Abstract:
In an elliptical step exercise apparatus where stride length can be varied the various user programs can take advantage of this feature to provide for an enhanced workout. A control system can be used to implement a preprogrammed exercise routine such as a hill program where stride is shortened as the user goes up a simulated hill and lengthened as the user goes down the hill. In an interval training program, stride length can be increased and decreased at periodic intervals. In a cross training program, stride length can be decreased when the user is pedaling backwards and increased when the user is pedaling forwards.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation in part of U.S. Non-Provisional patent applications Ser. No. P-109,352, filed Aug. 23, 2004; Ser. No. 10/787,788, filed Feb. 26, 2004; and Ser. No. 09/835,672, filed Apr. 16, 2001 and claims priority on U.S. Provisional Patent Applications Ser. No. 60/450,812, filed Feb. 27, 2003 and Ser. No. 60/501,988, filed Sep. 11, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention generally relates mechanisms to control exercise equipment and in particular to programs for controlling stride adjustment of elliptical exercise equipment.  
       BACKGROUND OF THE INVENTION  
       [0003]     There are a number of different types of exercise apparatus that exercise a user&#39;s lower body by providing a generally elliptical stepping motion. These elliptical stepping apparatus provide advantages over other types of exercise apparatuses. For example, the elliptical stepping motion generally reduces shock on the user&#39;s knees as can occur when a treadmill is used. In addition, elliptical stepping apparatuses tend to exercise the user&#39;s lower body to a greater extent than, for example, cycling-type exercise apparatuses. Examples of elliptical stepping apparatuses are shown in U.S. Pat. Nos. 3,316,898; 5,242,343; 5,383,829; 5,499,956; 5,529,555, 5,685,804; 5,743,834, 5,759,136; 5,762,588; 5,779,599; 5,577,985, 5,792,026; 5,895,339, 5,899,833, 6,027,431, 6,099,439, 6,146,313, and German Patent No. DE 2 919 494.  
         [0004]     A feature of some elliptical stepping apparatus is the ability to adjust stride length. Naturally, different people have different stride lengths and the exercise apparatus and it is desirable to accommodate each user so that they have a more comfortable and efficient workout. Existing elliptical stepping machines can compensate for people who have different stride lengths to a limited extent. However, such machines are not able to change the stride length during the operation of the device which can be a disadvantage. For example, existing elliptical stepping machines are not able to cope with the effect of increasing foot speed to result longer stride lengths. As a result, a problem with elliptical exercise machines is that they are not able to adjust horizontal stride length to compensate for various machine operating parameters or user exercise programs.  
       SUMMARY OF THE INVENTION  
       [0005]     It is therefore an object of the invention to provide a mechanism for adjusting stride length in an elliptical type machine in order to compensate or respond to various machine operating parameters or exercise.  
         [0006]     A further object of the invention is to use an adjustable stride mechanism and a control system to compensate for machine operating parameters such as pedal speed or direction.  
         [0007]     An additional object of the invention is to use an adjustable stride mechanism and program logic in the control system of an elliptical stepper machine to implement various exercise programs that utilize varying stride lengths. Such programs can include a hill program, a random program, an interval program and a cross training program that includes changing direction of the stepping motion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a side perspective view of an elliptical stepping exercise apparatus;  
         [0009]      FIG. 2  is a schematic and block diagram of representative mechanical and electrical components of an example of an elliptical stepping exercise apparatus in which the method of the invention can be implemented;  
         [0010]      FIG. 3  is a plan layout of a display console for use with the elliptical exercise apparatus shown in  FIG. 2 ;  
         [0011]      FIGS. 4 and 5  are views of a mechanism for use in adjusting stride length in an elliptical stepping apparatus of the type shown in  FIG. 1 ;  
         [0012]      FIGS. 6A, 6B ,  6 C and  6 D are schematic diagrams illustrating the operation of the mechanism of  FIGS. 4 and 5  for a 180 degree phase angle;  
         [0013]      FIGS. 7A, 7B ,  7 C and  7 D are schematic diagrams illustrating the operation of the mechanism of  FIGS. 4 and 5  for a 60 degree phase angle;  
         [0014]      FIGS. 8A, 8B ,  8 C and  8 D are schematic diagrams illustrating the operation of the mechanism of  FIGS. 4 and 5  for a zero degree phase angle;  
         [0015]      FIGS. 9A, 9B  and  9 C are a set of schematic diagrams illustrating angle measurements that can be used to determine stride length in an elliptical stepping apparatus of the type shown in  FIG. 1 ;  
         [0016]      FIG. 10  is a flow diagram illustrating the operation of exercise program operations in an apparatus of the type shown in  FIG. 1 ; and  
         [0017]      FIG. 11  is a flow diagram illustrating the operation of exercise program operations incorporating variable stride lengths in an apparatus of the type shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  depicts a representive example of an elliptical step exercise apparatus  10  of the type that can be modified to have the capability of adjusting the stride or the path of the foot pedal  12 . The exercise apparatus  10  includes a frame, shown generally at  14 . The frame  14  includes vertical support members  16 ,  18 A and  18 B which are secured to a longitudinal support member  20 . The frame  14  further includes cross members  22  and  24  which are also secured to and bisect the longitudinal support member  20 . The cross members  22  and  24  are configured for placement on a floor  26 . A pair of levelers,  28 A and  28 B are secured to cross member  24  so that if the floor  26  is uneven, the cross member  24  can be raised or lowered such that the cross member  24 , and the longitudinal support member  20  are substantially level. Additionally, a pair of wheels  30  are secured to the longitudinal support member  20  of the frame  14  at the rear of the exercise apparatus  10  so that the exercise apparatus  10  is easily moveable.  
         [0019]     The exercise apparatus  10  further includes the rocker  32 , an attachment assembly  34  and a resistance or motion controlling assembly  36 . The motion controlling assembly  36  includes the pulley  38  supported by vertical support members  18 A and  18 B around the pivot axle  40 . The motion controlling assembly  36  also includes resistive force and control components, including the alternator  42  and the speed increasing transmission  44  that includes the pulley  38 . The alternator  42  provides a resistive torque that is transmitted to the pedal  12  and to the rocker  32  through the speed increasing transmission  44 . The alternator  42  thus acts as a brake to apply a controllable resistive force to the movement of the pedal  12  and the movement of the rocker  32 . Alternatively, a resistive force can be provided by any suitable component, for example, by an eddy current brake, a friction brake, a band brake or a hydraulic braking system. Specifically, the speed increasing transmission  44  includes the pulley  38  which is coupled by the first belt  46  to the second double pulley  48 . The second double pulley  48  is then connected to the alternator  42  by a second belt  47 . The speed increasing transmission  44  thereby transmits the resistive force provided by the alternator  42  to the pedal  12  and the rocker  32  via the pulley  38 . The pedal lever  50  includes a first portion  52 , a second portion  54  and a third portion  56 . The first portion  52  of the pedal lever  50  has a forward end  58 . The pedal  12  is secured to the top surface  60  of the second portion  54  of the pedal lever  50  by any suitable securing means. In this apparatus  10 , the pedal  12  is secured such that the pedal  12  is substantially parallel to the second portion of the pedal lever  54 . A bracket  62  is located at the rearward end  64  of the second portion  54 . The third portion  56  of the pedal lever  50  has a rearward end  66 .  
         [0020]     In this particular example of an elliptical step apparatus, the crank  68  is connected to and rotates about the pivot axle  40  and a roller axle  69  is secured to the other end of the crank  68  to rotatably mount the roller  70  so that it can rotate about the roller axle  69 . The extension arm  72  is secured to the roller axle  69  making it an extension of the crank  68 . The extension arm  72  is fixed with respect to the crank  68  and together they both rotate about the pivot axle  40 . The rearward end of the attachment assembly  34  is pivotally connected to the end of the extension arm  72 . The forward end of the attachment assembly  34  is pivotally connected to the bracket  62 .  
         [0021]     The pedal  12  of the exercise apparatus  10  includes a toe portion  74  and a heel portion  76  so that the heel portion  76  is intermediate the toe portion  74  and the pivot axle  40 . The pedal  12  of the exercise apparatus  10  also includes a top surface  78 . The pedal  12  is secured to the top surface  60  of the pedal lever  50  in a manner so that the desired foot weight distribution and flexure are achieved when the pedal  12  travels in the substantially elliptical pathway as the rearward end  66  of the third portion  56  of the pedal lever  50  rolls on top of the roller  70 , traveling in a rotationally arcuate pathway with respect to the pivot axle  40  and moves in an elliptical pathway around the pivot axle  40 . Since the rearward end  66  of the pedal lever  50  is not maintained at a predetermined distance from the pivot axis  40  but instead follows the elliptical pathway, a more refined foot motion is achieved. It should be understood however that the invention can be implemented on other configurations of elliptical step apparatus having a variety of mechanisms for providing elliptical foot motion including the devices described in the patents referenced above as well as such machines shown in U.S. Pat. No. 6,176,814.  
         [0022]      FIG. 2  is a combination schematic and block diagram that provides an environment for describing the invention and for simplicity shows in schematic form only one of two pedal mechanisms typically used in an elliptical stepping exercise apparatus such as the apparatus  10 . In particular, the exercise apparatus  10  described herein includes motion controlling components which operate in conjunction with an attachment assembly to provide an elliptical stepping exercise experience for the user. Included in this example of an elliptical stepping exercise apparatus  10  are the rocker  32 , the pedal  12  secured to the pedal lever  50 , the pulley  38  supported by the vertical support members  18 A and  18 B and which is rotatable on the pivot axle  40 . This embodiment also includes an arm handle  80  that is connected to the rocker  32  at a pivot point  82  on the frame of the apparatus  10 . The crank  68  is generally connected to one end of the pedal lever  50  by an attachment assembly represented by the box  34  and rotates with the pulley  38  while the other end of the pedal lever  50  is pivotally attached to the rocker  32  at the pivot point  84 .  
         [0023]     The apparatus  10  as represented in  FIG. 2  also includes resistive force and control components, including the alternator  42  and the speed increasing transmission  44  that includes the pulley  38 . The alternator  42  provides a resistive torque that is transmitted to the pedal  12  and to the rocker  32  through the speed increasing transmission  44 . The alternator  42  thus acts as a brake to apply a controllable resistive force to the movement of the pedal  12  and the movement of the rocker  32 . Alternatively, a resistive force can be provided by any suitable component, for example, by an eddy current brake, a friction brake, a band brake or a hydraulic braking system. Specifically, the speed increasing transmission  44  includes the pulley  38  which is coupled by a first belt  46  to a second double pulley  48 . A second belt  47  connects the second double pulley  48  to a flywheel  86  of the alternator  42 . The speed increasing transmission  44  thereby transmits the resistive force provided by the alternator  42  to the pedal  12  and the rocker  32  via the pulley  38 . Since the speed increasing transmission  44  causes the alternator  42  to rotate at a greater rate than the pivot axle  40 , the alternator  42  can provide a more controlled resistance force. Preferably the speed increasing transmission  44  should increase the rate of rotation of the alternator  42  by a factor of 20 to 60 times the rate of rotation of the pivot axle  40  and in this embodiment the pulleys  38  and  48  are sized to provide a multiplication in speed by a factor of 40. Also, size of the transmission  44  is reduced by providing a two stage transmission using pulleys  38  and  48 .  
         [0024]      FIG. 2  additionally provides an illustration of a control system  88  and a user input and display console  90  that can be used with elliptical exercise apparatus  10  or other similar elliptical exercise apparatus to implement the invention. In this particular embodiment of the control system  88 , a microprocessor  92  is housed within the console  90  and is operatively connected to the alternator  42  via a power control board  94 . The alternator  42  is also operatively connected to a ground through load resistors  96 . A pulse width modulated output signal on a line  98  from the power control board  94  is controlled by the microprocessor  92  and varies the current applied to the field of the alternator  42  by a predetermined field control signal on a line  100 , in order to provide a resistive force which is transmitted to the pedal  12  and to the arm  80 . When the user steps on the pedal  12 , the motion of the pedal  12  is detected as a change in an RPM signal which represents pedal speed on a line  102 . It should be noted that other types of speed sensors such as optical sensors can be used in machines of the type  10  to provide pedal speed signals. Thereafter, as explained in more detail below, the resistive force of the alternator  42  is varied by the microprocessor  92  in accordance with the specific exercise program selected by the user so that the user can operate the pedal  12  as previously described.  
         [0025]     The alternator  42  and the microprocessor  92  also interact to stop the motion of the pedal  12  when, for example, the user wants to terminate his exercise session on the apparatus  10 . A data input center  104 , which is operatively connected to the microprocessor  92  over a line  106 , includes a brake key  108 , as shown in  FIG. 3 , that can be employed by the user to stop the rotation of the pulley  38  and hence the motion of the pedal  12 . When the user depresses the brake key  108 , a stop signal is transmitted to the microprocessor  92  via an output signal on the line  106  of the data input center  104 . Thereafter, the field control signal  100  of the microprocessor  92  is varied to increase the resistive load applied to the alternator  42 . The output signal  98  of the alternator provides a measurement of the speed at which the pedal  12  is moving as a function of the revolutions per minute (RPM) of the alternator  42 . A second output signal on the line  102  of the power control board  94  transmits the RPM signal to the microprocessor  92 . The microprocessor  92  continues to apply a resistive load to the alternator  42  via the power control board  94  until the RPM equals a predetermined minimum which, in the preferred embodiment, is equal to or less than 5 RPM.  
         [0026]     In this embodiment, the microprocessor  92  can also vary the resistive force of the alternator  42  in response to the user&#39;s input to provide different exercise levels. A message center  110  includes an alpha-numeric display screen  112 , shown in  FIG. 3 , that displays messages to prompt the user in selecting one of several pre-programmed exercise levels. In the illustrated embodiment, there are twenty-four pre-programmed exercise levels, with level one being the least difficult and level  24  the most difficult. The data input center  104  includes a numeric key pad  114  and a pair of selection arrows  116 , shown in  FIG. 3 , either of which can be employed by the user to choose one of the pre-programmed exercise levels. For example, the user can select an exercise level by entering the number, corresponding to the exercise level, on the numeric keypad  114  and thereafter depressing a start/enter key  118 . Alternatively, the user can select the desired exercise level by using the selection arrows  116  to change the level displayed on the alpha-numeric display screen  112  and thereafter depressing the start/enter key  118  when the desired exercise level is displayed. The data input center  104  also includes a clear/pause key  120 , show in  FIG. 3 , which can be pressed by the user to clear or erase the data input before the start/enter key  118  is pressed. In addition, the exercise apparatus  10  includes a user-feedback apparatus that informs the user if the data entered are appropriate. In this embodiment, the user feed-back apparatus is a speaker  122 , that is operatively connected to the microprocessor  92 . The speaker  122  generates two sounds, one of which signals an improper selection and the second of which signals a proper selection. For example, if the user enters a number between 1 and 24 in response to the exercise level prompt displayed on the alpha-numeric screen  112 , the speaker  122  generates the correct-input sound. On the other hand, if the user enters an incorrect datum, such as the number  100  for an exercise level, the speaker  122  generates the incorrect-input sound thereby informing the user that the data input was improper. The alpha-numeric display screen  112  also displays a message that informs the user that the data input was improper. Once the user selects the desired appropriate exercise level, the microprocessor  92  transmits a field control signal on the line  100  that sets the resistive load applied to the alternator  42  to a level corresponding with the pre-programmed exercise level chosen by the user.  
         [0027]     The message center  110  displays various types of information while the user is exercising on the apparatus  10 . As shown in  FIG. 3 , the alpha-numeric display panel  124 , shown on  FIG. 3 , is divided into four sub-panels  126 A-D, each of which is associated with specific types of information. Labels  128 A-K and LED indicators  130 A-K located above the sub-panels  126 A-D indicate the type of information displayed in the sub-panels  126 A-D. The first sub-panel  126 A displays the time elapsed since the user began exercising on the exercise apparatus  10  or the current stride length of the apparatus  10 . One of the LED indicators  130 A or  130 K is illuminated depending if time or stride length is being displayed. The second sub-panel  126 B displays the pace at which the user is exercising. In the preferred embodiment, the pace can be displayed in miles per hour, minutes per mile or equivalent metric units as well as RPM. One of the LED indicators  130 B- 130 D is illuminated to indicate in which of these units the pace is being displayed. The third sub-panel  126 C displays either the exercise level chosen by the user or, as explained below, the heart rate of the user. The LED indicator  130 F associated with the exercise level label  128 E is illuminated when the level is displayed in the sub-panel  126 C and the LED indicator  130 E associated with the heart rate label  128 F is illuminated when the sub-panel  126 C displays the user&#39;s heart rate. The fourth sub-panel  126 D displays four types of information: the calories per hour at which the user is currently exercising; the total calories that the user has actually expended during exercise; the distance, in miles or kilometers, that the user has “traveled” while exercising; and the power, in watts, that the user is currently generating. In the default mode of operation, the fourth sub-panel  126 D scrolls among the four types of information. As each of the four types of information is displayed, the associated LED indicators  130 G-J are individually illuminated, thereby identifying the information currently being displayed by the sub-panel  126 D. A display lock key  132 , located within the data input center  104 , shown in  FIG. 2 , can be employed by the user to halt the scrolling display so that the sub-panel  126 D continuously displays only one of the four information types. In addition, the user can lock the units of the power display in watts or in metabolic units (“mets”), or the user can change the units of the power display, to watts or mets or both, by depressing a watts/mets key  134  located within the data input center  104 .  
         [0028]     It should be appreciated, that the control and display mechanisms shown in  FIG. 2  only provide a representative example of such mechanisms and that there are a large number of such control and display systems that can be used to implement the invention.  
         [heading-0029]     Stride Length Adjustment Mechanisms  
         [0030]     The ability to adjust the stride length in an elliptical step exercise apparatus is desirable for a number of reasons. First, people, especially people with different physical characteristics such as height, tend to have different stride lengths when walking or running. Secondly, the length of an individuals stride generally increases as the individual increases his walking or running speed. As indicated in U.S. Pat. Nos. 5,743,834 and 6,027,43 as well as the patent applications identified in the cross reference to related applications above, there are a number of mechanisms for changing the geometry of an elliptical step mechanism in order to vary the path the foot follows in this type of apparatus.  
         [0031]      FIGS. 4-5 ,  6 A-D,  7 A-D and  8 A-D depict a stride adjustment mechanism  166  which can be used to remotely vary the stride length without the need to adjust the length crank  68  and thus is particularly useful in implementing the invention. Essentially, the stride adjustment mechanism  166 ′ replace the stroke link used to move the pedal lever  50  in earlier machines of the type shown in  FIG. 1 . This approach permits adjustment of stride length independent of the motion of the machine  10  regardless as to whether the machine  10  is stationary, the user is pedaling forward, or pedaling in reverse. One of the significant features of the stride adjustment mechanism  166  is a dynamic link, that is, a linkage system that changes its length, or the distance between its two attachment points, cyclically during the motion of the apparatus  10 . The stride adjustment mechanism  166  is pivotally attached to the pedal lever  50  by a link crank mechanism  168  at one end and pivotally attached to the crank extension  72  at the other end. The maximum pedal lever&#39;s  50  excursion, for a particular setting, is called a stroke or stride. The stride adjustment mechanism  166  and the main crank  68  with the crank extension  72  together drive the maximum displacement/stroke of the pedal lever  50 . The extreme points in each pedal lever stroke correspond to extreme points between the Main Crank Axis  40  and a Link Crank—Pedal Lever Axis  169 . By changing the dynamic phase angle relationship between the link crank  168  and the crank extension  72 , it is possible to add to or subtract from the maximum displacement/stroke of the pedal lever  50 . Therefore by varying the dynamic phase angle relationship between the link crank  168  and the crank extension  72 , the stroke or stride of the pedal lever  50  varies the length of the major axis of the ellipse that the foot pedal  12  travels.  
         [0032]     The preferred embodiment of the stride adjustment mechanism  166  shown in  FIGS. 4 and 5  takes full advantage of the relative rotation between the crank extension  72  and a control link assembly  170  of the stride adjustment mechanism  166  as the user moves the pedals  12 . In this embodiment, attachment adjustment mechanism  166  includes the control link assembly  170  and two secondary crank arms, the link crank assembly  168  and the crank extension  72 . The control link assembly  170  includes a pair of driven timing-pulley shafts  172  and  174 , a pair of toothed timing-pulleys  176  and  178  and a toothed timing-belt  180  engaged with the timing pulleys  176  and  178 . For clarity, the timing belt is not shown in  FIG. 4  but is shown in  FIG. 5 . Also included in the link crank assembly  168  is a link crank actuator  182 . One end of the crank-extension  72  is rigidly attached to the main crank  68 . The other end of the crank-extension  72  is rigidly attached to the rear driven timing-pulley shaft  174  and the pulley  178 . Also, the rear driven timing-pulley shaft  174  is rotationally attached to the rearward end of the control link assembly  170 . The forward end of the control link assembly  170  is rotationally attached to the forward driven timing-pulley shaft  172  and pulley  176 . The two timing-pulleys  176  and  178  are connected to each other via the timing-belt  180 . The forward driven timing-pulley shaft  172  is pivotally attached to the link crank  168 , but held in a fixed position by the link crank actuator  182  when the actuator  182  is stationary; the link crank  168  operates as if it were rigidly attached to the forward driven timing-pulley shaft  172 . The other end of the link crank  168  is pivotally attached to the pedal lever  50  at the pivot axle  169 . In this particular embodiment of the elliptical step apparatus  10  shown in  FIGS. 4 and 5 , the main crank  68  via a revolute joint on a linear slot supports the rearward end of the pedal lever  50 . Here, this is in the form of a roller &amp; track interface indicated generally at  184 . When the apparatus  10  is put in motion, there is relative rotation between the crank extension/rearward timing-pulley  178  and the control link  170 . This timing-pulley rotation drives the forward driven timing-pulley  176  via the timing-belt  180 . Since the forward driven timing-pulley  176  is rigidly attached to one end of the link crank  168 , the link crank  168  rotates relative to the pedal lever  50 . Because the control link  170  is a rigid body, the rotation of the link crank  168  moves the pedal lever  50  in a prescribed motion on its support system  184 . In order to facilitate installation, removal and tension adjustment of the belt  180  on the pulleys  176  and  178 , the control link  170  includes an adjustment device such as a turnbuckle  186  that can be used to selectively shorten or lengthen the distance between the pulleys  176  and  178 .  
         [0033]     In this mechanism  166 , there exists a relative angle indicated by an arrow  188  shown in  FIG. 4  between the link crank  202  and the crank extension  70 . This relative angle  188  is referred to as the LC-CE phase angle. When the link crank actuator  182  is stationary, the LC-CE phase angle  188  remains constant, even if the machine  10  is in motion. When the actuator  182  is activated, the LC-CE phase angle  188  changes independent of the motion of the machine  10 . Varying the LC-CE phase angle  188  effects a change in the motion of the pedals  10 , in this case, changing the stride length.  
         [0034]     In the embodiment, shown in  FIG. 5 , the link crank actuator  182  includes a gear-motor, preferably an integrated motor and gearbox  190 , a worm shaft  192 , and a worm gear  194 . Because the link crank actuator  190  rotates about an axis relative to the pedal lever  50 , a conventional slip-ring type device  196  is preferably used to supply electrical power, from for example the power control board  94  shown in  FIG. 2 , across this rotary interface to the DC motor of the gear-motor  190 . When power is applied to the gear-motor  190 , the worm shaft  192  and the worm gear  194  rotate. The rotating worm shaft  192  rotates the worm gear  194 , which is rigidly connected to the driven timing pulley  176 . In addition, the worm gear  194  and the forward pulley  176  rotate relative to the link crank  168  to effect the LC-CE Phase Angle  188  change between the crank extension  72  and the link crank  168 . A reverse phase angle change occurs when the motor  190  is reversed causing a reverse stride change, that is, a decrease in stride length. In this embodiment, less than half of the 360 degrees of the possible phase angle relationship between the link crank  168  and the crank extension  72  is used. In some mechanisms using more or the full range of possible phase angles can provide different and desirable ellipse shapes.  
         [0035]     The schematics of FIGS.  6 A-D,  7 A-D and  8 A-D illustrate the effect of the phase angle change between the crank extension  72  and the link crank  168  for a 180 degree, a 60 degree and a 0 degree phase relationship respectively. Also,  FIGS. 6A, 7A , and  8 A display the crank at 180 degree position;  FIGS. 6B, 7B , and  8 B show the crank at 225 degree position;  FIGS. 8C, 9C , and  10 C show the crank at a 0 degree position; and  FIGS. 8D, 9D , and  10 D show the crank at a 90 degree position. In FIGS.  6 A-D the elliptical path  218  represents the path of the pedal  12  for the longest stride; in FIGS.  7 A-D the elliptical path  218 ′ represents the path of the pedal  12  for an intermediate stride; and in FIGS.  8 A-D the elliptical path  218 ″ represents the path of the pedal  12  for the shortest stride.  
         [0036]     In certain circumstances, characteristics of stride adjustment mechanism of the type  166  can result in some undesirable effects. Therefore, it might be desirable to implement various modifications to reduce the effects of these phenomena. For example, when the stride adjustment mechanism  166  is adjusted to the maximum stroke/stride setting, the LC-CE Phase Angle is 180 degrees. At this 180-degree LC-CE Phase Angle setting, the components of the stride adjustment mechanism  166  will pass through a collinear or toggle condition. This collinear condition occurs at or near the maximum forward excursion of the pedal lever  50 , which is at or near a maximum acceleration magnitude of the pedal lever  50 . At slow pedal speeds, the horizontal acceleration forces are relatively low. As pedal lever speeds increase, effects of the condition increase in magnitude proportional to the change in speed. Eventually, this condition can produces soft jerk instead of a smooth transition from forward motion to rearward motion. To overcome this potential problem several approaches can be taken including: limit the maximum LC-CE phase angle  188  to less than 180 degrees, for example, restrict stride range to 95% of mechanical maximum; change the prescribed path shape  218  of the foot pedal  12 ; or reduce the mass of the moving components in the stride adjustment mechanism  166  and the pedal levers  50  to reduce the acceleration forces.  
         [0037]     Another problem can occur when the stride adjustment mechanism  166  is in motion and where the tension side of the timing-belt  180  alternates between the top portion and the lower portion. This can be described as the tension in the belt  180  changing cyclically during the motion of the mechanism  166 . At slow speeds, the effect of the cyclic belt tension magnitude is relatively low. At higher speeds, this condition can produce a soft bump perception in the motion of the machine  10  as the belt  180  quickly tenses and quickly relaxes cyclically. Approaches to dealing with this belt tension problem can include: increase the timing-belt tension using for example the turnbuckle  186  until the bump perception is dampened; increase the stiffness of the belt  180 ; increase the bending stiffness of the control link assembly  170 ; and install an active tensioner device for the belt  180 .  
         [0038]     A further problem can occur when the stride adjustment mechanism  166  is in motion where a vertical force acts on the pedal lever  50 . The magnitude of this force changes cyclically during the motion of the mechanism  10 . At long strides and relatively high pedal speeds, this force can be sufficient to cause the pedal lever  50  to momentarily lift off its rearward support roller  70 . This potential problem can be addressed in a number of ways including: the roller-trammel system  184 , as shown in  FIG. 4 ; limit the maximum LC-CE phase angle  188  to less than 180 degrees; restrict stride range to 95% of mechanical maximum; and reduce the mass of the moving components in the stride adjustment mechanism and the pedal levers.  
         [heading-0039]     Elliptical Step Programs  
         [0040]     As shown in  FIG. 10 , the exercise apparatus  10  can provide several pre-programmed exercise programs that can be used with a static or an adjustable stride length. In this embodiment of the invention a set of exercise programs  300  are stored within and implemented by the microprocessor  92 . The exercise programs  300  provide for a variable exercise and can enhance exercise efficiency. In this embodiment, the alpha-numeric display screen  112  of the message center  110 , together with a display panel  136 , guide the user through the various exercise programs. Specifically, the alpha-numeric display screen  112  prompts the user to select among the various pre-programmed exercise programs  300  and prompts the user to supply the data as indicated at a box  302  that can be useful in implementing the exercise program selected at a box  304 . The display panel  136  displays a graphical image that represents the current exercise program. One of the most basic exercise programs is a manual exercise program indicated at  306 . In the manual exercise program  306  the user, after entering a time, calorie or distance goal as indicated the first of a set of boxes indicated by  308 , selects one of the twenty-four previously described exercise levels at  310 . In this case, the graphic image displayed by the display panel  136  is essentially flat and the different exercise levels are distinguished as vertically spaced-apart flat displays. A second exercise program  312 , a hill profile program, varies the effort required by the user in a pre-determined fashion which is designed to simulate movement along a series of hills. In implementing this program  312 , the microprocessor  92  increases and decreases the resistive force of the alternator  42  thereby varying the amount of effort required by the user. The display panel  136  displays a series of vertical bars of varying heights that correspond to climbing up or down a series of hills. A portion  138  of the display panel  136  displays a single vertical bar whose height represents the user&#39;s current position on the displayed series of hills. A third exercise program  314 , termed the random hill profile program, also varies the effort required by the user in a fashion which is designed to simulate movement along a series of hills. However, unlike the regular hill profile program  312 , the random hill profile program  314  provides a randomized sequence of hills so that the sequence varies from one exercise session to another. A detailed description of a random hill profile program and of the regular hill profile program can be found in U.S. Pat. No. 5,358,105, the entire disclosure of which is hereby incorporated by reference.  
         [0041]     A fourth exercise program  316 , termed a cross training program, instructs the user to move the pedal  12  in both the forward-stepping mode and the backward-stepping mode. When this program  316  is selected by the user, the user begins moving the pedal  12  in one direction, for example, in the forward direction. After a predetermined period of time, the alpha-numeric display panel  136  prompts the user to prepare to reverse directions. Thereafter, the field control signal  100  from the microprocessor  92  is varied to effectively brake the motion of the pedal  12  and the arm  80 . After the pedal  12  and the arm  80  stop, the alpha-numeric display screen  112  prompts the user to resume his workout. Thereafter, the user reverses directions and resumes his workout in the opposite direction.  
         [0042]     A pair of exercise programs, a cardio program  318  and a fat burning program  320 , vary the resistive load of the alternator  42  as a function of the user&#39;s heart rate. When the cardio program  318  is selected, the microprocessor  92  varies the resistive load as shown at  322  so that the user&#39;s heart rate is maintained at a value equivalent to 80% of a quantity equal to 220 minus the user&#39;s age. In the fat burning program  320 , the resistive load is varied as shown at  324  so that the user&#39;s heart rate is maintained at a value equivalent to 65% of a quantity equal to  220  minus the user&#39;s heart age. Consequently, when either of these programs  318  or  320  is selected by the user at  304 , the alpha-numeric display screen  112  prompts the user to enter his age as one of the program parameters. Alternatively, the user can enter a desired heart rate. In addition, the exercise apparatus  10  includes a heart rate sensing device that measures the users heart rate as he exercises. In the apparatus shown in  FIG. 2 , the heart rate sensing device consists a pair of heart rate sensors  140  and  140 ′ that can be mounted either on the moving arms  80  or a fixed handrail  142 , as shown in  FIG. 1 . In the preferred embodiment, the sensors  140  and  140 ′ are mounted on the moving arms  80 . A set of output signals on the lines  144  and  144 ′ corresponding to the user&#39;s heart rate is transmitted from the sensors  140  and  140 ′ to a heart rate digital signal processing board  146 . The processing board  146  then transmits a heart rate signal over a line  148  to the microprocessor  92 . A detailed description of the sensors  140  and  140 ′ and the heart rate digital signal processing board  146  can be found in U.S. Pat. Nos. 5,135,447 and 5,243,993, the entire disclosures of which are hereby incorporated by reference. In addition, the exercise apparatus  10  includes a telemetry receiver  150 , shown in  FIG. 2 , that operates in an analogous fashion and transmits a telemetric heart rate signal over a line  152  to the microprocessor  92 . The telemetry receiver  150  works in conjunction with a telemetry transmitter that is worn by the user. In the preferred embodiment, the telemetry transmitter is a telemetry strap worn by the user around the user&#39;s chest, although other types of transmitters are possible. Consequently, the exercise apparatus  10  can measure the user&#39;s heart rate through the telemetry receiver  150  if the user is not grasping the arm  80 . Once the heart rate signal  148  or  152  is transmitted to the microprocessor  92 , the resistive load  96  of the alternator  42  is varied to maintain the user&#39;s heart rate at the calculated value.  
         [0043]     In each of these exercise programs, the user provides data at  308  that determine the duration of the exercise program. The user can select between a number of exercise goal types including a time or a calories goal or, in the preferred embodiment of the invention, a distance goal. If the time goal type is chosen, the alpha-numeric display screen  112  prompts the user to enter the total time that he wants to exercise or, if the calories goal type is selected, the user enters the total number of calories that he wants to expend. Alternatively, the user can enter the total distance either in miles or kilometers. The microprocessor  92  then implements the selected exercise program for a period corresponding to the user&#39;s goal. If the user wants to stop exercising temporarily after the microprocessor  92  begins implementing the selected exercise program, depressing the clear/pause key  120  effectively brakes the pedal  12  and the arm  80  without erasing or changing any of the current program parameters. The user can then resume the selected exercise program by depressing the start/enter key  118 . Alternatively, if the user wants to stop exercising altogether before the exercise program has been completed, the user simply depresses the brake key  108  to brake the pedal  12  and the arm  80 . Thereafter, the user can resume exercising by depressing the start/enter key  118 . In addition, the user can stop exercising by ceasing to move the pedal  12 . The user then can resume exercising by again moving the pedal  12 .  
         [0044]     The exercise apparatus  10  also includes a pace option as depicted by a set of boxes indicated at  326 . In all but the cardio program  318  and the fat burning program  320 , the default mode is defined such that the pace option is on and the microprocessor  92  varies the resistive load of the alternator  42  as a function of the user&#39;s pace. When the pace option is on, the magnitude of the RPM signal  102  received by the microprocessor  92  determines the percentage of time during which the field control signal  100  is enabled and thereby the resistive force of the alternator  42 . In general, the instantaneous velocity as represented by the RPM signal  102  is compared to a predetermined value to determine if the resistive force of the alternator  42  should be increased or decreased. In the presently preferred embodiment, the predetermined value is a constant of 30 RPM. Alternatively, the predetermined value could vary as a function of the exercise level chosen by the user. Thus, in this embodiment, if the RPM signal  102  indicates that the instantaneous velocity of the pulley  38  is greater than 30 RPM, the percentage of time that the field control signal  100  is enabled is increased according to Equation 1.  
       Equation 1  
       [0045]                    field   ⁢           ⁢   control   ⁢           ⁢   duty   ⁢           ⁢   cycle     =       field   ⁢           ⁢   control   ⁢           ⁢   duty   ⁢           ⁢   cycle     +             (       (     ❘       instantaneous   ⁢           ⁢   RPM     -     30   /         )     /   2     )     2     *   field   ⁢           ⁢   control   ⁢           ⁢   duty   ⁢           ⁢   cycle     )     256               Equation   ⁢           ⁢   1               
 where field duty cycle is a variable that represents the percentage of time that the field control signal  100  is enabled and where the instantaneous RPM represents the instantaneous value of the RPM signal  98 . 
 
         [0047]     On the other hand, in this embodiment, if the RPM signal  102  indicates that the instantaneous velocity of the pulley  38  is less than 30 RPM, the percentage of time that the field control signal  100  is enabled is decreased according to Equation 2.  
       Equation 2  
       [0048]                    field   ⁢           ⁢   control   ⁢           ⁢   duty   ⁢           ⁢   cycle     =       field   ⁢           ⁢   control   ⁢           ⁢   duty   ⁢           ⁢   cycle     -             (       (     ❘       instantaneous   ⁢           ⁢   RPM     -     30   /         )     /   2     )     2     *   field   ⁢           ⁢   control   ⁢           ⁢   duty   ⁢           ⁢   cycle     )     256               Equation   ⁢           ⁢   2               
 where field duty cycle is a variable that represents the percentage of time that the field control signal  100  is enabled and where the instantaneous RPM represents the instantaneous value of the RPM signal  102 . 
 
         [0050]     Moreover, once the user selects an exercise level, the initial percentage of time that the field control signal  100  is enabled is pre-programmed as a function of the chosen exercise level as described in U.S. Pat. No. 6,099,439.  
         [heading-0051]     Manual and Automatic Stride Length Adjustment  
         [0052]     In these embodiments of the invention, stride length can be varied automatically as a function of exercise or apparatus parameters. Specifically, the control system  88  and the console  90  of  FIG. 2  can be used to control stride length in the elliptical step exercise apparatus  10  either manually or as a function of a user or operating parameter. In the examples of  FIGS. 1 and 2  the attachment assembly  34  generally represented within the dashed lines can be implemented by a number of mechanisms that provide for stride adjustment such as the stride length adjustment mechanism depicted in  FIGS. 4 and 5 . As shown in  FIG. 2 , a line  154  connects the microprocessor  92  to the electronically controlled actuator elements of the adjustment mechanisms in the attachment assembly  34 . Stride length can then be varied by the user via a manual stride length key  156 , shown in  FIG. 3 , which is connected to the microprocessor  92  via the data input center  104 . Alternatively, the user can have stride length automatically varied by using a stride length auto key  158  that is also connected to the microprocessor  92  via the data input center  104 . In one embodiment, the microprocessor  92  is programed to respond to the speed signal on line  102  to increase the stride length as the speed of the pedal  12  increases. Pedal direction, as indicated by the speed signal can also be used to vary stride length. For example, if the microprocessor  92  determines that the user is stepping backward on the pedal  12 , the stride length can be reduced since an individuals stride is usually shorter when stepping backward. Additionally, the microprocessor  92  can be programmed to vary stride length as function of other parameters such as resistive force generated by the alternator  42 ; heart rate measured by the sensors  140  and  140 ′; and user data such as weight and height entered into the console  90 .  
         [heading-0053]     Adjustable Stride Programs  
         [0054]     As illustrated in  FIG. 11 , adjustable stride mechanisms make it possible to provide enhanced pre-programmed exercise programs of the type described above that are stored within and implemented by the microprocessor  92 . As with the previously described exercise programs, the alpha-numeric display screen  112  of the message center  110 , together with a display panel  136 , can be used to guide the user through the various exercise programs. Again, the alpha-numeric display screen  112  prompts the user to select at  304  among the various preprogrammed exercise programs and prompts the user to supply the data needed to implement the selected exercise program. In this embodiment, one of a group of adjustable stride length exercise programs  328  can be selected by the user utilizing a stride program key  160 , as shown in  FIG. 3 , which is connected to the microprocessor  92  via the data input center  104 . As indicated above, it should be appreciated, that the control and display mechanisms shown in  FIG. 2  only provide a representative example of such mechanisms and that there are a large number of such control and display systems that can be used to implement the invention. Representative examples of such stride length exercise programs are provided below.  
         [0055]     A first program  330  can be used to simulate hiking on a hill or mountain similarly to the hill program  312  of  FIG. 10 . For example, the program can begin with short strides and a high resistance to simulate climbing a hill then as shown in a box  332  after a predetermined time change to long strides at low resistance as indicated at a box  334  to simulate walking down the hill. The current hill and upcoming hills can be displayed on the display panel  136  where the length of the stride and the resistance change at each peak and valley. In one implementation, the initial or up hill stride would be 16 inches and the down hill stride would be 24 inches, where the program automatically adjusts the initial stride length to 16 inches at the beginning of the program. Also, the program can return the stride length to a home position, for instance 20 inches, during a cool down portion of the program.  
         [0056]     A second program  336  can be used to change both the stride length and the resistance levels on a random basis. Preferably, the changes in stride length and resistance levels are independent of each other as indicated at a box  338 . Also in one embodiment, the changes in stride length occur at different time intervals than the changes in resistance levels. For example, a random stride length change might occur every even minute and a random resistance level change might occur at every odd minute of the program. Preferably, the changes in increments will be plus or minus 2 inches or more. Again, the program can return the stride length to a home position, for instance 20 inches, during a cool down portion of the program.  
         [0057]     A third program  340  can be used to simulate interval training for runners. In one embodiment, by using stride length changes in the longer strides and having the processor  92  generates motivating message prompts on the display  136 , interval training and the gentle slopes and intervals one would experience when training as a runner outdoors are mimicked. In one example, as indicated in a box  342 , the program spans the stride range of 22″-26″ with an initial warm-up beginning at 22″ then moving to 24″. Here the program then alternates between the 24″ and 26″ strides thus mimicking intervals at the longer strides such as those experienced by a runner in training. In addition as indicated in a box  344 , the display  136  can be used to alert the user to “Go faster” and “Go slower” at certain intervals. Thus the prompts can be used to encourage faster and slower pedal speeds. A representative example of such a program is provided below: 
        Warm-up:     Prompt “Warm Up” message     Minute 00:00=22″ stride (If machine is not at 22″ at program start-up, then it will adjust to the 22″ stride length at program start.)     Minute 03:00=24″ stride     Minute 03:30=prompt “Go faster” message     Intervals:     Minute 04:00=26″ stride     Minute 08:30=prompt “Go slower” message     Minute 09:00=24″ stride     Minute 10:30=prompt “Go faster” message     Minute 11:00=26″ stride     Minute 15:30=prompt “Go slower” message 
 
 where the first change is initiated at the 03:00 minute mark, during the warm-up phase. Other aspects of this particular interval program include: stride adjustment increments of 2″; minimum duration of 10 minutes; and repeating the interval phase for the selected duration of the program. 
       
 
         [0071]     A fourth program  346  can be used to simulate a cross training exercise. Here, as shown in a box  348 , stride length is shortened when the user is pedaling in a backward direction and increased when the user is pedaling in a forward direction. As with the interval training program  340 , the display  136  can be used in the cross training program  346  to generate indications to the user at a predetermined time, such as 30 seconds, before the direction of pedal motion is to change.