Abstract:
An apparatus and a system include an electrically controlled motor comprising an output shaft, at least one winding and a rotor for exerting torque on the output shaft. An encoder senses and outputs a rotational position of the output shaft. A pulley is joined to the output shaft for converting a rotational motion to a linear motion. A cable is joined to the pulley where at least a portion of the cable is wound about the pulley. The cable is configured for joining to a resistance training system to provide a force element. A controller is in communication with the electrically controlled motor and the encoder for controlling the electrically controlled motor to exert a predetermined torque during motion of the cable in conjunction with operation of the resistance training system.

Description:
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    Not applicable. 
       REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER LISTING APPENDIX 
       [0002]    Not applicable. 
       COPYRIGHT NOTICE 
       [0003]    A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure as it appears in the Patent and Trademark Office, patent file or records, but otherwise reserves all copyright rights whatsoever. 
       FIELD OF THE INVENTION 
       [0004]    The present invention relates generally to fitness equipment. More particularly, the invention relates to an intelligent weight training resistance system. 
       BACKGROUND OF THE INVENTION 
       [0005]    The present invention relates to weight training systems. Most current fitness weight training devices rely on weight stacks or spring loading systems to provide resistance to a user. Weight stack devices are typically heavy and massive because the devices consist of actual weighted elements to provide resistance. There are known methods to reduce the actual amount of weight in the weight stacks by using pulley systems; however, pulley systems decrease the resolution of the weight selection. Furthermore, it is easy to get injured when using these systems. For example, if a user is trying to push up weight that is greater than his limit, as the weight is released it may pull the user&#39;s muscle. 
         [0006]    Spring loading types of systems are lighter than the weight stack systems; however, they tend to occupy a large amount of space to enable the spring loading rods to swing. Also spring loading systems cannot provide linear resistance throughout the range of motion. This greatly reduces the positive effect on the user during training. Another problem with spring loading systems is that over a period of time the system ages and may no longer provide the indicted weight. Thus, the user may receive false training information, which leads to bad exercise. 
         [0007]    In view of the foregoing, there is a need for improved techniques for providing a fitness weight training system that is lightweight, offers a small footprint, offers user definable resistance profiles, and offers injury protection functions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0009]      FIGS. 1A and 1B  illustrate an exemplary resistance training system, in accordance with an embodiment of the present invention.  FIG. 1A  is a front perspective view, and  FIG. 1B  is a diagrammatic side view; 
           [0010]      FIG. 2  is a graph illustrating exemplary torque output curves for two different motors from resistance training systems, in accordance with embodiments of the present invention; 
           [0011]      FIG. 3  is a diagrammatic side view of an exemplary resistance training system, in accordance with an embodiment of the present invention; 
           [0012]      FIG. 4  is diagrammatic front view of an exemplary resistance training system comprising a gear system, in accordance with an embodiment of the present invention; 
           [0013]      FIG. 5  is diagrammatic front view of an exemplary resistance training system comprising a synchronous belt, in accordance with an embodiment of the present invention; 
           [0014]      FIG. 6  is front perspective view of an exemplary resistance training system comprising a lever, in accordance with an embodiment of the present invention; 
           [0015]      FIG. 7  is a side view of an exemplary cable guiding system for a resistance training system, in accordance with an embodiment of the present invention; and 
           [0016]      FIG. 8  is an exemplary diagram of a motor, in accordance with an embodiment of the present invention. 
       
    
    
       [0017]    Unless otherwise indicated illustrations in the figures are not necessarily drawn to scale. 
       SUMMARY OF THE INVENTION 
       [0018]    To achieve the forgoing and other aspects and in accordance with the purpose of the invention, an apparatus and system for a resistance training system is presented. 
         [0019]    In one embodiment an apparatus includes an output shaft, means for exerting torque on the output shaft, means for sensing and for outputting a rotational position of the output shaft, means for converting a rotational motion to a linear motion, means for joining to a resistance training system to provide a force element, and means, in communication with the exerting means and the sensing means, for controlling the exerting means to exert a predetermined torque during motion of the joining means in conjunction with operation of the resistance training system. Another embodiment further includes means for enabling user setting of at least a value corresponding to the predetermined torque. Yet another embodiment further includes means for mitigating vibration. Still another embodiment further includes means for supporting the output shaft. Another embodiment further includes comprising means for enabling the joining means to be pulled in a plurality of directions relative to the converting means. 
         [0020]    In another embodiment an apparatus includes an electrically controlled motor comprising an output shaft, at least one winding and a rotor for exerting torque on the output shaft. An encoder senses and outputs a rotational position of the output shaft. A pulley is joined to the output shaft for converting a rotational motion to a linear motion. A cable is joined to the pulley where at least a portion of the cable is wound about the pulley. The cable is configured for joining to a resistance training system to provide a force element. A controller is in communication with the electrically controlled motor and the encoder for controlling the electrically controlled motor to exert a predetermined torque during motion of the cable in conjunction with operation of the resistance training system. Another embodiment further includes a user interface for enabling user setting of at least a value corresponding to the predetermined torque. Yet another embodiment further includes a flex coupling joining the pulley to the output shaft for mitigating vibration. Still another embodiment further includes at least one grounded bearing for supporting the output shaft. Another embodiment further includes a first pair of parallel rollers having a first space between the rollers, and a second pair of parallel rollers having a second space between the rollers. The second pair of parallel rollers is positioned perpendicular to the first pair of parallel rollers where an intersection of the first space and the second space produces a third space through which the cable passes for enabling the cable to be pulled in a plurality of directions relative to the pulley. In yet another embodiment the controller communicates an electrical current profile to the electrically controlled motor for electrically controlled motor to exert the predetermined torque. In still another embodiment the electrical current profile is at least, in part, determined by the rotor position relative to the winding and a level of current applied to the electrically controlled motor. In other embodiments the current profile represents a type of the force element, and types of the force element comprise linear and non-linear forces. 
         [0021]    In another embodiment a system includes an output shaft, means for exerting torque on the output shaft, means for sensing and for outputting a rotational position of the output shaft, means for transferring a force element to a user engaging in resistance training using the system, and means, in communication with the exerting means and the sensing means, for controlling exerting means to exert a predetermined torque during user operation of the system for resistance training. Another embodiment further includes means for converting a rotational motion to a linear motion, and means for joining the transferring means to the output shaft. Yet another embodiment further includes means for enabling user setting of at least a value corresponding to the predetermined torque. Still another embodiment further includes means for mitigating vibration. Another embodiment further includes means for enabling the joining means to be pulled in a plurality of directions. 
         [0022]    In another embodiment a system includes an output shaft. An electrically controlled motor exerts torque on the output shaft. An encoder senses and outputs a rotational position of the output shaft. A handle is joined to the output shaft for transferring a force element to a user engaging in resistance training using the system. A controller is in communication with the electrically controlled motor and the encoder for controlling the electrically controlled motor to exert a predetermined torque during user operation of the system for resistance training. Another embodiment further includes a pulley joined to the output shaft for converting a rotational motion to a linear motion, and a cable joined to the pulley, the pulley and the cable being configured for joining the handle to the output shaft. Yet another embodiment further a user interface for enabling user setting of at least a value corresponding to the predetermined torque. Still another embodiment further includes a flex coupling joining the pulley to the output shaft for mitigating vibration. Another embodiment further includes a first pair of parallel rollers having a first space between the rollers, and a second pair of parallel rollers having a second space between the rollers. The second pair of parallel rollers is positioned perpendicular to the first pair of parallel rollers where an intersection of the first space and the second space produces a third space through which the cable passes for enabling the cable to be pulled in a plurality of directions relative to the pulley. In yet another embodiment the controller communicates an electrical current profile to the electrically controlled motor for the predetermined torque. In still another embodiment the electrical current profile represents a type of the force element. In another embodiment types of the force element comprise linear and non-linear forces. In yet another embodiment the user interface displays to the user an amount of calories burned by the user. In still another embodiment absent a user applied force to the handle, the controller stops the electrically controlled motor. In another embodiment a rotational speed of the electrically controlled motor above a predetermined level initiates a modification of the electrical current profile to mitigate user injury. 
         [0023]    Other features, advantages, and aspects of the present invention will become more apparent and be more readily understood from the following detailed description, which should be read in conjunction with the accompanying drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The present invention is best understood by reference to the detailed figures and description set forth herein. 
         [0025]    Embodiments of the invention are discussed below with reference to the Figures. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. For example, it should be appreciated that those skilled in the art will, in light of the teachings of the present invention, recognize a multiplicity of alternate and suitable approaches, depending upon the needs of the particular application, to implement the functionality of any given detail described herein, beyond the particular implementation choices in the following embodiments described and shown. That is, there are numerous modifications and variations of the invention that are too numerous to be listed but that all fit within the scope of the invention. Also, singular words should be read as plural and vice versa and masculine as feminine and vice versa, where appropriate, and alternative embodiments do not necessarily imply that the two are mutually exclusive. 
         [0026]    It is to be further understood that the present invention is not limited to the particular methodology, compounds, materials, manufacturing techniques, uses, and applications, described herein, as these may vary. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “an element” is a reference to one or more elements and includes equivalents thereof known to those skilled in the art. Similarly, for another example, a reference to “a step” or “a means” is a reference to one or more steps or means and may include sub-steps and subservient means. All conjunctions used are to be understood in the most inclusive sense possible. Thus, the word “or” should be understood as having the definition of a logical “or” rather than that of a logical “exclusive or” unless the context clearly necessitates otherwise. Structures described herein are to be understood also to refer to functional equivalents of such structures. Language that may be construed to express approximation should be so understood unless the context clearly dictates otherwise. 
         [0027]    Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Preferred methods, techniques, devices, and materials are described, although any methods, techniques, devices, or materials similar or equivalent to those described herein may be used in the practice or testing of the present invention. Structures described herein are to be understood also to refer to functional equivalents of such structures. The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings. 
         [0028]    From reading the present disclosure, other variations and modifications will be apparent to persons skilled in the art. Such variations and modifications may involve equivalent and other features which are already known in the art, and which may be used instead of or in addition to features already described herein. 
         [0029]    Although Claims have been formulated in this Application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any Claim and whether or not it mitigates any or all of the same technical problems as does the present invention. 
         [0030]    Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. The Applicants hereby give notice that new Claims may be formulated to such features and/or combinations of such features during the prosecution of the present Application or of any further Application derived therefrom. 
         [0031]    As is well known to those skilled in the art many careful considerations and compromises typically must be made when designing for the optimal manufacture of a commercial implementation any system, and in particular, the embodiments of the present invention. A commercial implementation in accordance with the spirit and teachings of the present invention may configured according to the needs of the particular application, whereby any aspect(s), feature(s), function(s), result(s), component(s), approach(es), or step(s) of the teachings related to any described embodiment of the present invention may be suitably omitted, included, adapted, mixed and matched, or improved and/or optimized by those skilled in the art, using their average skills and known techniques, to achieve the desired implementation that addresses the needs of the particular application. 
         [0032]    Detailed descriptions of the preferred embodiments are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner. 
         [0033]    It is to be understood that any exact measurements/dimensions or particular construction materials indicated herein are solely provided as examples of suitable configurations and are not intended to be limiting in any way. Depending on the needs of the particular application, those skilled in the art will readily recognize, in light of the following teachings, a multiplicity of suitable alternative implementation details. 
         [0034]    At least some preferred embodiments of the present invention provide resistance training systems that incorporate the use of motors. At least some preferred embodiments are smaller than current systems and can provide multiple modes in weight training to be suitable for different users. Some embodiments may be implemented to be incorporated into current fitness equipment to enable this equipment to be smaller, lighter and more intelligent. At least some preferred embodiments enable a user to make a weight change on the fly, which can reduce injuries as well as increase the effectiveness of the training. At least some preferred embodiments reduce the chance of injury and provide better training to people who have little knowledge of fitness training to generally eliminate the need of a personal trainer, which reduces overall training cost and increases the effectiveness of the fitness training. At least some preferred embodiments may be implemented for home and commercial use as well as for professional athletes. At least some preferred embodiments may also be used in medical applications for the rehabilitation of muscle strength and for various bone linkages problems. 
         [0035]      FIGS. 1A and 1B  illustrate an exemplary resistance training system, in accordance with an embodiment of the present invention.  FIG. 1A  is a front perspective view, and  FIG. 1B  is a diagrammatic side view. A typical resistance training system consists of a cable or a lever that the user can pull or push. The cable or the lever is attached to a spring or weight brick to create the resistance. In the present embodiment, the resistance training system comprises a motor  101  with a pulley cable system to create friction or pulling force for fitness or rehabilitation purposes. Those skilled in the art, in light of the present teachings, will readily recognize that a multiplicity of suitable motors may be used for motor  101  including, but not limited to, BLDC motors, BLAC motors, AC induction motors, servo motors, stepping motors, etc. A motor shaft  103  is attached to a pulley  105  by using a flex coupling  107  to connect motor shaft  103  to a pulley shaft  109 . Flex coupling  107  reduces vibration; however, in alternate embodiments the motor shaft can be directly attached to the pulley as shown by way of example in  FIG. 3 . The use of motor  101  instead of bulky weight stacks or space consuming spring levers enables the resistance training system according to the present embodiment to be smaller and lighter than traditional resistance training systems. 
         [0036]    In the present embodiment, a cable  111  is attached to pulley  105 . Cable  111  winds around pulley  105 , and a handle  113  is provided to enable a user to more easily pull cable  111 ; however, handle  113  may be omitted. When the user pulls cable  111 , pulley  105  and pulley shaft  109  rotate, which causes motor shaft  103  to rotate, thus transferring the linear motion of cable  111  into a rotary motion, and when motor  101  rotates, cable  111  is wound around or unwound from pulley  105 , and thus translates the rotary motion of motor shaft  105  into the linear motion of cable  111 . An encoder  115  is attached to the back of motor  101 , which senses the position of motor shaft  103 . Those skilled in the art, in light of the present teachings, will readily recognize that a multiplicity of suitable types of encoders exist that may be used in the present embodiment including, but not limited to, magnetic encoders, resolver encoders, optical encoders, Hall sensors, or any type of device that can provide the information of the position motor shaft  103 . The encoder does not have to be mounted on the back of motor, it can be placed on the drum where the cable attached to or even use linear encoder instead. A purpose of the encoder device is to tell the controller the current position of the motor rotor and thus command the motor magnetic field to the proper position. So any other device that will give the position of the rotor directly or indirectly could be used for this application as well. In alternate embodiments, a servo closed loop control can be used to achieve the same function. In the present embodiment, when the user pulls cable  111 , the movement is sensed by encoder  115  and fed back to a controller  117 . Controller  117  then commands motor shaft  105  to move to the proper position and motor  101  to adjust the current of an electromagnetic coil within motor  101  to maintain the proper torque, which was previously set by the user. Per  FIG. 8 . When motor phase A and phase B have current in the winding as shown Ia and Ib, the winding creates two magnetic field, Ea and Eb. The controller adjust the amount of the current through the winding, by doing so, the controller can control the magnetic field that is generated by both of the coil. This magnetic field creates the magnetic force vector which make the rotor turn to the commanded position. This torque and other settings such as, but not limited to, weight, number of repetitions, time settings, etc. may be input by the user on a user interface  119 . User interface  119  may be connected to controller  117  through wires or wirelessly. User interface  119  is preferably a digital interface, which is easier to control than a mechanical interface. However, in an alternate embodiment a mechanical dial may be used as for the user input rather than a digital interface. In alternate embodiments, the encoder and the controller may be integrated together into a single unit mounted on the motor. Furthermore, the user interface in some embodiments may also be mounted on the motor. The controller can be linked with wire or wireless. In the present embodiment, support bearings  121  provide support for pulley shaft  109 . Alternate embodiments may be implemented with more, fewer or no support bearings depending on the actual configuration of the motor and the pulley. 
         [0037]    In typical use of the present embodiment, a user enters the weight or torque at which he would like to train into user interface  119 . In some embodiments the user may also enter other settings such as, but not limited to, number of repetitions, time settings, etc. If the user has entered a number of repetitions or time duration, interface  119 , in conjunction with controller  117 , will start increase current of motor  101  to the set value at the beginning of the session, and lower the current of motor  101  to idle value at the end of the repetitions or time. In some other embodiments, interface  119  may include audio and/or visual indicators to inform the user when to start the session and when the session is over. In some embodiments the user may stop at any time and reset the parameter of the session. Once the user has entered the parameter for the session, and the system indicates it is ready, the user then pulls on handle  113 , and motor  101  outputs the torque or weight entered to provide the desired resistance for training. Controller  117  controls motor  101  using position feedback from encoder  115  to determine the current position of motor shaft  103 . Based on the current position of motor shaft  103 , controller  117  adjusts a winding coil current phase position to create a lag related to the position of motor shaft  103 , which creates friction force or pull force on cable  111 . Once motor shaft  103  is moved from its original position by the user via cable  111 , encoder  115  reads the current position of motor shaft  103  and sends this information to controller  117 . Controller  117  then commands the driver of motor  101  to adjust the coil current Ia, Ib, thus move the magnetic field of the winding in order to keep the winding position lagging to the current rotor position. This enables a constant torque to be created by motor  101  so that, no matter where motor shaft  103  is positioned, there is always a force being applied to cable  111 . 
         [0038]    In the present embodiment, motor  101  enables the user to vary the resistance and force through the adjustment of the relative position of motor shaft  103  compared to the position of the magnetic field of the coil or by changing the winding current level. per  FIG. 8  assuming the motor have no load on the rotor shaft: when the winding have current running through, the rotor have a natural parking position as indicated in the figure as position  1 . By changing the current in winding A and B, this position will be changed because of the change of magnetic field in the motor. Once the user put load onto the motor shaft, the motor shaft will be at actual motor rotor position which is marked as  2  in the figure. The encoder then sends the current shaft position to the controller. The controller then commands the winding current to change in order to follow the actual rotor position and keep a certain distance to create the friction. Depends on the speed, current, and other factors, this difference is designed to be changed on the fly. The actual formula of the distance between position  1  and position  2  is to be kept as a commercial secret. On the other hand. By simply change the winding current in both windings, the controller can change the strength of the magnetic field. Then the torque that is generated can be changed as well. This enables the resistance training system to achieve instant weight change. The friction force that is created by motor  101  can be adjusted by the position of motor shaft  103  relative to the winding current phase position. With encoder  115  on the back of motor  101  sending current motor shaft position information to controller  117 , controller  117  can direct the electrical phase position of motor  101  to either lead or lag the position of motor shaft  103  to create either pulling force or friction. By adjusting the amount of lead or lag, controller  117  can adjust the force or friction created by motor  101 . At the same time, controller  117  can adjust the current level in the motor winding to create different friction force. (the forgoing sentence kind of duplicated what was added before, please review them) The ease with which the force output of motor shaft  103  can be changed enables the resistance training system to provide different force elements to make training more effective. Force elements include linear and non-linear forces modes such as output mode includes, but not limited to, constant force mode, which the output of the force is constant; linear spring mode, in which the force increases linearly as the length of the cable being pulled from the original location increases; inertia mode, the force output simulates the feel of pulling the actual weight; push mode, the force output simulates pushing a heavy item on a leveled surface, which provides friction only, but will not retract the cable once the user stop pulling the cable or the lever. In an alternate embodiment, force adjustment may also be achieved through force/load sensor feedback to the controller. In this embodiment, the torque output from the motor or the pulling force exerted on the handle is constantly monitored by a torque/force/load sensor and compared with the value that was set by the user on the user interface. If the torque or force varies at any point from this set value, the current of the motor is adjusted in real time to meet the force requirement. 
         [0039]    In the present embodiment, the current profile generated by controller  117  can be modified to imitate the feel of a spring type of device or to imitate the feel of lifting an actual weight. To imitate the feeling of a spring type of device, the force or torque output of motor  101  can be set to change linearly according to the distance that handle  113  travels from its original position. To imitate the feeling of lifting an actual weight, the force is modified based on the acceleration of handle  113 . Based on the input of encoder  115 , controller  117  can calculated the speed and acceleration of handle  113 , and based on Newton second Law, the force required to make this change in velocity can be calculated. This force is then factored into the force output by motor  101  to imitate the feeling of inertia. 
         [0040]    The present embodiment may also calculate the calories that have been consumed by the user. This calculation is based on the speed, force, and distance of the cable that is traveled. The number of calories burned is preferably displayed on user interface  119 . Alternate embodiments may be implemented without a calorie-counting feature. The present embodiment also includes an emergency stop or force cutback feature that activates when the speed of motor shaft  103  is too fast. Encoder  115  can feedback the current position of pulley  111 , and based on this, controller  117  can calculate the speed of motor shaft  103 . If the speed is too fast, controller  117  can either lower the current, thus lowering the torque, or stop motor  101  immediately. This feature provides injury protection to the user by generally preventing the user from pulling or releasing handle  113  too fast, which may cause the user to pull a muscle. Alternate embodiments may not include this feature. 
         [0041]      FIG. 2  is a graph illustrating exemplary torque output curves for two different motors from resistance training systems, in accordance with embodiments of the present invention. Constant resistance and force have been achieved with these motors by adjusting the current within the motors according to the speed of the motor shafts. The motors have characteristic torque output curves for different windings. The torque output curves show the maximum torque at different currents, voltages and speeds. In order to maintain a constant or preprogrammed torque output profile, the system must be able to output the proper torque at different speeds. To accomplish this, the encoder sends position information to the controller, and the controller then calculates the speed of the motor. Based on this calculation, the controller can find the corresponding current value to output the proper torque at that given moment. 
         [0042]    Those skilled in the art, in light of the present teachings, will readily recognize that the configuration of the resistance training system may vary widely in alternate embodiments. For example, without limitation, the pulley may be located in various different locations, multiple pulleys may be used, different types of mechanisms such as, but not limited to, gears, belts, levers, and chains may be used, etc.  FIGS. 3 through 7  illustrate some non-limiting examples of alternate embodiments of the present invention. 
         [0043]      FIG. 3  is a diagrammatic side view of an exemplary resistance training system, in accordance with an embodiment of the present invention. In the present embodiment, a pulley  303  is directly connected to a motor shaft  303  of a motor  301  without a flex coupling. A support bearing  321  provides support to a motor shaft  303 . 
         [0044]      FIG. 4  is diagrammatic side view of an exemplary resistance training system comprising a gear system  400 , in accordance with an embodiment of the present invention. In the present embodiment, a pulley  405  is connected to a motor shaft  403  of a motor  401  by gear system  400 . A small gear of gear system  400  is attached to motor shaft  403 , and a large gear of gear system  400  is attached to a pulley shaft  409 . The small gear rotates as motor shaft  403  rotates, and the rotation of the small gear causes the large gear, which meshes with the small gear, to rotate. This then causes pulley shaft  409  and pulley  405  to rotate. In alternate embodiments the sizes and number of the gears in the gear system may vary in order to translate the output torque of the motor shaft into the desired torque on the pulley. 
         [0045]      FIG. 5  is diagrammatic side view of an exemplary resistance training system comprising a synchronous belt  500 , in accordance with an embodiment of the present invention. In the present embodiment, synchronous belt  500  is connected to a motor shaft  503  of motor  501  and to a disc  502  on a pulley shaft  509 . A pulley  505   s  also attached to pulley shaft  509  and, therefore, rotates as disc  502  is rotated by belt  500 , which is rotated by motor shaft  503 . In alternate embodiments a chain-driven system may be used in place of a belt-driven system. 
         [0046]      FIG. 6  is diagrammatic side view of an exemplary resistance training system comprising a lever  600 , in accordance with an embodiment of the present invention. Lever  600  is attached directly to a motor shaft  603  of a motor  601 . In typical use of the present embodiment, a user pushes or pulls lever  600  rather than pulling a cable attached to a pulley. Since lever  600  can be pushed, the present embodiment can include a push mode. In the push mode, the user pushes lever  600 , and once the user stops pushing, lever  600  does not retreat. This mode enables the user to attempt to apply the most force that he can output, without fear that the system will be is over loaded. In this mode, the encoder feeds the current position of lever  600  to the controller, and the magnetic field of motor  301  only creates the lag without moving the position of motor shaft  603 . 
         [0047]      FIG. 7  is a side view of an exemplary cable guiding system  700  for a resistance training system, in accordance with an embodiment of the present invention. In the present embodiment, cable guiding system  700  comprises two pairs of parallel rollers sitting perpendicular to each other so that a small hole  702  is formed in the center of the four rollers. A cable  711 , which is wound around a pulley  705 , is fed through hole  702 . Cable guiding system  700  enables cable  711  to be pulled in any direction smoothly. 
         [0048]      FIG. 8  is an exemplary diagram of a motor, in accordance with an embodiment of the present invention. Motor phase A and phase B have currents Ia and Ib in the windings. The windings create two magnetic fields, Ea and Eb. Controller  117  adjusts the amount of the current through the windings, by doing so, controller  117  can control the magnetic field that is generated by both of the coil. This magnetic field creates a magnetic force vector which make the rotor turn to the commanded position. When the motor has no load on the rotor shaft and the windings have current running through them, the rotor has a natural parking position as indicated in the figure as position  1 . By changing the current in windings A and B, this position will be changed because of the change of magnetic field in the motor. Once the user put load onto the motor shaft, the motor shaft will be at actual motor rotor position, which is marked as position  2  in the figure. The encoder  115  then sends the current shaft position to controller  117 . Then controller  117  commands the winding currents to change in order to follow the actual rotor position and keep a certain lag distance to create the friction force. This lag difference may be changed on the fly. By changing the winding current in both windings, the controller can change the strength of the magnetic fields and the torque that is generated. 
         [0049]    Having fully described at least one embodiment of the present invention, other equivalent or alternative methods of providing a resistance training system according to the present invention will be apparent to those skilled in the art. The invention has been described above by way of illustration, and the specific embodiments disclosed are not intended to limit the invention to the particular forms disclosed. For example, the particular implementation of the system may vary depending upon the particular type of exercise being performed. The systems described in the foregoing were directed to single handle or lever implementations for use with exercises involving only one arm, leg or other part of the body; however, similar techniques are to provide systems with multiple handles or levers to enable a user to pull or push with multiple parts of the body at once for example, without limitation, using both arms in a rowing motion. In these implementations the multiple handles or levers may all be controlled by the same motor or may each be controlled by a separate motor. Multiple handle or lever implementations of the present invention are contemplated as within the scope of the present invention. The invention is thus to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the following claims. 
         [0050]    Claim elements and steps herein may have been numbered and/or lettered solely as an aid in readability and understanding. Any such numbering and lettering in itself is not intended to and should not be taken to indicate the ordering of elements and/or steps in the claims.