Patent Publication Number: US-6033344-A

Title: Fitness apparatus with heart rate control system and method of operation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of patent application Ser. No. 08/838,457, filed Apr. 4, 1997 now abandoned, which is a continuation of U.S. patent application No. 08/585,191, filed Jan. 11, 1996, now U.S. Pat. No. 5,618,245, which is a continuation-in-part of Ser. No. 08/549,604, filed Oct. 27, 1995, now abandoned, which is a continuation of U.S. patent application Ser. No. 08/192,407, filed Feb. 4, 1994, now U.S. Pat. No. 5,462,504. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to exercise equipment, and in particular to a method and apparatus for dynamically varying resistance mechanisms of a fitness apparatus in dependence on the user&#39;s heart rate. 
     BACKGROUND OF THE INVENTION 
     Modem fitness apparatuses, or exercise machines, including treadmills, steppers, stationary bicycles, and the like are often electronically controlled to vary their resistance levels. For example, stationary bicycles are electronically controlled to vary their resistance over the duration of an exercise routine to simulate uphill, level and downhill riding conditions. This varies the routine, purportedly to prevent the user of the apparatus from becoming bored with the otherwise repetitive exercise. 
     At the same time, it is also known to measure the heart rate or pulse of the user and adjust the level of exercise accordingly to maximize the cardiovascular benefits achieved from physical exercise without wasting time and effort. This also provides the benefit of being able to quickly detect dangerously high or accelerating heart rates. 
     To this end, pulse detection circuitry has been coupled with exercise equipment which provides a display to the user and/or a supervisor corresponding to the actual heart rate being achieved. The user or the supervisor can then make adjustments to the resistance level to adjust the heart rate as needed. 
     In U.S. Pat. No. 4,998,725, a microprocessor varies the incline of a treadmill or the resistance to the pedaling of a stationary bicycle to achieve a target heart rate. Adjustment of the resistance is only generally disclosed as increasing the resistance to increase the heart rate and decreasing the resistance to decrease the heart rate. 
     Several types of exercise equipment have more than a 25 single variable resistance mechanism that affects the user&#39;s heart rate. For example, conventional treadmills have both variable inclines and variable speeds, while many stationary bicycles have variable pedal resistance for the lower body as well as resistance-based exercise mechanisms for the upper body. Since numerous such mechanisms are often intended to be operated simultaneously, the resulting heart rate depends on the resistance of all operating mechanisms and their relationship to each other and to the heart rate. At the same time, the conditioning of the skeletal muscle groups being exercised depend on which resistance mechanisms are being varied. Although exercise equipment comprising interrelated resistance mechanisms have become increasingly popular, the prior art varies only a single one of the mechanisms to control heart rate. The results are unsatisfactory because achieving a target heart rate in such equipment by merely increasing or decreasing one of the resistance mechanisms does not consider and compensate for the benefits or detriments that may occur by varying the resistance of the other such mechanisms in relation thereto. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary object of the invention to provide an apparatus and method for dynamically controlling the resistance of a first resistance mechanism with respect to the resistance of at least one other resistance mechanism of a fitness apparatus in dependence on the heart rate of the user thereof. 
     It is a related object to provide a fitness apparatus of the above kind that optimizes the benefit obtained from exercise thereon. 
     It is another object to provide an apparatus and method as characterized above that is capable of benefiting virtually any user regardless of their level of physical conditioning. 
     It is yet another object to provide a fitness apparatus of the above kind that may further incorporate conventional features and alternative modes of operation. 
     It is still another object to provide a fitness apparatus whose modes of operation are simple to select and implement. 
     It is a resulting feature that the fitness apparatus may be combined with electronic heart rate supervision to ensure the safety of the user. In this regard, it is also an object of the invention to provide a fitness apparatus that maintains a level of cardiovascular exertion selected by a user of the apparatus. 
     Briefly, the invention provides a fitness apparatus for controlling the heart rate of a user with respect to a predetermined target heart rate, and includes pulse detection circuitry for regularly sensing the heartbeat of the user and providing a signal corresponding thereto. In one embodiment of the invention, the target heart rate is selected by the user as part of a start up operation. In another embodiment of the invention, the target heart rate is determined from the current heart rate of a user after the user has been exercising on the apparatus for an arbitrary period of time. 
     The fitness apparatus includes first and second resistance mechanism, both of which have resistance levels that vary in response to electrical signals. In addition, there is provided a controller including a processor, input circuitry operatively connected to receive external signals from the pulse detection circuitry and communicate the signals to the processor, and output circuitry operatively connected to the first resistance mechanism and the second resistance mechanism for independently transmitting electrical signals from the processor thereto. As the processor receives the pulse signal from the pulse detection circuitry, it determines the heart rate of the user, and, employing comparison circuitry therein, compares the heart rate of the user with the target heart rate. If the heart rate of the user is lower than the target heart rate, the processor provides electrical output signals to increase the resistance level of only the first resistance mechanism until a predetermined upper resistance limit is reached, before providing electrical output signals to increase the resistance level of the second exercise mechanism. If the heart rate of the user is higher than the target heart rate, the processor provides electrical output signals to decrease the resistance level of only the second resistance mechanism until a predetermined lower resistance limit is reached, before providing electrical output signals to decrease the resistance level of the first exercise mechanism. 
     The user may input data including the target heart rate and/or the maximum resistance levels, the data may be recalled from memory or the maximum resistance levels may be determined by the processor based upon the resistance levels when the actual heart rate of the user achieves the target heart rate. The invention may be incorporated into a treadmill having resistance mechanisms including a mechanism to vary the speed of the treadmill belt and a mechanism to vary the grade of the treadmill. In the treadmill embodiment, the processor may determine the maximum speed and grade based upon the current speed and grade when the measured heart rate of the user achieves the target heart rate. 
     Other objects and advantages will become apparent from the following detailed description when taken in conjunction with the drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating a treadmill and user thereon having heart rate monitoring capabilities according to one aspect of the invention; 
     FIG. 2 is a left front partial view of the treadmill of FIG. 1 illustrating the resistance mechanisms when at a level grade; 
     FIG. 3 is a right front partial view of the treadmill illustrating the resistance mechanism for varying the grade of the treadmill shown at an inclined grade; 
     FIG. 4A is a block diagram of the electronic control system for controlling a fitness apparatus including its resistance mechanisms in accordance with the invention; 
     FIGS. 4B-4E are state machine diagrams representing functions performed by the processing circuitry of FIG. 4A in accordance with received and stored data; 
     FIGS. 5A-5D are flow diagrams of the general controller software steps for implementing the invention in a treadmill; 
     FIG. 6 is a graphical representation illustrating the heart rate of a first representative user relative to the settings of the resistance mechanisms of a treadmill; 
     FIG. 7 is a graphical representation illustrating the heart rate of a second representative user relative to the settings of the resistance mechanisms of a treadmill; and 
     FIG. 8 is a flow diagram of the general controller software steps for determining the maximum speed and grade of a treadmill in one alternate embodiment according to the invention. 
     While the invention is susceptible of various modifications and alternative constructions, a certain illustrated embodiment thereof is shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     I. The Apparatus 
     Turning now to the drawings and referring first to FIGS. 1-3, there is shown a fitness apparatus in the form of a treadmill generally designated 10 having a plurality of resistance mechanisms incorporated therein. In the treadmill 10 described herein, the first resistance mechanism 12 (best seen in FIG. 2) consists of a speed varying mechanism while the second resistance mechanism takes the form of a grade-adjustment mechanism 14 (best seen in FIG. 3). 
     FIGS. 2 and 3 are left front and right front partial views of a treadmill having speed and grade incline mechanisms that can be controlled in accordance with one aspect of the invention as described in more detail below. One such treadmill, the HRC 700 (and other Heart Rate Control treadmills in the HRC series) is available from True Fitness Technologies, Inc., O&#39;Fallon, Mo. 
     To vary the speed of the treadmill 10, and thus increase the resistance of the first resistance mechanism 12, a variable-speed drive motor 16 is mechanically coupled in a conventional manner by a drive belt 18 to a drive roller 20 to rearwardly move a rotating surface, i.e., a continuous belt 22 riding upon a low-friction support surface 24. Although it is preferable to employ the drive belt 18 to couple the drive roller 20 to-the drive motor 16, it can be appreciated that gears or the like may be alternatively employed. A freely-rotating rear roller 26 is provided to redirect the continuous belt 22 forwardly beneath the support surface 24 in the conventional manner. 
     The continuous belt 22 is arranged so as to not slip on the drive roller 20 under ordinary loads, for example by providing proper tensioning, coefficients of friction and/or having treads in the underside of the belt 22 underside to mate with the drive roller 20. Thus, as the drive motor 16 rotates at any given speed, the belt 22 rotates with a speed corresponding thereto. 
     Regardless of how configured, the drive motor 16 is operated by drive signals from a system controller 30, illustrated in FIG. 4A, and may, for example, be a stepping motor, in which event the signals are pulses. Preferably, the drive motor is a DC motor, such as one commercially available from Pacific Scientific, Rockford, Ill., Model No.3632-5313-7-3, for which the drive signals are voltages of appropriate levels applied to the motor for specified periods of time. In any case, the system controller 30, described in more detail below, provides one or more signals that ultimately determine the resistance level of the first resistance mechanism 12, i.e., the speed of the treadmill 10 in the illustrated embodiment. In a preferred embodiment, the controller 30 adjusts the speed between 0.0 miles per hour and 12.0 miles per hour in one-tenth of a mile per hour increments. 
     To vary the grade (i.e., the incline angle) of the rotating treadmill surface, and thus increase the resistance of the second resistance mechanism 14 by altering the amount of exertion required by the user to remain on the apparatus 10, a conventional motor-driven screw drive 32 is employed (FIG. 3). 
     To this end, a motor 36 turns its shaft within a Delrin incline nut 34 that is mechanically coupled to a welded incline riser assembly 58. The incline riser assembly attaches to the frame at a pivot point 38. When the incline nut 34 is drawn toward the incline motor 36 by the turning action of the incline motor shaft, the incline riser assembly 58 is pivoted downwardly and the treadmill 10 is angled upwardly to provide an inclined surface for the user. Wheels 64 are attached to the lower portion of the incline riser assembly 58 to allow the assembly to pivot. Also, the wheels 64 enhance the portability of the apparatus 10. In order to lower the incline riser assembly 58, the incline motor 36 is simply operated in reverse, which is accomplished in a conventional manner. 
     II. The Controller 
     The incline motor 36 is operated by signals from the controller 30 and may, for example, be a stepping motor, in which event the signals are pulses, or an AC or DC motor, in which event the signals cause voltages of appropriate levels to be applied to the incline motor 36 for specified periods of time. For example, in a preferred embodiment a conventional treadmill incline mechanism is employed wherein the signal activates a solid state switch which applies power to a fractional AC motor until the grade is incremented by the desired amount. The motor 36 may be a screw type AC capacitor-start motor, model MC 42-1009H from Hubbell Special Products of Kenosha, Wis. In any case, the controller 30 provides one or more signals that ultimately determine the resistance level of the second resistance mechanism 14, i.e., the grade of the treadmill in the exemplified embodiment. In a preferred embodiment, the controller 30 adjusts the grade between a declining angle or grade of approximately minus three(-3) percent and an incline of approximately 15 percent in one-half percent increments. Note that the incline motor 36 is preferably a reversible motor of a type that remains locked in position when power is removed so that the incline riser assembly 58 does not move in response to gravitational forces. Alternatively, mechanical means such as gears, stops and the like may provide the reversibility and locking features. 
     Preferably, as shown in more detail in FIG. 4A, the system controller 30 includes a microprocessor 72, a memory 74, a timer 75 and input/output (I/O) circuitry 76 connected in a conventional manner. A preferred microprocessor is an SAB 8OC32 available from Siemens Corporation, although it can be appreciated that any suitable microprocessor may be utilized. The memory 74 is intended to include random access memory (RAM), read only memory (ROM), or any other type of storage means. The I/O circuitry 76 ordinarily includes conventional buffers, drivers, relays and the like, such as for driving the motors 16, 36 with sufficient power. Conventional circuitry for latching output signals from the microprocessor 72 is ordinarily included in the output circuitry 76 where appropriate. Thus, output signals from the microprocessor 72, interfaced through appropriate output circuitry 76, control the treadmill drive motor 16 and incline motor 36. 
     The speed and grade of the apparatus is determined by (and thereby ordinarily known to) the controller 30, thus the controller can employ an open-loop control architecture. It is preferred, however, to include a speed sensor 78 for detecting the actual speed of the unit and an incline sensor 80 for determining the grade. Such sensors are well known, and for example the speed sensor 72 is preferably a Hall-effect type disposed to provide a value to the controller 30 indicative of the revolutions per minute of the drive roller 20. The controller 30 subsequently converts this value to miles per hour. These sensors feed back to the controller 30 speed and grade information for dynamic control of the motors 16 and 36 in a closed-loop control architecture. 
     Ordinarily, the incline sensor 80 comprises an appropriately positioned limit switch 80a that determines 0.0 percent grade and a potentiometer inside of a linear actuator 80b (i.e., Model NC42-1009H actuator Hubbell Corporation of Kenosha Wis., which includes a Clarstat RV4NAY5D102A) that indicates an amount of incline motor 36 rotation, and may further include an upper limit switch which is actuated at a maximum incline. For example, as is common in treadmills, to increase or decrease the incline of the lift frame 48, in a closed-loop motor control operation the controller 30 ordinarily provides an output signal which causes a relay or solid state switch within output circuitry 76 to apply power of the appropriate polarity to the incline motor 36. The incline motor 36 then rotates in the appropriate direction until the potentiometer and linear actuator [counter switch] 80b in the incline sensor 80 indicate an amount of rotation corresponding to a one-half percent of grade increase or decrease, at which time the signal (and power) is removed. 
     As shown in step 110 of FIG. 5A, upon power-up of the apparatus 10, the controller 30 initially operates the incline motor 36 to lower the lift frame 48 (step 11) to 0.0 percent grade as indicated by the incline sensor 80 (step 112), i.e., upon actuation of the appropriately positioned limit switch 80a. This actuation takes place, for example, as a portion of the incline riser assembly 58 contacts the switch 80a, a condition which only occurs when the assembly is fully lowered. Once lowered, an internal byte reserved in memory 74, acting as a counter to record the number of increments and decrements to the incline motor 36, is zeroed at step 114. This internal counter is incremented and decremented whenever the grade is increased or decreased by an incremental step, as indicated by counter switch 80b, for example during the adjustment procedure as described in more detail below. Thus, at all times the controller 30 is aware of the amount of incline of the treadmill 10, and will not provide signals to adjust the incline beyond the corresponding upper limit (16 percent, or a count of +32 increments) or the lower limit (zero percent, or a count of zero increments). 
     If desired, an upper limit switch may be further added, so that the controller 30 does not solely rely on an incremented or decremented counter in its memory 74 to determine the upper incline limit, which can be significant if an error or memory failure occurs. The addition of an upper limit sensor provides an additional safeguard to ensure proper adjustment of the incline riser assembly 58. If further desired, a clutch or other mechanical safety mechanism may be further provided in one or both of the motors 16, 36 to prevent damage thereto in the event of a sensor failure. 
     III. Heart Rate Monitoring 
     In order to maintain the heart rate of the user at a target value, the resistance levels of the resistance mechanisms 12, 14 are varied with respect to one another in dependence on the user&#39;s actual (average) heart rate. To detect the user&#39;s actual (average) heart rate, the apparatus employs pulse detection circuitry 82 (FIG. 4A) and a suitable timer, such as timer 75. Any conventional pulse detection circuitry will suffice, provided it is capable of supplying a signal corresponding to the user&#39;s heartbeat to the input circuitry 76 of the controller. The connection between the pulse detection circuitry and the controller can be either wireless or wired. The heartbeat can be picked up from any suitable area of the user&#39;s body, including chest or fingers. As utilized herein, pulse detection circuitry includes electrocardiograph-type detection devices which sense electric currents or potentials on the user to provide a signal corresponding to the heartbeat, or any other type of devices which sense heartbeats and provide corresponding signals. 
     However, it is preferable to employ pulse detection circuitry comprising an electronic sensor such as transducer 84 (which may be electrodes), amplifier 86 and transmitter 88 to remotely communicate an appropriate signal, such as a signal at infrared or RF frequencies, to a suitable receiver 90 at the system controller 30 without the need for transmitting conductors. 
     For example, one such telemetry-type ECG transmitter system is attached to the user by chest belt 92 or the 15 like so that the transducer 84 acting as the sensor contacts the user&#39;s skin just below the pectoral muscles. The transducer 84 picks up the user&#39;s heartbeat, and provides a signal which is then amplified and/or otherwise modified (such as by filtering and/or encoding) by amplifier 86 before being transmitted by transmitter 88 to the receiver 90 at the controller 30. To detect the heartbeat, the transducer 84 may comprise a pair of electrodes or the like which provide varying potential differences representative of the heartbeat to amplifier 86. 
     Although not necessary to the invention, it can be appreciated that in a commercial setting such as at a health club, it may be first necessary to encode the transmitted pulses so that each machine receives only pulses from a single, corresponding transmitter. To this end, digital or other well-known encoding and decoding techniques may be employed, and the receivers may further be programmable so as to function with any appropriate transmitter, but only one, at any time. In a preferred embodiment, the transmitter employs an RF frequency and includes microprocessor-based circuitry that combines an encryption code with the detected pulse for transmission to the receiver, so that the system responds only when receiving the proper code. 
     Regardless of how the pulse is detected, transmitted and received, an actual (average) heart rate is then determined at the controller 30, ordinarily by summing the amount of time between a known number of heartbeats and converting the total time to a number of beats per minute (bpm). Of course, the conversion of the detected pulse to the average heart rate may occur prior to transmission to the receiver such that a value indicative of the calculated heart rate may be transmitted to the controller 30 instead of individual pulses. 
     In any case, one such method of determining an actual (average) heart rate at the controller 30 consists of executing an interrupt routine upon the detection of a pulse, for example on its falling edge. In this manner, the heart rate is always being updated as it occurs, regardless of the current step being executed by the microprocessor 72. In the interrupt routine, a time is recorded for each pulse, and thus the measured heart rate for that pulse is calculated in bpm based on the time between the falling edges of that pulse and of the previous pulse. Preferably, a comparison with extreme limits, for example, comparing the heart rate to see if it is less than 30 bpm or greater than 250 bpm, is first performed to help eliminate bad pulses which may be caused by noise or the like. Consecutive bad readings may lead to an error condition. 
     Assuming the calculated heart rate is reasonable, several consecutive readings (e.g., four) are averaged together to determine the heart rate, defined herein as the actual or current (average) heart rate, to be compared against the scheduled target heart rate. Error corrections may be first made to the readings if significant changes in the times between individual pulses are detected, for example if the time difference corresponds to a heart rate that is outside of the previous average heart rate plus or minus 10 bpm. 
     Of course, when compared with the target heart rate to determine an adjustment direction as described in more detail below, the current actual average heart rate cannot be changed via the interrupt in the middle of a comparison or other calculation, and thus the value obtained in the interrupt is protected before being used in the calculations or comparisons. For example, this can be accomplished by setting a variable equal to the calculated average at a known point in the routine, and then using that variable in the comparison. 
     IV. Modes Of Operation 
     Regardless of how the heart rate is obtained and determined, the controller 30 responds to the actual heart rate to operate the resistance mechanisms 12, 14 as represented in the steps illustrated in the flow diagrams of FIGS. 5A-5E. Of course, it can be readily appreciated that the apparatus is capable of operating in any number of other desirable ways prior to or after executing the steps of FIGS. 5A-5E. As described hereinafter, there are two different ways of obtaining the target heart rate. The target heart rate is either preset or selected by the user during an exercise session. 
     In a first mode of operation described hereinafter (an &#34;automatic&#34; mode), the target heart rate is determined before the user begins exercising. The user selects the target heart rate prior to beginning an exercise session. The maximum values of the resistance levels can also be preset or they can be determined at the time the target heart rate is reached as explained more fully below. 
     In this automatic mode of operation, the user operates the fitness apparatus for a period of time prior to controlling the resistance mechanisms to achieve the desired (target) heart rate. Thus, a warm-up exercise period, in which the user first attains the desired heart rate level is first executed at step 120 as described in more detail below. Although not necessary to the invention, it is often desirable to operate the apparatus at reduced resistance levels for a cool-down period in which the actual (average) heart rate gradually abates to lower levels, also described in more detail below. 
     In an alternative mode of operation also described hereinafter (an &#34;on-the-fly&#34; mode), the target heart rate is automatically determined from the actual heart rate of the user at some time during an otherwise uncontrolled exercise session. In this mode of operation, the controller 30 captures the actual heart rate of the user in response to a prompt by the user. The actual heart rate is used by the controller 30 as explained hereinafter to set a target heart rate, which is then used by the controller to control the resistance levels of the first and second resistance mechanisms 12 and 14 in a manner similar to that of the first mode. 
     A. The Automatic Mode 
     Turning first to a more detailed description of the automatic mode of operation, at step 116 of FIG. 5A the apparatus waits for the user to initially enter or cause to be entered at step 118 a target heart rate, maximum grade, maximum speed, and a time duration for maintaining the actual (average) heart rate at the target level. Additionally, if desired, other variables such as a maximum heart rate for that particular user may be entered at that time. While the target heart rate may be a single fixed number (or range of heart rates above and/or below the input number), it is to be understood that any number of target heart rates may be scheduled in a sequence or calculated therefrom in a predetermined or even random routine. By way of example, the target heart rate may be entered as 145 bpm for 10 minutes, 25 percent lower (109 bpm) for 5 minutes and back to 145 bpm for 15 minutes. 
     These settings may be manually entered, entered by a key-card or other identifying device, or recalled from the internal memory 74. For example, a user may press a key to recall from the memory 74 his or her personal previously-entered settings. To this end, the apparatus 10 ordinarily includes a control console 94 which provides user data input devices 96 such as switches, keypads and the like connected to the input circuitry 76 of the controller 30, along with a visual display 98 connected to the output circuitry 76 of the controller 30. 
     Alternatively, certain of the parameters may be determined by the controller 30 based upon other information available thereto. For example, the controller 30 may determine the maximum or target heart rate based upon the age, weight and/or sex of the user. Moreover, rather than being directly input by the user, the maximum resistance levels of the resistance mechanisms 12, 14 may be based upon the resistance levels that are present when the measured heart rate of the user achieves the target heart rate, such as when concluding a warm-up stage as described below. 
     Once the necessary settings are entered, the apparatus preferably enters a warm-up stage at step 120 during which the user ordinarily increases his heart rate up to the target rate by manually increasing, through commands entered at the user input device 96, the resistance levels of the first and second resistance mechanisms 12, 14 up to the previously entered maximum limits. 
     Once the actual (average) heart rate equals or exceeds the entered target heart rate (step 122), the controller 30 begins executing software instructions in the target heart rate control stage of operation, referred to hereinafter as the &#34;target&#34; stage of operation. Note that as shown in FIG. 5A, throughout the warm-up stage the actual (average) heart rate is continually being updated, although as previously described, this preferably occurs as the pulses are detected and not at any specific time, and thus is shown as broken line step 124. 
     B. The &#34;On-The-Fly&#34; Mode 
     The &#34;on-the-fly&#34; mode of operating the fitness apparatus allows a user to select enter the target stage with a target heart rate determined from the actual heart of the user at the time the target stage is entered. Referring to the flow diagram of FIG. 5D, the user enters the &#34;on-the-fly&#34; mode through steps 194 and 195 by operating the apparatus in a manner similar to the warm-up stage of the automatic mode. Unlike the automatic mode, however, there is no requirement in the &#34;on-the-fly&#34; mode for the user to set a target heart rate or set maximum resistance values prior to beginning the exercise session. When the heart rate of the user reaches a desired value, the user identifies the actual heart rate as the target heart rate by pressing a button or the like on the user input 96(FIG. 4A). The controller detects the user input at step 195 on the flow diagram. In response to its sensing an appropriate input by the user at the user input 96, at step 197 the controller 30 then inputs the current heart rate from the pulse detector 82 in step 196 of the flow diagram of FIG. 5D. When controller 30 captures the current heart rate, it also captures the current operating status of the machine at step 198, i.e.--the speed and grade of the fitness apparatus. The captured current values of the speed and grade are used by the controller 30 as the initial values of speed and grade for the target stage, which is initiated by the user through the user input 96. 
     From these initial speed and grade values, the controller 30 also determines the maximum values for the speed and grade of the fitness apparatus at step 199. The maximum values are determined in the same manner as they are when the target stage is entered through the automatic mode. Specifically, the values are determined in keeping with the steps of FIG. 8, which are described hereinafter. 
     After the target stage is entered through the &#34;on-the-fly&#34; mode, the speed and grade of the fitness apparatus is adjusted in step 200 in the same manner as in the automatic mode as described in the steps of the flow diagrams of FIGS. 5B and 5C. 
     In keeping with the &#34;on-the-fly&#34; mode of operation, the user may warm-up at step 194 of the flow diagram of FIG. 5D by freely adjusting the speed and/or grade of the fitness apparatus. The fitness apparatus is started and initialized in the same manner as described by steps 110, 111, 112 and 114 of the flow diagram of FIG. 5A. At any time during the exercise session, the user can enter the target stage of operation by providing the appropriate input to the controller 30 by way of the user input 96. Alternatively, the &#34;on-the-fly&#34; mode may include a feature in which the target stage is automatically entered some time after the user has started an exercise session. No matter how the system may transition to the target stage in the &#34;on-the-fly&#34; mode, the current heart rate is captured during the transition and used to determine the target heart rate. 
     The user of the fitness apparatus is connected to the pulse detection circuitry 82 so that the user&#39;s heart rate begins to appear on the treadmill display 98 after an exercise session is started. As the user continues to exercise, his or her heart rate increases at a rate based on the user&#39;s physical condition and on the rate at which the user increases the speed and/or grade of the fitness apparatus. When the display 98 prompts the user that he or she has reached a heart rate that the user wants to maintain, the user initiates the target stage through an appropriate input to the user input, which is recognized by the controller 30 at step 195. 
     V. The Target Stage Of The Modes 
     As shown in FIGS. 5B-5C, the actual (average) heart rate is maintained at the target heart rate by adjusting the resistance level of the first resistance mechanism 12 with respect to the resistance level of the second resistance mechanism 14. However, for safety purposes the actual (average) heart rate is first compared at step 130 to determine if the actual rate exceeds the target heart rate by 20 bpm. If so, a dangerous condition is assumed, and at step 131 the controller activates an alarm 100 in console 94 and begins to shut down the treadmill in a predetermined shut down pattern, generally by rapidly reducing the grade and decelerating the speed 15 in a manner that is gradual enough so that the user does not fall forward but that is still quick enough to significantly reduce the heart rate. Of course, rather than base the danger rate on the target rate plus 20 bpm, an actual or absolute upper limit may be utilized, which can either be manually entered at the beginning of an exercise session or predetermined and fixed for all sessions. 
     If the danger level has not been reached, the executing software program moves to step 132 to determine if the actual rate exceeds the scheduled target heart rate by 14 bpm. If so, in the exemplified embodiment the workload (grade and/or speed resistance) is immediately reduced by twenty percent at step 133 in an attempt to quickly reduce the actual (average) heart rate before reaching a potentially dangerous level. This has been found to rapidly reduce the heart rate. 
     If the actual rate is below this warning level, at step 134 the software program checks to determine if the time spent exercising in the target stage (i.e., the actual time not including the warm-up time) has exceeded the previously loaded total time duration. If so, the software program preferably enters a reduced-workload cool down stage, described in more detail below. 
     If the exercise time has not exceeded the total time, the software program effectively executes a delay at step 136, either by actually delaying or by skipping over any adjustment to the speed and grade until at least some minimum time has elapsed. In a preferred software program, no actual delay is performed but an effective delay occurs by not performing any adjustment to the resistance mechanisms 12, 14 until at least eight seconds have elapsed since the previous adjustment. This prevents an occasional detection of a bad heart rate or minor fluctuations from causing frequent adjustments to the machine that are only temporary and may in fact be incorrect. 
     Once enough time has elapsed, an adjustment may be forthcoming. At this time, at step 140 the software program determines whether to increase or decrease the workload, or if an adjustment is even necessary, since the actual (average) rate may still be within plus-or-minus three bpm of the scheduled target heart rate wherein no adjustment is to be made. 
     However, in the exemplified embodiment the comparison of the target heart rate with the actual (average) rate is not entirely straightforward at this point, instead factoring in the acceleration, if any, of the most recently obtained (current) actual average heart rate from the previous heart rate. Although factoring in the heart rate acceleration is not necessary to the invention, it provides a way to adjust the workload in anticipation of the target heart rate being reached, preventing overshooting that is not predictable, and may at times be dangerous. 
     To accomplish the adjustment, the difference between the previous (average) heart rate and the current (average) heart rate (acceleration factor) is combined with the difference between the current (average) heart rate and the scheduled target heart rate to determine the direction of the adjustment, if any. These differences can be weighted to obtain a desirable result in actual applications. Thus, it has been found that the following equation obtains a satisfactory result: 
     
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Adjustment direction = (Target heart rate - current heart rate)/3 -       
(Current heart rate - previous heart rate)/4.                             
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     Applying this equation as represented in the state machine diagram of FIG. 4B, if the adjustment direction is less than or equal to -1, the workload will be reduced, if greater than or equal to +1 the workload will be increased, and if between -1 and +1 the workload will remain the same. Preferably, so that the machine does not continually oscillate between two settings, this equation allows the actual (average) rate to vary between plus or minus three bpm of the entered target heart rate, although other reasonable ranges are equally feasible. 
     In one possibility, as represented in step 142 and in the state machine diagram of FIG. 4B, if no action is necessary the software program loops back without making an adjustment. Note that even if no action is taken, the average heart rate continues to be calculated and/or updated whenever ready, as described above, at step 143. 
     If the comparison (step 144) results in a requested increase to the workload, i.e., the actual (average) heart rate is slower than the scheduled rate, (taking into consideration any acceleration factor, if desired), the level of resistance of the first resistance mechanism 12 is compared at step 146 to determine if it is already at its predetermined upper resistance level. As represented at step 148 and in the state machine diagram of FIG. 4C, the resistance level of the first resistance mechanism 12 is increased if not at this maximum level. 
     Thus, by way of example, if the first resistance mechanism 12 adjusts the speed of the treadmill 10, and the maximum speed entered for that particular user is 6.0 miles per hour, the controller 30 will supply a signal to the motor 16 to increase the speed and thereby the heart rate, regardless of the grade of the treadmill 10, if the speed of the treadmill 10 is below 6.0 miles per hour. If the next time through the loop the actual heart rate is again below the target level, this increasing of the speed will continue in one-tenth mile per hour increments up to the 6.0 mile per hour predetermined maximum. Thus, the speed will keep increasing up to the maximum entered speed, if necessary to increase the actual heart rate to the target level. 
     In keeping with the invention, if the actual heart rate is slower than the target heart rate and the first resistance mechanism 12 is already at the predetermined upper resistance level, as shown in step 150 and in the state machine diagram of FIG. 4C, the resistance level of the second resistance mechanism 14 is increased. Thus, in the above example, only when the 6.0 mile per hour predetermined maximum speed is reached will the grade be increased in an effort to further increase the heart rate to the target heart rate. 
     In the exemplified embodiment, if the second resistance mechanism 14 adjusts the grade of a treadmill 10, and the maximum grade is set to 4.0 percent, the controller 30 will supply a signal (step 152) to the incline motor 36 to increase the grade (and thereby increase the heart rate) when the maximum speed of the treadmill has been reached. Of course, the grade will not be increased if already at its maximum as indicated by step 150. This increasing of the grade will continue, in one-half percent increments each time through the loop, up to the 4.0 percent predetermined maximum, if necessary, to increase the actual (average) heart rate to the target level. 
     In the situation where the heart rate must be decreased, the workload is ordinarily removed in the reverse order. Thus, if the heart rate is faster than the target rate and the second resistance mechanism 14 is not at a predetermined lower resistance level (step 154 and the state machine diagram of FIG. 4D), the resistance level of the second resistance mechanism is decreased at step 156. However, if the second resistance mechanism 14 is already at the predetermined lower resistance level, the resistance level of the first resistance mechanism 12 is decreased at step 160, provided it is not already at a minimum as determined at step 158. 
     Thus, in keeping with the example, to lower the actual heart rate, grade is first reduced to predetermined minimum level, ordinarily 0.0 percent, before any speed reduction occurs. Of course, it can be readily appreciated that it is equivalent to alternatively consider the grade of the machine as the first resistance mechanism so that the grade is first increased to its maximum before the speed (second resistance mechanism) is adjusted. However, the manner described in detail herein has been found to favorably maintain the target heart rate. Moreover, as described previously, when reducing heart rate, the workload is preferably removed in the reverse order that it was added. Although not necessary to the invention, since some speed is always necessary, this pattern enables the apparatus to function in a repeatable manner. 
     VI. Other Operating Modes 
     It should be noted that with the present invention, not only may a number of target heart rates be sequenced together, but a number of corresponding maximum and minimum grades and speeds may be sequenced in time. By way of example, a user wishing to improve both speed and grade might first find it beneficial to have a very low maximum grade for a certain time duration, thus ensuring some training at a higher speed, and then having a low maximum speed for a certain duration thus ensuring some training at the higher grade. The ability of the apparatus to operate in these sequenced stages is even more apparent with an apparatus that exercises different muscle groups simultaneously, such as a combination bicycle/rowing machine, where a user might wish to maintain a certain heart rate yet exercise different muscles at different exertion levels that vary throughout an exercise routine. 
     In summary, the resistance mechanisms 12, 14 are incrementally varied as described above and the actual heart rate is ordinarily maintained at or near the target level for the time duration entered. 
     VII. Setting Limits 
     In one embodiment of the invention, as represented by the flow diagram of FIG. 8, the maximum resistance levels are determined by the resistance settings at which the user is currently exercising when either the target heart rate is first achieved in the automatic mode (i.e., at the conclusion of the warm-up stage) or the target rate is determined from the present heart rate of the user in the &#34;on-the-fly&#34; mode. In the automatic mode, as shown in step 180 of the flow diagram of FIG. 8, when the measured heart rate equals or exceeds the target heart rate, the warm-up stage is completed in the treadmill device. Before entering the target stage of operation for the treadmill, however, the maximum speed and grade are determined by the controller 30 rather than being directly input by the user. To this end, the controller 30 determines the maximum speed and grade of the treadmill based upon the current speed and grade at the moment that the user reaches the target heart rate. Similarly in the &#34;on-the-fly&#34; mode, after the user has prompted the controller 30 to determine the target rate from the current heart rate and before entering the target stage, the controller determines the maximum speed and grade of the treadmill based upon the current actual speed and grade. 
     Thus, the current speed is evaluated at step 182 as soon as the target heart rate has been achieved in the automatic mode or selected in the &#34;on-the-fly&#34; mode. If the speed is less than five miles per hour at this time, the controller 30 will set the maximum speed for that user to the current speed at step 184. Conversely, if the current speed is greater than five miles per hour at step182, then at step 186 the controller sets the maximum speed for that user at the current measured speed plus one mile per hour. For example, a first user reaching his target heart rate at 3.5 miles per hour will be assigned a maximum speed of 3.5 miles per hour, while a second user reaching her target heart rate at 6.5 miles per hour will be assigned a maximum speed of 7.5 miles per hour. 
     If the user indicates that no grade is desired, such as by entering the target stage of operation with zero grade, no grade will be used. In the &#34;on-the-fly&#34; mode, the user can accomplish this by simply prompting the controller 30 to determine a target rate from the present actual rate when the treadmill is at zero grade. In the automatic mode, a user can maintain zero grade by simply not incrementing grade during the manually-controlled warm-up stage. The zero grade condition is checked at step 188 of FIG. 8, and, in the situation where the target stage was entered with zero grade, at step 190 the maximum grade is set to zero. Conversely, if the target stage was entered with a non-zero grade, at step 192 the maximum grade is set to four percent above the grade at which the target stage was entered. At this time, the target stage is entered and the resistance levels are adjusted up to these maximums in order to control the heart rate of the user as previously described. 
     The above target heart rate-based maximum values, including the five mile per hour cutoff before adding one mile per hour to the maximum speed, and either the zero grade or current grade plus four percent values, were selected so as to differentiate between walking and running workouts. By way of example of walking workouts, a user entering the target stage at 3.5 miles per hour and 4% grade will have maximums of 3.5 miles per hour and 8% grade, while a user entering the target stage at 4.2 miles per hour and 6% grade will have maximums of 4.2 miles per hour and 10% grade. By way of example of running workouts, a user entering the target stage at 6 miles per hour and 0% grade will have maximums of 7 miles per hour and 0% grade, while a user entering the target stage at 5 miles per hour and 2% grade will have maximums of 6 miles per hour and 6% grade. 
     In general, the controller 30 assumes that a walker will prefer to utilize grade and have the grade automatically varied to control the heart rate, while a runner will prefer to not use grade at all, allowing only speed variations to control the heart rate. However, while these assumptions generally provide the desired different types of workouts, it can be appreciated that values other than those exemplified herein may be substituted without departing from the spirit and scope of the present invention. 
     VIII. Cool Down Stage 
     Although not necessary to the invention, at the end of the exercise routine, a cool-down stage is entered for an indefinite period of time wherein the grade is reduced to 0.0 percent and the speed is reduced by 40 percent to gradually lower the 15 heart rate. During the cool-down stage, the user regains manual control of the speed and grade via the user input device 96. 
     IX. Examples Of Operation 
     By way of example, two representative graphs are included illustrating the actual heart rate with respect to the speed and grade of a treadmill over a period of time for a user operating the treadmill in the automatic mode. In FIG. 6, a target heart rate of 145 bpm was entered, along with a maximum speed of 4.5 miles per hour and a maximum grade of 5.0 percent. The apparatus attempted to maintain the heart rate at the target (145 bpm) level for an entered total time duration of 10 minutes. 
     As shown in FIG. 6, a warm-up period occurred for approximately 7.5 minutes before the target level was reached, as indicated by point 200. As can be seen, during the warm-up stage the grade was manually increased to a maximum of 5.0 percent, while the speed was gradually increased to its maximum of 4.5 miles per hour. 
     Once the target stage was entered, which in the automatic mode occurred automatically upon achieving the target heart rate, the twenty percent warning reduction occurred at point 202 as the actual heart rate (approximately 162 bpm) was more than 14 bpm above the target rate of 145 bpm. Accordingly, the grade was quickly reduced to 0.0 percent. From that point on, the speed was lowered as the heart rate increased or raised as the heart rate decreased as shown during the period between approximately 8.5 minutes and 17.5 minutes. At point 204, or 17.5 minutes, the total time entered was exceeded and thus the executing routine entered the previously described cool-down stage. As can be seen, the speed was quickly reduced and the heart rate decreased accordingly. 
     In FIG. 7, a target heart rate of 155 bpm was entered, along with a maximum speed of 5.0 miles per hour and a maximum grade of 5.0 percent. The apparatus attempted to maintain the heart rate at the target (145 bpm) level for a total time duration of 10.5 minutes. As shown in FIG. 7, a warm-up period occurred for approximately 4 minutes before the target level was reached, as indicated by point 210. As can be seen, during the warm-up stage the grade was manually increased to approximately 3.0 percent, while the speed was increased to its maximum of 5.0 miles per hour. 
     Once the target stage was entered, which occurred automatically upon achieving the target heart rate, in accordance with one aspect of the invention the grade was decreased by the controller 30 while the speed remained constant. Only when the grade was reduced to 0.0 percent, as indicated by point 114, was the speed varied (reduced). From that point on, only the speed was adjusted to maintain the heart rate at the target level, until at point 216 the cool-down stage was entered. 
     X. Further Modes Of Operation 
     Finally, it can be appreciated that other modes of operation including conventional modes of operation and variations of the target stage of operation may be implemented with the apparatus 10. Thus, for example, one alternative operating mode that has been found to be beneficial, described as an interval heart rate control mode, or &#34;interval&#34; mode, is based on the same general principles of the automatic mode, but further requires periods of rest times and work times that are ordinarily entered by the user or recalled from memory for that specific user. 
     In this interval mode, after a warm-up period to reach the target heart rate, the user automatically enters the first work time period wherein the system maintains the user at the target rate in the manner described above for the target stage in the automatic or &#34;on-the-fly&#34; modes. However, after the length of time entered for this work period expires, the user enters a rest period wherein the workload is reduced fifty percent, and the heart rate lowered, first by reducing grade, and then speed, if necessary. The system records the grade and speed that the user was previously at before any reduction occurred, and then returns the user to those levels at the end of the rest time. The system alternates between the work setting and the rest setting, with an overall tendency to reduce the amount of speed and grade in general throughout the interval mode, as the user tires from the workout thereby influencing the effects of the resistance on the heart rate. 
     It can be readily appreciated that other modes are also feasible since control of the resistance mechanisms can be varied over the time of the exercise in any number of ways and sequences. In addition, manual adjustment of the target heart rate (resulting in resistance adjustments) may be allowed at any time during operation, although for safety reasons this is ordinarily limited to plus or minus 10 bpm in the target stage of operation, and plus or minus 5 bpm in the interval mode of operation. 
     As can be seen from the foregoing description, there is provided a method and apparatus for dynamically controlling the resistance of a first resistance mechanism with respect to the resistance of at least one other resistance mechanism of a fitness apparatus in dependence on the heart rate of the user thereof The fitness apparatus optimizes the benefit obtained from exercise thereon, and, since an individual user may input operational data, the apparatus and method is capable of benefiting virtually any user regardless of their level of physical conditioning. The fitness apparatus may further incorporate conventional features and alternative modes of operation, and ordinarily is combined with electronic heart rate supervision to ensure the safety of the user. 
     All of the references cited herein are hereby incorporated in their entireties by reference.