Abstract:
An exercise machine with controlled motion and user force matching resistance. The machine includes a frame to which is rigidly mounted a motor driven reciprocating drive. A user engageable arm is pivotally mounted to the frame. The reciprocating drive is connected to the arm by a rigid connecting rod. The reciprocating drive drives the arm through a predetermined stroke following a pre-determined velocity profile. The user performs the exercise by applying force to the arm. The arm applies a generally equal counterforce to the force applied by the user. The pre-determined motion of the arm is generally independent of the force applied by the user. The stroke of the arm has a fixed fully contracted position and a user adjustable fully extended position. Adjustments to the fully extended position are made by changing the location of the joint between the connecting rod and the arm. Motion of the arm starts upon application of force applied by the user, and stops when the user force is removed.

Description:
BACKGROUND 
     Prior Art 
       [0001]    Controlled movement exercise with user force matching resistance is recognized as a highly effective form of exercise since it allows the user to exert the maximum force he or she is capable of at each position throughout the full range of the exercise motion. It is also considered as among the safest forms of resistance exercise and is employed in machines used for physical therapy. 
         [0002]    Despite these advantages, machines using controlled movement with user force matching resistance are rarely seen outside rehabilitation clinics due to their high cost, complexity and difficulty of adjustment and operation. Much of the complexity and cost comes from the motion and resistance controlling features themselves, as they include specialized electro-mechanical actuators, complex feedback features and often computer control in order to provide controlled movement resistance. Many make use of stepper or servo motors which in addition to being more expensive than a standard 120 volt single phase electric motor, have the additional expense of requiring a specialized power supply called an amplifier or driver. 
         [0003]    Most of the prior art machines use some form of geared drive between the motor and the output arm. However, there have been some attempts made at producing a machine using a linkage between the motor and the output arm, but all have had shortcomings. U.S. Pat. No. 4,635,933 to Schnell (1987) shows one such attempt using a crank mechanism driven by an electric motor. However, the design specifies that the electric motor be a reversible variable speed/variable torque type motor, which will require a control circuit to control the motor thereby adding to the expense of the machine. The means of adjusting the output stroke shown, simply changing the length of the crank or rocker arms, will simultaneously change the starting and ending points of the exercise stroke, likely causing the user to have to change position. The starting and stopping of the machine is in control of the user and is performed by an action of a body part, such as a hand or foot, which is not being exercised. 
         [0004]    U.S. Pat. No. 4,884,801 to Schnell (1989) shows another device using a flexible transmission member attached to a motor-driven crank to a user-actuated member. However, this device requires that the user activate the motor by the separate act of activating a switch either by hand or foot. There is also no provision to have the motor-driven crank stop or start in any particular position to allow for ease of adjustment or having a definite starting point to begin the exercise. Also, removal of the user force does not stop the motor. Furthermore, the stroke adjustment means shown will simultaneously change the starting and ending points of the exercise stroke, likely causing the user to have to change position. 
       Advantages 
       [0005]    Accordingly several advantages of one or more aspects are as follows: to provide an exercise device with controlled motion and user force matching resistance in which the motion and resistance features are driven by a standard 120 volt single phase electric motor, which supplies resistance in response to force generated by the user regardless of magnitude or fluctuation, which starts automatically on application of user force and stops automatically on removal of user force, which allows the user to perform both concentric and eccentric contractions, which does not require feedback or computer controls to provide resistance and maintain velocity, in which forced concentric contractions and eccentric contractions may be safely performed without a spotter, in which eccentric contractions only training is possible without a spotter, and which is simple for the user to adjust and operate. Other advantages of one or more aspects will be apparent from a consideration of the drawings and ensuing description. 
     
    
     
       DRAWINGS 
       Figures 
         [0006]      FIG. 1  shows a perspective view of an exercise machine in accordance with a first embodiment. 
           [0007]      FIG. 2  shows a perspective view of the frame subassembly from the first embodiment. 
           [0008]      FIG. 3  shows an exploded view of the adjustable seat subassembly from the first embodiment. 
           [0009]      FIG. 4  shows an exploded view of the exercise arm subassembly from the first embodiment. 
           [0010]      FIG. 5  shows an exploded detail view from  FIG. 4 . 
           [0011]      FIG. 6  shows a perspective view of the reciprocating drive from the first embodiment. 
           [0012]      FIG. 7  shows a perspective view of the reciprocating mechanism from the first embodiment. 
           [0013]      FIG. 8  shows a rear perspective view of the reciprocating mechanism from the first embodiment. 
           [0014]      FIG. 9  shows a perspective view of the connecting rod subassembly from the first embodiment. 
           [0015]      FIG. 10  shows the connecting rod subassembly connections from the first embodiment. 
           [0016]      FIG. 11  shows a perspective view of the control panel subassembly from the first embodiment. 
           [0017]      FIG. 12  shows an electrical schematic of the operating circuit from the first embodiment. 
           [0018]      FIG. 13  shows a block diagram detailing force measured and displayed from the first embodiment. 
           [0019]      FIG. 14  shows the user seated in the exercise machine from the first embodiment with the exercise arm in the fully contracted position. 
           [0020]      FIG. 15  shows the user seated in the exercise machine from the first embodiment with the exercise arm in the fully extended position. 
           [0021]      FIG. 16  shows a perspective view of an exercise machine in accordance with a second embodiment. 
           [0022]      FIG. 17  shows a perspective view of an exercise machine in accordance with a third embodiment. 
           [0023]      FIG. 18  shows a perspective view of a reciprocating mechanism in accordance with a second embodiment. 
           [0024]      FIG. 19  shows a perspective view of a reciprocating mechanism in accordance with a third embodiment. 
           [0025]      FIG. 20  shows a perspective view of a reciprocating mechanism in accordance with a fourth embodiment. 
           [0026]      FIG. 21  shows a perspective view of a reciprocating mechanism in accordance with a fifth embodiment. 
           [0027]      FIG. 22  shows a perspective view of a reciprocating mechanism in accordance with a sixth embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     FIGS.  1  Through  15 —First Embodiment 
       [0028]    A first embodiment of the exercise machine, designated broadly as  10 , is illustrated in  FIG. 1 . In this embodiment machine  10  is configured to perform a chest press exercise. Machine  10  includes a base or frame subassembly  12  to which is slidably connected an adjustable user support or seat subassembly  14 . An exercise arm subassembly  16  is pivotally connected to frame  12 . A reciprocating drive subassembly  18  is fixedly connected to frame  12 . A control panel subassembly  20  is pivotally connected to frame  12 . The output of drive subassembly  18  is connected to arm subassembly  16  by a link or connecting rod subassembly  22 . These components are described in detail below. 
         [0029]    Referring to  FIG. 2 , frame  12  includes a group of longitudinal frame members  24 A,  24 B and  24 C. Member  24 B includes a series of holes  26 . Holes  26  extend through both vertical faces of member  24 B, and are used in adjusting the longitudinal position of seat subassembly  14 . Members  24 A,  24 B and  24 C are rigidly and fixedly connected to a transverse frame member  28 A and a transverse frame member  28 B. A group of threaded holes  30  through the top horizontal faces of members  24 A,  24 B and  28 B are used to attach drive subassembly  18  to frame  12 . These assembled members are held off the floor by a group of feet  32 . A threaded hole  34  is located at two places on the front vertical face of member  28 A. Holes  34  are used to attach a pair of split bearing assemblies  36 . Each bearing subassembly  36  includes a bearing base section  38  having a set of through holes  40  and a bearing top section  42  having a set of through holes  44 . Both base section  38  and bearing top  42  have a half-cylindrical cut bearing surface  46 . A set of bolts  48  pass through holes  44  in bearing top  42 , holes  40  in base section  38  and into holes  34 , securing bearing assemblies  36  to member  28 A. 
         [0030]      FIG. 3  shows details of seat subassembly  14  which includes a back rest  52  connected to an upright column  54  using a set of bolts  56  through a group of holes  58  into threaded holes (not shown) in the rear face of back rest  52 . A seat holder bracket  60  is fixedly connected to the lower portion of column  54 . Bracket  60  includes a hole  62  that extends through both sides of bracket  60 . A seat adjustment bar  64  containing a group of adjustment holes  66  extending through both vertical side faces and a group of holes  68  in the top surface, is fixedly connected to the underside of a seat bottom  70  by a set of bolts  72  which go through holes  68  into a group of threaded holes (not shown) in the bottom face of seat bottom  70 . A seat adjustment pin  74  extends through hole  62  in bracket  60  and one of holes  66  in bar  64 . A carriage  76  is fixed to the bottom of column  54 . Carriage  76  has a hole  78  extending through both sides of carriage  76  and a set of holes  80  extending through both sides of carriage  76 . A pair of rods  82  extends through holes  80 . Rods  82  have a groove  84  at each end. An e-clip  86  fits into groove  84  at each end to hold rods  82  in carriage  76 . Carriage  76  is slidably mounted on member  24 B. Downward and sideways motion of carriage  76  is prevented by the body of carriage  76 , while upward motion is prevented by rods  82 . Carriage  76 , and thereby seat subassembly  14 , can slide along the length of member  24 B. To secure the position of seat subassembly  14 , a pin  88  is inserted through hole  78  in carriage  76  and into one of holes  26  in member  24 B. 
         [0031]    Referring to  FIGS. 4-5 , arm subassembly  16  includes an arm tube  90  having a lower horizontal section, two vertical sections and two collinear upper horizontal sections separated by a gap. A group of flanges  92 A,  92 B and  92 C are fixedly attached to the lower horizontal section of tube  90 . Flange  92 C has a series of through holes  94  laid out in a circular pattern. A pair of strain gauges  96 A and  96 B is mounted on the front surface of one vertical section of tube  90 . A second pair of strain gauges  96 C and  96 D (not shown) is mounted directly behind the first pair on the rear surface of the same vertical section of tube  90 . A pair of strain gauges  96 E and  96 F is mounted on the front surface of the opposite vertical section of tube  90 . A second pair of strain gauges  96 G and  96 H (not shown) is mounted directly behind the first pair on the rear surface of the same vertical section of tube  90 . An adjustment plate  98  has a series of tapped holes  100  laid out in a circular pattern, and a cutout  102  which allows it to fit over the lower horizontal section of tube  90 . Plate  98  is attached to flange  92 C using bolts  104 . Plate  98  has a circular arc shaped channel  106  with a series of through holes  108  running along the center of the channel, and tapped holes  110  in the top surface. A cap  112  has a pair of through holes  114  and is mounted to the top of plate  98  with a pair of bolts  116 . 
         [0032]    Referring to  FIG. 6 , drive subassembly  18  includes an electric motor  118 , a speed reducer  120 , a stand  122  and a reciprocating mechanism subassembly  124 . Speed reducer  120  is mounted to stand  122  using bolts (not shown). Stand  122 , motor  118  and mechanism  124  are mounted on a base plate  126  using bolts partially shown. A drive pulley  128  is mounted on the output shaft of motor  118 . A driven pulley  130  is mounted on the input shaft of speed reducer  120 . Drive pulley  128  drives driven pulley  130  through a flexible belt  132 . 
         [0033]    Referring to  FIGS. 7 and 8 , mechanism  124  includes a guide rail  134 , supported by a front post  136 A and a rear post  136 B. Rail  134  is attached to post  136 A and post  136 B by a pair of bolts  138 . A set of through holes  140  in the bottom flange of post  136 A and post  136 B allow mechanism  124  to be attached to plate  126 . A carriage  142  is slidably fixed over rail  134 . The outside vertical face of carriage  142  includes a stud  144 A, a stud  144 B and stud  144 C. An activation lever  146  contains a stud  148 A, a stud  148 B and a stud  148 C. Lever  146  is pivotally mounted on stud  144 A and is held in place by an e-ring clip  150 . A limit switch  152 A is mounted to the outside face of post  136 A using a set of screws  154 . A limit switch  152 B is mounted to the outside face of post  136 B using screws  154 . A limit switch  152 C is mounted to the top face of rail  134  using screws  154 . An extension spring  156  is connected between stud  144 B and stud  148 A. The inside vertical face of carriage  142  contains a slot  158 . A hub  160  is connected to a crank arm  162  which has a cam roller  164  mounted to its end. Roller  164  rides in slot  158 . Hub  160  is mounted on the output shaft of reducer  120 . 
         [0034]    Referring to  FIG. 9 , rod subassembly  22  includes a tube  166  at the front end of which is connected a yoke  168 . Yoke  168  includes a through hole  170  and a slot  172 . A pair of cylindrical projections  174 A and  174 B are concentric to hole  174  and project a short distance past the inside faces of slot  172 . A flat end  176  is attached to the rear end of tube  166 . A through hole  178  is located at the rear end of end  176 . 
         [0035]      FIG. 10  shows how the output of mechanism  124  is transmitted to arm subassembly  16  through rod subassembly  22 . Flat end  176  is pivotally mounted on stud  148 B and is secured in place by an e-clip  180 . Cylindrical Projections  174 A and  174 B ride in channel  106 . The location of yoke  168  along channel  106  is selected by a locating pin  182 . Referring to  FIG. 11 , control panel subassembly  20  includes a control box  184  which is mounted to a support tube  186 . Tube  186  is pivotally mounted on support stud  50 . Box  184  includes a display screen  188 , a three position DPDT control switch  190 , and a pair of normally open momentary push button switches  192 A and  192 B. 
         [0036]      FIG. 12  shows a control circuit schematic  194  which controls the operation of machine  10 . Components of circuit  194  contained in box  184  include a transformer  196  and a low voltage relay  198 . Circuit  194  is supplied with a standard AC voltage source  200 . Transformer  196  steps down the supplied 120 VAC to a safe lower level. Relay  198  operates at the low voltage supplied by transformer  196  and is capable of switching the supplied 120 VAC. Components of circuit  194  external to box  184  include switch  190 , switches  192 A and  192 B, switches  152 A,  152 B and  152 C, and motor  118 . 
         [0037]    Referring to  FIG. 13 , a display output diagram  202  is shown which details the operation of the display. Diagram  202  includes components internal and external to box  184 . External components include strain gauges  96 A,  96 B,  96 C and  96 D, connected to form a whetstone bridge  202 A, and strain gauges  96 E,  96 F,  96 G and  96 H, connected to form a second whetstone bridge  202 B. A source of electrical potential V supplies the excitation voltage to bridges  202 A and  202 B. Internal components include a pair of amplifiers  204 A and  204 B, a pair of analog to digital converters  206 A and  206 B, a micro-processer  208  and a multifunction display  210 . The arrangement shown in  FIG. 13  is well known in the art. 
       Operation 
       [0038]    Referring now to  FIGS. 1 , thru  15 , to use machine  10 , a user  212  first takes position in seat subassembly  14  as shown in  FIG. 14 : seated on seat bottom  70  with his or her back against back rest  52 . Seat subassembly  14  acts as a positioning system to allow adjustment of the position of user  212  relative to the arm subassembly  16 . If control panel subassembly  20  is positioned in front of seat subassembly  14 , user  212  can rotate control panel subassembly  20  to one side to gain access to seat bottom  70 . Once seated, user  212  rotates control panel subassembly  20  to its position in front of seat subassembly  14 . To perform the exercise, user  212  first adjusts the position of seat subassembly  14  to suit user  212 &#39;s seated shoulder height and reach. To begin these adjustments arm subassembly  16  should be in the fully contracted position, referred to as the initial position. If arm subassembly  16  is not already in this position, it may be moved there by placing control switch  190  into the adjustment mode position and pressing and holding switch  192 B. This action supplies low voltage DC power to relay  198 , which is activated and provides 120 VAC power to motor  118 . At this point drive subassembly  18  resumes its cycle at whatever point it stopped at previously, meaning that it may first cause arm subassembly  16  to move towards the fully extended position before moving towards the fully contracted position. Once arm subassembly  16  moves near its fully contracted position, carriage  142  contacts and activates limit switch  152 B, opening the circuit, removing power from relay  198 , which removes 120 VAC power from motor  118 . There will be some rotational inertia of motor  118  that will continue to move drive subassembly  18  and hence arm subassembly  16  slightly further. The activation point of limit switch  152 B can be adjusted to account for this additional motion, so that the final stopping point is as close to the fully contracted position as possible. Alternately an electromagnetic brake may be added to quickly stop motor  118 &#39;s rotation. 
         [0039]    Once arm subassembly  16  is in the fully contracted position, seat subassembly  14  adjustment can be achieved. User  212  adjusts the vertical position of seat subassembly  14  to a comfortable position to grasp upper horizontal portions of tube  90 . This will put user  212 &#39;s shoulder joint generally even with the upper horizontal sections of tube  90 . This adjustment is accomplished by removing pin  74  from bracket  60 , moving seat bottom  70  and attached bar  64  up or down as required, and replacing pin  74  back through hole  62  in bracket  60  and hole  66  in bar  64  closest to the desired position. User  212  then adjusts the front to back position of seat subassembly  14  to a comfortable position to grasp upper horizontal sections of tube  90  as close to user  212 &#39;s chest as is comfortable. This adjustment is accomplished by removing pin  88  from hole  78 , moving seat subassembly  14  to the rear or front as required, and replacing pin  88  through hole  78  in carriage  76  and hole  26  in member  24 B closest to the desired position. This type of adjustable seat is well known in the art. 
         [0040]    The adjustments of seat subassembly  14  being completed, user  212  next adjusts the fully extended point of the stroke of arm subassembly  16 . With control switch  190  in the adjustment mode position user  212  presses and holds adjustment switch  192 A. This action supplies low voltage DC power to relay  198 , which is activated and provides 120 VAC power to motor  118 . At this point drive subassembly  18  resumes its cycle at whatever point it stopped at previously, meaning that it may first cause arm subassembly  16  to move towards the fully contracted position before moving towards the fully extended position. Once arm subassembly  16  moves near its fully extended position, carriage  142  contacts and activates limit switch  152 A, opening the circuit, removing power from relay  198 , which removes 120 VAC power from motor  118 . There will be some rotational inertia of motor  118  that will continue to move drive subassembly  18  and hence arm subassembly  16  slightly further. The activation point of limit switch  152 A can be adjusted to account for this additional motion, so that the final stopping point is as close to the fully extended position as possible. Alternately an electromagnetic brake may be added to quickly stop motor  118 &#39;s rotation. 
         [0041]    At this point user  212  adjusts the fully extended position of arm subassembly  16  to a comfortable position. Ideally this position will allow user  212 , with his or her back firmly against back rest  52  and applying considerable force against the upper horizontal sections of tube  90 , close to full extension of his or her arms without locking the elbows, as depicted in  FIG. 15 . This adjustment is accomplished by removing pin  182  from hole  170  and moving yoke  168  of rod subassembly  22  up or down in channel  106 . Moving yoke  168  up will move arm subassembly  16  towards user  212 , resulting in a shorter total stroke. Moving yoke  168  down will move arm subassembly  16  away from user  212 , resulting in a longer total stroke. Once the desired fully extended position of arm subassembly  16  is determined, pin  182  is reinserted into hole  170  in yoke  168  and hole  108  in plate  98  closest to the desired position. This adjustment of the fully extended position of arm subassembly  16  does not affect the fully contracted position of arm subassembly  16  thereby requiring no adjustments of seat subassembly  14 . This is because the pattern of adjustment holes  108  in plate  98  are located on an circular arc, the radius of which is equal to the distance between holes  178  and  170  of rod subassembly  22 , and the center of which is concentric with stud  148 B when arm subassembly  16  is in the fully contracted position. This means that once the initial seat adjustments are made, they do not need to be further adjusted for changes to the fully extended position of arm subassembly  16 . This design feature allows an alternative method of fully extended position adjustment. If user  212  has used machine  10  in the past and is familiar with the desired fully extended position of arm subassembly  16 , the fully extended position may be set while arm subassembly  16  is in the fully contracted position by removing pin  182  from hole  170  and moving yoke  168  of rod subassembly  22  up or down in channel  106  until hole  170  lines up with the pre-known hole  108  in channel  106 . 
         [0042]    Once seat subassembly  14  and arm subassembly  16  are adjusted, user  212  could choose to follow the steps outlined above and return arm subassembly  16  to the start position prior to beginning the exercise, or user  212  could begin the exercise from the fully extended position of arm subassembly  16 . To begin the exercise, user  212  places control switch  190  into the ON position. With user  212 &#39;s back against back rest  52 , user  212  then grasps the two collinear upper horizontal sections of arm subassembly  16  and pushes them away from the his or her body. Seat subassembly  14  acts as a buttress to counter the user force applied to arm subassembly  16  and keep user  212  in place. The force applied by user  212  creates tensile force in rod  22  which transmits the force to lever  146 . The force must be sufficient to overcome the pre-loaded tension in spring  156 . This pre-load is selected to provide a means to automatically shut off power to electric motor  118  and hence the motion of arm subassembly  16  once user  212  removes force from arm subassembly  16 , and to prevent inadvertent low force contact with arm subassembly  16  from starting the machine at an undesirable time. Once this initial force is overcome, rod subassembly  22  pulls lever  146  against stud  144 D. This movement forces stud  148 C into limit switch  152 C. This completes the circuit supplying low voltage DC to relay  198  which thereby supplies 120 VAC to electric motor  118 . This causes drive subassembly  18  to begin cycling through its motion, driving the stroke of arm subassembly  16 . Arm subassembly  16  will continue to cycle between the positions of  FIGS. 14 and 15  as long as sufficient force is applied by user  212  to overcome the preloaded force in spring  156 . As a consequence user  212  can start out the exercise with his or her full strength and continue until user  212 &#39;s strength is insufficient to overcome the pre-loaded tension in spring  156 . The power output of motor  118  is chosen so that the rotational speed of the motor  118  and reducer  120 , and hence the cycle speed of mechanism  124  do not vary significantly regardless of the force applied by user  212  to arm subassembly  16 . In addition, the cycle speed is chosen so that from the aspect of user  212 , the movement may be considered quasi-static, resulting in a natural reaction force generated by machine  10  through arm subassembly  16  that has the same magnitude but the opposite direction of the force applied by user  212 . User  212  may also chose to apply the minimum force necessary to overcome the pre-loaded tension in spring  156  during the movement of arm subassembly  16  towards the fully extended position, and then apply full available strength during the movement of arm subassembly  16  towards the fully contracted position. This would constitute an eccentric contractions only exercise; know commonly in resistance training as negatives. These eccentric only contractions can also be added at the end of a concentric/eccentric exercise once the muscles become too exhausted to perform concentric contractions. These eccentric only or eccentric only after exhaustion movements are normally performed with the aid of a spotter who supplies the needed additional force to perform the concentric contraction, while allowing user  212  to perform the eccentric portion. 
       FIGS.  16 - 17   
     Alternate Embodiments 
       [0043]    A second embodiment of the exercise machine, designated broadly as  214 , is illustrated in  FIG. 16 . In this embodiment machine  214  is configured to perform a shoulder press exercise. As shown in  FIG. 16 , machine  214  contains seat subassembly  14 , arm subassembly  16 , drive subassembly  18 , control panel subassembly  20  and connecting rod subassembly  22 . These subassemblies have the same form and function as in the first embodiment described above. The only substantial difference in form is in the frame subassembly, herein designated as  12 ′. The frame members have been rearranged and additional members added to facilitate the different exercise movement. 
         [0044]    A third embodiment of the exercise machine, designated broadly as  216 , is illustrated in  FIG. 17 . In this embodiment machine  216  is configured to perform a leg press exercise. As shown in  FIG. 17 , machine  216  contains seat subassembly  14 , drive subassembly  18 , control panel subassembly  20  and connecting rod subassembly  22 . These subassemblies have the same form and function as in the first embodiment described above. The only substantial differences in form are in the frame subassembly, herein designated as  12 ″, and the arm subassembly, herein designated as  16 ′. As in the second embodiment above, the frame members in the third embodiment have been rearranged and additional members added to facilitate the different exercise movement. The arm subassembly has been reconfigured to interact with the user&#39;s feet. 
       FIGS.  18 - 22   
     Additional Embodiments 
       [0045]    Additional embodiments of some subassemblies of the machine can provide additional capabilities. For example, in  FIG. 18  studs  144 B,  144 C, and  144 D, switch  152 C and spring  156  in mechanism  124  are replaced with studs  144 B′,  144 C′, and  144 D′, switch  152 C′ and spring  156 ′. Switch  152 C′ is wired in circuit  194  just as switch  152 C is. With these changes, application of a compressive force on rod  22  rather than a tensile force on rod  22  will rotate lever  146  toward switch  152 C′, forcing stud  148 C into switch  152 C′ to activate circuit  194 . This embodiment of mechanism  124  is designated broadly by  124 ′ in  FIG. 18 . If mechanism  124  in machine  214  is replaced with mechanism  124 ′ then machine  214  embodiment becomes a pull down exercise machine embodiment. 
         [0046]    Similarly in machine  10  embodiment shown in  FIG. 1 , if seat subassembly  14  is rotated 180 degrees about its vertical axis, and mechanism  124  is replaced with mechanism  124 ′, machine  10  embodiment becomes a rowing exercise machine embodiment. 
         [0047]    Additionally, mechanism  124  may be configured as shown in  FIG. 19 . In this configuration studs  144 B and  144 C, switch  152 C and Spring  156  are combined with studs  144 B′, and  144 D′, switch  152 C′ and spring  156 ′. Lever  146  is balanced between the two pre-tensioned springs  156  and  156 ′ such that rotation of lever  146  is resisted in both directions. Studs  144 C and  144 D′ are positioned to allow sufficient movement of lever  146  in both directions so that full movement in one direction causes stud  148 C to activate switch  152 C while full movement in the opposite direction causes stud  148 C to activate switch  152 C′. Switch  152 C′ is wired in parallel with switch  152 C so that activation of either switch  152 C or switch  152 C′ will activate circuit  194 . This embodiment of mechanism  124  is designated broadly by  124 ″ in  FIG. 19 . If mechanism  124  is replaced with mechanism  124 ″ in machine  10 , then machine  10  becomes a combination chest press and rowing machine. If mechanism  124  is replaced with mechanism  124 ″ in machine  214 , then machine  214  becomes a combination shoulder press and pull down machine. Mechanism  124  in  FIGS. 7 and 8  may be modified to include a cam  218  and a follower  220  as shown in  FIG. 20 , a face cam  222  and follower  220  as shown in  FIG. 21 , or a six bar linkage  224  as shown in  FIG. 22 . 
       CONCLUSION, RAMIFICATIONS AND SCOPE 
       [0048]    Accordingly, the reader will see that the exercise machines of the various embodiments will provide exercise for the user that has both controlled motion that does not vary significantly regardless of the force applied by the user, and supplies a resistance as a consequence of the natural reactive force that matches the force applied by the user, regardless of magnitude or fluctuation. Furthermore, the exercise machine has the additional advantages in that:
       it is powered by a standard 120 volt single phase electric motor;   it starts automatically on application of user force and stops automatically on removal of user force;   it allows the user to perform both concentric and eccentric contractions;   it does not require feedback or computer controls to provide resistance and maintain velocity;   it allows forced concentric contractions and eccentric contractions may be safely performed without a spotter;   it allows eccentric contraction only training without a spotter;   it is simple for the user to adjust and operate.       
 
         [0056]    While the above description contains many specificities, these should not be construed as limitations on the scope of the embodiments but as merely providing illustration of some of several embodiments. For example frame  12  may include additional members, certain components may be formed from multiple pieces, motor  118  may be directly connected to speed reducer  120 , or motor  118  may be integrated with speed reducer  120  forming a gearmotor. Thus the scope of the embodiments the should be determined by the appended claims and their legal equivalents, rather than by the examples given.