Patent Publication Number: US-7901326-B2

Title: User-specific performance monitor, method, and computer software product

Description:
CROSS-REFERENCE-TO RELATED APPLICATION 
     This application claims priority to Finnish Patent Application Serial No. 20065290, filed on May 4, 2006, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for determining an exertion parameter of a physical exercise, a user-specific performance monitor, and a computer software product. 
     2. Description of the Related Art 
     Physical exercises, such as walking and running, involve physical exertion, which may be determined by measuring a motion variable associated with the physical exercise with a user-portable device. 
     In prior art solutions, measurement of physical exertion is insensitive to the effect of elevation differences of the terrain on the physical exertion. 
     Thus, it is useful to examine techniques for determining the user&#39;s exertion during a physical exercise. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method, a user-specific performance monitor and a computer software program in such a manner that when the user&#39;s exertion level is determined, the effect of elevation differences in the terrain is taken into account. A first aspect of the invention provides a method for determining an exertion parameter of a physical exercise, the method comprising determining, in a user-specific performance monitor, a propagation variable characterizing the user&#39;s propagation; determining, in the user-specific performance monitor, a gravitational motion variable characterizing the user&#39;s motion in the direction of the gravitational field; and calculating the user&#39;s exertion parameter by means of the propagation variable and the gravitational motion variable. 
     A second aspect of the invention provides a user-specific performance monitor comprising: means for determining a propagation variable characterizing the user&#39;s propagation, means for determining a gravitational motion variable characterizing the user&#39;s propagation in the direction of the gravitational field; and means for calculating the user&#39;s exertion parameter by means of the propagation variable and the gravitational motion variable. 
     Another aspect of the invention provides a computer software product comprising coded instructions for executing a computer process in a digital processor, the computer process being suitable for determining a user exertion parameter of a physical exercise and comprising the steps of: determining, in a user-specific performance monitor, a propagation variable characterizing the user&#39;s propagation; determining, in the user-specific performance monitor, a gravitational motion variable characterizing the user&#39;s motion in the direction of the gravitational field; and calculating the user&#39;s exertion parameter by means of the propagation variable and the gravitational motion variable. 
     Preferred embodiments of the invention are disclosed in the dependent claims. 
     The invention is based on the idea that when the user&#39;s exertion level is calculated during a physical exercise, a propagation variable and a gravitational motion variable are used, which take the effect of the earth&#39;s gravitational field on the physical exertion into account. 
     The method, user-specific performance monitor and computer software product of the invention provide a plurality of advantages. One advantage is a reliable estimate of the user&#39;s exertion during a physical exercise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in greater detail in connection with preferred embodiments and with reference to the attached drawings, in which 
         FIG. 1  shows a first example of the structure of a user-specific performance monitor; 
         FIG. 2  shows a second example of the structure of a user-specific performance monitor; 
         FIG. 3  shows an example of the user&#39;s propagation route; 
         FIG. 4  shows a third example of the structure of a user-specific performance monitor; 
         FIG. 5  shows a first example of a method according to an embodiment of the invention; 
         FIG. 6  shows a second example of a method according to an embodiment of the invention, and 
         FIG. 7  shows a third example of a method according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the example of  FIG. 1 , a user-specific performance monitor  100  comprises a central processing unit (CPU)  106  and a memory unit (MEM)  108 . The central processing unit  106  comprises a digital processor and executes a computer process for determining an exertion parameter of the user of the user-specific performance monitor  100  according to coded instructions stored in the memory unit  108 . 
     The user-specific performance monitor  100  is a user-portable and user-operated electronic device, which measures and registers parameters associated with the user&#39;s exercise. In this context, the user-specific performance monitor  100  is called performance monitor  100 . Performance may refer to, for instance, walking, running or skiing without, however, restricting to these. 
     The user-specific performance monitor  100  may also comprise a motion measurement unit (MMU)  102 , which measures variables characterizing the user&#39;s motion. 
     According to an embodiment, the motion measurement unit  102  comprises a satellite positioning unit, which receives radio signals from satellites of the satellite positioning system and determines the location and/or time of the performance monitor. The satellite positioning system may be, for instance, a GPS system (Global Positioning System), the Russian GLONASS system (Global Navigation Satellite System) or the European Galileo system. In this case, the motion measurement unit  102  may supply the location information and possibly the time information associated with the user&#39;s propagation to the central processing unit  106  or the memory unit  108 . According to an embodiment, the motion measurement unit  102  determines the user&#39;s propagation velocity and the velocity component in the direction of the gravitational field and supplies the propagation velocity and the velocity component in the direction of the gravitational field to the central processing unit  106 . 
     According to an embodiment, the motion measurement unit  102  comprises a motion-sensitive sensor, such as an acceleration sensor, registering motion of the user. The acceleration sensor transforms the acceleration caused by motion or gravity into an electric signal. A variety of technologies may be used for measuring the motion. Piezoresistor technology employs material, resistance of which changes when it is compressed together. Mass acceleration produces a force which is directed at the piezoresistor. As constant current is led through the piezoresistor, voltage that acts over the piezoresistor changes according to the compression caused by the acceleration. In piezoelectric technology, a piezoelectric sensor generates a charge when the acceleration sensor is accelerated. In silicon bridge technology, a silicon chip is etched in such a manner that silicon mass remains at the end of a silicon bar for the silicon chip. When the silicon chip is subjected to acceleration, the silicon mass directs a force at the silicon bar and the resistance of the silicon bar changes. Micro-machined silicon technology is based on the use of a differential capacitor. Voice coil technology is based on the same principle as a microphone. Examples of suitable motion sensors include Analog Devices ADXL105, Pewatron HW and VTI Technologies SCA-serie. 
     Acceleration information generated by the acceleration sensor may be supplied to the central processing unit  106  or the memory unit  108 . 
     The motion measurement unit  102  may also be based on other suitable technologies, such as a gyroscope integrated onto a silicon chip, a micro vibration switch in a surface mounting component, a mechanical pendulum or a sensor sensitive to the magnetic field. 
     According to an embodiment, the motion measurement unit  102  comprises a pressure sensor for measuring the pressure of the environment. The pressure sensor may measure absolute pressure, and it may be based on a comparison between the prevailing pressure and the vacuum. The pressure sensor may comprise a silicon film, which includes piezoresistive resistors, for instance. 
     Pressure information may be converted into elevation information by means of a table or a mathematical function, for example. The presented solution pays attention to pressure changes in connection with elevation differences, and thus a pressure value may be allowed to have an error. 
     Pressure differences correspond to slightly different elevation differences at different heights. For instance, a pressure difference of 1 hPa at sea level corresponds to an elevation difference of about 8 meters, at 3000 m to an elevation difference of about 11 meters, and at 6000 m to an elevation difference of about 15 meters. According to an embodiment, the pressure gauge is thus a calibrated pressure gauge. The motion measurement unit  102  may also perform an automatic temperature compensation, which is specified by calibrating, if necessary. The temperature compensation may be based on temperature dependence of the weight of an air column, when the temperature profile of the atmosphere is known as a function of elevation. 
     The motion measurement unit  102  may comprise a preprocessing unit for processing primary motion information, such as location information, acceleration information and/or vibration information. The processing may comprise conversion of primary motion information into secondary motion information, such as conversion of location information into velocity information, conversion of pressure information into location and/or velocity information in the direction of the gravitational field, and/or conversion of acceleration information into information on the quantity or pulses of motions. The processing may further comprise filtering of primary and/or secondary motion information. 
     The user-specific performance monitor  100  may also comprise a user interface (UI)  104 , which typically includes a display unit (DISP)  110  and a display controller. The display unit  110  may include LCD (Liquid Crystal Display) components, for instance. The display unit  110  may display, for instance, an exertion parameter, location altitude, inclination of propagation base, number of steps taken and/or the covered distance graphically and/or numerically to the user. 
     The user interface  102  may also comprise a keypad (KP)  112 , by which the user may enter commands in the performance monitor  100 . 
     With reference to  FIG. 2 , the performance monitor may comprise a central processing unit  202  to be attached to the user&#39;s  200  upper limb and one or more peripheral devices  204 ,  206 . 
     The central processing unit  202  typically comprises the user interface  112 , the memory unit  108  and the central processing unit  106  of  FIG. 1 . According to an embodiment, the central processing unit  202  comprises the motion measurement unit  102 . 
     According to an embodiment, the peripheral device  204  is a heart rate transmitter, which measures electromagnetic pulses induced from the user&#39;s heart and signals the pulse information to the central processing unit  202 . In this case the performance monitor  100  is generally known as a heart rate monitor. 
     According to an embodiment, the peripheral device  206  is a motion sensor to be attached to the user&#39;s inferior limb and measuring motion information on the inferior limb, such as its acceleration, and signaling primary or secondary motion information on the acceleration to the central processing unit  202 . 
     With reference to  FIG. 3 , let us examine an example of a propagation route  300  of the user  200 . A horizontal axis  302  illustrates horizontal location coordinates, and a vertical axis  304  illustrates vertical location coordinates. In this example the vertical axis  304  is parallel to the earth&#39;s gravitational field. 
     The propagation route  300  may be divided into propagation points  1 A to  1 J, at each of which a propagation variable characterizing the user&#39;s propagation and a gravitational motion variable characterizing motion in the direction of the gravitational field may be determined. 
     Propagation motion is typically motion in the direction of the propagation route  300 , which may include components parallel to the horizontal axis  302  and to the vertical axis  304 . The propagation variable may be propagation velocity, location and/or pulse frequency of propagation, number of pulses, pulse width, step contact time or some other motion variable to be associated with the propagation variable. 
     Motion in the direction of the gravitational field is motion in the direction of the vertical axis  304  or motion in the direction opposite to the vertical axis  304 . 
     The propagation points  1 A to  1 J may represent measurement points, at which the propagation variable and the gravitational motion variable are determined. The propagation variable and the gravitational motion variable may be determined at predefined time intervals, in which case the location of the propagation points on the propagation route typically depends on the propagation velocity of the user. The predefined time interval may depend on the resolution of the determination of the propagation variable and/or the gravitational motion variable. The predefined time interval may be few dozens of seconds or a few minutes. In an embodiment, the predefined time interval is one minute. 
     The propagation point  1 A to  1 J may be associated with an elementary propagation variable and an elementary gravitational motion variable. 
     According to an embodiment, the elementary propagation variable is an elementary distance  3 A to  3 I measured in a predefined time interval, which may be the distance between the successive propagation points  1 A to  1 J. The elementary distance  3 A to  3 I may be processed, for instance, as a unit of distance, such as meters, or a unit proportional to distance, such as a number of pulses in connection with the user&#39;s propagation. 
     According to an embodiment, the elementary gravitational motion variable is an elementary elevation difference  2 A to  2 H between the successive propagation points  1 A to  1 J. The elementary elevation difference  2 A to  2 H may be processed as a unit of elevation difference, such as meters, or a unit proportional to elevation difference, such as pressure. 
     With reference to  FIG. 4 , the performance monitor  400  comprises a propagation determination unit (PDU)  402 , an elevation determination unit (EDU)  404  and an exertion counter (EC)  406  functionally connected to the propagation determination unit  402  and the elevation determination unit  404 . 
     The propagation determination unit  402  determines a propagation variable  434  characterizing the user&#39;s propagation and supplies the propagation variable  434  to the exertion parameter counter  406 . 
     The elevation determination unit  404  determines a gravitational motion variable  426  characterizing the user&#39;s motion in the direction of the gravitational field and supplies the gravitational motion variable  426  to the exertion counter  406 . 
     The exertion counter  406  calculates the user&#39;s exertion parameter on the basis of the propagation variable  434  and the gravitational motion variable  426 . 
     The exertion parameter characterizes, for example, the user&#39;s energy consumption on the propagation route  300  or the instantaneous energy consumption in a time unit at a point of the propagation route  300 . 
     The propagation variable  434  may be, for example, the elementary distance  3 A to  3 I, motion pulses formed during the covered elementary distance  3 A to  3 I, propagation velocity determined at a propagation point  1 A to  1 J or average velocity in the covered elementary distance  3 A to  3 I. 
     The gravitational motion variable  426  may be, for instance, the elementary elevation difference  2 A to  2 H between the successive propagation points  1 A to  1 J, velocity of ascent or descent, pressure measured at the propagation points  1 A to  1 J, or pressure difference between the successive propagation points  1 A to  1 J. 
     According to an embodiment, the performance monitor  400  comprises a pulse measuring device (PMD)  410  for measuring motion pulses generated by the user&#39;s limb. The pulse measuring device  410  generates motion pulse information  422  from the user&#39;s limb movement and supplies the motion pulse information  422  to a pulse filter  412 . The motion pulse information  422  may comprise electric signals, each of which represents a motion pulse, such as a limb swing. 
     According to an embodiment, the pulse filter  412  filters the motion pulse information  422  on the basis of predefined time properties and supplies the accepted motion pulses  420  to the propagation determination unit  402 . 
     The pulse filter  412  accepts the motion pulses that fulfill the predefined criteria. According to an embodiment, the pulse filter  412  accepts the successive motion pulses, the time interval of which is within predefined limits. For example, a step frequency, a step pair frequency or a frequency of an arm swing are typically 1 to 2 pulses per second. The filtering may be implemented by rejecting the successive motion pulses, the time interval of which is below the predefined lower limit or the time interval of which is above the predefined upper limit. 
     The predefined upper limit and lower limit may depend on the location of the pulse measuring device  410  on the user&#39;s body. If the pulse measuring device  410  is attached to an upper limb, the predefined lower limit may be, for instance, 0.4 seconds. The predefined upper limit may be, for instance, 2.0 seconds, which corresponds to 30 pairs of steps in a minute. 
     Determining the user&#39;s exertion parameter is typically connected to determination of the user&#39;s energy consumption at the points of the propagation route. 
     The energy consumption E TOT  of the user during the propagation route  300  may be presented as a sum of elementary energy consumptions E i : 
                       E   TOT     =         ∑   i     ⁢           ⁢     E   i       +     E   0         ,           (   1   )               
where the elementary energy consumption E i  is the energy consumption during the covered elementary distance  3 A- 3 I. The term E 0  represents energy consumption, which includes the energy that is consumed at rest and possibly during easy domestic chores.
 
     The elementary energy consumption E i  may be presented as a function of the elementary propagation variable Q Ti  and the elementary gravitational motion variable Q Gi  
 
 E   i   =E   i ( A   1   ,A   2   ,Q   Ti   ,Q   Gi )  (2)
 
where A 1  and A 2  are scaling factors that convert the motion parameters Q Ti  and Q Gi  into a desired unit, take into account characteristics of one or more users, which may include age, sex, height and weight, and which scale the motion parameters Q Ti  and Q Gi  with one another.
 
     According to an embodiment, energy consumption or an exertion parameter proportional to energy consumption is expressed with a value for the user&#39;s oxygen consumption, i.e. the VO2 value, the unit of which is milliliter, for instance. The oxygen consumption of one liter corresponds to about 5.0 kcal. 
     According to an embodiment, the elementary energy consumption may be presented in the form:
 
 E   i   =A   1   ×Q   Ti   +A   2   ×Q   Gi .  (3)
 
     The term A 1 ×Q n  characterizes the energy the user uses for propagating during the covered elementary distance  3 A to  3 I and consists of the energy consumption associated with the user&#39;s body and limb movements. 
     The term A 2 ×Q Gi  characterizes the effect of the earth&#39;s gravitation on the user&#39;s energy consumption. When the user moves in the gravitational field, his/her potential energy changes, and, for example, during an uphill ascent, in this case when the inclination of the propagation base is positive, energy consumed by the user is converted into potential energy absorbed in the mass of the user and his/her equipment, which is experienced by the user as increased energy consumption or intensity. Accordingly, during a downhill descent, in this case when the inclination of the propagation base is negative, the user experiences that it is easier for him/her to move, and thus the energy consumption per distance unit or time unit with a constant velocity is lower than during an uphill ascent. 
     When moving downhill, however, the user cannot convert his/her potential energy back into energy to be used in metabolism entirely, and thus alone the negative value of the gravitational motion variable present in downhill descents is not sufficient when the user&#39;s energy balance is considered. 
     According to an embodiment, the exertion counter  406  calculates the user&#39;s exertion parameter by using, in the case of a negative inclination factor, the first functional dependence of the exertion parameter on the propagation variable and the gravitational motion variable and, in the case of a positive inclination factor, the second functional dependence of the exertion parameter on the propagation variable and the gravitational motion variable. The second functional dependence differs from the first functional dependence in that with at least one value pair of the propagation variable and the gravitational motion variable, the second functional dependence produces an exertion parameter which is different from the exertion parameter produced by the first functional dependence with said value pair. Thus, the equation (2) may be divided into equations
 
 E   i   neg   =E   i   neg ( A   1   neg   ,a   2   neg   , . . . A   N   neg   ,Q   Ti   ,Q   Gi ),  (4)
 
 E   i   pos   =E   i   pos ( A   1   pos   ,A   2   pos   , . . . A   M   pos   ,Q   Ti   ,Q   Gi )  (5)
 
where the equation (4) illustrates the first functional dependence and the equation (5) illustrates the second functional dependence. A parameters of the equations (4) and (5) may be selected in such a manner that they form a continuous representation. The first functional dependence and the second functional dependence may be expressed by a common function of the propagation variable and the gravitational motion variable, such as a polynomial representation. In this case, however, when the inclination factor is negative, the function produces different values than when the inclination factor is positive.
 
     The first functional dependence and the second functional dependence may be determined by matching the A parameters characterizing functional dependencies with test results, for example. Another way of defining parameters is to use results obtained from literature. 
     If the equations (4) and (5) differ from one another, this may cause that, for instance, after the user has proceeded to a certain point on the propagation route  300  and returned back to the starting point, the energy consumption generated from the gravitational motion variable remains other than zero. 
     According to an embodiment, the first functional dependence and the second functional dependence are expressed as polynomial series
 
 E   i   neg   =A   i   neg   ×Q   Ti   +A   2   neg   ×Q   Gi   +A   3   neg   ×Q   Ti   2   +a   4   neg   ×Q   Gi   2   +A   5   neg   ×Q   Ti   ×Q   Gi   (6)
 
 E   i   pos   =A   i   pos   ×Q   Ti   +A   3   pos   ×Q   Ti   2   +A   4   pos   ×Q   Gi   2   +A   5   pos   ×Q   Ti   ×Q   Gi   (7)
 
     According to an embodiment, the performance monitor  400  comprises an inclination determination unit (IDU)  414  for calculating an inclination factor proportional to the inclination of the propagation base by means of the propagation variable  434  and the gravitational motion variable  426 . As an example, let us examine the propagation point  1 D, and the inclination factor α of the propagation base representing this propagation point may be determined by means of the elementary distance and the elementary elevation difference in the proximity of the propagation point  1 D by using the sine rule 
                       sin   ⁢           ⁢   α     =       C   ×   Δ   ⁢           ⁢     p   i         D   ×     K   i           ,           (   8   )               
where Δp i  is the pressure difference corresponding to the elementary elevation difference, K i  is the filtered number of pulses measured from the user&#39;s motion and corresponding to the elementary distance, and α is the angle between the propagation base and the earth&#39;s horizontal level  302 . The coefficient C converts the pressure difference into the elevation difference, and the coefficient D converts the number of pulses into the distance traveled. The inclination factor may also be determined by means of a plurality of elementary distances and elementary elevation differences.
 
     The inclination factor may also be determined, for instance, by means of location and elevation readings given by a satellite positioner. 
     The inclination determination unit  414  receives the propagation variable  434  and the gravitational motion variable  426  and determines the inclination factor by means of the equation (8) or the average of the equation (8), for example. The shown solution is not limited to the use of the equation (8), but the inclination factor may be calculated by means of any suitable relation. 
     The inclination factor may also act as a variable in the equations (6) and (7) describing the elementary energy consumption, whereby the equations (6) and (7) may be presented in the form of
 
 E   i   neg   =B   1   neg   ×K   i   +B   2   neg   ×K   i ×α i   (9)
 
 E   i   pos   =B   1   pos   ×K   i   +B   2   pos   ×K   i ×α i .  (10)
 
     According to an embodiment, the performance monitor comprises a propagation efficiency estimator (PEE)  416 , which receives inclination information  428  from the inclination determination unit  414  and determines the propagation factor proportional to the user&#39;s propagation efficiency as a function of the inclination factor. 
     Propagation efficiency characterizes the user&#39;s ability to move on an inclined propagation base. For example, a steep but descending propagation base requires accurate, well-coordinated movements, which are achieved by shortening the steps. Thus, the propagation efficiency on a steeply descending propagation base may be poorer than on an even or gently descending propagation base. 
     The propagation efficiency estimator  416  supplies a propagation factor  430  to the exertion counter  406 , which calculates the user&#39;s exertion parameter by means of the propagation variable, the gravitational motion variable and the propagation factor  430 . 
     According to an embodiment, the negative inclination factor has a different propagation factor than the positive inclination factor. 
     According to an embodiment, the elementary energy measured at time intervals of one minute, for example, is obtained from the expressions 
                     E   i   neg     =       CK   i   2     +     H   ×       Δ   ⁢           ⁢     h   i         K   i   2         +     J   ×         (     Δ   ⁢           ⁢     h   i       )     2       K   i   2         +     E   0               (   11   )                 E   i   pos     =       CK   i   2     +     D   ×   Δ   ⁢           ⁢     h   i       +       E   0     .               (   12   )               
The first term CK i   2  of the expressions (10) and (11) takes into account the energy consumption associated with propagation and the term D×Δh takes into account the energy consumed by the growing potential energy. The term
 
             H   ×       Δ   ⁢           ⁢     h   i         K   i   2             
takes into account the propagation efficiency on a negative inclination. The term
 
             H   ×       Δ   ⁢           ⁢     h   i         K   i   2             
implicitly includes the inclination angle of the propagation base  300 . The term
 
             J   ×         (     Δ   ⁢           ⁢     h   i       )     2       K   i   2             
includes released potential energy and also implicitly includes the inclination angle of the propagation base. The coefficients C, D, H and J correspond to the A and B parameters described above.
 
     According to an embodiment, the performance monitor  400  may be programmed to take into account the additional exertion caused by the unevenness or softness of the propagation base. The effect of the propagation base on the energy consumption may be taken into account by means of a terrain factor T, the values of which for different terrain types may be as follows: asphalt 1.0, gravel road 1.1, terrain 1.2, brushwood 1.5, swamp 1.8 and loose sand 2.1. The terrain factor may be taken into account in the expressions (11) and (12) in the following way: 
     
       
         
           
             
               
                 
                   
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     According to an embodiment, the performance monitor  400  comprises an activity indicator (AI)  408  for determining the user&#39;s activity by means of the propagation variable  434 . The activity indicator  408  supplies activity information  418  to the exertion counter  406 , which calculates the user&#39;s exertion parameter, if the user&#39;s activity exceeds a predefined activity limit. This procedure may eliminate situations, in which the exertion parameter is determined erroneously due to the use of auxiliary means, such as a lift, a vehicle or skis. 
     According to an embodiment, the activity indicator  408  identifies the filtered limb movements as rhythmic motion, if the number of time intervals of the filtered, successive motion pulses according to a predefined quantity threshold is within a predefined range of thresholds. The identified rhythmic function may be used for determining the physical activity level. Thus, rhythmic functions are identified so that during them, the majority of motion intervals within a selected range have the same duration as the preceding motion interval. It is advantageous to test the rhythmicity only after very short motion intervals, such as motion pulses with the duration of below 0.6 seconds as described above, have been filtered away. The quantity threshold predefined in the activity indicator may be 65 to 95% of the total number of time interval periods, and the predefined range of thresholds may be ±10 to 30% of the average length of the time interval period. According to an embodiment, the predefined quantity threshold is 75% of the total number of time interval periods and the predefined range of thresholds is +25% of the length of the previous time interval period or the average of the time interval periods. 
     Further with reference to  FIG. 4 , the propagation determination unit  402  may be implemented by means of the motion measurement unit  102  shown in  FIG. 1  and a coded computer process stored in the memory unit  108  and to be performed in the central processing unit  106 . 
     The elevation determination unit  404  may be implemented by means of the motion measurement unit  102  shown in  FIG. 1  and a coded computer process stored in the memory unit  108  and to be performed in the central processing unit  106 . According to an embodiment, the elevation determination unit  404  comprises a pressure gauge for measuring the pressure of the environment. 
     The exertion counter  406  may be implemented by means of a coded computer process stored in the memory unit  108  and to be performed in the central processing unit  106 . 
     The inclination determination unit  414  may be implemented by means of a coded computer process stored in the memory unit  108  and to be performed in the central processing unit  106 . 
     The propagation efficiency estimator  416  may be implemented by means of a coded computer process stored in the memory unit  108  and to be performed in the central processing unit  106 . 
     The pulse measuring unit  410  may be implemented by means of the motion measurement unit  102  and a coded computer process stored in the memory unit  108  and to be performed in the central processing unit  106 . 
     The pulse filter  412  may be implemented by means of a coded computer process stored in the memory unit  108  and to be performed in the central processing unit  106 . 
     With reference to  FIGS. 5 ,  6  and  7 , methods according to embodiments of the invention are examined. 
     In  FIG. 5 , the method starts in  500 . 
     In  502 , a propagation variable  434  characterizing the user&#39;s propagation is determined in a user-specific performance monitor  100 ,  202 ,  204 ,  206 ,  400 . 
     In  504 , a gravitational motion variable  426  characterizing the user&#39;s motion in the direction of the gravitational field is determined in the user-specific performance monitor  100 ,  202 ,  204 ,  206 ,  400 . 
     In  506 , the user&#39;s activity is determined. 
     In  508  it is tested, whether the activity exceeds a predefined activity limit. 
     If the activity exceeds the predefined activity limit, the user&#39;s exertion parameter is calculated in  510  by means of the propagation variable  434  and the gravitational motion variable  426 . According to an embodiment, the user&#39;s exertion parameter is calculated by using, when the inclination of the propagation base is negative, the first functional dependence of the exertion parameter on the propagation variable and the gravitational motion variable and, when the inclination of the propagation base is positive, the second functional dependence of the exertion parameter on the propagation variable and the gravitational motion variable, the second functional dependence differing from the first functional dependence. 
     The method ends in  512 . 
     With reference to  FIG. 6 , the method starts in  600 . 
     In  602 , the inclination factor proportional to the inclination of the propagation base is estimated by means of the propagation variable  434  and the gravitational motion variable  426 . 
     In  604 , the propagation efficiency of the user is calculated as a function of the inclination of the propagation base. 
     In  606 , the user&#39;s exertion parameter is calculated by means of the propagation variable, the gravitational motion variable and the propagation efficiency. According to an embodiment, the user&#39;s exertion parameter is calculated by using, when the inclination of the propagation base is negative, the first functional dependence of the propagation efficiency on the propagation variable and the gravitational motion variable and, when the inclination of the propagation base is positive, the second functional dependence of the propagation efficiency on the propagation variable and the gravitational motion variable, the second functional dependence differing from the first functional dependence. 
     The method ends in  608 . 
     With reference to  FIG. 7 , the method starts in  700 . 
     In  702 , motion pulses generated by the user&#39;s limb are measured. 
     In  704 , the motion pulses that fulfill predefined criteria are filtered away. 
     In  706 , a propagation variable is determined by means of unfiltered motion pulses. 
     The method ends in  708 . 
     An aspect of the invention provides a computer software product, which comprises coded instructions for executing a computer process in a digital processor, the computer process being suitable for determining the user exertion parameter of a physical exercise. The computer process is illustrated in connection with  FIGS. 5 ,  6  and  7 . 
     The computer process may be included in coded instructions which are executed in the central processing unit  106  of the performance monitor  100 . Some process steps, such as calculating the exertion parameter, may be performed in an external calculation system, such as a PC or a mobile device, provided that the data of the propagation variable and that of the gravitational motion variable may be transferred between the performance monitor  100 ,  400  and the external calculation system. The coded instructions may be stored in the memory unit  108  of the performance monitor  100 . 
     The coded instructions may be included in the computer software product and they may be transferred by means of a distribution medium. The distribution medium is, for instance, an electric, magnetic or optical distribution medium. The distribution medium may be a physical distribution medium, such as a memory unit, an optical disk or a telecommunication signal. 
     Although the invention is described above with reference to the example according to the attached drawings, it is obvious that the invention is not restricted thereto but may be modified in a variety of ways within the scope of the appended claims.