Patent Publication Number: US-7901337-B2

Title: Arm exercise machine with self-aligning pivoting user support

Description:
RELATED APPLICATION 
     The present application is a Continuation of U.S. patent application Ser. No. 11/848,012, which claims the benefit of U.S. provisional patent application No. 60/824,745 filed Sep. 6, 2006, and the contents of each of the aforementioned applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to an exercise machine for performing isolation exercises, and is particularly concerned with an arm exercise machine with a self-aligning pivoting user support. 
     2. Related Art 
     Two most commonly performed arm exercises are the biceps curl and triceps extension. These are isolation exercises, so-called because they involve a single joint, the elbow; require the movement of just one body part, the lower arm; and target a specific muscle group, biceps (curl) and triceps (extension). Because only one joint action is involved, isolation exercise machines use exercise arms with rotational movement that align the pivoting joint of the user with the pivot axis of the arm. It is important that the user is properly positioned when performing these exercises, in order to reduce joint stress and reduce the risk of injury. 
     There are three major sticking points or hurdles that a user must overcome in order to perform a biceps curl. The first is in the beginning of the exercise, where starting off with the arms fully extended places the elbows in a bio-mechanically weak position and makes it difficult to initiate the curling motion under load. The second is breaking through the gravitational apex of the movement where the elbow is bent at 90 degrees. The final hurdle is achieving full flexion and properly completing the exercise. When performing the exercise with free weights (barbell or dumbbells) users often overcome these sticking points by performing what is often called “cheat” curls. This requires the user to bend their knees slightly, lean forward at the waist and then explode the weight up by thrusting with the legs, swinging the arms and arching the back rearward. This uses momentum to bring the weight to the top of its arc and complete the exercise. While it is considered one of the best ways to increase muscle mass because it allows the user to handle more weight than normally possible with stricter form, it can be harmful to the low back. This version of a biceps curl also involves other body parts as well as inertia to complete the movement, and does not focus strictly on the biceps. To help maintain a stricter form, most biceps curl machines place the user in a fixed seated position with their arms positioned against a pad. While this prevents the user from involving their legs, back and shoulders in the exercise, focusing strictly on their biceps, it can put too much stress on the elbow. 
     In order to achieve the full exercise range-of-motion, there must be enough pre-stretch at the beginning of the exercise, but too much forces the elbow to hyper-extend under load. Equally important is achieving full flexion to the elbow and completing the exercise. If the resistance is too heavy at the end of the movement, the user will stop short, barely passing the apex; if the resistance is too light there could be a “caming over” effect, where it feels as if the speed at which the handles are moving increases after they pass the gravitational apex. 
     The same problem points exist for the user performing a triceps extension as on a biceps curl. The beginning of the exercise places the user&#39;s hands in close to their body with the elbow bent. This again is a bio-mechanically weak position and makes it difficult to initiate the pushing motion under load. Next is breaking through the gravitational apex of the movement where the elbow is bent at ninety degrees. The final problem point is achieving full extension and properly completing the exercise. 
     When performing the triceps extension exercise with free weights (barbell or dumbbells) the user is either standing or lying on their back. They start with their upper arms extended outward, elbows bent and hands at head level. They then straighten their arms, moving only at the elbow. The same “cheat” method of swinging or throwing the weights upward to create momentum and involve other muscle groups (shoulders and/or back) is also used during this exercise. 
     To maintain a strict form, most triceps extension machines place the user in a fixed seated position, arms positioned against a pad, often with their back supported to help brace against the outward push on the exercise arm. In order to achieve the full exercise range-of-motion, there must be enough pre-load at the beginning of the exercise, but too much makes it difficult to unfold a bent arm under load. Equally important is achieving full extension to the elbow and completing the exercise. If the resistance is too heavy at the end of the movement then the user will stop short, barely passing the apex; if the resistance is too light there could be a “caming over” effect, where it feels as if the speed at which the handles are moving increases after they past the gravitational apex. 
     In attempting to overcome or reduce the problem points discussed above, prior art biceps and triceps exercise machines have used various angles for the arm support pad, added counter-balancing weight to the exercise arm and installed devices to alter the resistance curve during various stages of the exercise movement. 
     SUMMARY 
     An isolation arm exercise machine in one embodiment has a user support which is pivotally mounted on a main frame by a pivotal mounting system and has a primary support portion and a secondary portion which support different locations on a user&#39;s body and are fixed relative to one another throughout an exercise movement. A user engagement device having at least one user engaging portion is pivotally mounted on the main frame or user support, and movement of the user engagement device is linked to movement of the user support by a connecting link. A load provides resistance to movement of the user support, exercise arm, and/or connecting link. The pivotal mounting system may be a single pivot mount or a four-bar pivotal linkage. 
     The arm exercise machine in one embodiment is a biceps curl exercise machine, and in another embodiment it is a triceps extension machine. In yet another embodiment, the machine is designed for selectively performing either biceps curl or triceps extension exercises. 
     The exercise machine is configured to make it easier for a user to perform the initial lift, break the gravitational apex and fully complete an isolation arm exercise. Because the user support and exercise arm move together, the user tends to maintain the same positioning throughout the exercise. By pivoting the user support and tying its pivoting action to the movement of the exercise arm, the user can be supported in a desired form or position to perform an isolation arm exercise while still experiencing the feel of a free-weight “cheat” movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The details of the present invention, both as to its structure and operation, may be gleaned in part by study of the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
         FIG. 1  is a rear perspective view of an arm exercise machine according to a first embodiment; 
         FIG. 2  is a front perspective view of the machine of  FIG. 1 ; 
         FIG. 3  is a top plan view of the machine of  FIGS. 1 and 2 ; 
         FIG. 4A  is a side elevation view of the machine of  FIGS. 1 to 3  in a start position for an arm exercise; 
         FIG. 4B  is a side elevation view of the machine of  FIGS. 1 to 3  in a finish position for an arm exercise; 
         FIGS. 5A and 5B  are side elevation views similar to  FIGS. 4A and 4B  but illustrating a user in position on the machine and performing a biceps curl exercise; 
         FIG. 6A  is a side elevation view of a biceps curl exercise machine according to another embodiment, illustrating an exercise start position; 
         FIG. 6B  is a side elevation view the machine of  FIG. 6A , illustrating a finish position for a biceps curl exercise; 
         FIG. 7A  is a side elevation view of the machine in the position of  FIG. 6A , illustrating a user in position on the machine; 
         FIG. 7B  is a side elevation view of the machine in the finish position of  FIG. 6B , with a user positioned on the machine; 
         FIGS. 8A to 8D  are perspective views of the self-aligning handle of the machine of  FIGS. 6 and 7 , illustrating various different hand grip positions; 
         FIG. 8E  is a front elevation view of the handle of  FIGS. 8A to 8D , showing the range of movement of the rotating hand grips; 
         FIG. 9  is a front perspective view of a third embodiment of a biceps curl exercise machine; 
         FIG. 10  is a rear perspective view of the machine of  FIG. 9 ; 
         FIG. 11  is a front elevation view of the machine of  FIGS. 9 and 10 ; 
         FIG. 12  is a top plan view of the machine of  FIGS. 9 to 11 ; 
         FIG. 13A  is a side elevation view of the machine of  FIGS. 9 to 12  in a start position for a biceps curl exercise; 
         FIG. 13B  is a side elevation view of the machine of  FIGS. 9 to 12  in a finish position for a biceps curl exercise; 
         FIGS. 14A and 14B  are side elevation views similar to  FIGS. 13A and 13B  but illustrating a user in position on the machine and performing a biceps curl exercise; 
         FIG. 15  is a front perspective view of a biceps curl exercise machine according to a fourth embodiment; 
         FIG. 16  is a rear perspective view of the machine of  FIG. 15 ; 
         FIG. 17A  is a side elevation view of the machine of  FIGS. 15 and 16  in a start position for a biceps curl exercise; 
         FIG. 17B  is a side elevation view similar to  FIG. 17A  illustrating a finish position for a biceps curl exercise; 
         FIGS. 18A and 18B  are side elevation views similar to  FIGS. 17A and 17B  but illustrating a user in position on the machine and performing a biceps curl exercise; 
         FIG. 19  is a side elevation view similar to  FIGS. 18A and 18B  but illustrating the start and finish position for a biceps curl superimposed; 
         FIG. 20  is a front perspective view of a combination biceps curl/triceps extension exercise machine according to another embodiment, with the machine in a starting position for a biceps curl exercise; 
         FIG. 21  is a front perspective view of the machine in the finish position for a biceps curl exercise; 
         FIG. 22A  is a side elevation view illustrating the machine in the start position of  FIG. 20 ; 
         FIG. 22B  is a side elevation view similar to  FIG. 22A  illustrating a finish position for a biceps curl exercise; 
         FIG. 23A  is a side elevation view similar to  FIG. 22A  with a user seated on the machine and ready to perform the exercise; 
         FIG. 23B  is a side elevation view similar to  FIG. 23A  but illustrating a finish position for the biceps curl exercise; 
         FIG. 24  is a front elevation view of the machine of  FIGS. 20 to 23  in a start position for a triceps extension exercise; 
         FIG. 25  is a front perspective view of the machine of  FIG. 24  in the finish position; 
         FIG. 26A  is a side elevation view illustrating the machine in the start position of  FIG. 24  for a triceps extension exercise; 
         FIG. 26B  is a side elevation view similar to  FIG. 26A  but illustrating the finish position of a triceps extension exercise; 
         FIG. 27A  is a side elevation view of the machine in the position of  FIG. 26A  but with a user seated on the machine and ready to perform the triceps extension exercise; 
         FIG. 27B  is a side elevation view similar to  FIG. 27A  but illustrating a machine and user finish position for a triceps extension exercise; 
         FIG. 28  is a front perspective view of a triceps extension exercise machine according to another embodiment, with the machine in a start position for a triceps extension exercise; 
         FIG. 29  is a rear perspective view of the machine in the position of  FIG. 28 ; 
         FIG. 30  is a rear perspective view similar to  FIG. 29  illustrating a finish position for a triceps extension exercise; 
         FIG. 31  is a front elevation view of the machine of  FIGS. 28 to 30  in a start position; 
         FIG. 32  is a front elevation view of the machine of  FIGS. 28 to 30  in a finish position; 
         FIG. 33A  is a side elevation view of the machine of  FIGS. 28 to 32  in a start position for a triceps extension exercise; 
         FIG. 33B  is a side elevation view of the machine of  FIGS. 28 to 32  in a finish position for a triceps extension exercise; and 
         FIGS. 34A and 34B  are side elevation views similar to  FIGS. 33A and 33B  but illustrating a user in position on the machine and performing a triceps extension exercise. 
     
    
    
     DETAILED DESCRIPTION 
     Certain embodiments as disclosed herein provide for arm exercise machines with a self-aligning pivoting seat or user support, designed for performing isolation arm exercises such as biceps curls or triceps extensions, or both. Triceps extension and bicep curl exercises are isolation exercises in which a single joint is involved, and in which only one body part is moved, specifically the lower arm. They exercise one muscle group, the triceps muscles at the back of the arm in one case, and the biceps muscles at the front of the arm in the other case. In certain embodiments disclosed herein, a pivoting user support is linked to an exercise arm for movement with the arm. 
     After reading this description it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. 
       FIGS. 1 to 5  illustrate a biceps curl exercise machine  10  according to a first embodiment. Machine  10  has a main frame  12 , a user support  14  pivotally mounted on the frame via a pivot mount  15 , and an exercise arm assembly  16  pivotally mounted on the user support and linked to the main frame via a pivoting connecting link  18  so that movement of the exercise arm assembly results in pivoting movement of the user support. The user support  14  is linked to a weight stack  20  mounted in weight stack frame or housing  22  via a cable and pulley linkage  24 . 
     The main frame  12  has a base section or strut  25  having a ground-engaging pad or foot  26  at each end, a transverse guide tube  28  extending between the strut  25  and the weight stack frame  22 , a first upright strut  30  at the forward end of base strut  25 , and a rearward inclined, upright post or stand-off  32  at an intermediate point in the length of the strut. Pivot mount or bracket  15  is mounted at the upper end of post  32 . A connecting rod  33  extends between forward strut  30  of the main frame and the outer side of the weight stack housing  22 , as illustrated in  FIG. 2 . 
     User support  14  has a seat support frame comprising a generally upright rear tube  34 , a generally upright forward tube  35 , and a cross bar or pivot mounting bar  36  extending between tubes  34  and  35 . A seat pad  38  is adjustably mounted at the upper end of the rear tube  34  via seat support post  40  which is telescopically engaged in an open upper end of tube  34 . Seat support post has a series of openings for releasable engagement with pull pin  42  to adjust the seat pad height based on user size and preference. Arm support pads  44  are mounted at the upper end of forward tube  35  via mounting brackets  45 . Adjustment of the seat height accommodates users of different heights by varying the distance between the seat and the arm support pads. A pivot housing  47  extends upwardly from the upper end of the forward tube between the arm support pads. Foot support bar  46  is transversely mounted at the lower end of tube  35  and a foot support  48  is mounted at each end of bar  46  for engagement by a user&#39;s feet. Cross support  36  is pivotally attached to pivot mount  15  for rotation about user support pivot axis  50 . 
     Cable and pulley linkage  24  includes a pulley  52  mounted on base strut  25  and a pulley  54  mounted on the underside of user support cross bar  36  approximate its forward end. Cable  55  extends from an anchor  56  on base strut  25 , around pulley  54 , and then around pulley  52 . Cable  55  is then linked to the weight stack through the guide tube  28  in any suitable manner, including additional cables and pulleys. 
     Exercise arm assembly  16  comprises a main arm  58  having a pivot mount  59  at one end pivotally connected between pivot brackets  60  of the pivot housing  47  at the top of user support forward or upright tube  35  for rotation about first exercise arm pivot axis  62 , and a generally U-shaped handle arm member  64  having a central region pivotally attached to a pivot mount  65  at the forward end of main arm  58  for rotation about handle arm pivot axis  67 . Each section or arm of the U-shaped handle arm member  64  has an angled step  71  that places the outer ends of the handle arm member at a wider spacing than the inner, web connecting portion. This design allows multiple gripping positions for the user&#39;s hands. The pivotal connection between the handle arm member and the main exercise arm enables the user engaging handles to self-align to the user during the exercise and automatically adjust to the user&#39;s arm length. A stand-off tube (not visible in the drawings) extends from the main arm pivot mount  59  inside the pivot housing  47  at the top of user support. 
     Connecting link  18  comprises a link arm or bar  66  which is pivotally attached at one end to a link connecting pivot mount  68  at the upper end of main frame forward upright  30  for rotation about first pivot axis  70 . Link  18  is pivotally attached at its second end to a link connecting pivot mount at the end of the stand-off tube of main arm  58  within the housing  47  for rotation about a second pivot axis  72  (see  FIG. 3 ). The first pivot axis  70  of the connecting link is positioned above and forward of the user support pivot axis  50 , as best seen in  FIG. 4B . A bumper plate  74  with a rubber bumper is mounted on link arm  66  approximate the first pivot point  70  of the link arm  66 , as illustrated in  FIG. 4B . Exercise arm  58  rests on bumper plate  74  in the rest or exercise start position, as illustrated in  FIG. 4A . 
     In this embodiment, the user support is pivotally mounted to the main frame via the user support pivot mount  15 . The exercise arm is pivotally connected by its first pivot mount  59  to the pivot housing  47  located between the user support arm pads. The connecting link pivotally joins the main frame with the exercise arm via the link connecting pivot mount  68  at the upper end of main frame upright  30  and the link connecting pivot mount at the end of the main arm stand-off within pivot housing  47 . 
       FIG. 4A  illustrates the start position for a biceps curl exercise, while  FIG. 4B  illustrates the finish position.  FIGS. 5A and 5B  illustrate the same start and finish position with a user  80  seated on the machine and performing a biceps curl exercise. To perform the exercise, the user sits on the seat  38 , which rests at a slight forward inclination, places their feet on the foot rests  48  and rests their upper arms on the angled arm support pads  44 . The user aligns the pivot of their elbows as closely as possible with the pivot axis  62  at the exercise arm pivotal connection to the user support. Elbow groove  75  in the arm support pads  44  helps align the user. The user then grabs the user engaging handle  64  and starts the exercise movement by pulling the handle upward, towards their head. 
     This movement causes the exercise arm  16  to pivot about axis  62  relative to the user support, which rotates the stand-off secured to the main arm pivot mount  59  downward. As the stand-off rotates downward, it causes the connecting link  66  to rotate as well as it pivots about its connections to both the exercise arm and the main frame. This in turn forces the user support  14  to rotate, tilting it rearward about the user support pivot axis  50  at the user support&#39;s pivotal connection to the main frame. This pivot is designed to reorient the user&#39;s position from a forward lean to a rearward lean, duplicating the rearward arching motion of a “cheat” curl. This movement is done without changing the position of the user on the user support. Through out the entire “cheat” movement, the user is in a stabilized position with their feet and upper torso supported. This stabilized position provides a strict exercise movement by preventing the involvement of other muscle groups and focusing effort just on the biceps. 
       FIGS. 5A and 5B  show a user  80  on the machine in the start and finish positions respectively, with the vertical line  76  representing the gravitational centerline of the pivotal movement. This embodiment places a portion of the user and user support on each side of the pivot&#39;s gravitational centerline in both the starting and finishing positions. By linking movement of the user support to movement of the exercise arm and positioning the user support pivot so that the combined weight of the user support and user is distributed on both sides of the pivot&#39;s gravitational centerline, the user support provides a counter-balancing effect on the exercise arm as it moves and its weight is re-distributed. 
     In the starting position, more of the combined user and user support weight is distributed towards the front side of the pivot. As the exercise arm is moved, more of this combined weight passes through the gravitational centerline until a more even distribution of weight is achieved. This re-distribution is gradual and continuous throughout the exercise motion and is not noticed by the user. By starting with a portion of the combined weight on the rearward or non-load side of the gravitational centerline, the initial lifting resistance is reduced. Re-distributing more of the combined weight to the non-load side at the end of the exercise increases the counter-balancing effect, lightening the resistive load slightly, which allows the user to come to full flexion and properly complete the exercise movement. This slight counter-balancing move mimics the momentum used on a free weight “cheat” curl to raise the weight to the top of its arc and finish the exercise. 
       FIGS. 6 to 8  illustrate a second embodiment of a biceps curl exercise machine  100 . Machine  100  has a main frame  102 , a user support  104  pivotally mounted on the frame via a pivot mount  105 , and an exercise arm assembly  106  pivotally mounted on the user support and linked to the main frame via a pivoting connecting link assembly  108  so that movement of the exercise arm assembly results in pivoting movement of the user support. The exercise arm assembly  106  is linked to a weight stack  110  mounted in weight stack frame or housing  112  via a cable and pulley linkage to provide resistance to movement of the arm by a user. 
     The main frame  102  comprises a base section  114  for engaging the floor and an upright tube  115  located at the forward end of the base section. Upright tube has a rearward inclined upper section  113 . A swivel plate  116  is pivotally mounted to a swivel plate bracket approximate the end of upright tube  115  for rotation about pivot axis  117 . Swivel plate  116  forms part of the pivoting link assembly  108 . A stand-off tube  118  is mounted at an intermediate position on frame base section  114  and user support pivot mount  105  is located at the upper end of stand-off post  118 . 
     The user support  104  has a generally horizontal base tube  120  with user supporting foot rests  122  mounted at or adjacent its forward end and a seat adjuster tube  124  mounted at its second or rearward end in a generally T-configuration. An upright tube or strut  125  with user supporting arm pads  126  mounted at its upper end extends upwardly from the base tube  120  at an intermediate location between foot rests  122  and the seat adjuster tube  124 . A pivot housing  128  protrudes upward from the center of the arm support pads  126 . A first link connecting pivot mount  130  is located at an intermediate point along upright tube  125  between the base tube  120  and arm pads  126 . The base tube  120  of the user support is pivotally attached to the user support pivot mount or bracket  105  for rotation about user support pivot axis  132 . A seat post  134  is telescopically engaged in the seat adjuster tube  124  and has a mounting plate  135  at its upper end on which a seat pad  136  is mounted for supporting a seated user. This provides vertical adjustment to the seat and is designed to accommodate users of different heights by varying the distance between the seat and the arm support pads. 
     The exercise arm  106  has a main tube  138 , a user engaging handle bar  140  (illustrated in more detail in  FIG. 8 ), and a stand-off  142 . The stand-off  142  is mounted to the main tube at a location intermediate the ends of the tube. The main tube is pivotally attached at its first end to the pivot housing  128  at the top of the user support upright strut  125  for rotation about a first pivot axis  144 . The second end of main tube  138  is pivotally connected to the user engaging handle bar  140 . The user engaging handle bar  140  is illustrated in more detail in  FIG. 8  and is of general “U” shape with user engaging handgrips  145  rotatably mounted at the end of each leg of the handle bar. This arrangement allows multiple gripping positions for the user&#39;s hands, and  FIGS. 8A to 8D  illustrate some of the possible gripping positions. The grips can be positioned at any angle through 360 degrees, as indicated in  FIG. 8E . This provides wrist pronation and supination during the exercise movement. 
     Pivot connecting brackets  146  are located at the central web of the “U” shaped handle, and brackets  146  are pivotally connected to the second end of main tube  138  for rotation about pivot axis  148 . This connection enables the user engaging handles to self-align to the user during the exercise and automatically adjust to the user&#39;s arm length. A cam  149  (see  FIG. 6B ) is located approximate the first end of the main tube  138  for receiving a load bearing cable of the cable and pulley linkage. 
     The connecting link assembly  108  comprises a first and second linkage bar  150 ,  152  and the swivel plate  116  pivoted at the end of the main frame upright  115 . The first linkage bar  150  is shorter than the second linkage bar  152 . The first linkage bar is pivotally attached to the pivot mount  130  on the user support upright  125  at one end, for rotation about pivot axis  154 . The second end of the first linkage bar is pivotally attached to the swivel plate  116  for rotation about pivot axis  155 . The first end of the second linkage bar is pivotally attached to the exercise arm stand-off  142  for rotation about pivot axis  156 . The second end of the second linkage bar is pivotally attached to the swivel plate  116  for rotation about pivot axis  158  (see  FIG. 6B ). The connecting link assembly  108  therefore pivotally links both the exercise arm and the user support to the main frame. The main user support pivot axis  132  beneath seat  136  is positioned lower than and rearward of the pivot axis  154  of the first linkage bar of the connecting link assembly. 
     In this embodiment, the user support  104  is pivotally mounted to the main frame via the user support pivot mount  105 . The exercise arm is pivotally connected by its first pivot mount at axis  144  to the pivot housing  128  located between the user support arm pads  126 . The first connecting linkage bar  150  pivotally joins the user support to the swivel plate  116  and the second linkage bar  152  pivotally joins the exercise arm to the swivel plate. The cable and pulley linkage which connects the weight stack to the exercise arm cam  149  includes a pulley  165  mounted on stand-off tube  118  on base section  114  of the main frame and a pulley  166  mounted on the underside of the user support. A cable (not illustrated) runs from pulley  165  to pulley  166 , and then attaches to the cam  149  on the exercise arm main tube  138  (see  FIGS. 6B and 7B ). 
       FIGS. 6A and 7A  illustrate a start position for a biceps curl exercise on machine  100  while  FIGS. 6B and 7B  illustrate an exercise finish position. A user  80  is shown in position on the machine in  FIGS. 7A and 7B . The gravitational centerline  160  of the user support pivot is shown in dotted lines in  FIGS. 7A and 713 . To perform the exercise, the user sits on the seat  136 , which rests in a substantially horizontal position, places their feet on the foot rests  122 , and rests their upper arms on the horizontal arm support pads  126 . They then grab the user engaging hand grips  145  and start the exercise movement by pulling the handle upward, towards their head. In carrying out is exercise, the user aligns the pivot of their elbows as closely as possible with the exercise arm pivot axis  144  to the user support. In order to assist the user in properly aligning their elbow for this exercise, an indicating decal can be used to identify the pivot point or axis  144  of the exercise arm. 
     This movement causes the exercise arm  138  to pivot about its connection to the user support, which pulls the second connecting link bar  152  upwards, causing the swivel plate  116  to rotate about its connection to the upright tube  115  of the main frame. As the swivel plate  116  rotates, it pulls the first connecting linkage bar  150  forward, which in turn pulls the user support  104 , causing it to rotate forward about its connection to the main frame at pivot axis  132 , unlike the previous embodiment where the user support rotates rearward. This different movement direction results from the attachment of the multi-part connecting link to the forward end of the user support.  FIGS. 6B and 7B  illustrate a finish position for a biceps curl exercise on machine  100 . 
     This pivotal action is designed to reorient the user&#39;s position from a generally upright position (see  FIG. 7A ) to a forward lean (see  FIG. 7B ). This movement feels like it is bringing the user and the exercise arm handles together at a quicker pace, simulating the speed found in the explosive inertia or momentum of a free weight “cheat” curl. However, because the exercise arm is mounted to, and travels with, the user support, it is the sensation of leaning forward as the handles approach the user that creates the feeling of momentum. Because the load is connected to the exercise arm, resistance remains substantially constant during the exercise, with the only variation being the small amount of combined weight (user and user support) that passes through the gravitational centerline  160 . 
     The rocking movement of the user support is achieved without changing the position of the user on the user support. Through out the entire “explosive” movement, the user is in a stabilized position with their feet and upper torso supported. This stabilized position provides a strict exercise movement by preventing the involvement of other muscle groups and focusing effort just on the biceps. 
       FIGS. 7A and 7B  show the portion of the user and user support on each side of the gravitational centerline  160  of the user support pivot in both the starting and finishing positions and how the combined weight is re-distributed during the exercise. By linking movement of the user support to movement of the exercise arm and positioning the user support pivot so that the combined weight of the user support and user is distributed on both sides of the gravitational centerline  160 , the user support provides a counter-balancing effect on the exercise arm as it moves and its weight is re-distributed. This slight re-distribution is gradual and continuous throughout the exercise motion and barely noticed by the user. Because the user support falls forward towards the load during the exercise, the portion of the user and user support on the load side, forward of the user support pivot, acts as a counter-balance, helping to reduce the initial lifting resistance. Redistributing more of the combined weight to the load side at the end of the exercise increases the counter-balancing effect, lightening the resistive load slightly, which allows the user to come to substantially full flexion and complete the exercise movement. This slight counter-balancing move, coupled with the user&#39;s forward leaning orientation, mimics the explosive movement used on a free weight “cheat” curl. 
       FIGS. 9 to 14  illustrate a third embodiment of a biceps curl machine  180 . Machine  180  has a main frame  182 , a user support  184  pivotally mounted on the main frame by means of a pivot mount  185 , an exercise arm assembly  186  pivotally mounted on the user support, a connecting link assembly  188  pivotally connecting the exercise arm assembly to the main frame, and a weight stack  190  housed in a vertical weight stack support frame  192  for providing exercise resistance. The weight stack  190  is linked to the user support by a cable and pulley linkage, part of which is visible in the drawings. 
     In machine  180 , the starting position of the user has changed from a generally upright orientation to a slightly reclined orientation and the roughly horizontal arm support pads positioned in front of the user have been replaced with generally vertical pads placed alongside the user. The user support has a back pad in addition to a seat pad. However, apart from these changes, the same major elements are present in this machine as are found in the other embodiments. 
     In machine  180 , the main frame  182  comprises a base section  194  for engaging the floor and an upright, rearward inclined tube or strut  195  located at the rearward end of the base section. A short upright post  196  with a bumper pad  198  at its upper end is located at the forward end of base section  194 . A stand-off post  200  is mounted at an intermediate position on rear strut  195 , and user support pivot mount  185  is associated with the outer end of stand-off post  200 . A connecting rod  202  is secured between rear strut  195  of the main frame and the outer face of weight stack frame  192 . A guide tube  204  for the cable and pulley linkage extends between the base section  194  of the main frame and the weight stack frame or housing  192 . 
     The user support comprises a generally “L” shaped seat support tube  205  with foot rests  206  mounted at the end of the forwardly extending leg  208  of support tube  205 . An adjuster tube  210  is vertically mounted on forwardly extending leg between the foot rests  206  and the bend in the L-shaped tube. A seat post  212  is telescopically engaged in the open upper end of adjuster tube  210 . Pull pin  213  extends through tube  210  for engagement in an aligned opening in seat post  212  and can be released in order to adjust seat height. Seat pad  214  is secured to a mounting plate at the upper end of seat post  212 . This arrangement accommodates users of different heights by varying the distance between the seat and the user engaging handles of exercise arm assembly  186 . 
     A back pad  215  is mounted on the upright leg  216  of the L-shaped user support tube. The L-shaped tube is pivotally attached to user support pivot mount or bracket  185  at a location just above the bend in the tube via pivot sleeve  207  for rotation about user support pivot axis  218 . A pair of downwardly angled arm supports  220  with arm support pads  222  mounted at their respective first ends are fixedly mounted to the upper portion of the upright leg  216  of the seat support tube at their respective second ends, as best illustrated in  FIG. 10 . Arm support pads  222  extend on opposite sides of the back pad in a generally vertical orientation and at an angle to the back pad, as best seen in  FIG. 12 . 
     The exercise arm  186  has a generally “U” shaped main tube or arm  224  and a pair of user engaging handle arms  225  pivotally attached at each end of the main tube, with a hand grip  226  at the end of each handle arm. The main arm  224  has a pair of connecting brackets  228  located at the central web of the U-shape, as best illustrated in  FIG. 10 . Each bracket is pivotally attached to a stand-off post or tube  230  located on the upright leg  216  of the seat support tube for rotation about a first pivot axis  232 . Stand-off tube  230  is located between the user support pivot axis  218  and the attachment point for the arm supports  220 . Each bracket  228  is also pivotally attached to the connecting link assembly  188  for rotation about a second pivot axis  234  spaced from pivot axis  232 , as explained in more detail below. Arm  224  has opposite side portions which extend generally downward from the pivot attachment to the user support in the start or rest position of  FIG. 13A . 
     The two user engaging handle arms  225  are generally L-shaped and are each connected to respective pivot mounts  223  at each end of the main tube  224  at the end of the longer leg of the L-shape via a universal pivot joint  235 . Hand grips  226  are each rotatably and telescopically mounted over the shorter leg of the L-shape to provide rotational movement for the hand grip on the handle arm. The universal pivot joints  235  are designed to enables the user engaging handles to self-align to the user during the exercise and automatically adjust to the user&#39;s hand position by providing minor adjustments in width positioning and wrist pronation/supination. 
     The connecting link  188  comprises a pair of generally L-shaped connecting plates  236  which are pivotally attached at one end to the handle arm connecting brackets  228  for rotation about pivot axis  234 , as best illustrated in  FIG. 10 . Each connecting plate  236  is pivotally attached at the other end to pivot mount  237  at the upper end of main frame upright  195  for rotation about pivot axis  238 . It can be seen in  FIGS. 10 ,  13 A and  13 B that the user support pivot point or axis  218  is positioned lower than and forward of the connecting link pivot axis  238 . 
     In this embodiment, the user support is linked to the weight stack via a pulley and cable linkage which includes a cable  240  extending from an anchor  242  on the underside of the forwardly extending leg  208  of the seat support frame and around a pulley  244  on the base section  194  of the main frame (see  FIG. 13B ). Cable  240  is linked in any suitable manner to the weight stack through guide tube  204 . 
     User support  184  in this embodiment is pivotally mounted to the main frame via the user support pivot system. The exercise arm is pivotally mounted on the user support by pivotally attaching the exercise arm connecting brackets  228  to the pivot connection on stand-off  230  on the rear of the upright leg  216  of the seat support frame. The connecting link pivotally joins a pivot mount on the main frame with a second pivot connection on the exercise arm connecting brackets  228 . 
       FIGS. 13A and 14A  illustrate the start position for a biceps curl on the machine  180 , with a user  80  seated on the machine in  FIG. 14A . A stand-off  245  on connecting brackets  246  which rigidly connect the arm supports  220  to the rear or upright back pad support leg  216  restricts rearward movement of the exercise arm beyond the start position of  FIG. 13A , to place the exercise arm in a convenient position at the start of an exercise. The handle arms  225  extend forward in a generally horizontal orientation on opposite sides of the seat in the start position of  FIG. 13A . The forwardly extending leg  208  of the seat support frame rests on the bumper pad  198  in the exercise start position, as illustrated in  FIGS. 9 and 13A . 
     To perform a biceps curl exercise, the user  80  sits on the seat  214  with their back against the back pad  215 , upper arms against the arm support pads  222 , and feet on the foot rests  206 . This places the user in a slightly reclined starting position, as illustrated in  FIG. 14A . They then grab the user engaging hand grips  226  and start the exercise movement by pulling the handles upward. In this machine, there is no pivot point for alignment with the user&#39;s elbows. The universal connections or joints  235  on the user engaging handle arms  225  compensate for this and automatically adjust to the user arm length and hand position. 
     Pulling the handle arms  225  upward causes the exercise arm  224  to pivot about its connection to the user support at pivot point or axis  232 , as well as at its pivotal connection to the connecting link  236  at pivot point or axis  234 , and causes the user support to be pulled rearward, rotating about pivot axis  218  at its pivotal connection to the main frame. This pivotal action is designed to reorient the user&#39;s position from a slight recline to a substantial recline and duplicate the rearward arching motion of the “cheat” curl. This movement is done without changing the position of the user on the user support. Throughout the entire movement, the user is in a safe stabilized position with their feet and upper torso supported. This stabilized position provides a strict exercise movement by preventing the involvement of other muscle groups and focusing effort just on the biceps. 
     As in the previous embodiments, the user support pivot mount in this embodiment is arranged so that part of the combined weight of the user support and user is positioned on both sides of the gravitational center line  180 A of the pivotal movement in both the start position and end position (see  FIGS. 14A and 14B ). As in the first embodiment, more weight is positioned forward of the gravitational center line  180 A in the start position of  FIG. 14A  than in the end position of  FIG. 14B . 
     A fourth embodiment of a biceps curl machine  250  is illustrated in  FIGS. 15 to 18 . This embodiment has some similar features to the embodiment of  FIGS. 6 to 8 , but the single pivot mount of that embodiment is replaced in this embodiment with a four-bar pivot linkage  255 , and the exercise arm design is somewhat different. The machine  250  has a main frame  252 , a user support  254  pivotally mounted on the main frame by a four-bar pivot linkage  255 , an exercise arm assembly  256  pivotally mounted on the user support, and a pivoting connecting link  258  joins the exercise arm assembly to the main frame. A weight stack  260  mounted in weight stack frame or housing  262  is linked to the user support by a cable and pulley linkage to provide exercise resistance, in a similar manner to the previous embodiments. 
     The main frame  252  has a base section  264  for engaging the floor and an inclined upright tube  265  located at the forward end on the base section. The base section  264  is connected to the weight stack support frame  262  by a guide tube  266  for the cable and pulley linkage. A connecting rod  268  is connected at one end to the upright tube  265  and at the other end to the outer face of the weight stack support frame  262 . 
     The user support  254  has an angled upright tube  270  at its forward end with user supporting foot rests  272  mounted on its lower end and a user supporting arm pad  274  mounted at its upper end. A pair of pivot brackets  275  protrude upward from the user support  254  through a recess at the center of the arm support pad  274 , as best illustrated in  FIG. 16 . A downwardly angled seat support tube  278  is attached by welding or other fastening means at an intermediate position along upright tube  270  and projects rearward from the tube  270 . A seat pad support tube  280  is attached transversely to the rear end of seat support tube  278  and has an open end in which a seat post  281  is telescopically engaged. Seat post  281  has a mounting plate at one end for attaching seat pad  282  for supporting a user. This arrangement is designed to accommodate users of different heights by varying the distance between the seat and the arm support pads. 
     The user support four-bar pivot linkage system  255  comprises two spaced, parallel rearward links  284  and a single forward link  285 . The rearward links are pivotally connected at one end to a pivot housing  286  on main frame base section  264  for rotation about first pivot axis  288 , and are pivotally connected at the other end to a pivot housing  290  on the underside of seat support tube  278  for rotation about second pivot axis  292 . The forward link  285  comprises two spaced plates connected by a central connecting tube  294 . Link  285  is pivotally connected at one end to a pivot housing  295  at the upper end of a stand-off  296  on the base section  264  of the main frame, for rotation about third pivot axis  298  spaced forward and upward from first pivot axis  288 . The opposite end of link  285  is pivotally connected to the seat support tube  278  for rotation about a fourth pivot axis  300  spaced forward from second pivot axis  292 . By using the four-bar linkage as the user support pivot system, all the pivoting action can take place under the user with the pivot mounts conveniently located on the main frame and user support. However, the theoretical pivot for the user support is actually located elsewhere. The theoretical pivot is the point where a single pivot would have to be located in order to mimic the same user support movement and gravitational centerline of the user support movement, as described in more detail below in connection with  FIG. 19 . 
     The advantage of the four-bar pivot system with the theoretical pivot is that it takes the movement pattern of a single point pivot that might normally be located in an area impossible to access due to either structural or user interference and provides pivot mounts in accessible locations which together provide for rotation of the user support about the otherwise inaccessible location. 
     The exercise arm assembly  256  comprises a main arm  302  and user engaging handles  304 . The main arm  302  has a first pivot mount  305  at a first end pivotally attached to the pivot brackets  275  at the upper end of the forward upright tube  270  of the user support for rotation about pivot axis  306 . 
     The user engaging handles  304  each have an angled step that places the outer ends wider than their lower, inner ends. This design allows multiple gripping positions for the user&#39;s hands. A connecting bracket  308  located at the lower ends of the handles is connected to the second end of the main arm  302  at a second pivot mount for rotation about pivot axis  310 . This connection enables the user engaging handles to self-align to the user during the exercise and automatically adjust to the user&#39;s arm length. A link connecting third pivot mount  312  is mounted on the main arm at a location intermediate its ends (see  FIG. 16 ). 
     The connecting link  258  comprises an elongate main tube  314  having a pivot mount  315  at its first end which is pivotally attached to a pivot bracket  316  at the end of main frame upright  265  for rotation about a first link pivot axis  318 , and a U-shaped bracket  320  attached to the second end of the main tube  314  at the center web of the U-shape. The ends of the U-shaped bracket  320  are pivotally connected to the pivot mount  312  on exercise arm  302  for rotation about a second link pivot axis  322 . 
     In this embodiment, the user support  254  is pivotally mounted to the main frame via the user support pivot system  255 . The exercise arm is pivotally connected by its first pivot mount  305  to the pair of pivot brackets  275  at the center of the user support arm pad  274 . The connecting link  258  joins the exercise arm  256  with the main frame  252 . The user support  254  is linked to the weight stack via the cable and pulley linkage which includes a double pulley  325  on the base section  264  of the main frame and a pulley  326  on the underside of the seat support tube  278 . A cable (not illustrated) extends from an anchor on seat support tube  278 , around a first pulley of the double pulley  325 , around pulley  326  on the seat support tube  278 , and then around the second pulley of double pulley  325  in a similar manner to some of the previous embodiments, and is linked through the guide tube to the weight stack in any suitable manner. 
       FIGS. 17A and 18A  illustrate the biceps curl machine  250  in a start position for a biceps curl exercise, with a user  80  shown seated on the machine in  FIG. 18A . To perform the exercise, the user sits on the seat  282 , which rest in a horizontal position, place their feet on the foot rests  272 , and rests their upper arms on the horizontal arm support pad  274 . This places the user in a generally upright orientation, as illustrated in  FIG. 18A . They then grab the user engaging handles  304  and start the exercise movement by pulling the handles upward, towards their head, until they reach a finish position for the exercise as illustrated in  FIGS. 17B and 18B . It is desirable for the user to align the pivot of their elbows with the exercise arm&#39;s pivotal connection to the user support at axis or pivot point  306  ( FIG. 17A ). A position indicating decal may be placed on the arm support pad to help a user to identify the pivot point  306  of the exercise arm for alignment purposes. 
     The exercise movement causes the exercise arm to pivot about pivot axis  306  at its connection to the user support. This in turn pulls the connecting link at its connection to the exercise arm, causing the link to rotate about pivot axis  318  at its connection to the upright tube  265  of the main frame. This action pulls the user support forward and downward, causing it to rotate forward about its four-bar pivot connection to the main frame. 
     This pivotal action of the user support is designed to reorient the user&#39;s position from a generally upright position to a forward lean. This movement feels like it is bringing the user and the exercise arm handles together at a quicker pace, simulating the speed found in the explosive inertia or momentum of the free weight “cheat” curl. However, because the exercise arm is mounted to, and travels with, the user support, it is only the sensation of leaning forward as the handles approach that creates the feeling of momentum. Because the load is connected to the user support, the resistance remains constant during the exercise, with the only variation being the small amount of combined weight (user and user support) that pass through the gravitational centerline. 
     This rocking movement is done without changing the position of the user on the user support. Through out the entire “explosive” movement, the user is in a stabilized position with their feet and upper torso supported. This stabilized position provides a strict exercise movement by avoiding or substantially avoiding the involvement of other muscle groups and focusing effort just on the biceps. 
     As mentioned above,  FIGS. 18A and 18B  illustrate a user  80  on the machine in the start and finish positions respectively. The dotted line  330  represents the gravitational centerline of the pivotal movement. In performing the exercise, the user goes from an upright orientation to a forwardly inclined orientation as their arms go from an extended to a flexed (bent at the elbow) position. A portion of the user and user support is balanced on each side of the gravitational centerline  330  in both the start and finish positions. 
       FIG. 19  illustrates plotting of the theoretical pivot point  332  for the user support four bar pivot linkage  255 . In this drawing, the start and finish positions of the machine and user in  FIGS. 18A and 18B  are overlapped. Moving parts of the machine are indicated by an A after the reference number for the start position and a B after the reference number for the finish position. In order to plot the theoretical pivot point  332 , the centerline of the arcing movement for each link  284 ,  285  of the user support pivot system is calculated. The centerline C of the movement of link  284  extends from the center of the line joining the start and finish positions of second pivot axis  292 A,  292 B through the first pivot axis  288 , which is fixed. The centerline D of the movement of link  285  extends from the center of the line joining the start and finish positions  300 A,  300 B of the fourth pivot axis through the fixed third pivot axis  298 . The point in space where the two centerlines C and D intersect is the theoretical pivot point  332  of the user support. The gravitational centerline  330  is the vertical line extending through theoretical pivot point  332 . A single fixed pivot would not work for machine  250  as it would be located below ground level, as seen in  FIG. 19 . This would force the machine to be raised approximately eight inches in order to duplicate this pivoting movement using a single fixed pivot and would make entering and exiting the user support more difficult. 
       FIGS. 20 to 27  illustrate a dual unction arm exercise machine  350  according to another embodiment. This machine can perform both biceps curl and triceps extension exercises, with  FIGS. 20 to 23  depicting a biceps curl and  FIGS. 24 to 27  depicting a triceps extension. The general frame work and movement pattern of this machine is similar to that of the previous embodiment, except that it has a bi-directional exercise arm and a flexible line is used as a connecting link. 
     In this embodiment, the main frame and user support pivot system, and the weight stack and weight stack frame attachment to the main frame are the same as in the embodiment of  FIGS. 15 to 19 , and like reference numbers have been used for like part as appropriate. The user support  352  is pivotally mounted on the main frame base section  264  by a four-bar pivotal linkage system, as in the previous embodiment. An exercise arm assembly  354  is pivotally mounted on the user support, and a connecting link comprising a cable and pulley system  355  extends between the main frame, user support, and exercise arm, as explained in more detail below. 
     As in the previous embodiment, the user support  352  has an angled upright tube  356  at its forward end, with user supporting foot rests  358  mounted on the lower end of tube  356  and a user supporting arm pad  360  mounted at the upper end. The arm pad  360  has an indented region at its center, and a pair of cam mounting pivot brackets  362  protrude upward from tube  356  through the center of the arm support pad  360 , replacing the pivot brackets  275  of the previous embodiment. A downwardly angled seat support tube  364  extends rearward from upright tube  356  at a location spaced above foot rests  358 , and a seat pad support tube  365  is attached transversely to the rear end of seat support tube  364 . Seat pad support tube  365  has an open end in which a seat post  366  is telescopically engaged. Seat post  366  has a mounting plate at one end for attaching seat pad  368  for supporting a user. This arrangement is designed to accommodate users of different heights by varying the distance between the seat and the arm support pads. 
     The exercise arm assembly  354  has a curved main tube or arm  370 , user engaging handles  372 , and a range-of-motion (ROM) adjuster  374 . The main tube  370  has a first pivot mount  375  attached at a first or outer end. The user engaging handles  372  have an angled step that places the outer ends wider than the lower, inner ends. This design allows multiple gripping positions for the user&#39;s hands. A connecting bracket  376  is located at the lower ends of the handles  372  and is pivotally connected to the main arm  370  at first pivot mount  375  for rotation about pivot axis  378 . This connection enables the user engaging handles to self-align to the user during the exercise and automatically adjust to the user&#39;s arm length. A pair of mounting brackets (not visible in the drawings) project outward from the main tube near the second end of the main tube or arm  370 . The ROM adjuster  374  comprises a round cam which is pivotally mounted together with the mounting brackets on the end of main arm  370  to the cam mounting pivot brackets  362  on the user support for rotation about pivot axis  400 . The ROM adjuster cam  374  has spaced adjustment holes around its perimeter, and an adjuster pin or pull pin  379  is mounted approximate the second end of exercise arm main tube  370  for selective engagement in the cam adjustment holes to secure the exercise arm at a selected position around cam  374 , depending on the exercise to be performed. This arrangement is designed to provide bi-directional exercise movement. A cam lever arm  380  pivotally associated with the cam  374  has a pulley  382  mounted on is outboard edge. 
     As noted above, the connecting link in this embodiment comprises a pulley and cable system. The connecting link pulley and cable system  355  has a first cable or flexible line  385  attached to the upright tube  356  of the user support at anchor  386  and then reeved around a pulley  388  mounted on a link connecting pivot mount  390  on the main frame upright  265 . The cable  385  is then reeved around a pulley  392  mounted on user support upright tube  356  at a location above the cable attachment point or anchor  386 . The cable is then reeved around the pulley  382  located on the outer edge of cam lever arm  380  before finally attaching to cam  374 . 
     The user support  352  is linked to the weight stack by a load-bearing cable  394  which extends from an anchor or attachment point  395  on the seat support  364  around a first pulley  396  on main frame base section  264 , then around a pulley  398  on the underside of seat support  364  forward of anchor  395 , and finally around pulley  399  on base section  264 , before linking to the weight stack  260  through guide tube  266  in any suitable manner. 
       FIGS. 20 ,  22 A, and  23 A illustrate the machine  350  configured for performing a biceps curl exercise, with a user  80  shown seated on the machine in  FIG. 23A . In order to perform this exercise, the exercise arm assembly  354  is positioned as indicated in  FIGS. 20 ,  22 A and  23 A, with the main arm  370  extending downward and the handles  372  pivoted into a generally upright, slightly rearward inclined orientation. To perform a biceps curl exercise, the user  80  sits on the seat, places their feet on the foot rests  358  and rests their upper arms on the arm support pad  360 . This places the user in a generally upright orientation. They then adjust the exercise arm to extend downward, by pulling lock pin or pull pin  379  out of the aligned opening in cam or ROM plate  374 , rotating the exercise arm assembly to the desired start position of  FIG. 23A , and then releasing the pin to re-engage in another opening in the cam or ROM plate. The user  80  then grabs the user engaging handles  372  with their arms extending straight and starts the exercise movement by pulling the handle upward, towards their head. This movement causes the exercise arm, cam and cam lever arm to pivot about their connection to the user support at pivot point  400 , which pulls the connecting link cable  385  as it wraps around the cam. This causes the user support to pivot about its connection to the main frame, tilting forward and pulling the load bearing cable  394 . The rotation continues until the finish position of  FIGS. 21 ,  22 B and  23 B is reached, with the user&#39;s arms bent and their hands adjacent their head. 
       FIGS. 24 ,  26 A and  27 A illustrate the start position for a triceps extension exercise while  FIGS. 25 ,  26 B and  27 B illustrate a finish position for this exercise, with a user  80  shown on the machine performing the exercise in  FIGS. 27A and 27B . To perform a triceps extension exercise the user simply adjusts the exercise arm to extend upward as illustrated in  FIGS. 24 ,  26 A and  27 A, using the ROM adjuster mechanism, then grabs the user engaging handles  372  with their arms bent upwardly and rearward, as in  FIG. 27A . User  80  starts the exercise movement by pushing the handles  372  downward, away from their head. This movement causes the exercise arm  370  and cam  374  to pivot about pivot axis  400  at their connection to the user support, which pulls the connecting link cable as it wraps around the cam, all of which causes the user support  352  to rotate and pull on load-bearing cable  394 . During this movement, cam lever arm  380  does not rotate with the cam. 
     In the exercise finish position of  FIG. 27B , the user has their arm extending straight out in front, and the user support seat has moved from a generally horizontal to a forward inclined orientation, and the user moves from upright to a slight forward lean. 
     The same user support movement with the four-bar linkage and theoretical pivot are present on this machine as described above in connection with the embodiment of  FIGS. 15 to 19 , and this movement does not change the position of the user on the user support. Through out the entire “explosive” movement, the user is in a stabilized position with their feet and upper torso supported. This stabilized position provides a strict exercise movement by reducing or eliminating any involvement of other muscle groups and focusing effort just on the biceps or triceps depending on the chosen exercise. 
       FIGS. 28 to 34  illustrate a triceps extension exercise machine  450  according to another embodiment. This machine is similar to the embodiment of  FIGS. 9 to 14 , and like reference numerals have been used for like parts as appropriate. The main difference between this machine and the machine  180  of  FIGS. 9 to 14  is the exercise arm and connecting link arrangement, which puts the exercise arm in the proper start position for a triceps extension exercise, as discussed in more detail below, and links the exercise arm movement to the user support so as to produce a similar rearward rocking motion to that of machine  180  even though the exercise arm rotates in the opposite direction. 
     In machine  450 , the starting position places the user in a slightly reclined orientation in the start of the exercise (see  FIGS. 33A and 34A ) and finishes with them in a substantially reclined orientation (see  FIGS. 33B and 34B ). 
     Machine  450  has a main frame  182 , a user support  184  pivotally mounted on the main frame by means of a pivot bracket  185 , an exercise arm assembly  452  pivotally mounted on the user support, a connecting link assembly  454  pivotally connecting the exercise arm assembly to the main frame, and a weight stack  190  housed in a vertical weight stack support frame  192  for providing exercise resistance. The weight stack  190  is linked to the user support by a cable and pulley linkage, part of which is visible in the drawings. 
     In this embodiment, as in the machine of  FIGS. 9 to 14 , the main frame has a base section  194  for engaging the floor and an upright tube  195  located at the rearward end of the base section. A stand-off tube  200  is mounted at an intermediate position on rear upright  195  and has a pivot mount  185  associated with its outer end. 
     The user support  184  has a generally L-shaped seat support tube or frame with foot rests  206  mounted at the end of horizontal leg  208 . An adjuster tube  210  is vertically mounted on horizontal leg  208  between the foot rests  206  and the bend in the L shape, and is designed for telescopic adjustment with seat post  212  on which seat pad  214  is mounted. This arrangement accommodates users of different heights by varying the distance between the seat and the user engaging handles of the exercise arm assembly  452 . Seat support tube  205  is pivotally attached to pivot bracket  185  via pivot mount  207  for rotation about user support pivot axis  218 . A back pad  215  is mounted on the vertical leg  216  of the L-shaped seat support tube, just above pivot axis  218 . A pair of downwardly angled arm supports  220  with arm support pads  222  mounted at their respective first ends are fixedly mounted to the upper portion of vertical leg  216  by their respective second ends. A stand-off tube  230  with a second pivot connection is attached to the back side of the vertical leg of the seat support tube, at a location between first pivot connection  218  and the attachment point for arm supports  220 . 
     The handle portions of the exercise arm assembly  452  are identical to those of the embodiment of  FIGS. 9 to 14 , and like reference numerals have been used for these parts. The exercise arm assembly  452  comprises a generally U-shaped main tube or arm  455  and a pair of user engaging handle arms  225 . The main tube  455  has a pivot mount  223  attached at each end of its legs and a pair of connecting brackets  456  located at the central web of the U-shape. The brackets  456  are pivotally mounted on a pivot mount  457  on stand-off  230  on the user support upright leg  216  for rotation about exercise arm pivot axis  458 . The two user engaging handle arms  225  are of general “L” shape and have a universal pivot joint  235  associated with the end of their long leg attached to main tube  455  via pivot mount  223 . A hand grip  226  for engagement by the user is telescopically mounted over the short leg of each handle arm  225 . The telescopic mounting is designed to provide rotational movement for the hand grips on handle arms  225 . The universal pivots are designed to enable the user engaging handle arms to self-align to the user during the exercise and automatically adjust to the user&#39;s hand position by providing minor adjustments in width positioning and wrist pronation/supination. 
     The connecting link  454  comprises a pair of generally L-shaped plates  460  having generally rounded edges. One end of each plate is pivotally mounted on pivot mount  237  at the end of main frame upright  195  for rotation about pivot axis  238 . The second end of each link plate  460  is pivotally attached to exercise arm connecting brackets  456  for rotation about a second pivot axis  462  which is spaced from the first exercise arm pivot axis  458 . It can be seen by comparison of  FIG. 33A  with  FIG. 13A  that the exercise arm connecting brackets  456  and connecting link  454  in this embodiment are of similar shape to connecting brackets  228  and connecting link  188  of machine  180 , but are inverted relative to the connecting brackets and connecting link in machine  180 . Additionally, the exercise arm  455  is rotated through ninety degrees relative to the orientation of exercise arm  224  in machine  180  of the third embodiment. This means that, in the start or rest position of  FIGS. 28 ,  29 ,  31 ,  33 A and  34 A, the opposite side portions of arm  455  project forward from link  456  on opposite sides of back rest  215 , instead of extending straight down behind the seat as in machine  180 . This means that handle arms  225  are oriented generally upward in the start or rest position. The connecting link pivot axis  462  is also positioned differently relative to the exercise arm pivot axis  458  on the user support. 
     In this design the user support is pivotally mounted to the main frame via the user support pivot mount  185 . The exercise arm is pivotally mounted to the user support by pivotally attaching a first pivot mount of connecting brackets  456  to a pivot connection on the seat support stand-off  230 . The connecting link pivotally joins pivot mount  237  on the main frame with a second pivot mount on connecting brackets  456 . 
     In order to perform the exercise, the user  80  sits on the seat with their back against the back pad  215 , upper arms against the arm support pads  222  and feet on the foot rests  206 . This places the user in a slightly reclined starting position. The user then grabs the user engaging hand grips  226  with their arms bent at the elbow and the handle arms  225  extending generally upwardly at a slight rearward angle, as illustrated in  FIG. 34A . The user starts the exercise movement by pushing the handles forward and downward. In this design there is no pivot point for the user to align their elbow with. The universal connection  235  on the user engaging handle arms compensates for this and automatically adjusts to the user arm length and hand position. 
     This movement causes the exercise arm to pivot about its connections to both the user support and the connecting link at pivot axes  458  and  462 . This causes the user support  184  to be pulled rearward, rotating about pivot axis  218  at its connection to the main frame. This pivotal action is designed to reorient the user&#39;s position from a slight recline to a substantial recline and duplicate the motion of “cheating” or explosively throwing the weights. This movement is done without changing the position of the user on the user support. Throughout the entire movement the user is in a stabilized position with their feet and upper torso supported. This stabilized position provides a strict exercise movement by preventing the involvement of other muscle groups and focusing effort just on the triceps. As in previous embodiments, the gravitational center line (vertical line extending through user support pivot axis  218 ) is positioned such that portions of the combined weight of the user and user support are located on both sides of the gravitational center line throughout the exercise movement. 
     In the above embodiments, the seat and arm support travel together to keep the user in the same position throughout the exercise motion. The user does not have to worry about balancing on a moving platform or pad. The user is placed in an exercise alignment from start to finish. The combined exercise arm and user support movement provide a self-aligning exercise motion that allows the user to achieve a full range of exercise motion and combines traditional exercise machines with free weight movements. 
     By linking movement of the user support to movement of the exercise arm and positioning the user support pivot so that the combined weight of the user support and user is distributed on both sides of the gravitational centerline, the user support provides a counter-balancing effect on the exercise arm as it moves and its weight is re-distributed. This balanced weight distribution positions a portion of the user and user support on each side of the gravitational centerline in both the start and finish positions. As the exercise arm is moved, a portion of this combined weight passes through the gravitational centerline, re-distributing the weight. This re-distribution is gradual and continuous throughout the exercise motion and is not noticed by the user. 
     In some of the above embodiments, a four-bar pivot system with a theoretical pivot is used for supporting the user support on the main frame. This arrangement takes the movement pattern of a single point pivot that might normally be located in an area impossible to access due to either structural or user interference and places the pivoting linkage beneath the user support and out of the way of the exercise movement. Without a four-bar pivot system, the desired combined exercise arm and user support movement may not be possible in some machine designs. In other embodiments described above, a single pivot mount connects the user support to the main frame and provides the desired movement of the user support. 
     The rocking movement of the user support can make the exercise more fun to perform. Repetitious exercise movement can be tedious and boring. By adding motion to the user support, performing the exercise may be enjoyable and the user&#39;s interest in their workout may increase. This is a benefit to both the individual user, who may be motivated to exercise more regularly, and the fitness facility, where retention of members is a primary objective. 
     In the above embodiments, the weight stack and frame can be positioned on either side of the main frame and user support, as desired. The guide tube and connecting rod between the main frame and weight stack frame are releasably connected to one or both frames, and can be removed to allow the weight stack frame to be reversed and placed on the opposite side of the machine. The guide tube and connecting rod are then re-attached and the cable and pulley linkage re-connected. 
     It should be understood that all the different elements used in the various embodiments may be mixed and interchanged with one another. The arm pads and/or back pad could be made adjustable; various types of user engaging handles could be used; the exercise arm could be unidirectional or bi-directional and may be a rigid exercise arm or a flexible line; the connecting links could be made adjustable, solid links could be replaced with flexible ones; and the connecting links could be made to push or pull to urge rotation of the user support. Any of the various designs could have the resistance associated with any of the moving parts (user support, exercise arm or connecting link). 
     It should also be noted that different types and forms of components could be used in the above embodiments without affecting the scope of this invention. Cables could be replaced with belts, ropes, chains or the like, pulleys replaced with sprockets, and tubes could be replaced with solid rods or bars. The arm rest, back pad (where present) and/or foot rest could be made adjustable. The foot rest can travel with the user support or be fixed to the frame. Other types of resistance know to the art could by used instead of the weight stack such as weight plates, hydraulic, pneumatic, electro-magnetic or elastic band resistance. 
     The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other embodiments without departing from the spirit or scope of the invention. Thus, it is to be understood that the description and drawings presented herein represent a presently preferred embodiment of the invention and are therefore representative of the subject matter which is broadly contemplated by the present invention. It is further understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and that the scope of the present invention is accordingly limited by nothing other than the appended claims.