WO2008023978A1

WO2008023978A1 - System for measuring weight loss, a force sensor pad, a shoe and a portable monitoring device

Info

Publication number: WO2008023978A1
Application number: PCT/NL2007/050408
Authority: WO
Inventors: Alberto Ruiz Luca De Tena
Original assignee: Sportmarketingconsultancy B.V.
Priority date: 2006-08-24
Filing date: 2007-08-20
Publication date: 2008-02-28
Also published as: NL2000197C2

Abstract

The invention relates to a system for measuring weight loss comprising at least one micro-chip (12, 21). The at least one micro-chip (12, 21) is arranged to receive a force signal (F) from a force sensor pad (11) and is arranged to receive an acceleration signal (A) from an accelerometer (13). The force signal (F) is an indication o f the force exerted by a user on the ground, and the acceleration signal (A) is an indication of acceleration of the user when touching the ground. The at least one micro-chip (12, 21) is arranged to compute an indication for the weight (M) of the user based on the received force signal (F) and the acceleration signal (A).

Description

System for measuring weight loss, a force sensor pad, a shoe and a portable monitoring device.

TECHNICAL FIELD

The present invention relates to a system for measuring weight loss comprising at least one micro-chip. The invention further relates to a force sensor pad, a shoe and a portable monitoring device.

STATE OF THE ART

Long-distance running is a very popular sport. Many runners, professionals and amateurs, regularly or occasionally run certain distances to exercise. Some runners also participate in long-distance running contests, like (half-) marathons. An important aspect for successful completion of a long-distance run is adequately drinking fluids during the run in order to prevent dehydration and hyponatremia, and attain adequate levels of hydration. The amount of fluid a runner needs to drink during a run can be predicted based on the duration of the run, the weather conditions etc. Based on such predictions, a marathon runner may plan when and how much he or she will drink during the run.

However, such predictions are not very accurate as the conditions during the run may change and the exact amount of fluid loss during a run may be different for different persons and may also be different for the same person from time to time. In fact, drinking adequately is important in many activities and (endurance) sports, such as walking, race walking, soccer, cricket etc.

Therefore, it is an object of the invention to provide a runner with more detailed information about how much fluid he or she needs to drink during an activity to compensate for a loss of fluids.

SHORT DESCRIPTION

According to an aspect there is provided a system for measuring weight loss, characterized in that the at least one micro-chip is arranged to receive a force signal from a force sensor pad and is arranged to receive an acceleration signal from an accelerometer, the force signal being an indication of the force exerted by a user on the ground, and the acceleration signal being an indication of acceleration of the user when touching the ground, the at least one micro-chip being arranged to compute an indication for the weight of the user based on the received force signal and the acceleration signal.

According to an aspect, there is provided a force sensor pad, formed as an insole and suitable to be positioned in a shoe, comprising at least one force sensor element, arranged to generate a force signal being an indication of the force exerted by a user on the force sensor pad. According to an aspect, there is provided a shoe, wherein the shoe further comprises such a force sensor pad.

According to an aspect, there is provided a portable monitor comprising a microchip, characterized in that the micro-chip is arranged to receive a force signal being an indication of a force exerted by a user on the ground and an acceleration signal being an indication of the acceleration of the force sensor pad, wherein the micro-chip is arranged to compute an indication for the weight of a user based on the received force signal and the acceleration signal.

SHORT DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: Figure 1 schematically depicts an embodiment.

Figure 2 schematically depicts a portable monitor according to an embodiment, - Figure 3 schematically depicts an innersole according to an embodiment,

Figure 4 - 6 schematically depict flow diagrams according to an embodiment, Figure 7 schematically depicts a monitoring device according to an embodiment.

DETAILED DESCRIPTION According to an embodiment of the invention, a system is provided which provides feedback to runners on their real fluid losses during a run. The system may further provide information about the necessary amount of fluid intake. This information may for instance be provided right before arrival at a drinking post. Fluid losses may be monitored by measuring changes in bodyweight of a runner while running.

Fig. 1 schematically depicts an embodiment of the invention. Fig. 1 shows a runner, wearing at least one shoe 10 comprising a first micro-chip 12 that is arranged to receive information from a force sensor pad 11 and an accelerometer 13. The first micro-chip 12 is further arranged to transmit information to a portable monitor 20 that may be worn by the user around its wrist. The portable monitor 20 is further shown in Fig. 2 and may comprise a second micro-chip 21 arranged to receive information from the first micro-chip 12. The second micro-chip 21 may further be arranged to output data via an output device, such as a display 22 or a speaker (not shown).

The portable monitor 20 may for instance be a embodied as a wrist-watch. Beside the functionality described here, the portable monitor 20 may be arranged to have further functionality. The portable monitor 20 may further be arranged to function as an ordinary watch or a heartbeat monitoring device etc.

At least one of the first and the second micro-chip 12, 21 may further be arranged to perform processing steps as will be explained in more detail below. The micro-chips 12, 21 may both perform part of the processing steps or one of the first and second micro-chip 12, 21 may perform all of the processing steps.

The micro-chips 12, 21 may be dedicated chips that are arranged to perform certain predetermined functionality. The micro-chips 12, 21 may also comprise a processor unit (not shown) that is arranged to read and execute programming instructions stored in a memory (not shown).

The force sensor pad 11 is arranged to measure a force that is exerted on the force sensor pad 11. The force sensor pad 11 may be a flat device that may be placed inside a shoe 10. The pad may be any kind of pad capable of measuring a force.

An example of a force sensor pad 11 is shown in top view in Fig. 3. The force sensor pad 11 may be formed like an insole (innersole) that is to be inserted in the shoe 10. The force sensor pad 11 may built in the shoe 10, or may be a separate pad that is to be positioned in the shoe 10 by a runner before starting the run. The force sensor pad 11 may be a piezo-electric pad comprising at least one force sensor element 14, such as a piezo-element 14. Such a piezo-element 14 is made of a piezoelectric material that produces a voltage when a mechanical force is applied to it, as will be understood by a skilled person. During running, this mechanical force is generated by a foot of the runner when he or she touches the ground and the foot of the runner exerts a force on the force sensor pad 11. The amount of force applied to the force sensor pad 11 will depend on the weight of the runner and the impact of the runner when he or she touches the ground. The force sensor pad 11 is arranged to transmit a force signal F to the first micro-chip 12, being an indication of the force exerted on the force sensor pad 11.

The accelerometer 13 is arranged to measure accelerations of the shoe 10 and transmit an acceleration signal A to the first micro-chip 12, being an indication of the acceleration experienced by the accelerometer 13. The accelerometer 13 measures the acceleration with which the shoe 10 strikes the ground. The accelerometer 13 may be positioned in the vicinity of the piezo-element 14.

Both the piezo-element 14 and the accelerometer 13 may be positioned near the heel part of the shoe 10, because this is the area in the shoe 10 which is likely to provide the most representative data of the body weight of the runner. The heel part is the part of the shoe a user normally first hits the ground with. During this first contact, a peak value is generated which may be used as a trigger to start computations. Also, during this peak value it may be assumed that the user leans on the heel part solely, providing measurements that provide a good estimation of the body weight of the user.

The piezo-element 14 may also be positioned at an other position, for instance at the front of the foot. However, at this position also impulse forces resulting from the push-off of the next step are relatively high.

Of course, the force sensor pad 11 may also comprise more than one piezo- element 14 that may be distributed over the surface of the force sensor pad 11.

In general, the force sensor pad 11 may be any kind of pad or flat shaped device that is capable of measuring a force or pressure. So, in general, any kind of force sensor pad may be used.

The force signal F and the accelerometer A are used to compute an indication for the mass of the runner. Therefore, force sensor pad 11 and accelerometer 13 both measure in a substantial similar direction. The force sensor pad 11 may be arranged to measure force F in a direction substantial perpendicular to the surface of the force sensor pad 11. The accelerometer 13 may be arranged to measure acceleration A in a direction substantial perpendicular to the surface of the force sensor pad 11. Forces and accelerations in the plane of the force sensor pad 11 are not to be measured or are not to be taken into account, as these mainly provide information about forces and accelerations exerted by the user on the ground to move forward, accelerate or to slow down.

The first micro-chip 12 is arranged to receive the force signal F and the acceleration signal A. The first micro-chip 12 may convert the analogue force signal F and acceleration signal A into digital signals and transmit these signals to the second micro-chip 21 at the portable monitor 20.

The first micro-chip 12 and the accelerometer 13 may also be integrated in the force sensor pad 11 to provide a compact solution, that may easily be used in combination with any shoe 10.

The transfer of data from the first micro-chip 12 to the second micro-chip 21 may be established by any suitable communication link, such as a wireless communication link or a wired communication link. A wireless communication link may be a Bluetooth communication link as will be known to a skilled person. Of course, also other types of wireless communication links may be used, for instance using radio frequent signals, infrared signals and the like

The signals transmitted from the first micro-chip 12 to the second micro-chip 21 may comprise an identification code. This identification code may be read and recognized by the receiving second micro-chip 21 to verify that the received signals indeed originate from the shoe 10 associated with the portable monitor 20, and not from an other shoe, for instance from a shoe of an other runner who happens to pass by.

The second micro-chip 21 is arranged to compute an indication of the mass (body weight) of the runner, based on the received force signal F and acceleration signal A.

The accelerometer 13 measures the acceleration of the shoe 10 when the shoe 10 touches the ground. The force sensor pad 11 collects values of the force (pressure) exerted by the body on the ground, resulting in force signal F. It will be understood that force signal F is not a direct indication of the mass of the runner, as the force exerted by the runner on the force sensor pad 11 is also influenced by the impact of the shoe 10 on the ground. The acceleration signal A may however be used to compensate for this impact, as the acceleration signal A is an indication for this impact. By using a well-known formula describing the relation between force and acceleration (F = M-(A + g)), where F represent the force, A the acceleration measured by the accelerometer 13, g represent the gravity coefficient (g ~ 10m/s²) and M the mass, the second micro-chip 21 may compute an indication of the mass M of the runner. The force F and the acceleration A may be assumed to act in a substantial similar direction, i.e. the direction of the gravitational coefficient g.

It will be understood that the force sensor pad 11 may not detect the total force exerted by the runner on the ground. This may be because the piezo-element 14 does not cover the total area of the foot.

Also, the human body is a non-rigid object, and therefore its centre of mass varies with body movement. When running, the centre of mass may not be in line with the force sensor of the force sensor pad 11, for instance in the heel of the shoe. Therefore the data collected by the force sensor pad 11 is part of a resultant force. In order to compensate for this, the coordinates of the centre of mass and the direction associated with the centre of mass towards the heel where the force is being exerted, are needed.

In order to compensate for such errors, the initial weight of the runner may be inputted in the second micro-chip 21 just before starting a run. Assuming that no substantial mass loss occurs within the first minutes of a race, this initial period may be used to compute a correction factor that may be used when computing the indication for the mass of the runner to take into account such errors. This is explained in more detail below.

The second micro-chip 21 may be arranged to display information about the body weight of the runner during the run using display 22. In order to cancel out fluctuations in the indication of the body weight per step due to measurement errors and the like, the micro-chip 21 may be arranged to compute a mean value of the indication of the body weight over a predetermined amount of time, or a predetermined amount of foot steps. The displayed information may be based on a computed running average.

The computed indication of the body weight may be displayed directly on the display 22. However, to make the system more intuitive and easy-to-use, the second micro-chip 21 may be arranged to compute and display the weight loss by comparing the measured and computed indication of the weight during the run with the initial weight of the runner (as determined at the start of the run).

To make the system even more intuitive and easy-to-use, the second micro-chip 21 may further be arranged to compute and display the amount of fluid that needs to be drunk by a runner, for instance indicated in one of kilograms, (milli-) litres, or amount of units, where a unit is a predetermined amount of fluid, for instance corresponding to a single cup of water as handed out at a drinking post.

So, based on the above it will be understood that the system as presented here may function in a first set-up phase and in an actual monitoring phase. During the setup phase, data are read in, such as the body weight of the runner, and initial measurements are performed resulting in a correction factor. During the monitoring phase, the body weight of the runner is monitored and measurement results and warnings are displayed. Fig. 4 schematically depicts a flow diagram. In a first action 120 the system may be started. Next, the system starts executing the set-up phase in action 130, which is further explained below with reference to Fig. 5. After the set-up phase has ended, the system proceeds executing the monitoring phase in action 140, which is further explained below with reference to Fig. 6.

Set up phase

Fig. 5 schematically depicts a flow diagram of the set-up phase. The set-up phase is started in a first action 131.

At a next action 132, the initial body weight M_1n (for instance 75 kg) of a runner may be read in by the second micro-chip 21. The micro-chip 21 may be arranged to ask the user to input his or her initial body weight using display 22. The user may input this initial body weight M_1n by using buttons provided on the portable monitor 20 (not shown) or via a wireless transmission, for instance received from a scale SC. Once the initial body weight M_1n has been read in and stored in memory (not shown), the second micro-chip 21 may perform measurements during a predetermined period of time (for instance 2 minutes), or a predetermined amount of steps (for instance 100 steps) in a next action 133. In this action 133, the second micro-chip 21 receives a force signal F and an acceleration signal A from the first micro-chip 12.

Based on the received force signal F and the acceleration signal A, a number of indications M₁ for the body weight of the runner is determined in an action 134, where i = 1, 2, 3, .... This may be done by determining peak values in the force signal F_peak,i, for instance F_peak, i = 1500N. The second micro-chip 21 may be arranged to be triggered by peaks in the force signal F. According to a variant, the second micro-chip 21 may be arranged to be triggered by peaks in the acceleration signal A.

Each peak in the force signal F may be assumed to represent a single step of the runner, as the peak value is likely to be caused by the impact of the shoe 10 hitting the ground. This way information may be collected from each step. Also this approach prevents using information measured when the shoe 10 is not in contact with the ground. Furthermore, as a result of being triggered by the peak value, all subsequent measurements are performed for a similar moment during the step cycle, so subsequent measurements may easily be compared. From the acceleration signal A, the corresponding acceleration value A_peak, i is determined, i.e. the value of the acceleration at the time of the peak value F_peak,i- The acceleration may for instance be A_peak, i = 20m/s . Applying F = M(A+g), results in a value OfM₁ = 50 kg.

This may be repeated during the predetermined amount of time, or the predetermined amount of steps (i.e. a predetermined amount of peak values in the force signal F). In action 135 it is determined whether the set-up phase may be ended, i.e. if the predetermined amount of time or steps have been reached. If not, the second microchip 21 returns to action 133. If so, the second micro-chip 21 continues executing action 136. It is assumed that during the set-up phase no substantial loss of body weight occurs. In this action 136, the obtained results for M_1;, are averaged in an action 134

' M, resulting in an average value for M_av, where M_av = — max

In a next action 137 a correction factor C is determined, to take into account differences between the initial actual body weight M_1n of the runner and the measured body weight M_av. The correction factor may be C = M_1n/ M_av. According to the example given, this may result in a correction factor C of 75/50 = 1.5. The correction factor C takes into account all kinds of measurements errors.

Also, during the set-up phase, the micro-chip 21 may be arranged to ask the user using display 22 to input the amount of fluid present in cup that is being handed out at the drinking posts. This amount may be expressed in weight (e.g. 0,2 kg) or in volume (e.g. 200 ml). The user may input this information using buttons provided on the portable monitor 20 (not shown) or via a wireless transmission.

Monitoring phase

After the set-up phase has ended, the second micro-chip 21 may start executing the monitoring phase in an action 141. In a next action 142 of the monitoring phase, the second micro-chip 21 reads in the force signal F and the acceleration signal A from the first micro-chip 12 in the shoe 10. In an action 143, based on the received force signal F and acceleration signal A, the second micro-chip 21 computes an indication of the body weight M,, where j = 1, 2,

3 ... This may be done in many ways, for instance as described above with reference to action 134, i.e. by detecting peak values in the force signal F and determining corresponding values in the acceleration signal A. In a next action 144, the computed indication of the body weight M_j is corrected using the predetermined correction factor C, resulting in a corrected indication of the body weight M_{j1 corr} = C-M_j.

In order to cancel out fluctuations that may occur due to an unsteady walking technique of the runner, measurement errors, measurement fluctuations caused by hills, corners and the like, an average action 145 may be executed. In this average action 145 a number of determined indications of the body weight may be averaged. This may be done in many ways, for instance by computing a running average. Computing a running average may be done by computing an average value based on a predetermined last number of results, for instance based on the last 100 measurements. The displayed results may be only updated once every minute or so, in order to prevent constant fluctuations in the displayed results, making the displayed results difficult to interpret for the runner.

In a final action 146, the results may be outputted, for instance by displaying the computed body weight using display 22.

The second micro-chip 21 may be arranged to simply output the averaged indication of the body weight as determined in action 145. However, the second microchip 21 may also be arranged to display the weight loss, i.e. compute and display the difference between the determined average indication of the body weight and the initial body weight M_1n. According to a further variant, the second micro-chip 21 may also be arranged to compute and display the amount of fluid that the runner needs to drink, for instance at the next drinking post. This amount may be expressed in weight (e.g. 0,4 kg) or in volume (e.g. 400 ml).

In case during the set-up phase the micro-chip 21 has read in the amount of fluid present in a standard cup as used during the run, for instance the cups that are handed out at the drinking posts, the second micro-chip 21 may also output the amount of cups the user needs to drink. The purpose of providing units of volume is to offer a more intuitive way with which to measure the fluid consumption.

So in case the runner according to the example as used above, now weights 74,6 kg, the second micro-chip may display 74,6 kg as the current weight of the runner, or display a weight loss of 0,4 kg (compared to the initial body weight of 75 kg), or may display an advised fluid intake of 400 ml, or may display an advised number of cups of 2 (400/200 = 2).

It will be understood that the second micro-chip 21 may also be arranged to provide a warning when a predetermined threshold of fluid loss has been detected. This threshold may be adjustable by the user. The threshold may for instance be 0,5 kg. So, in case the second micro-chip determined a fluid loss of more than 0,5 kg, an additional warning is given, for instance a visual warning (blink) or an acoustic warning (beep).

Monitoring system According to an embodiment, the portable monitor 20 may also be arranged to output information about the loss of body weight, or the advised amount of fluid to a remote monitoring device 50, as shown in Fig. 7.

The portable monitor 20 may output this information using any kind of suitable communication link, such as a wireless communication link. The communication link may be established by using radio frequent signals, infrared or Bluetooth or the like.

Such a monitoring device 50 may be positioned along a route of a run or a running track and may be managed by the organization of the run. The monitoring device 50 may comprise a suitable input device 51 and a processing unit 52. The monitoring device 50 may further comprise memory 53, comprising programming lines readable and executable by the processing unit 52 allowing the processing unit 52 to perform the functionality described here. The memory 53 may be any kind of suitable computer memory known to a skilled person, such as RAM, ROM, EEPROM and the like.

The processing unit 52 may be arranged to receive information via the input device 51. The information may comprise an identification code being associated with specific runners and information about the measured weight loss or fluid loss of that specific runner.

The processing unit 52 may further be arranged to compare the received information with a predetermined threshold and provide a warning using a warning unit 54 when a specific runner has a fluid loss that exceeds this predetermined threshold.

The warning unit 54 may be a display displaying the identification and the fluid loss of the specific runner. The warning unit 54 may also be arranged to provide an acoustic warning.

Based on the received identification code the runner having a fluid loss that exceeds the threshold may be tracked down and offered additional fluid or be removed from the run. Further remarks

The above embodiments all describe a force sensor pad 11, a first micro-chip 12 and an accelerometer 13 provided in a single shoe 10. However, it will be understood that a runner may also wear a second shoe being provided with similar functionality. The second micro-chip 21 may then be arranged to receive signals from both the first and the second shoe. According to such an embodiment, more data are being received by the system and more accurate computations may be performed. Also, errors may be cancelled out as a result of an unstable walking technique, for instance a walking technique in which more weight is put on one foot than is on the other. Furthermore, a runner might feel more comfortable wearing two similar shoes, having similar pads and having similar weights.

Also, a second shoe 10 may be provided which does not comprise the force sensor pad 11 etc. but comprises a counterweight (for instance provided by an innersole) to balance the force sensor pad 11, the accelerometer 13 and the micro-chip 12 in the first shoe 10, giving the runner a more stable feeling.

It will be understood that all the material used in the embodiments described above may be made of light weight material, in order to make running as comfortable as possible.

It will further be understood that the set-up phase described above is an optional phase, and is mainly used to compute a correction factor C. However, this correction factor C may be a standard correction factor, for instance stored in memory during a previous use of the system. In case the measurements of the force sensor pad 11 are sufficiently accurate, the correction factor may be omitted (or set to one).

The initial weight M_1n of the runner may be known from previous use or may be determined during a predetermined first amount of time or number of steps, using the standard correction factor, if necessary.

According to the embodiments described above, most functionality is performed by the second micro-chip 21. However, it will be understood that many or all computational steps may be performed by the first micro-chip 12 as well. In fact, the whole system may incorporated in a single unit attached to the shoe, including the display 22. according to such an embodiment, only a single micro-chip is to be provided. So, before using the system, the runner may position the force sensor pad 11 in his or her shoe(s) and wear the portable monitor 20. The runner weighs himself minutes before the race and inputs his or her bodyweight in the portable monitor 20. The runner may also input the amount of fluid provided in each cup used during the run, or handed out at the drinking posts.

During the race the portable monitor 20 informs the runner about at least one of

- his or her real bodyweight,

- loss of body weight,

- advised fluid intake in amounts of fluid ((milli-) litres or kg), - advised fluid intake in amounts of cups.

During the run, the second micro-chip 21 (or first micro-chip 12) computes the loss of fluid or loss of bodyweight for the runner and informs him or her about this. The second micro-chip 21 may also alert the runner when he or she has lost too much fluid and comes close to dangerous levels of dehydration. Bluetooth receptors placed along the route of the run may help the organization to keep track of each runner hydration status and be alerted when a runner is in danger of becoming either dehydrated or hyponatremia

A hyponatremic patient or runner is one that suffers a condition of severe over drinking when ingesting larger quantities of fluid than needed or that his or her body can take during the run. Hyponatremia can have fatal consequences for a runner including brain- and lung- oedema and eventually death. The potential severity of hyponatremia in runners is associated to gains in weight. A device that could inform on the body weight and hydration status during the race can inform if the runner is under drinking or over drinking and help him or her follow adequate hydration patterns. Therefore, it will be understood that the embodiments described above may also be used to inform and/or warn a runner about possible hyponatremia by computing and displaying possible weight gain during the run.

It will be understood that the above embodiments may be used in all kinds of sports, in which the feet of the user are at least part of the time in contact with the ground, such as running, walking, race walking, soccer, cricket etc.

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. System for measuring weight loss comprising at least one micro-chip (12, 21), characterized in that the at least one micro-chip (12, 21) is arranged to receive a force signal (F) from a force sensor pad (11) and is arranged to receive an acceleration signal (A) from an accelerometer (13), the force signal (F) being an indication of a force exerted by a user on the ground, and the acceleration signal (A) being an indication of acceleration of the user when touching the ground, the at least one micro-chip (12, 21) being arranged to compute an indication for a weight (M) of the user based on the received force signal (F) and acceleration signal (A).

2. System according to claim 1, wherein the micro-chip (12, 21) computes the indication for the weight (M) of the user by applying the formula F = M (A + g), where F is the force signal, A is the acceleration signal, g is the gravity coefficient and M is the indication for the weight of the user.

3. System according to any one of the preceding claims, wherein the micro-chip (12, 21) is arranged to detect a peak value in one of the force signal (F) and the acceleration signal (A) and the indication of the weight (M) is computed based on the detected peak value in the force signal (F) or acceleration signal (A).

4. System according to any one of the preceding claims, wherein the micro-chip (12, 21) is arranged for applying a correction factor (C) to the determined indication for the weight of the user (M).

5. System according to claim 4, wherein the micro-chip (12, 21) is arranged to receive an initial body weight (M_1n) of the user and to determine the correction factor (C) by comparing the determined indication for the weight (M) as determined during an initial set-up phase with the initial body weight (M_1n).

6. System according to claim 5, wherein the correction factor (C) equals C = M_m/M, wherein M_1n is the initial body weight and M is the determined body weight during the set up phase.

7. System according to any one of the preceding claims, wherein the system comprises an output device for outputting at least one of the indication for the weight (M), the difference between the indication for the weight and the initial body weight (M_1n), an advised fluid intake expressed in one of kilograms, litres or units, each unit representing a predetermined amount of fluid.

8. System according to any one of the preceding claims, comprising a force sensor pad (11), formed as an insole and suitable to be positioned in a shoe (10), comprising at least one force sensor element (14), arranged to generate the force signal (F) being an indication of the force exerted by a user on the force sensor pad (11).

9. System according to any one of the preceding claims, comprising an accelerometer (13) arranged to measure an acceleration signal (A).

10. System according to any one of the preceding claims, comprising a portable monitor (20) comprising the at least one micro-chip (21).

11. System according to any one of the preceding claims, wherein the force sensor pad (11) and the accelerometer (13) both are arranged to measure in a substantially similar direction.

12. Force sensor pad (11), formed as an insole and suitable to be positioned in a shoe (10), comprising at least one force sensor element (14), arranged to generate a force signal (F) being an indication of the force exerted by a user on the force sensor pad (11).

13. Force sensor pad (11) according to claim 12, in which at least one force sensor element (14) is positioned at a heel part of the force sensor pad (11).

14. Force sensor pad (11) according to any one of the claims 12 - 13, in which the force sensor element (14) is a piezo-element 14.

15. Force sensor pad (11) according to any one of the claims 12 - 14, where the force sensor pad (11) further comprises a micro-chip (12).

16. Force sensor pad (11) according to any one of the claims 12 - 15, where the force sensor pad (11) further comprises an accelerometer (13) arranged to measure an acceleration signal (A) being an indication of the acceleration of the force sensor pad (11).

17. Force sensor pad according to claim 16, wherein the force sensor pad (11) and the accelerometer (13) both are arranged to measure in a substantially similar direction.

18. Shoe (10) characterized in that the shoe (10) comprises a micro-chip (12) and an accelerometer (13), the first micro-chip (12) being arranged to receive a force signal (F) from a force sensor pad (11) and an acceleration signal (A) from the accelerometer (13).

19. Shoe (10) according to claim 18, wherein the shoe (10) further comprises a force sensor pad (11) according to any one of the claims 12 - 17.

20. Pair of shoes, comprising a first shoe (10) and a second shoe (10) according to one of the claims 18 - 19.

21. Pair of shoes, comprising a first shoe (10) according to one of the claims 18 - 19, and a second shoe, comprising a counterweight to balance the weight of the first shoe (10).

22. Portable monitor (22) comprising a micro-chip (21), characterized in that the micro-chip (21) is arranged to receive a force signal (F) being an indication of a force exerted by a user on the ground and an acceleration signal (A) being an indication of the acceleration of the force sensor pad (11), wherein the micro-chip (21) is arranged to compute an indication for the weight (M) of a user based on the received force signal (F) and the acceleration signal (A).

23. Portable monitor (20) according to claim 22, wherein the micro-chip (21) is arranged to compute the indication for the weight (M) of the user by applying the formula F = M (A + g), where F is the force signal, A is the acceleration signal, g is the gravity coefficient and M is the indication for the weight of the user.

24. Portable monitor (20) according to any one of the claims 22 - 23, wherein the micro-chip (21) is arranged for applying a correction factor (C) to the determined indication for the weight of the user (M).

25. Portable monitor (20) according to any one of the claims 22 - 24, wherein the first micro-chip (21) is arranged to receive an initial body weight (M_1n) of the user and determine the correction factor (C) by comparing the determined indication for the weight (M) as determined during an initial set-up phase with the initial body weight (M_1n).

26. Portable monitor (20) according to claims 25, wherein the correction factor (C) equals C = M_m/M, wherein M_1n is the initial body weight and M is the determined body weight during the set up phase.