Motion detection module, handle and method

Abstract

The invention relates to a motion detection module suitable for detecting motion of a retractable handle or grip at a distal end of a flexible power transfer, wherein the flexible power transfer runs over a rotating body, wherein the rotating body comprises a circumference comprising one or more segments of a polygon, characterised in that the motion detection module is configured for capturing the motion of the flexible power transfer by sensing the polygon effect.

Description

[0001] The invention relates to a motion detection module and method.

[0002] More specifically, the invention relates to a motion detection module for indoor rowing machines.

[0003] Over the last decade, this 'indoor' rowing has developed into a discipline of its own. Here, performance of individuals can be compared for e.g. training purposes. In order to make dedicated training plans, accurate capture of the performance is key for the individual athlete.

[0004] The rise of 'virtual' competition has further increased the need for accurate capture of performance.

[0005] Performance in many sports, including rowing is measured by the amount of energy over time or work exerted by the athlete.

[0006] Nowadays especially, indoor rowing machines are increasingly used to train for rowing when regular outdoor training is less expedient or impossible. In exceptional circumstances, such as e.g. when a pandemic outbreak occurs, outdoor rowing or contests may not be possible at all. In the latter case, there is an ever growing need for remote competition.

[0007] In remote competition, multiple users can connect to a web based or remote system and have their performance parameters real time uploaded and compared with the performance parameters of others. These systems are however confronting the users with various problems. First, there is a wide variety of rowing machines available on the market, and each has its own calibration errors.

[0008] Furthermore, the accuracy of the current systems is too low to provide fair comparison of the performance of the individual user / contesters when compared amongst them.

[0009] In existing rowing machines, dissipation of the energy is typically obtained with a fluid mechanical device, being either a fan, turning in air, or a set of paddles turning in a liquid. Typically, these machines are provided with a flywheel and a dissipator, where the dissipator is either a set of paddles moving through an amount of water or a fan mounted on the flywheel moving through air. In these rowing machines, the ambient conditions can have a substantial impact on the fluid dynamics of both air and water, introducing unpredictable and over time varying errors.

[0010] Besides this effect, in the machines where water is inserted as energy dissipating fluid, the amount of water is similarly having a substantial impact on the accuracy of the measurement of the force and energy exerted.

[0011] In existing rowing machines, as described herein above, the amount of exerted power by a user or athlete is derived from the speed increase, the acceleration of a flywheel. As said, this flywheel may be in the form of a fan turning in air, or a set of paddles turning in a liquid, or a metal disc with magnetic brakes.

[0012] Since the amount of power is thus deduced or obtained indirectly, this method is prone to inaccuracies due to varying ambient conditions like pollution, temperature, altitude, amount of water, friction etc. Furthermore, it also allows each manufacturer to have his own method of calculation of the methods and formulae to calculate the amount of exerted power by the athlete from the acceleration and deceleration of the flywheel and thus may introduce a factory biased way of the calculation of the power exerted by the athlete.

[0013] On the other hand, in bio-mechanic research, the power produced by an athlete, is measured as close as possible to the point where force and displacement originate. For an athlete on a rowing machine, it is tried to obtain these values from the motion of the handle. Researchers in this field therefore not seldomly, record the trajectory of the handle on video or film with the help of a number of cameras, in order to determine the exact stroke-length, for later processing in combination with the force-curve, taken from a force-sensor mounted in or on the handle or in the chain.

[0014] In the art, various options and techniques have been disclosed to calculate, to measure and / or obtain the travel of the handle and the amount of force exerted on the handle, in order to deduce the amount of work exerted by a user of a rowing machine.

[0015] The US patent application US2011 / 0118086 discloses a control system and method for exercise equipment to provide an accurate simulation. More specific a stationary exercise bike is claimed having a flywheel with a variable resistance force and two sensors; a resistance force measuring sensor and a flywheel velocity and position sensor.

[0016] The article "Long-range automatic precision displacement measuring of winding system using double timing belt transmission" by Duxi Liu c.s. of the School of Mechanical Engineering, Northwest Polytechnical University, Xi'an, China discloses a solution for the design of more precise double timing belt clamping conveyors. Based on the mechanical theory behind winding systems with long travel range the paper proposes to use circular arc tooth time belts to reduce the measurement errors.

[0017] The international patent application WO2020127238A1 discloses a rowing device, of which the performance parameters are measured and calculated by the use of force sensors. These sensors are described in general terms, it seems not to be explained how the force is measured, let alone that the distance of travel of the handle is measured using a force sensor. Accordingly, this machine is unable to calculate the work exerted by a user accurately, it can only be deduced indirectly.

[0018] Another alternative is proposed in the Japanese patent application JPH01107779A. This document discloses a rowing machine with a force measurement by means of an eddy current device. The speed of a rotor and of the eddy current disc are measured and a the exerted power is calculated from these measurements. Here again the power is not measured by measuring both force and distance of travel of the handle and thus again the power can only be deduced indirectly.

[0019] A further approach is proposed in the Chinese patent application CN109847263A. This document discloses a rowing machine, where force and distance is measured, the force exerted on the handle by the user is measured in the handle on both the left and right hand side, as well as in the foot pedals. The displacement of the seat and the handle appears to be measured. It is not clear from this document, how the travel of the handle is exactly measured, which makes it uncertain how, if even possible, the exerted power is calculated.

[0020] Another way of deducing the distance of travel of the handle is proposed in the European patent application EP0214748A2. This document discloses another rowing machine, wherein the power is calculated by using an electrically controlled resisting force and by measuring the travel of the handle with a toothed disc and a light sensor. From the exerted resisting force and the travel of the handle, the applied power can be determined. Since the measurements are made indirectly, the accuracy of the deduced work of the user in this example is again very low.

[0021] A last alternative is proposed in the Chinese utility model CN207627861U. This document discloses a power measurement module in the handle of a rowing device, wherein force is measured by a force sensor and the travel of the handle is determined by a combination of a gyroscope and accelerator sensor. The measured signals are processed and transmitted through blue tooth to a receiver.

[0022] Using accelerometer-gyroscope combinations in order to determine motion introduces a high level of uncertainty. Thus, a standard, yet unknown and each rowing-stroke varying error is introduced, making this system not suitable for the application in a fair contest environment.

[0023] Accordingly it is an object of the invention to mitigate or solve the above described and / or other problems of motion detection modules in the art, while maintaining and / or improving the advantages thereof.

[0024] More specifically the object of the invention can be seen in providing a highly accurate and relatively inexpensive built in or add on motion detection module for fitness devices, e.g. rowing machines that can accurately detect the motion of the handle, the force exerted on the handle and thus calculate the amount of work or energy exerted by a user.

[0025] These and / or other objects are reached by a motion detection module according to claim 1. By sensing the polygon effect, the detection of the motion of the flexible power transfer and / or the handle or grip at its distal end can be obtained directly and accurately.

[0026] The motion detection module can comprise a sensor configured for sensing variations in the vibrations, accelerations, the acoustics, the exerted force and / or variations in any other dynamic property of the flexible power transfer, due to the polygon effect. The sensor can for instance be a force sensor.

[0027] The application of a force sensor renders the device relative simple, since the force sensor can measure the force and the motion as is elucidated herein below.

[0028] The module can comprise a signal processor wherein the signal processor may comprise a frequency band width filter configured to separate the measured signal from the force sensor in a first relative low frequency force signal and a second relative high frequency motion signal.

[0029] By splitting the signal, the relative high frequency signals can serve for measuring the distance or time of travel, while the relative low frequency signal can serve for measuring the force exerted by the user. Thus an elegant and relative straight forward and accurate calculation of the exerted force over the travelled distance can be obtained while using only one sensor.

[0030] The force sensor can be mounted in a handle or a grip of a fitness device, such as a rowing machine.

[0031] Preferably, the force sensor is mounted between the handle or grip and the flexible power transfer, such as a cable or chain, wherein the flexible power transfer is configured to be retractably connected to a base of a rowing machine at its proximal end.

[0032] The signal processor can be configured to deduce the amount of force exerted by a user from the first relative low frequency repetitive force signal, and the signal processor can be further configured to deduce the travel of the handle from the second relative high frequency repetitive force signal. As indicated herein above, thus the separate signals can serve for their separate purposes, one being the calculation of travel, the other being for the measurement of the exerted force.

[0033] The module may be equipped with a wireless transmission to a computer or mobile device. Thus, no cables or connections are needed, that may interfere with the usage of the fitness device in question.

[0034] The module can equipped with an electronic on switch to power its signal processor. Thus the user can operate the module while holding the handle e.g. during use.

[0035] The module can be equipped with an automatic off switch, configured to switch off when e.g. over a prolonged time, no force is detected. Thus the use of power of the module can be saved.

[0036] The signal processor in the module can be configured to perform various other functions, such as a gaming console, radio or television operation. Thus, the use of the fitness device can be integrated in a game surrounding, where during the use of the fitness device, the user may experience a video / audio or 3D game interface, through which he or she has to move by using the machine.

[0037] The invention further encompasses a method of deducing the distance of travel of a flexible power transfer of a fitness device, such as a rowing machine during its use, according to claim 12.

[0038] Thus an accurate calculation of the distance of travel of the handle can be obtained.

[0039] Herein, the motion detection module can comprise a force sensor, such that the measurement of both travel and exerted power can be obtained by one and the same sensor.

[0040] Additionally the method of deducing the distance of travel of a flexible power transfer of a fitness device can be further comprising the steps of: Obtaining a signal from the force sensor during the use of the device; splitting the measured signal of the motion detection module in a high and a low frequency band, using the low frequency band signal as the force signal; using the high frequency band signal in a counter to count the number of cycles resulting from the polygon effect; calculating the distance of travel by the number of high frequency cycles; Using the obtained force signal and the calculated travel of the handle or grip to calculate the amount of work or energy that is exerted by the user during the motion of the grip or the handle of the fitness device.

[0041] The signals of the sensor can be calculated and processed within the hard- and / or software of the signal processor of the motion detection module, and the obtained data about the amount of work or energy exerted by a user can be transmitted to a centralised or distributed application for competition rowing, either real time or in a specific time delay period independent of the location of the users.

[0042] In this way, training and competition can be done independently or in a competition environment, where competition can be performed while the specific location of the users and the specific time the users on which they perform their races or training can be irrelevant for the competition. A once performed race by a first user can be used in a time delayed race for a second user. As is indicated herein above, by using one sensor for measuring both force over time and distance over time a highly accurate, yet relative simple adaptation of existing and / or newly built rowing machines can be provided.

[0043] The measurement device can be integrated in the handle of the rowing machine, and no further adaptations are needed or necessary.

[0044] Once the sensor is calibrated, the various external factors such as temperature, air pressure and air humidity, system friction etc. do not interfere with the accuracy of the measured values.

[0045] In order to further elucidate the invention, exemplary embodiments will be described with reference to the figures. In the figures: Figure 1A depicts a first schematic perspective view of a typical rowing machine according to the state of the art; Figure 1B depicts a schematic partially worked open cut out view of the rowing machine according to figure 1A; Figure 2 depicts a schematic perspective view of an exemplary embodiment of the invention; Figure 3 depicts a schematic, explanatory representation of the effect underlying the invention; Figure 4 depicts a schematic graphical representation of the effect underlying the invention; Figure 5 depicts a schematic modular functional design diagram of a further embodiment of the invention; Figure 6 depicts a schematic partially exploded perspective view of an alternative embodiment of the invention; and Figure 7 depicts a schematic perspective view of the embodiment of figure 6.

[0046] The figures represent specific exemplary embodiments of the inventions and should not be considered limiting the invention in any way or form. Throughout the description and the figures the same or corresponding reference numerals are used for the same or corresponding elements.

[0047] The expression "Polygon effect" used herein is to be understood as, though not to be considered limited to the effect occurring where a flexible power transfer such as a chain or a toothed belt is running over a rotating body, such as a pulley, a gear wheel or a sprocket, and any divergence of roundness in the rotating body expresses a slight variation in force, motion and / or acceleration, due to the divergence in the roundness. For example a chain guided over a sprocket for the transfer of force, experiences a typical variation in speed of travel of the chain at the passing of each chain link of that chain at each dent of the sprocket.

[0048] In the case a sprocket has for example 17 teeth, the sprocket actually represents a polygon having 17 angles. The effect in variation of speed with these 17 angles is just below 2%.

[0049] The expression "flexible power transfer" used herein is to be understood as, though not to be considered limited to an elongated element, having a longitudinal axis which is at least flexible in one axis, perpendicular to its longitudinal axis, such that it can run over a substantially round rotating body, such as pulley, a sprocket or a gear wheel. Typically the flexible power transfer is a chain, a toothed belt, a rope or the like, where the power is transferred from a substantially linear traction to a rotating motion and / or vice versa.

[0050] The expression "distal end" used herein is to be understood as, though not to be considered limited to an end of a flexible power transfer that is extending, connected or connectable to a handle or grip, and that is configured to be moved from a retracted into an extracted or extended position back and forth.

[0051] The expression "proximal end" used herein is to be understood as, though not to be considered limited to an end of a flexible power transfer that is connected to e.g. a base of a fitness device, such as a rowing machine, and that remains relative proximal to the machine, even when the distal end is in an extracted position. Typically the proximal end is connected to the base by means of a spring or a elastically extendable material, such as a rubber band.

[0052] In figure 1, a schematic perspective view of a rowing machine 1 is shown. The rowing machine 1 is operated by a user U, who holds in his hands H a handle 2, which is described in more detail herein below.

[0053] The User U is seated on a sliding seat 3, which can slide over a hollow beam of base 4. Base 4 is provided with some adjustably mounted footholds 5, on which the feet F of the user U can be strapped.

[0054] The handle 2 is connected to a first end of chain 6, which chain 6 runs over a sprocket 7. The sprocket 7 is mounted inside the base 4 of the rowing machine 1 and is directly coupled and connected to a flywheel 8, which can rotate inside a housing 9. The housing 9 is mounted on the base 4, and typically the flywheel 9 in the housing is connected to a dissipator, typically a fan that can rotate in a volume of air.

[0055] During use, the user U is exerting a pulling force in his arms and a pushing force in his legs. Thus while stretching his body, the handle 2 is moved in a direction D away from the sprocket 7 and the flywheel 8. While the chain 6 runs over and engages with the sprocket 7, during the stretching motion of the user the sprocket 7 and the flywheel 8 commence to rotate. This rotating motion is dissipated by the fan or by any other means e.g. an eddy current disk.

[0056] Inside the base 4 at the distal end is a first end of a spring or an elastic cord mounted. The spring or the cord is at its other end connected to the second end of the chain. By this arrangement, if the user releases the tension on his body, the chain is retracted back into the base 4 of the rowing machine 1. During the reverse motion of the chain 6 and thus the reverse motion of the sprocket 7, the sprocket 7 is decoupled from the flywheel, such that the flywheel can maintain its motion, while the chain 6 is retracted into the base 4 of the rowing machine 1.

[0057] In figure 2, a schematic perspective view of a handle 2 is depicted. The handle is provided with two grips 10 and 11, to be held by the user with his left hand and right hand respectively. The grips 10 and 11 can be provided with a soft cover 12 and 13 respectively, for improving the cushioning between the inside of the hands of the user and the handle 2.

[0058] The handle 2 comprises a rod 14 extending from the grip 10 to grip 12 and is provided with a housing 15. The housing 15 can be closed of with a cover 16, and inside the housing 15 a force sensor 17 and a signal processor 18 are provided. The signal processor 18 is equipped with a logic circuitry for performing its tasks. The logic circuitry can be equipped with a battery holder 19.

[0059] The chain 6 is attached to the handle through the force sensor 17, such that the force exerted on the handle by user U can be measured. The chain 6 may be connected by means of a connector 20, which connector 20 is attached to the force sensor 17.

[0060] In figure 3 a detail of the chain 6 is depicted. The chain 6 runs over and engages with sprocket 7. As seen in this image, although the sprocket appears to be round, the lines 22, 23, 24, 25 and 26 show that the motion of the chain around the sprocket 7, while the chain 6 is being pulled actually is slightly uneven. The chain 6 is during the active stretching of the user experiencing a nett force in the direction 27, towards its first end and the handle 2. During retraction, the chain 6 is experiencing a nett force in the direction 28, towards the second end of the chain 6 by the force of the spring or rubber cord inside the base 4 exerted on the chain 6. During the passing of the links 21A, 21B and 21C over the sprocket 7, each time there is a light acceleration and a light deceleration. This effect, also referred to as the polygon effect can be noticed by a user U, during his training.

[0061] The light acceleration and deceleration in motion of the chain 6 during use of the rowing machine 1, imply similarly light variations in the force, the user 4 is experiencing when pulling handle 2 towards him. These light variations in force can be measured, as is shown in figure 4 and 4A. These figures depict a schematic, explanatory representation of this polygon effect. In figure 4 the abscissa 30 represents time or the calculated distance of travel and the ordinate 31 represents the force measured by the force sensor 17. Curve 29 represents a characteristic of the force pattern, typically experienced during one rowing stroke of the user U. In the retracted state I, where the chain 6 is retracted in the base 4, the force is relatively low. When the user starts pulling, he exerts a force during the extension of his legs and the retraction of his arms up to a maximum in phase II. At the end of the motion of the user U, in phase III, the user U has fully stretched his legs and maximally retracted his arms, and the force is again relative low in phase III. After this phase III, the user U relaxes, and moves back towards the fly wheel 8 of the rowing machine 1.

[0062] During this entire pulling motion of the user U, the handle 2 and the chain 6 is experiencing a major force characteristic, on which is superposed a high frequency relative small force pattern due to the polygon effect of the sprocket 7. This is represented by figure 4A, in which a detail of the force curve 29 is shown. Curve 29 comprises a sinusoidal variation. The high frequency, relative small variation can be electrically separated from the main force characteristic by applying a frequency band pass filter.

[0063] In Figure 5 a schematic modular design diagram is depicted showing how the measured force is processed. The motion sensor generates a signal that is magnified in a first amplifier 33, than split at junction 34 and sent to a frequency band pass filter 35, where the relative low frequency, relative large force characteristic is filtered out such that a naked high relative frequency signal remains, which is sent to a second amplifier 36 and then to a signal processor 37. The signal processor 37 is provided with a power source 38, typically a battery, and a series of functional switches 39 like an on switch and / or an off switch.

[0064] In the signal processor 37 the number of undulations in the relative high frequency signal are counted and added up during each rowing motion of the user U. The obtained number represents the motion of travel of the handle 2, and can be calculated by multiplying this number with the length of a link 21A-21C.

[0065] In the module, comprising the signal processor 18, from the junction 34, the main characteristic force signal is sent through an analogue digital converter 40, which is sending this digital signal to the signal processor 37. In the signal processor 37, the amount of work exerted by user U is calculated, by aggregating the exerted force, obtained by the relatively low frequency signal, over the travelled distance of the handle, obtained by the relatively high frequency signal.

[0066] In this way a very elegant and relatively simple design can generate highly accurate calculation of the amount of work the user U is delivering to the rowing machine 2. Finally, in order to get the information out to a computer or a hand held mobile device, the module is equipped with a transmitter 41 and an antenna 42. This can be e.g. a blue tooth transmitter or any other suitable transmitter.

[0067] The thus obtained values representing the personal performance of user U can be used in a web application to store and compare with the user performance of other users. Since the obtained exerted energy is now highly accurate, a fair comparison and a fair competition between users on a real time basis or on a delayed time basis can now be performed, totally independent from their location and totally independent from any locally existing ambient conditions.

[0068] In Figure 6 an alternative design of a handle 2 for a rowing machine 1 is depicted. In this figure, the handle 2 has a rounded off wedge shape, wherein for example an extruded rod 14 is provided with two grips 10 and 11, each having a cover 12 and 13 respectively. At the ends of the rod 14, two battery holders 19A and 19B can be inserted for providing the power to the signal processor 18.

[0069] The signal processor 18 comprises a series of integrated circuits 46, 47 and 48, mounted on a printed circuit board 43, which is connected by a set of brackets 49 and 50 to a base 51. Mounted on the base 51 is a force sensor 17, which is in its middle connected through an opening in the base 51 by means of connector 52 to a chain 6. On the force sensor 17 are integrated two strain gauges 44 and 45, which are providing a force signal to the signal processor 18.

[0070] The signal processor 18 and the base 51 can slide into the rod 14 of the handle 2, as is shown in figure 7 where the connector 52 is extending from the rod 14 through a centralised opening. The design as represented in figures 6 and 7 is made as symmetrical as possible, such that handle 2 is equally balanced, which can be beneficial during its use.

[0071] The invention is to be understood not to be limited to the exemplary embodiments shown in the figures and described in the specification. For instance the application of the polygon effect may also be integrated in e.g. a bicycle for determination of the distance of travel of the bicycle or the power exerted on it by a user. An additional calculation may be integrated in the invention for conversion to the amount of bodily fat being converted in energy.

[0072] The invention is furthermore applicable in various power lifting applications, where force and distance can be measured and distance or time specific work can be calculated.List of reference signs

[0073] 1.Rowing machine 2.Handle 3.Sliding seat 4.Base 5.foothold 6.Chain 7.Sprocket 8.Flywheel 9.Housing 10.Grip 11.Grip 12.Cover 13.Cover 14.Rod 15.Housing 16.Cover 17.Force sensor 18.signal Processor 19.Battery holder 19A.Battery holder 19B.Battery holder 20.connector 21A-GLinks 22.Line 23.Line 24.Line 25.Line 26.Line 27.Direction 28.Direction 29.Curve 30.Distance 31.Force 32.force variations 33.Instrument amplifier 34.Junction 35.Frequency band pass filter 36.Operational amplifier 37.signal processor 38.Battery 39.Operational switches 40.Analogue-digital convertor 41.Transmitter 42.Antenna 43.Printed circuit board 44.Strain gauge 45.Strain gauge 46.Integrated circuit 47.Integrated circuit 48.Integrated circuit 49.Bracket 50.Bracket 51.Base 52.Connector I.Phase II.Phase III.Phase FFeet HHands UUser

Claims

1. A motion detection module for detecting motion comprising: - a retractable handle (2) or grip (11, 12) attached at a distal end of a flexible power transfer (6), - a rotating body (7) where the flexible power transfer (6) runs over, the rotating body (7) having a circumference comprising one or more segments of a polygon, characterised in that the motion detection module is configured for capturing the motion of the flexible power transfer (6) by sensing variations in one or more dynamic properties caused by the polygon effect.

2. A motion detection module according to claim 1, comprising a sensor configured for sensing variations in the vibrations, accelerations, the acoustics, the exerted force and / or variations in any other dynamic property of the flexible power transfer (6), due to the polygon effect.

3. A motion detection module according to claim 1 or 2, wherein the module comprises a force sensor (17).

4. A motion detection module according to claim 3, wherein the module comprises a signal processor (18, 37) wherein the signal processor (18, 37) comprises a frequency band width filter (35) configured to separate the measured signal from the force sensor (17) in a first relative low frequency force signal and a second relative high frequency motion signal.

5. A motion detection module according to claim 3 or 4, wherein the force sensor (17) is mountable in the handle (2) or grip (11, 12) of a fitness device (1), such as a rowing machine (1).

6. A motion detection module according to claim 5, wherein the force sensor (17) is mountable between the handle (2) or grip (11, 12) and the flexible power transfer (6), such as a cable or chain (6), wherein the flexible power transfer (6) is configured to be retractably connected to a base (4) of a rowing machine (1) at its proximal end.

7. A motion detection module according to any of claims 4-6, wherein the signal processor (18, 37) is configured to deduce the amount of force exerted by a user from the first relative low frequency repetitive force signal, and the signal processor (18, 37) is further configured to deduce the travel of the handle (2) from the second relative high frequency repetitive force signal.

8. A motion detection module according to any of the preceding claims, wherein the module is equipped with a wireless transmission to a computer or mobile device.

9. A motion detection module according to any of the preceding claims, wherein the module is equipped with an electronic on switch (39) to power its signal processor (18).

10. A motion detection module according to any of the preceding claims, wherein the module is equipped with an automatic off switch (39), configured to switch off when e.g. over a prolonged time, no force is detected.

11. A motion detection module according to any of the preceding claims, wherein the signal processor (18, 37) is configured to perform various other functions, such as a gaming console, radio or television operation.

12. A method of deducing the distance of travel of a flexible power transfer (6) of a fitness device (1), such as a rowing machine (1) during its use, comprising the following steps, to be executed in any suitable order: a) providing a fitness device (1), such as a rowing machine (1), b) providing the motion detection module according to claim 1, which is equipped with a retractable handle (2) or grip (11, 12) at a distal end of a flexible power transfer (6), wherein the flexible power transfer (6) runs over a rotating body (7), wherein the rotating body (7) comprises a circumference comprising one or more segments of a polygon; c) using the fitness device (1), such as a rowing machine (1); d) detecting the polygon effect with the motion detection module; e) counting the number of phases in a signal comprising variations due to the polygon effect; f) calculating the distance of travel of flexible power transfer (6) by multiplying the counted number of phases in the signal with the length of the segments of the polygon of the rotating body (7).

13. The method according to claim 12, wherein the motion detection module comprises a force sensor (17).

14. The method according to claim 13, comprising the following additional steps: A) Obtaining a signal from the force sensor (17) during the use of the device; B) splitting the measured signal of the motion detection module in a high and a low frequency band; C) using the low frequency band signal as the force signal; D) using the high frequency band signal in a counter to count the number of cycles resulting from the polygon effect, as indicated in claim 12, step d); E) calculating the distance of travel by the number of high frequency cycles as is indicated in claim 12, step e) and f); F) using the obtained force signal and the calculated travel of the handle (2) or grip (11, 12) to calculate the amount of work or energy that is exerted by the user during the motion of the grip (11, 12) or the handle (2) of the fitness device (1).

15. The method according to claims 12 - 15, wherein the signals of the sensor are calculated and processed within the hard- and / or software of the signal processor (18, 37) of the motion detection module, and the obtained data about the amount of work or energy exerted by a user is transmitted to a centralised or distributed application for competition rowing, either real time or in a specific time delay period independent of the location of the users.

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