Patent Publication Number: US-11383132-B2

Title: Physical exercise apparatus and method for training on such an apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit under 35 USC § 371 of PCT Application No. PCT/EP2019/081983 entitled PHYSICAL EXERCISE APPARATUS AND METHOD FOR TRAINING ON SUCH AN APPARATUS, filed on Nov. 20, 2019 by inventors Alain Betrancourt, Ambroise Chaigne and Pauline Malosse. PCT Application No. PCT/EP2019/081983 claims priority of French Patent Application No. 18 71683, filed on Nov. 21, 2018. 
     FIELD OF THE INVENTION 
     The present invention relates to a physical exercise apparatus comprising, inter alia, a saddle with two saddle parts capable of pitch, roll and yaw movement relative to a frame. The present invention also relates to a method for training a user on such an apparatus. 
     BACKGROUND OF THE INVENTION 
     In the fields of sports training, functional rehabilitation or fitness maintenance for the elderly, it is known, for example from WO-A-2013/135697 to use a proprioception saddle which comprises two saddle parts capable of pitch T, roll R and yaw L movement relative to the frame of a physical exercise apparatus. Before the user begins pedaling, a health care professional or trainer can adjust the exercise machine a priori, taking into account the user&#39;s body measurements and, possibly, pathology. Depending on the user&#39;s build, it is not easy to check that the latter is correctly seated on the saddle because the pelvis and thighs hide the saddle. It is thus uncertain whether the user&#39;s posture on the exercise machine is correct. If the user&#39;s posture is not correct, he or she may not benefit fully from the exercise and may even generate an additional pathology through misuse. Moreover, the possible progress of the user during successive exercise sessions cannot be quantified. 
     SUMMARY OF THE INVENTION 
     The invention intends to rectify these drawbacks more particularly by proposing a new physical exercise apparatus that makes it possible to ensure that the user is correctly positioned on the saddle and makes it possible to detect any progress made by the user, in particular the progress in his/her pelvic flexibility. 
     To this end, the invention relates to a physical exercise apparatus comprising a frame equipped with a crankset and a saddle, this saddle itself comprising a chassis fastened to the frame, two saddle parts and means for articulating each saddle relative to the chassis about a pitch axis, about a roll axis and about a yaw axis. According to the invention, the apparatus also comprises sensors for detecting a pitch movement T, a roll movement R and a yaw movement L of each saddle part about the pitch, roll and yaw axes, respectively, these movements resulting from a user pedaling. The apparatus also comprises at least one calculation unit configured to determine the angular amplitudes of the pitch, roll and yaw movements T, R and L from the sensor output signals, and of the position of the bearing point of an ischium on each saddle part. Finally, this apparatus comprises at least one screen for displaying the position on each saddle part of a bearing point of the user&#39;s ischium while pedaling, depending on the angular amplitudes determined by the calculation unit. 
     Thanks to the invention, the user or the person assisting him/her, in particular a health professional or a trainer, is able to evaluate whether his/her posture on the saddle of the physical exercise apparatus of the invention is correct, by locating on the display screen the position of the support points of his/her ischia while pedaling. This allows the user or the person assisting him/her to possibly modify the user&#39;s posture in order to correct an asymmetry or an imbalance of his supports. In addition, the apparatus of the invention may allow, possibly by keeping track of the parameters determined by the calculation unit, to compare these parameters from one exercise session to another or during the session, in order to evaluate the user&#39;s possible progress. 
     According to advantageous but non-mandatory aspects of the invention, such a physical exercise apparatus may incorporate one or more of the following features, taken in any technically permissible combination:
         The detection sensors comprise at least one inertial cell attached to each saddle part.   The inertial cells detect pitch and roll movements and at least one optical sensor is used to detect the yaw movement of each saddle part.   The calculation unit is configured to determine a deviation between the position of each bearing point on the saddle part and a reference position and the screen is configured to show this deviation.   The screen is positioned in front of the user sitting on the saddle, preferably on a handlebar of the apparatus.       

     According to another aspect, the invention relates to a method for training a user on a physical exercise apparatus as mentioned above, with this method comprising the steps of:
         a) detecting the pitch T, roll R and yaw L movements by means of sensors;   b) determining the angular amplitudes of the pitch, roll and yaw movements; and   c) displaying the positions of the ischium support points on the screen, depending on the angular amplitudes determined by the calculation unit.       

     This method facilitates verification of the user&#39;s posture and possible correction thereof, taking into account the data displayed on the screen. 
     According to advantageous but non-mandatory aspects of the invention, this method may incorporate one or more of the following features:
         Inertial cells detect pitch and roll movements, at least one optical sensor is used to detect the yaw movement of each saddle, and step b) comprises the following sub-steps:   b1) calculating approximate pitch and roll amplitude values, preferably by a 6-axis Madgwick algorithm, based on vector components of the pitch and roll movements determined by the inertial cells;   b2) calculating vector components corresponding to a magnetometer output signal, based on the output signal of the optical sensor and the approximate values calculated in sub-step b1);   b3) calculating pitch, roll and yaw amplitude values, preferably by a 9-axis Madgwick algorithm.   In step c), the screen also displays the angular amplitudes determined in step b).   The method comprises the additional steps of:   d) determining a single symbol ( 588 ) representing the angular amplitudes (α, β, γ), with each angular amplitude (α, β, γ) corresponding to a respective dimension of said symbol;   e) displaying the symbol determined in step d) on the screen ( 29 ).   The calculation unit is configured to determine a deviation between the position of each bearing point on the saddle part and a reference position, the screen is configured to display this deviation, and, in step c), the screen displays a representation of the saddle parts, the ischium support positions relative to the representation of the saddles, and a representation of the reference position relative to the representation of the saddles.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other advantages thereof will become clearer in the light of the following description of an embodiment of a physical exercise apparatus and method for training in accordance with the outline thereof, given by way of example only and made with reference to the appended drawings in which: 
         FIG. 1  is a schematic representation of the principle of a physical exercise apparatus in accordance with the invention; 
         FIG. 2  is a larger scale side view of the saddle and a schematic representation of certain other components of the apparatus of  FIG. 1 ; 
         FIG. 3  is a block outline diagram of a method according to the invention; 
         FIG. 4  is a view of a display screen of the apparatus of  FIGS. 1 and 2  implementing the method of  FIG. 3  and 
         FIG. 5  is a larger scale view of detail V in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The apparatus  2  shown in  FIG. 1  is intended to allow a user to perform physical exercise by pedaling, thereby improving pelvic mobility and/or maintaining or even developing cardiovascular capabilities. 
     The apparatus  2  comprises a frame  22  equipped with a crankset  24  and which supports a saddle  26  as well as handlebars  28 , according to a known breakdown for an exercise bike. The apparatus  2  is of the exercise bike type. 
     The crankset  24  comprises two cranks and two pedals, with only one of these cranks and one of these pedals being visible in  FIG. 1 , with references  242  and  244  respectively. 
     A braking system for the crankset  24 , not shown and adjustable, is provided, inside a cover  25 , in order to allow modulating the effort that a user must exert to pedal, depending on the exercise to be performed. 
     The saddle  26  is supported by a seat post  27  mounted in an adjustable manner on the frame  22  and immobilized thanks to a tightening screw, not shown, controlled by a knob  272 . 
     A screen  29  is mounted on the upper part of the frame  22 , between the two branches  282  and  284  of the handlebars  28 . Thus, this screen  29  is visible to a user sitting on the saddle  26 . 
     The saddle  26  comprises a chassis  262  attached to the seat post  27 , thus mounted to the frame  22  through the seat post. The saddle  26  also comprises two saddle parts, namely a left saddle part  264  and a right saddle part  266 . The saddle further comprises articulation members for each saddle relative to the chassis  262 . These articulation members comprise a cradle  267  for articulating the saddle parts, each independently of the other saddle part, about a pitch axis A 26  defined by the cradle  267 . The cradle  267  is itself supported by an elastically deformable element  268  which constitutes another articulation member of the saddle parts. The elastically deformable element  268  is provided to deform elastically during a roll movement R of the cradle  267  about an axis B 26  parallel to the forward/rearward direction of the saddle  26 . On the other hand, the elastically deformable element  268  is provided to deform elastically during a yaw movement L of the cradle  267  about an axis C 26  that is generally vertical and parallel to, or coincident with, a longitudinal axis of the seat post  27 . The pitch movements of the saddle parts  264  and  266  are independent of each other, whereas their roll movements R and yaw movements L are the same, since they result from the elastic deformation of the element  268  that is common to them. 
     Preferably, the technical teaching of WO-A-2013/135697 is applied here. 
     In a variant, another structure can be provided for the saddle  26 , in particular with saddle parts with independent pitch, roll and yaw movements. 
     The saddle  26  is equipped with two inertial cells. An inertial cell is positioned under each of the saddle parts  264  and  266 , with only the cell arranged under the saddle part  266  visible in  FIG. 2 , with reference  30 . This reference is used to designate each of these two cells. 
     Each inertial cell  30  is capable of detecting accelerations along three axes of an orthogonal reference frame X-Y-Z of a space in which the apparatus  2  is installed. Thus, each inertial cell  30  is capable of providing three acceleration components Ax, Ay and Az, parallel to the X, Y and Z axes respectively, and three rotation components Gx, Gy and Gz, about these axes. Each inertial unit  30  operates at a frequency of 100 Hz. 
     In practice, each inertial cell  30  can be formed by an electronic card marketed by the company NXP under the reference BRKT-STBC-AGM01, which integrates two types of inertial sensors, namely a FXOS8700 accelerometer-magnetometer and a FXPS21002 gyrometer. Here, the magnetometer function of the FXOS8700 component is not used. In other words, this magnetometer is not active. 
     In a variant, other types of inertial cells can be used. 
     The components Ax, Ay, Az, Gx, Gy, and Gz determined by one of the inertial cells  30  are representing the pitch movement T and roll movement R of the saddle part  264  or  266  under which the inertial cell  30  in question is installed. 
     The output signals from the two inertial cells  30  are supplied to a calculation unit  40  which comprises, among other things, a microprocessor  41  programmed to perform calculation operations detailed below, as well as a data storage memory  44 . 
     A data link  32  connects each inertial cell  30  to the calculation unit  40  and allows the output signal S 30  of the inertial cell  30  in question to be conveyed, this output signal including the components Ax, Ay, Az, Gx, Gy and Gz. 
     The apparatus  2  also comprises an optical sensor  50  positioned beneath the saddle  26  and having a viewing direction, shown as arrow F 50  in  FIG. 2 , directed toward the saddle  30  in a direction generally parallel to the axis C 26 . The optical sensor  50  is used to determine the yaw movement L of the saddle  26  about the axis C 26 . 
     To do so, a target, not shown, may be attached underneath the saddle  26 , to facilitate aiming the optical sensor  50 . The target consists of two marker points, either reflectors or light emitting diodes or LEDS. 
     The optical sensor  50  is mounted on the seat post  27  by means of a support  54  and connected to the calculation unit  40  by a data link  52  through which the output signal S 50  of the optical sensor  50  flows, which comprises an angle corresponding to the instantaneous deviation of the saddle  26  about the axis C 26 , relative to a rest position, and/or the angular amplitude γ of the yaw movement L of the saddle  26 . The optical sensor outputs signal S 50  representing the position 2D, that is, the pixel coordinates of the target light points, with reflectors or with LEDS, which it detects. 
     The optical sensor  50  operates at a frequency of 50 Hz. 
     In practice, the optical sensor  50  can be of the SEN0158 type marketed by DFRobot. 
     In a variant, other optical sensor types may be used. 
     A sensor assembly  60  is integrated into the physical exercise apparatus  2 , in the vicinity of the crankset  24  and enables detecting the rotation speed V of the crankset  24 , the duration D of the pedaling and the instantaneous power P of the pedaling. This data is collected at a frequency of the order of 1 Hz, in order to verify in particular that the speed V and the power D are not too high in the context of a relaxation exercise that aims to increase the mobility of a user&#39;s pelvis. The sensor assembly  60  also comprises a sensor, not shown and which may be worn by the user, for determining the user&#39;s heart rate F while pedaling. 
     The sensor assembly  60  is connected to the calculation unit  40  by a data link  62  that allows the output signal S 60  of this sensor assembly to be conveyed, this output signal including the quantities V, D and P. 
     It is noted that, even if inertial units incorporating a magnetometer, including the one mentioned above as an example, are known in the literature, the use of a magnetometer is not preferred in the embodiment of the invention represented in the Figures, because a magnetometer is subject to electromagnetic disturbances that may distort the result of the measurements. Since such disturbances are capable of occurring in the area where the apparatus  2  is installed, especially because the user or the person assisting him/her, in particular a caregiver or a trainer, may be carrying a cell phone or other electronic device. In addition, some users may have a metal hip prosthesis fitted, which that constitutes a relatively large ferromagnetic mass positioned in the vicinity of the saddle  26  that may interfere with the operation of a magnetometer. In contrast, the angular amplitude γ of the yaw movement L is relatively small, typically less than 15°, to the point that an absolute error of a few degrees on the measurement of this angle would induce a large relative error. 
     Using the optical sensor  50  to supplement the measurement of the yaw movement L relative to the measurement of the pitch T and roll R movements, obtained by the inertial cells  30 , avoids the drawbacks arising from the electromagnetic disturbances of a magnetometer. 
     However, if the room in which the exercise apparatus  2  is installed can be protected against electromagnetic disturbances and if those present in this room are not carrying electromagnetic devices or a significant ferromagnetic mass, the use of inertial cells with an active magnetometer can be envisaged, instead of the optical sensor  50 . 
     The calculation unit  40  is connected to the screen  29  by a wired data link  42  over which the output signal S 40  of the calculation unit  40  circulates. This output signal comprises information for the user to view on the screen  29  while sitting on the saddle  26 . 
     The signal S 40  also includes information, which may be the same or different from that displayed on the screen  29 , for the person assisting the user. In this regard, the signal S 40  may be sent via a wireless data link, such as a radio link, including by means of a wireless network  100 , such as a Wi-Fi network or a Bluetooth network, to a cell phone  200  or a laptop  300 . The cell phone  200  or the computer  300  can be those of the person assisting the user, or even those of the user. These two items can be used to display and store the data received from the calculation unit  40 , for analysis after an exercise session on the apparatus  2 . This data can also be stored in the memory  44 . 
     To the extent that they are used with the apparatus  2 , the cell phone  200  and the computer  300  are considered to be display screens for the apparatus  2 , although this is not their sole function, unlike the screen  29 . 
     In the example, the calculation unit consists of an electronic card. In a variant, the calculation unit  40  consists of several physical units distributed throughout the apparatus  2 . In practice, the unit  40  may be located under the cover  25  or on the back of the screen  29   
     The distance between the unit  40  and the sensors should be as short as possible. Rather than a unit  40  located far from the saddle  26  and the sensors  30  and  50 , a unit  40  located close by is preferred. The position under the cover  25  is therefore only an example. 
     During an exercise session of an user on the apparatus  2 , the various electronic components mentioned above are started in a first step  100 , then the user starts pedaling and keeps pedaling for the duration of the exercise, in a subsequent step  102 . 
     In a step  104  subsequent to the start of step  102 , each inertial cell  30  is used to detect the pitch T and roll R movements of the saddle  264  or  266  under which it is installed, about the axes A 26  and B 26 , respectively, and to send the signal S 30  that comprises the components Ax, Ay, Az, Gx, Gy, and Gz to the calculation unit  40 . 
     In parallel to step  104 , a step  106  is implemented by means of the optical sensor  50 , to detect the yaw movement L and to send the signal S 50  that comprises the yaw angle detected by the optical sensor  50  to the calculation unit  40 . 
     Still in parallel to step  104 , another step  108  is implemented to detect the parameters V, D and P by means of the sensor assembly  60 , which then outputs the signal S 60 . 
     The calculation unit  40  is configured to receive the signals S 30 , S 50  and S 60  and implement several calculation steps by means of the microprocessor  41 . 
     In a first calculation step  110 , a Madgwick algorithm is implemented to determine quaternions representing approximate values of the angular amplitudes of the pitch T and roll R movements. 
     The angular amplitude of the pitch movement T is denoted α and the angular amplitude of the roll movement R is denoted β. The approximate values of the angular amplitudes of pitch and roll determined in step  110  are denoted α′ and β′, respectively. 
     The Madgwick algorithm used in this step is described in Sebastian Madgwick&#39;s paper “ An efficient orientation filter for inertial and inertial/magnetic sensor arrays ” dated Apr. 30, 2010 and in the paper by Sebastian Madgwick et al. entitled “ Estimation of IMU and MARG orientation using a gradient descent algorithm ” (2011 IEEE International Conference on Rehabilitation Robotics—Rehab Week Zurich, June 29-Jul. 1, 2011). 
     In this case, the Madgwick algorithm is used with six input parameters. 
     After step  110 , a step  112  is implemented in which the value of the angle detected by the optical sensor  50  is converted into three components Mx, My and Mz, equivalent to the output signals of a magnetometer. The conversion step  112  is performed using the approximate values α′ and β′ of the pitch and roll angles as correction variables for the yaw angle detected by the optical sensor  50  and which is incorporated into the signal S 50 . In this step  112 , the microprocessor  41  uses a rotation matrix to convert the data from the optical sensor  50  into data of the Mx, My, and Mz type. 
     The conversion algorithm used in step  112  comprises the implementation of a rotation matrix of the type: 
     
       
         
           
             
               
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     http://doucets.free.fr/Matrice_de_Rotation/rotations_intro_doc.html 
     This matrix has been simplified and adapted to the problem of the 3D articulated saddle. It is then expressed in the following form: 
     
       
         
           
               
             
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     After step  112 , a step  114  is implemented during which a Madgwick-type algorithm is again used, this time with nine input parameters, namely the quantities Ax, Ay, Az, Gx, Gy and Gz, Mx, My and Mz. This version of the Madgwick algorithm is thus more elaborate than the one used in step  110  where only six input parameters are used. In this step, the algorithm makes it possible to determine quaternions and, on this basis, to calculate the Euler angles of the movements of the saddle parts. 
     At the end of step  114 , the angular amplitudes α, β and γ of the pitch movements. 
     The computational frequency of step  110  may be equal to the frequency of step  104 , or 100 Hz. The frequency of steps  112  and  114  is to equal 100 Hz. In a variant, it may be equal to the frequency of step  106 , or  50 , roll and yaw are calculated. Hz. 
     Steps  110 ,  112  and  114  are performed in duplicate to recover quantities representing the three movements, pitch R, roll R and yaw L of each saddle part  264  or  266 . Six angle values representing the angular amplitudes of these movements are thus obtained, namely
         the angle α G  of pitch of the left saddle part  264 ;   the angle α D  of pitch of the right saddle part  266 ;   the angle β G  of roll of the left saddle part  264 ;   the angle β D  of roll of the right saddle part  266 ;   the yaw angle γ G  of the left saddle part  264  and   the yaw angle γ D  of the right saddle part  266         

     In this regard, it may be noted that steps  104  and  110  are implemented with a first inertial cell  30  for the left saddle part  264  and with a second inertial cell  30  for the right saddle part  266 . 
     After step  114 , a selection step  116  is implemented by the computational unit  40 , at a frequency equal to that of step  114 , to select four representative angles from the aforementioned six angles. Since the pitch movements T of the saddle parts  264  and  266  are independent, angles α G  and α D  are each selected. Since the roll movements R of the saddle parts are linked, the angles β G  and β D  can as identical or nearly identical and only one of them and only one of them is selected, which is referred to as β in the following. Similarly, as the yaw movements L of the saddle parts are linked, the angles γ G  and γ D  can be considered as identical or nearly identical and only one of them is selected, which is referred to as γ in the following. 
     After step  116 , a step  118  is implemented, in which the signal S 40  is sent from the calculation unit  40  to the screen  29 . This signal S 40  comprises the selected angles α G , α D , β, and γ, as well as the speed V, the duration D, the pedaling power P, and the heart rate F that have been provided by the sensor assembly  60 . 
     The screen  29  receives the signal S 40  in a step  120  and displays, in a step  122 , certain data from this signal S 40  using a human/machine interface visible in  FIG. 4 . 
     On this human/machine interface, two icons  564  and  566  represent the saddle parts  264  and  266 , respectively. In this, the icons  564  and  566  form saddle part symbols for the saddle parts  264  and  266  respectively. A text box  580  is used to display a user identifier, such as a first and last name. Buttons  590 ,  592 , and  594  are provided for respectively starting, pausing, or completely stopping the operation of the exercise apparatus  2 . The step  100  mentioned above is initiated by pressing the start button  590   
     A horizontal bar  582  is positioned at the bottom of the screen  29  and is used to display the pedaling time and/or power, in particular by means of a color code. In the example, this pedaling time is represented by a rectangle  584  whose horizontal width increases depending on the time pedaling. Within the bar  582 , several areas  582   a ,  582   b ,  582   c  and  582   d  can be displayed during which different pedaling powers are to be implemented by the user, four pedaling powers P 1 , P 2 , P 3  and P 4  in the example, marked by different colors or in some other way. 
     A graphic area  586  is used to display a sign  588  whose geometry varies depending on the angles of the pitch T, roll R, and yaw L movements. The sign  588  forms an angular amplitude symbol for angles α G , α D , β and γ, that is, the angles α G , α D , β G , β D  γ G  and γ D , since angles β G  and β D  are the same, as are angles γ G  and γ D . 
     The result of the selection step  116  is displayed on the screen  29  in the form of a point P G  of support of the user&#39;s left ischium on the saddle  264 , as well as a point P D  of support of the of the user&#39;s right ischium on the saddle  566 . 
     Specifically, the graphical interface of the screen  29  is designed such that the x-axis, which is coincident with the axis A 26  in the embodiment of  FIG. 4 , represents the value of the roll angle β, while the y-axis, which is coincident with the axis B 26  in the embodiment of  FIG. 4 , represents the value of the left and right pitch angles α G  and α D . 
     Thus, it is possible to display the point P G  depending on the values of the angles α G  and β in the A 26  and B 26  axis frame and the P D  point depending on the values of the angles α D  and β in the same frame. 
     In practice, the support of a user&#39;s ischia on the saddle parts  264  and  266  is not ad hoc, but is distributed over a relatively small area, less than a few cm 2 . The bearing point of an ischium is defined as the center of such an area. 
     Ideally, the bearing point P G  is inscribed inside a curve C G  that delimits an area corresponding to a correct positioning of the left part of the user&#39;s pelvis on the saddle part  264 . This curve C G  is materialized on the screen  29  by a dashed line within the icon  564 . Similarly, a curve C D  defines an area within the icon  566 , in which the point P D  should normally be located. The areas S G  and S D  enclosed by the curves C G  and C D  on the screen  29  define the locations of acceptable reference positions for the points P G  and P D . The definitions of the curves C G  and C G  and the surfaces S G  and S D  can be stored in the memory  44 , allowing the unit  40  to determine possible deviation between the position of each bearing point, P G  or P D , and a corresponding reference position, that is, a point on the surface S G  or S D . The screen  29  is configured to show this deviation by displaying the relative position of the points P G  and P D  and the surfaces S G  and S G . 
     In  FIG. 4 , the point P G1 , located outside the surface S G , corresponds to the case where the user is too far forward on the saddle  26 , which results in the pitch amplitude being too large. This leads to a risk of sliding forward, which calls for adjustment of the saddle&#39;s backward movement. 
     The point P G2 , also located outside the surface S G , represents the case where the user is too far back, which results in the pitch being too little. This leads to insufficient movement, or not optimal for good physiological movement, and calls for adjustment of the position of the person on the bike with the backward or height of the saddle. 
     It is also possible to consider the case where the support points P G  and P D  are not arranged symmetrically in relation to the space defined between the saddle parts  264  and  266 , which can be seen on icons  564  and  566  due to a lack of symmetry in the positioning of these points P G  and P D  on the screen  29 . This lack of symmetry in the positioning must be corrected because it induces leads to insufficient movement, or not optimal for good physiological movement, and calls for the person to center him/herself correctly on the seat. 
     Thus, assuming that the curves C G  and C D  are permanently displayed on the screen  29 , in particular as part of the icons  564  and  566 , it is possible for the user looking at the screen  29  located in front of him/her to identify whether his/her support points P G  and P D  are correctly located and, if necessary, to correct his/her posture, in an intuitive way, by moving on the saddle part, possibly being guided by the person assisting him/her 
     The position of the points P G  and P D  in a horizontal direction in  FIG. 4 , that is, parallel to the axis A 26 , has an influence on the angular amplitude β of the roll movement R. The closer the points P G  and P D  are to the space between the saddle parts, that is, to the axis B 26 , the greater the roll movement R. Note that the spacing between the points P G  and P D  is a result of the user&#39;s anatomy and cannot be modified. 
     The human/machine interface also comprises a representation of the yaw movement L, in the form of an arrow F L  that oscillates around the axis B 26 , with an angular amplitude that is a function of the value of this angle. To facilitate visualization of the arrow F L , the point of articulation P L  of this arrow on the screen  29  is offset, along the axis B 26 , from the axis C 26 . This allows the arrow F L  to be not located in the same part of the icons  564  and  566  as the curves C G  and C D . 
     In contrast, the sign  588  is developed based on the parameters calculated by the unit  40  in the step  116 . 
     As seen in  FIG. 5 , the sign  588  is two-dimensional and extends, in width, parallel to an axis L 588  and, in height, parallel to an axis H 588 . Conventionally, the width of the part of the sign  588  to the left of the axis H 588  can be taken to represent the quasi-instantaneous value of the roll angle βG observed for the left saddle part  264 . Similarly, the width of the part of the sign  588  to the right of the H 588  axis represents the quasi-instantaneous roll angle β D  of the right saddle part  266 . “Quasi-instantaneous” means that the roll angle values are averages of the last values taken, for example, the last 10 positions. 
     The median M 588  of the sign  588  is defined as a curve equidistant from its inner edge b 588  and its outer edge B 588 . 
     Conventionally, the height between the end points of the median M 588  in the left part of the sign  588  can be taken to represent the average value α G  of the pitch angle of the left saddle part  264 , while the same distance in the right part of the sign  588  represents the average value α D  of the pitch angle of the right saddle part  266 . L 588 . The averages used for the pitch angle values are calculated over the last 10 values, over values since the beginning of the session, or according to any other suitable calculation rule. 
     Conventionally, the distance between the median M 588  and the inner edge b 588  may also be considered to represent the average value γ G  of the yaw angle of the left saddle  264 , while the distance between the median M 288  and the outer edge B 588  represents the average value γ D  of the yaw angle of the right saddle part  266 . The average used for the yaw angles is done in the same way as for the pitch angles, or in another suitable way. 
     The person skilled in the art will then understand that the particular way of displaying the angular amplitude(s) α, β, γ is a second aspect of the invention which is distinct from a first aspect of the invention corresponding to the detection of the movement(s) among the pitch T, roll R and yaw L movements, and the associated determination of the angular amplitude(s) α, β, γ. 
     In particular, this second aspect of the invention comprises determining a single symbol  588  representing a plurality of angular amplitudes α, β, γ, with each angular amplitude α, β, γ corresponding to a respective dimension of said symbol. 
     As an optional addition, the single symbol  588  determined represents a plurality of angular amplitudes α, β, γ of each of the two saddle parts  264 ,  266 , with the single symbol broken down into separate first and second parts, with the first part corresponding to the left saddle part  264  and the second part corresponding to the right saddle part  266 . To facilitate user interpretation of the displayed quantities, the first and second parts are preferably arranged on opposite sides of a reference axis, such as the H 588  axis, with the first part to the left of the reference axis, for example, and the second part to the right of said reference axis. 
     As a further optional addition, at least two angular amplitudes α, β each correspond to a dimension of said symbol along a respective direction, distinct from one angular amplitude α, β to the other. In the example of  FIG. 5 , the representation of the angular amplitude β G , β D  of the roll movement R of each saddle part  264 ,  266  corresponds to a dimension of the symbol  588  along a horizontal direction, that is, parallel to the L 588  axis, and the representation of the angular amplitude α G , α D  of the pitch movement T of each saddle part  264 ,  266  corresponds to a dimension of the symbol  588  along a direction perpendicular to the direction associated with the roll movement R, such as a vertical direction, that is, parallel to the H 588  axis. 
     In the example described above, a single sensor  50  is used to measure the yaw angle γ, considering that the saddle parts  264  and  266  are integral in rotation about the C 26  axis, and the values of the angles γ G  and γ D  are then identical, which corresponds to the fact that the curve M 588  is the median of the sign  588 . However, it could be otherwise, with an optical sensor under each saddle part  264 ,  266  in particular, according to the following variant. 
     In order to easily identify the position of the median M 588 , the parts of the sign  588  positioned on either side of this median may be colored differently. 
     The display of the sign  588  on the screen  29  allows the user to verify that the movements of each saddle part  264  and  266  are regular and harmonious, that is, noticeably smooth. The symmetry of the sign  588  with respect to the axes L 588  and H 588  also allows the user to ensure that the saddle movements are balanced. In practice, the geometry of the  588  sign is comparable to that of the “infinity” sign. An indication of the smoothness and compliance of the pedaling movement, with respect to a preset exercise program, may be that the shape of the sign  588  is close to that of the “infinity” sign. 
     According to an embodiment of the invention not shown, an optical sensor may be positioned under each saddle part  264  and  266 , which then allows the respective yaw movements of the two saddle part to be determined independently of each other. The calculation steps  110  to  118  and display step  122  are then adapted. 
     In the aforementioned case where the inertial cells have an active magnetometer, instead of the optical sensor, the calculations performed in cell  40  are adapted. The steps  110  and  112  are omitted and the step  114  is performed directly from the output signals of the inertial cells  30 . 
     The values of the amplitudes α, β and γ of the pitch, roll and yaw angles, calculated in step  114 , can be stored in the memory  44  as well as in the memories of the devices  200  and  300 , if necessary. It is thus possible to observe the variations of these values during a physical exercise session on the apparatus  2  and to compare these values during successive physical exercise sessions on this apparatus, or even during the same session. The invention thus makes it possible to monitor the user&#39;s performance. 
     It is also possible to store the values V, P, F and D for an exercise session or, more precisely, a table giving the values of the speed V, the power P and the heart rate F depending on the time D elapsed since the start of the session, which makes it possible to evaluate changes in a user&#39;s pace and effort during a session. Again, this allows for tracking of a user&#39;s progress. 
     Preferably, the sign  588  is obtained by incorporating the amplitudes of the pitch T, roll R, and yaw L movements over a period of use of the device, such as during an exercise session. 
     Instead of the Madgwick algorithm mentioned above, it is possible to use other algorithms of comparable types for steps  110  and  114 , including a Mahony algorithm. Likewise for the algorithms for the steps of inversion  112 , or another type of rotation matrix can be used, and of selection  116 , or another selection can be made, for example based on an average of the values of the angles β G  and β D , on the one hand, γ G  and γ D , on the other hand. 
     The data links  32 ,  42 ,  52  and  62  are wired links, for example, or, in a variant, wireless links, such as radio links. 
     According to an embodiment of the invention not shown, the screen  29  may be omitted and the human/machine interface for displaying the support points P G , P D  takes place only on a screen of an ancillary hardware, such as the screen of a telephone  200  or of a computer  300 , or any other screen of a user terminal which is then considered to be part of the physical exercise apparatus  2 . 
     The embodiment and variants contemplated above may be combined to generate new embodiments of the invention.