110  being moveably mounted to the base frame  42 . Here the brake arm  110  is pivotal mounted by way of a bolt  112 . A counterweight or other bias such as a spring  114  may be used to position a foot  116 , such as a pliable bumper stopper mounted on the brake arm  110  toward a support  118  on the base frame  42 . The brake  62  may be coupled to the brake arm  110 , shown here as a pivotal mounting at joint  120  on one end of the brake  62  and the other end of the brake  62  being mounted to the guide arm  56  at joint  122 . This system allows for a buffer in the event that the brake  62  cannot extend rapidly enough to allow substantially free movement of the guide arm  56 , and therefore the carriage  50 , during the lifting phase. When the guide arm  56 , and therefore also the carriage  50 , are descending, the brake  62  may engage to slow their movement in a safe manner similar to that as previously disclosed. 
     The optimal “feel” of a “lift” performed by any athlete may be due to subtle changes in position, velocity or technique. The value to the exercise of a “ground to throwing” motion of lifting a mass from at or near ground level and continuing to full body extension and literally throwing the mass, has great potential. The amount of muscles used is substantial. The load to be lifted is potentially great as these are potentially large and powerful muscle groups used. Furthermore, the movement used in tire flipping is consistent with components of many athletic events from power lifting, to weight lifting, football, wrestling and numerous other sport activities. This is a testimony to the usefulness of the movement, as actual tires are used for tire flipping in spite of the list of limitations, including outdoor use only, large space required and the inability to alter the size and weight of a given tire, as presented herein. As such, the general use of the device  40  has many advantages for many athletes across the board. For a small population that train for strong man competitions where a test may be actual tire flipping, it may be desirable to simulate the feel of an actual tire in the device  40 . 
     In  FIG. 17  a simulated tire  124  is presented as Prior Art. For the purposes of the “feel” of flipping an actual tire, one of the areas to consider would be the mass moment of inertia of the tire. This is the distribution of the mass relative to the movement or in this case, the rotation, of the device  40 . The mass moment of inertia of a cylindrical ring of an outside diameter “L” and a thickness of five inches (dimension generalized as typical for our purposes) with the axis of rotation extended to Line X′-X′ would be characterized by the equation:
 
 I   X′X′   =M/ 2*( L/ 2−5) 2   +M *( L/ 2) 2    (Equation 1)
 
where “M” is the mass of the ring or tire. In order to reproduce the mass moment of inertia of the simulated tire in the device  40 , the composite total of the structure of the device  40  and added weight plates  68  could be added and made equal to that of the ring or simulated tire, as depicted in Equation 1. In many cases where heavier lifts are done, the majority of the mass of the device  40  plus the weight plates  68  will be mass of the weight plates  68 . Therefore. the appropriate location of the weight horns  54  relative to the center of mass of the device  40  would be desirable.
 
     In  FIG. 18  a top view of the carriage  50  is shown with an evenly distributed mass of weight plates  68  on the weight horns  54 . A generalized composite of the structure of the carriage  50  was constructed with the center of mass positioned along line X-X and translated to Line X′-X′ by the parallel axis theorem. This line X′-X′ is representative of the axis of rotation of the device  40  as presented in this disclosure. The distance “L” was generalized to be a position at or near a portion of the lifting platform  52 . In this condition Line X-X may not be exactly centered on “L” depending on the position of the supports  48  relative to the shape and location of the end of the carriage  50 . These are design considerations and not relevant to the novelty of the invention. The locations and dimensions have been generalized to apply to the device  40  in its general form. The mass moment of inertia of a generalized carriage  50  with a variety of evenly distributed weight plates  68  was calculated to be mathematically equal to Equation  1  above for different values of “L”. The dimension “y” was determined to satisfy the mathematical equation under a combined mass range of 500 pounds to 1000 pounds. The results of the calculations are presented in  FIG. 19 . The math suggests an optimal relationship of the dimension “y” versus the length “L” for a 500 pound weighted carriage  50  is generalized in equation 2;
 
 y= 0.3897 *L− 6.470   (Equation 2)
 
and in a similar manner, the relationship of the dimension “y” versus the length “L” for a 1000 pound weighted carriage  50  is generalized in equation 3.
 
 y= 0.3765* L− 6 . 475     (Equation 3)
 
Few athletes will lift over 1000 pounds and many high school and older athletes will lift over 500 pounds in the simulated tire weight, so these may be considered reasonable ranges.
 
     The dimension “y” as shown in  FIG. 18 , is the distance on each side of the center of the carriage  50 . Therefore the math reveals an optimal center to center range between the weight horns  54  of twenty-four to forty-six inches (12*2=24 to 23*3=46). A preferred dimension “L” may be 60 inches as a typical “tire” size for many athletes. As such, the math suggests an optimal “y” dimension of sixteen to seventeen inches. This suggests a desirable center to center dimension of the weight horns  54  as being twice that or thirty-two to thirty-four inches. 
     The foregoing detailed description of the present invention is provided for purposes of illustration, and it is not intended to be exhaustive or to limit the invention to the particular embodiment shown. The embodiments may provide different capabilities and benefits, depending on the configuration used to implement key features of the invention.