Abstract:
An apparatus for musculoskeletal stimulation allows independent electronic control of vibration parameters and overall biasing force so that an optimum combination of these parameters may be obtained regardless of the user&#39;s weight and without the need for adjustment of mechanical weights or springs.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application 61/788,904 filed Mar. 15, 2013 and hereby incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    This invention was made with government support under AG037354 awarded by the National Institutes of Health. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention provides a method and apparatus for applying a stimulating vibration to a person&#39;s arms or legs and in particular to an apparatus providing improved control of vibration and biasing force. 
         [0004]    During periods of disuse (physical inactivity), the body “deconditions” at a rapid rate, a phenomenon known as disuse atrophy. In deconditioning, muscle fibers reduce in strength and size, muscles shorten and denervate, tendons and ligaments develop adhesions and permanently lose their flexibility resulting in loss of range of motion and bones may lose their strength. Such deconditioning can result in an increased fall injury risk and secondary complications such as obesity, cardiovascular disease, diabetes, and other life threatening ailments can arise. 
         [0005]    Weight-bearing physical activity is the best known method for reducing or reversing disuse atrophy, but the underlying causes of disuse atrophy often limit one&#39;s ability to perform the necessary exercises. 
         [0006]    Harness-based treadmills and aquatic therapy pools are capable of enabling persons with reduced mobility to perform physical activity under partial bodyweight loading. However, these modalities are costly to acquire, require significant space in a rehabilitation facility, are difficult to operate and may also be impractical for weakened individuals. 
         [0007]    Electrical stimulation is an alternative means of inducing muscle activation in users who are unable to perform physical activity on their own. However, electrical muscle stimulation is site-specific, meaning it affects tissue(s) only in the vicinity of the electrode supplying electricity to the muscle, and it can cause discomfort and pain if used as a sole means to maintain muscle strength in the absence of physical activity. 
         [0008]    An alternative to the above techniques is vibration therapy. Typical vibration therapy provides whole body vibration with the user standing on a vibrating platform. This also can be impractical for users with limited mobility, U.S. Pat. No. 7,662,115 and US patent application 2012/0209156 describe vibration therapy systems that may be applied to user limbs, such as the legs, with a recumbent or supine individual. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides an improved system for applying vibration therapy to user limbs that allows isolated separate electronic control of vibration and biasing force applied to the limb. The invention permits a variety of therapy profiles to be implemented including those which vary bias force, vibration, and/or limb position in an exercise routine. 
         [0010]    In one embodiment, the invention provides an apparatus having an operator surface adapted to communicate with a distal portion of a user&#39;s limb to communicate forces thereto. A bias system communicates with the operator surface to receive a first electrical signal controlling a bias position of the limb and a vibration system communicates with the operator surface to receive a second electrical signal independent of the first electrical signal controlling a vibration applied to the limb. A control circuit provides the first and second electrical signals according to operator input commands. 
         [0011]    It is thus a feature of at least one embodiment of the invention to permit independent control of vibration and bias force to allow each to be optimized separately. 
         [0012]    The first electrical signal may provide an indication of desired force between the operator surface and the limb and the bias system may use feedback control of the force between the operator surface and the limb by receiving the first electrical signal and adjusting motion of the operator surface according to a difference between the first electrical signal and a signal indicating a force between the operator surface and the limb. 
         [0013]    It is thus a feature of at least one embodiment of the invention to provide electronically controllable bias force that can be maintained, for example, over different levels of vibration and different positions of the operator surface for more consistent treatment. 
         [0014]    The controller may receive a third electrical signal providing an indication of desired position of the operator surface and may output an indication of a difference between the third electrical signal and a signal indicating a position of the operator surface. 
         [0015]    It is thus a feature of at least one embodiment of the invention to provide for dynamic motion during vibration therapy by guiding a user with respect to limb movement independent of the vibration and the bias force. 
         [0016]    The vibration system may provide feedback control of a vibration of the operator surface by receiving the second electrical signal and adjusting vibration of the operator surface according to a difference between the first electrical signal and a signal related to a position of the operator surface. 
         [0017]    It is thus a feature of at least one embodiment of the invention to provide electrically-controllable vibration that may be held constant or varied as desired. 
         [0018]    The apparatus may include a sensor providing the signal related to a position of the operator surface providing one of position, velocity, and acceleration of the operator surface. 
         [0019]    It is thus a feature of at least one embodiment of the invention to permit control of vibration amplitude, force and other qualities. 
         [0020]    The control circuit may provide stored data describing a schedule of the first and second electrical signals over time to regenerate the first and second electrical signals. 
         [0021]    It is thus a feature of at least one embodiment of the invention to permit the apparatus to be used in predefined exercise routines in which bias force and vibration may be varied over time. 
         [0022]    The control circuit may provide an output adapted to be received by a user of the apparatus providing an indication that a desired force is being applied by the user to the operator surface. 
         [0023]    It is thus a feature of at least one embodiment of the invention to permit instructions to the user with respect to applying force when the apparatus is used in an active mode without limb constraint, for example, during dynamic motion exercises. 
         [0024]    In one example. the output to the user may be initiation of vibration of the operator surface. 
         [0025]    It is thus a feature of at least one embodiment of the invention to provide a subtle yet intuitive indication that the user is applying the appropriate level force to the platform in the active mode. 
         [0026]    Alternatively the output may be a display providing a visual guidance as to the application of the desired force. 
         [0027]    It is thus a feature of at least one embodiment of the invention to provide guidance to the user that can offer information about applying the correct amount of force and any force shortfall or excess. 
         [0028]    The control circuit may provide an output to the user of the apparatus indicating desired position of the operator surface as moved by extension or retraction of the user&#39;s legs or arms. 
         [0029]    It is thus a feature of at least one embodiment of the invention to permit dynamic motion exercises, for example, under constant bias force. 
         [0030]    The apparatus may include a seat for receiving a user positioned so that the user&#39;s feet may rest upon the operator surface with a lower portion of the user&#39;s legs substantially normal to the operator surface when the user is seated on the seat. 
         [0031]    It is thus a feature of at least one embodiment of the invention to provide an apparatus that may be used conveniently by users who can support themselves in a seated position. 
         [0032]    The apparatus may further include a user joint restraint constraining motion of the user&#39;s limb against force exerted on the user&#39;s limb by the operator surface. 
         [0033]    It is thus a feature of at least one embodiment of the invention to allow the apparatus to be used in the passive mode without requiring significant user strength or participation. 
         [0034]    The joint restraint may be a knee restraint for restraining upward motion of the user&#39;s knees when the user is seated in the seat providing at least one padded bolster held on a swing arm pivoting downward to apply the padded bolster against the upper surface of the user&#39;s knees when the user is seated in the seat supported by the operator surface and limiting upward motion of the user&#39;s knees. 
         [0035]    It is thus a feature of at least one embodiment of the invention to provide a simple joint restraint that does not unduly block entrance or exit from the seat when retracted. 
         [0036]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a perspective view of one embodiment of the present invention providing seated vibration therapy; 
           [0038]      FIG. 2  is a simplified side elevational view of the embodiment of  FIG. 1  showing motion of the various elements including a knee brace and a foot platform attached to an actuator assembly with respect to a user seated in the apparatus; 
           [0039]      FIG. 3  is a block diagram of the actuator assembly showing the principal components that provide both separate vibration and coarse position control of the foot platform, the figure further showing a high-resolution optical position encoder, a force/position sensing load cell, limit switches, and rotary encoder; 
           [0040]      FIG. 4  is a block diagram of a feedback circuit implemented a controller being a component of the embodiment of  FIG. 1 ; 
           [0041]      FIG. 5  is a diagram of a signal provided by the load cell as may be separated into a bias in vibratory feedback signals by signal processing; 
           [0042]      FIG. 6  is a kinematic diagram of the knee brace of  FIG. 1  showing its control and positioning; and 
           [0043]      FIG. 7  is a control flow diagram showing control signal profiles that may be used to implement different exercise regimes using the system of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0044]    Referring now to  FIGS. 1 and 2 , a musculoskeletal stimulation device  10  may provide for a seat  12  presenting a substantially horizontal seating surface  14  and a back support  16  extending upward from a rear edge of the seating surface  14 . The seat  12  maybe positioned on a pedestal  18 . 
         [0045]    The back support  16  may be adjustable in inclination (reclining) as is generally understood in the art and may provide left and right arm supports  20  extending horizontally forward so that a seated user  11  on the seat  12  may rest his or her forearms on the arm supports  20 . The arm supports  20  may be pivotable upward against the sides of the back support  16  to facilitate ingress and egress from the scat  12 . The seat  12  may swivel about a vertical axis to facilitate ingress and egress. 
         [0046]    The pedestal  18  supports the seat  12  above the floor and may be fixed relative to a force unit  22  attached to a floor support  23  and positioned in front of the seat  12 . Relative fixation between the seat  12  and the force unit  22  may be provided either by means of a connecting structure  24  communicating between the pedestal  18  and the floor support  23  or by connection of both the pedestal  18  and the floor support  23  directly to the floor which then provides for this mechanical communication. Alternatively, relative fixation between the seat  12  and the force unit  22  may be provided for by sufficiently high friction forces between the floor and floor support  23  as well as between the floor and the pedestal  18  that exceed the force generated or applied. 
         [0047]    The force unit  22  supports a vibration surface  26  facing the seat  12 , for example, a textured plate. The vibration surface  26  is positioned to receive the feet of the user  11  when the user  11  is positioned in the seat  12  with his or her feet slightly elevated with bent knees. In this respect, the top of the vibration surface  26  may slope away from the user  11  by about 30 degrees from vertical. Pressure by the feet and legs of the user  11  against the vibration surface  26  is resisted by the structure of the force unit  22  communicating through the connecting structure  24  or floor to the pedestal  18  and the back support  16 . 
         [0048]    The force unit  22  may hold an actuator assembly  28  communicating with the vibration surface  26  to impart a vibration motion  30  and/or a bias motion  32  to the vibration surface along an actuation axis  34  generally normal to the surface of the vibration surface  26  and aligned with the lower leg of the user  11 . The floor support  23  may provide angulation to the force unit  22  to provide the desired angle of the actuation axis  34 . 
         [0049]    Generally, the vibration motion  30  and the bias motion  32  may be actively resisted by conscious muscular action of the user  11 , as will be described below, in a dynamic mode or passively resisted by structure of the legs of the user  11  as braced against knee bolsters  36  limiting the bending of the knees of the user  11 , in a passive mode, as will also be described below. 
         [0050]    Referring now to  FIG. 3 , a rear surface of the vibration surface  26  may attach to a mounting plate  40  within the force unit  22 . The mounting plate  40  may be suspended, for example, at four corners on axially extending compression springs  42  allowing it to move in vibration along axis  34 . The remaining ends of the axially extending compression springs  42  are fixed to a carriage  45  communicating through linear slides  43  with a stationary structure fixed relative to the floor support  23 . The slides  43  provide for translation of the carriage  45  along axis  34  and may, for example, be recirculating linear ball bearings or other types well known in the art. 
         [0051]    Also within the force unit  22 , a voice coil  44  is centered between the compression springs  42  and attached at one end to the rear surface of the mounting plate  40 . The voice coil  44  may produce short-excursion, high-force vibrations according to a vibration control signal  46  received from a controller  48  whose operation will be described below. In this application, the voice coil  44  may provide excursions of less than half an inch with forces in the range of 1 to &gt;100 pounds at frequencies of from 10 to 100 hertz depending on the mass being driven. Voice coils of this type are commercially available from a variety of vendors and normally provide a tubular solenoid with multiple turns of conductor positioned about a magnet so that the current through the conductor generates an axial force in proportion to that current. 
         [0052]    A high-resolution optical position sensor  47  may be attached to the carriage  45  to measure displacement of the vibration surface  26  along axis  34  with respect to the carriage  45  for precise characterization of short excursion vibrations of the vibration surface  26  as will be discussed. An output of the optical position sensor  46  may be provided to the controller  48 . 
         [0053]    The opposite end of the voice coil  44  is attached to a first end of a load cell  49  whose second end is attached to an actuator shaft  50  at a first end of a linear actuator  52 . A second end of the linear actuator  52  is attached to the structure fixed with respect to the floor support  23 . 
         [0054]    As so positioned, the load cell  49  may measure an axial force exerted between the front of the vibration surface  26  and the structure of the floor support  23 . The load cell  49  may provide for a force signal  51 , reflecting this axial force, to the controller  48  as will be described below 
         [0055]    The linear actuator  52  may be attached at its end opposite the shaft  50  structure fixed against movement along axis  34  with respect to the floor support  23 . Generally the linear actuator  52  may provide substantially greater translation of the vibration surface  26  than the voice coil  44  but at much lower operating speeds. For example, the linear actuator  52  may provide a range of extension of much more than one inch and typically on the order of 12 inches at a rate of less than one inch per second and typically less than three inches per second. Linear actuators of this type are commercially available from a variety of vendors and may provide, for example, a threaded shaft extending along axis  34  and engaging with a threaded collar, one of the two being rotatable by the stepper motor  54  to control extension of the actuator shaft  50  driven by movement of the threaded shaft through the threaded collar. 
         [0056]    The stepper motor  54  may receive a stepper motor command signal  56  from the controller  48  that may be used to rotate the stepper motor by a given number of steps associated with a predetermined angular movement. The relative movement of the stepper motor  54  and hence the linear actuator  52  can therefore be easily determined by counting the steps of the stepper motor command signal  56 . Absolute position of the stepper motor  54  and linear actuator  52  can be determined by “homing” the stepper motor  54  or actuator shaft  50  upon start up of the musculoskeletal stimulation device  10  by moving the vibration surface  26  to a known position against a limit switch or the like. Alternatively, or in addition, a rotary encoder  58  (absolute or incremental) may be attached to the stepper motor or a linear encoder may be attached between the linear actuator and floor support  23  to provide absolute position signal  60  to the controller  48 . 
         [0057]    The first and second limit switch  51  may be positioned to detect motion of the carriage  45  outside of the range established by the limit switches  51  representing a full travel range of the linear actuator  52 . These limit switches  51  may also communicate with the controller  48  to prevent over travel of the carriage  45 . 
         [0058]    It will be appreciated that the vibration motion  30  and the bias motion  32  may be provided respectively by voice coil  44  and linear actuator  52 . Generally the voice coil  44  can excite the vibration surface  26  at high rates, for example, to provide motion of the vibration surface  26  having a power spectrum concentrated at substantially greater than  10  hertz to provide vibratory excitation. In contrast, the linear actuator  52  may excite the vibration surface  26  to provide a pattern of motion having a power spectrum concentrated at substantially less than one hertz to provide a substantially steady-state force application. 
         [0059]    The controller  48  may also communicate with a user interface  100 , for example, providing a touchscreen for receiving commands from the user  11  and providing a display to the user  11 . An emergency stop line  59  communicates between the controller  48  and an emergency stop button  101  (shown in  FIG. 1  as will be described below). A clutch line  61  provides control to an electronic clutch  116  which will also be described below. 
         [0060]    The controller  48  will generally provides one or more electronic computer processors communicating with electronic memory for storing a program to be executed by the electronic computer according to data and the program in the memory. The memory provides a non-transient storage medium for this program. 
         [0061]    Referring now to  FIG. 4 , the controller  48  executing the program may implement two independent feedback loops for electrically controlling the voice coil  44  and the linear actuator  52 , for example, to independently control the bias motion  32  and vibration motion  30  discussed above with respect to  FIG. 2 . Different parameters of bias motion  32  and vibration motion  30  including force, excursion range, frequency, energy, and power may be controlled as will be discussed below. A minor feedback loop (not shown) may also be provided to control the position of the linear actuator  52  for machine initialization and the like. 
         [0062]    Control of the voice coil  44  may be according to a vibration command signal  66 , for example, indicating a desired vibration quality such as force, excursion, energy or the like. The vibration command signal  66  will be provided to a summing junction  68  (typically implemented in software within the controller  48 ) receiving a feedback signal  70  having the same dimensions (e.g. force, excursion, energy etc.) as the vibration command signal  66 . The summing junction  68  subtracts the feedback signal  70  from the vibration command signal  66  to produce an “error signal” in the form of the vibration control signal  46  communicating with the voice coil  44 . 
         [0063]    The feedback signal  70  may be provided by the optical position sensor  47  to provide direct control of vibration motion (e.g. amplitudes, frequency etc.) as well as position derived quantity such as energy, force and the like. 
         [0064]    Control of the linear actuator  52 , may be according to a bias force command signal  64 , indicating a desired bias force. The bias force command signal  64  will be provided to summing junction  76  (also typically implemented in software within the controller  48 ) receiving feedback signal  78 . The feedback signal  78 , also having units of force, is subtracted from the bias force command signal  64  to produce a stepper motor command signal  56  to the stepper motor  54  of the linear actuator  52 . The feedback signal  78  may be derived from the load cell  51  to provide direct control of bias force as well as force derived quantities such as, energy transfer and the like. In a second embodiment. the load cell  44  may be used to develop both feedback signals  70  and  78 . In this embodiment, the motion of the voice coil  44  is mechanically summed with motion of the linear actuator  52  (by virtue of their series connection) as depicted in  FIG. 3 . This mechanical summing is represented by summing junction  72  in  FIG. 4  and provides a combined mechanical displacement to the load cell  49 . The load cell may produce a load signal  51  that will generally contain a high-frequency vibration motion  30  superimposed on (providing excursions about) a low-frequency bias motion  32 . The load signal  51  may be provided to a vibration extractor  74  (also typically implemented in software) that may process the load signal  51  to provide a variety of different parameters related to vibration including vibration excursion, peak vibration force, energy absorption and the like. Vibration excursion may, for example, be extracted by applying a high pass filter to the signal  51  and then measuring the amplitude of the result. This extracted amplitude can then provide feedback signal  70  of the vibration excursion. It will be understood that other parameters such as vibration force may be deduced from the known dynamic qualities of the load cell  49  and the associated structure of the actuator assembly  28  (masses and spring constants) and energy transfer may be deduced by comparing the load signal  51  to the vibration command signal  66 . Generally, it will be appreciated that energy transfer may be controlled by monitoring a variety of parameters including but that are not limited to peak-to-peak vibration displacement, vibration frequency, vibration acceleration, alternating vibratory force, vibration wave form, joint flexion angle, direction of applied vibration, direction of applied bias three, bias force magnitude, treatment duration, compliance of user and system as well as combination of user in system, etc. 
         [0065]    The output of the vibration extractor  74  in any of these cases provides the feedback signal  70 . It will be understood that a first feedback loop including vibration command signal  66 , summing junction  68 , voice coil  44 , load cell  49 , and vibration extractor  74  may control the vibration produced by the voice coil  44  to a precise input designated by vibration command signal  66 . Generally the frequency of the vibration may be controlled “open loop” by providing a predetermined frequency of sine wave to the voice coil  44  or a predetermined electrical signal to a vibrating (rotary imbalance) motor or other motor used to drive vibration motion, but it will be appreciated that frequency may also be controlled “closed loop” using the above described feedback loop. 
         [0066]    Control of the vibration uses sensors other than the load cell  49 , for example, accelerometers, optical position sensors, linear variable differential transformers (LVDTs) or the like, to provide any of position, acceleration, force or velocity feedback for corresponding measurements of the corresponding dimensions of the vibration command signal  66  which may be characterized in any of these ways. 
         [0067]    Referring still to  FIGS. 4 and 5 , the load signal  51  may also be provided to a bias force extractor  80  which extracts only the bias motion  32  from the load signal  51 . This bias force extractor  80  may also be implemented in software, for example, as a low pass filter or window averaging circuit or the like. This extracted bias force provides feedback signal  78 . 
         [0068]    Thus it will be understood, therefore, that a second feedback loop including bias force command signal  64 , summing junction  76 , linear actuator  52 , load cell  49  and bias force extractor  80  may control the force amplitude of the bias force produced by the linear actuator  52  to a precise input value designated by bias force command signal  64 . The ability to provide feedback control of a particular bias motion  32  is important during the application of vibration when the user  11  may unconsciously increase force on the footplate in response to the simulation. This feedback control moves the vibration surface  26  back to offset this unconscious increased pressure by the user. 
         [0069]    Referring still to  FIG. 4 , a position command signal  62  indicating a desired position of the vibration surface  26  may be received by a summing junction  82  (typically implemented in software within the controller  48 ) also receiving a feedback signal  84  (either developed internally by monitoring the stepper motor command signal  56 , or obtained as absolute position signal  60  from the encoder  58  or from a linear encoder located to monitor relative position between floor structure  23  and footplate  26 ) and subtracting it from the position command signal  62  to produce the position error signal  63 . In one example (not depicted), the error signal  63  may be provided to the linear actuator  52  instead of the signal from summing junction  76  to permit closed loop control of the position of the linear actuator  52 , for example, during initialization of the musculoskeletal stimulation device  10 . 
         [0070]    As shown, however, the position error signal  63  maybe output to provide an indication to the user  11  of a desired position of the vibration surface  26  so that a feedback loop is effectively implemented through the user  11  as will be described below. 
         [0071]    Referring now to  FIG. 7 , the ability to accurately control both vibration and bias force on the vibration surface  26  allows the present invention to implement a number of training sequences that may be executed by the controller  48 , for example, from stored data structures  90  and executed by a profile execution program  92  held in memory. 
         [0072]    In one example, a vibration profile  94  may describe a peak vibration force that varies over time and a bias force profile  96  may describe a bias force that varies over time. Typically the bias force profile  96  will adopt values between about 10 pounds to at least 80 pounds of force. The vibration profile  94  and bias force profile  96  can control the musculoskeletal stimulation device  10  to allow the user  11  to experiences vibration at a range of different bias forces. This control is affected by providing changing signals  66  and  64  according to the vibration profile  94  and bias force profile  96 . 
         [0073]    In addition to controlling a vibration force, vibration frequency may be controlled in a second dimension providing a vibration frequency profile  94 ′. In one nonlimiting example. vibration frequency may change from 13 hertz to rise to 34 hertz and then to drop again to 13 hertz over a period of about 10 seconds. 
         [0074]    As noted, an analysis of the driving signal for the voice coil  44  versus the feedback signal  70  can reveal information about loading and energy transfer from the vibration surface  26  to the user  11  and other load/energy/power parameters including amplitude, averages, and the like. An analysis of the feedback signal  70  while sweeping through frequencies with the vibration profile  94  can provide information about a resonance of the combined user  11 /musculoskeletal stimulation device  10  that may help identify the frequency of greatest muscle activation. 
         [0075]    Similarly, a bias force profile  96  may be applied to change the bias force during the session spanned by the vibration profile  94  and vibration frequency profile  94 ′. In a passive mode implemented by the placement of the bolsters  36  against the knees of the user  11  (shown in  FIGS. 1 and 2 ), this bias force profile  96  is simply applied to the feedback loops of  FIG. 4  as input vibration command signal  66 . In an active mode with the bolsters removed, the user  11  must control his or her legs to apply the necessary force based on information provided to the user from the musculoskeletal stimulation device  10 . 
         [0076]    For example, user  11  can monitor a display on a user interface  100  communicating with the controller  48  (shown generally in  FIGS. 1 and 4 ). The display, for example, may provide a compliance zone and a marker moving with respect to that compliance zone that can be manipulated into the compliance zone by the user by changing the force of his or her legs against the vibration surface  26 . Generally movement of the vibration surface  26  under the feedback control described with respect to  FIG. 4 , controlling bias force will greatly simplify this task of maintaining a desired force by the user  11  and the display to the user may simply show the relative position of the linear actuator  52  within its compliance or operating range so that the user  11  may center linear actuator  52  within that range. While the linear actuator  52  is operating within its compliance range, it will provide the necessary force control. The feedback loop for bias force may be slowed, for example, to respond (be updated) only at intervals of three seconds and with limited excursion during each update, to assist users  11  having reduced reaction speed. Alternatively, or in addition, movement of the vibration surface  26 , under the guidance of the force feedback loop, may be limited in speed so that when the user pushes against the vibration surface  26 , at a force slightly exceeding the prescribed force of the feedback loop, the vibration surface  26  recedes at a constant rate allowing the user  11  to implement a leg press exercise. Generally, guidance to the user  11  with respect to the necessary three to be applied to the vibrations surface  26  by the user  11 , is provided in the form of the vibration surface  26  moving toward the user  11  (when the user&#39;s force is below that required) and away from the user  11  (when the user  11  applies excess force to the vibration surface  26 ). The device will automatically stop treatment (movement and vibration) if an overload force is detected in excess of a predetermined amount or percentage of the prescribed setpoint of the feedback control or if the vibration surface  26  reaches an extreme of travel, for example as detected by limit switches  51  shown in  FIG. 3 . 
         [0077]    As noted generally above, the vibration of the vibration surface  26  may stop if the desired force level is not being maintained by the user  11  (i.e., the user  11  is not pressing hard enough against the vibration surface  26 ). This can prevent unwanted noise when a user is backing their legs off (i.e. reducing force on the vibration surface  26 ) during a leg press. The presence or absence of: or adjustment, of vibration can also indicate to a user  11  (as a user-implemented feedback loop) that they should increase the force applied to the vibration surface  26  while retracting their legs in order to maintain a prescribed level of bias force (slightly above the target load during pushing and slightly below the target load during retraction). 
         [0078]    In an alternative embodiment, in the active mode, the vibration of vibration surface  26  may be controlled to switch off when a desired bias force is not obtained as a result of improper muscular resistance by the user  11 . In this mode, the user  11  is instructed to press on the vibration surface  26  with increasing force until vibration begins and then to moderate the pressure on the vibration surface  26  to sustain vibration. 
         [0079]    In another example, a position profile  104  may be provided together with profiles  94  and  96  and the user  11  instructed to use his or her legs to try to move the vibration surface  26  while it is vibrating, and against the bias force of the profile, to follow the desired position profile  104 . This may be accomplished again by a display on user interface  100  showing a trajectory of the position profile  104  and the current position  106 . The user  11  may manipulate the current position  106 . increasing or decreasing force on the vibration surface  26  to move the vibration surface  26  responding under feedback control to maintain a given force. In this way a dynamic exercising of the user&#39;s muscles under vibration with a predetermined load may be provided. A position profile  104  may be implemented with a bias force profile  96  only and without a vibration profile (that is, with zero vibration) so that the present invention may provide dynamically loaded motion without vibration. 
         [0080]    Generally the profiles of  94 ,  96  and  104  may include periods of rest and or repetitions. The profiles  94 ,  96 , and  104  may he entered or modified by operator input commands from the user  11  or others. Such operator input commands may define or modify, for example, the shape of standard curves or may provide arbitrary profile curves through the entry of multiple data points. These operator input commands may be may be entered through the interface  100  or another computer connected to the controller  48  according to techniques well known in the art. 
         [0081]    Referring now to  FIGS. 1 ,  2 , and  6 , the bolsters  36  may be generally padded cylinders extending across actuation axis  34  to fit on either side of the knees as separated by an equalizer arm  110 . The equalizer arm  110  extending between the bolsters  36  may pivot at a pivot  111  midway along the equalizer arm  110  and join the equalizer arm  110  to one end of a swing arm  112 . The swing arm  112  may communicate to its opposite end with the floor support  23  through a second pivot  114 . In this way, the bolsters  36  may be moved down against the knees of the user  11  by downward rotation of the swing arm  112  with rotation of the bolsters  36  about the pivot  111  equalizing force above and below the knees of the user  11 . Alternatively, the swing arm  112  may be moved upward to move the bolsters  36  away from the knees of the user  11  to allow the user  11  to freely exit the musculoskeletal stimulation device  10 . 
         [0082]    Pivot  114  is attached to an electronic clutch  116  so that it may be locked in a position to restrain upward motion of the knees of the user  11  for operation of the musculoskeletal stimulation device  10  in a passive mode. In this case the bolsters  36  resist upward force of the knees of the user  11 . The clutch  116  may communicate with the controller  48  according to a desired mode of operation as may be programmed in the controller  48 . 
         [0083]    A gas spring  118  may communicate between the floor support  23  and the swing am  112  to provide a viscously damped upward bias to the swing arm  112  when the clutch  116  is released. 
         [0084]    An emergency stop button  101  (shown in  FIG. 1 ) may communicate with the controller  48  to receive operator input commands to terminate a session controlled by a profile, stopping movement of the linear actuator  52  and vibration of the voice coil  44  and releasing the clutch  116 . Footplate  26  may also communicate with controller  48  to return to a default position when the emergency stop button  101  is depressed. 
         [0085]    The performance of the user  11  during execution of a profile  94 ,  96 , or  104  may also be recorded, for example, by logging the feedback signals  70 ,  78  and  84  or the error signals. The log data may be displayed to a user  11  in real time or after the profile to assess performance improvement by the user  11 . It will be appreciated that this data may be displayed locally, printed, transmitted, wirelessly, or transmitted by digital storage media for use by others. 
         [0086]    Feedback loops may also be used to drive other devices used in conjunction with the treatment device referenced herein. For example, neuromuscular electrical stimulation devices attached to the user  11  may compliment treatment by emitting a voltage that is synchronous, phase shifted, or otherwise related to the applied vibration or bias force signal. Ultrasound and diathermy devices (not shown) may be applied in the same manner, as could be other complimentary therapeutic modalities. 
         [0087]    The inventors contemplate that the present invention is not limited to use on the legs but may find use as an analogous system for exercising the arms or other portions of the body. 
         [0088]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”. “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within -a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0089]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0090]    References to “a controller” can be understood to include one or more microprocessors that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices. Furthermore, references to memory, unless otherwise specified, can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor-controlled device, external to the processor-controlled device, and can be accessed via a wired or wireless network. 
         [0091]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.