MUSCLE FATIGUE DETERMINATION METHOD

Abstract

A muscle fatigue determination method including a step of electrostimulating a muscle at an electric charge at different frequencies. The electric charge is determined recursively in order to generate reliable and accurate forces of the muscle in response to the electrostimulation. The method further includes the steps of determining these forces and a muscle fatigue based on them.

Claims

1. A method for determining a muscle fatigue of a muscle, the method comprising the following steps in the following order: (a) setting an electric charge and a muscular forces target interval; (b) electrostimulating the muscle with an isolated pulse at the electric charge; (c) determining a force developed by the muscle in response to the electrostimulation of step (b); (d) if the force determined at step (c) does not belong to the muscular forces target interval: (d.1) comparing the force determined at step (c) with the muscular forces target interval, (d.2) modifying the electric charge depending on the comparison of substep (d.1), and (d.3) repeating steps (b) to (d); (i) electrostimulating the muscle at the electric charge at different frequencies; (ii) determining forces developed by the muscle in response to the electrostimulations of step (i); (iii) determining the muscle fatigue on basis of the forces determined at step (ii).

2. The method according to claim 1, wherein the electric charge is defined by an electric intensity of pulses constituting electrostimulations, so that the modification of the electric charge at substep (d.2) corresponds to a modification of the electric intensity.

3. The method according to claim 1, wherein the comparison of substep (d.1) comprises a determination of a ratio of a reference force of the muscular forces target interval to the force determined at step (c).

4. The method according to claim 3, wherein the reference force is chosen among: a lower bound or an upper bound of the muscular forces target interval, said lower bound increased by a force step, or said upper bound decreased by a force step.

5. The method according to claim 3, wherein the modification of the electric charge is determined at substep (d.2) by the formula E′ F=E F′, wherein: E is the electric charge, E′ is the modified electric charge to be determined, F is the force determined at step (c), and F′ is the reference force.

6. The method according to claim 1, wherein the step (c) and (ii) are performed by an instrument arranged for measuring the forces to be determined at steps (c) and (ii), and wherein the electric charge and/or the muscular forces target interval are set at step (a) depending on the muscle and/or on at least one technical feature of the instrument.

7. The method according to claim 1, wherein: the electric charge set at step (a) is comprised between 10 and 40 mA, and/or a lower bound of the muscular forces target interval set at step (a) is comprised between 2 and 10 N.

8. The method according to claim 1, comprising a number of occurrences of the following step after step (iii): (iv) (iv.1) increasing the electric charge by a charge step; (iv.4) repeating steps (i) to (iii).

9. The method according to claim 8, wherein step (iv) comprises the following substep between substeps (iv.1) and (iv.4): (iv.2) executing steps (b) and (c).

10. The method according to claim 9, wherein step (c) further comprises determining a time duration for the muscle to develop the force in response to the electrostimulation of step (b).

11. The method according to claim 10, wherein step (iv) comprises the following substep between substeps (iv.2) and (iv.4): (iv.3) comparing the time duration determined at the occurrence of step (c) originating from the preceding substep (iv.2) to the time duration determined at the last occurrence of step (c) preceding the first occurrence of step (i).

12. The method according to claim 11, wherein the execution of the method is stopped after any occurrence of substep (iv.3) following which the time durations compared at substep (iv.3) deviate from at least 10 ms.

13. The method according to claim 8, wherein each electrostimulation of step (i) at each frequency comprises a repetition of pulses with an electric intensity comprised between 10 and 100 mA, wherein the increasing of the electric charge at substep (iv.1) corresponds to an increasing of the electric intensity of the pulses, and wherein the charge step is comprised between +0.5 and +5 mA.

14. The method according to claim 8, wherein the number of occurrences of step (iv) is comprised between 5 to 30.

15. The method according to claim 1, wherein each electrostimulation of step (i) at each frequency is preceded and/or followed by a rest period of at least 300 ms.

16. The method according to claim 1, wherein each electrostimulation of step (i) at each frequency lasts at most 500 ms.

17. The method according to claim 1, wherein the frequencies of step (i) comprise: a first frequency comprised between 0 and 50 Hz, and a second frequency comprised between 50 and 200 Hz, the first frequency differing by at least 10% from the second frequency; wherein the forces determined at step (ii) comprise: a first force developed by the muscle in response to the electrostimulation of step (i) at the first frequency, and a second force developed by the muscle in response to the electrostimulation of step (i) at the second frequency; and wherein step (iii) comprises the following substeps: (iii.1) computing a ratio of the first force to the second force, (iii.2) comparing the ratio computed at substep (iii.1) to a threshold, and (iii.3) determining the muscle fatigue on basis of the comparison of substep (iii.2).

18. The method according to claim 1, wherein the muscle fatigue is a long-lasting peripheral muscle fatigue.

19. A method for planning a sport activity, comprising the following steps: (0) identifying a muscle to be stimulated during the sport activity; (1) executing the method according to claim 1 for determining a muscle fatigue of the muscle identified at step (0); and (2) planning the sport activity on basis of the muscle fatigue determined at step (1).

20. The method according to claim 1, wherein the muscle is a lower limb muscle of a human, and wherein the method further comprises the following steps, before step (a): (α) providing a system comprising: an apparatus for generating the electrostimulations of steps (b) and (i), comprising a controller for selecting electrostimulations parameters; a muscular force measuring device comprising: seat adapted to receive the human in a seated position and to be positioned on a horizontal support, a leg support element adapted to receive and to maintain stable at least part of a leg of the lower limb, an instrument adapted to measure the forces to be determined at steps (c) and (ii) at the level of the leg support element in response to the electrostimulations generated by the apparatus at steps (b) and (i), and a mechanical structure mechanically coupling the seat and the leg support element, and comprising a connecting member to the instrument at level of the leg support element; and a logical unit: connected to the instrument so that the logical unit is adapted to receive measurements of the forces to be determined at steps (c) and (ii) from the instrument, adapted to receive the electric charge and the muscular forces target interval set at step (a), and configured for executing substeps (d.1) and (d.2) and step (iii) from the electric charge and the muscular forces target interval set at step (a) and from the forces measured by the instrument at steps (c) and (ii); (β) positioning the seat on the horizontal support; (γ) positioning the human on the seat in the seated position, and positioning at least part of the leg on the leg support element, so that the lower limb is only in direct external physical contact with the muscular force measuring device; wherein the electric charge and the muscular forces target interval set at step (a) are received by the logical unit, wherein the electrostimulations of steps (b) and (i) are generated by the apparatus, wherein the forces determined at steps (c) and (ii) are measured by the instrument, wherein the comparison of substep (d.1), the modification of the electric charge of substep (d.2) and the determination of the muscle fatigue of step (iii) are performed by the logical unit based on the electric charge and the muscular forces target interval set at step (a) and on the forces measured by the instrument at steps (c) and (ii); and wherein the muscular force measuring device remains stationary with respect to the horizontal support during an execution of steps (b), (c), (i) and (ii) thanks to a whole weight of the human exerted at level of the seat.

Description

DRAWINGS DESCRIPTION

[0170] Other characteristics and advantages of the disclosed subject matter will appear on reading the following detailed description, for the understanding of which, it is referred to the attached figures where:

[0171] FIG. 1 illustrates a flow chart of the method according to a representative embodiment of the present disclosure;

[0172] FIG. 2 illustrates a continuous experimental force measurement as a function of time during an execution of step (b) of the method according to a representative embodiment of the present disclosure;

[0173] FIG. 3 illustrates an experimental curve of forces measured at step (c) of the method according to a representative embodiment of the present disclosure depending on the electric intensity of the isolated pulse of step (b);

[0174] FIG. 4 illustrates curves of the (global and/or maximal) force developed by a muscle in response to an electrostimulation of step (i) at a frequency as a function of this frequency;

[0175] FIG. 5 illustrates a continuous experimental force measurement as a function of time during an execution of step (i) of the method according to a representative embodiment of the present disclosure; and

[0176] FIG. 6 illustrates a muscular force measuring device in a system for implementing a representative embodiment of the disclosed method.

[0177] The drawings in the figures are not scaled. Similar elements can be assigned by similar references in the figures. In the framework of the present document, identical or analogous elements may have the same references. The presence of reference numbers in the drawings cannot be considered to be limiting, in particular if these numbers are indicated in the claims.

DETAILED DESCRIPTION

[0178] Description of representative embodiments of the disclosed subject matter are hereafter described with references to figures, but the present disclosure is not limited by these references. In particular, the drawings or figures described below are only schematic and are not limiting in any way.

[0179] As shown in FIG. 1, the illustrated muscle fatigue determination method proposes to electrostimulate a muscle at different frequencies μ.sub.1, μ.sub.2, μ.sub.3, . . . , μ.sub.n at step (i), in order to determine, and preferably to measure, the respective (maximal) forces F.sub.1, F.sub.2, F.sub.3, . . . , F.sub.n developed by the muscle in response to each of the electrostimulations respectively at each frequencies μ.sub.1, μ.sub.2, μ.sub.3, . . . , μ.sub.n at step (ii), and finally to determine a muscle fatigue of the muscle based on the so determined forces F.sub.1, F.sub.2, F.sub.3, . . . , F.sub.n at step (iii). The number of electrostimulations n∈ is greater or equal to 2, and comprised, for instance, between 2 and 50. Preferably, the number n is equal to 2, 3, 4 or 5. More preferably, the number n is equal to 2.

[0180] Electrostimulations of step (i) are performed at an electric charge E, corresponding to an electric intensity of pulses of which is made any of these electrostimulations. The electric charge E is typically comprised between 10 and 100 mA.

[0181] In order to use an electric charge E allowing to perform an accurate and reliable forces determination at step (ii) and muscle fatigue determination at step (iii), the method comprises steps (a) to (d) as described hereabove. In step (a), an initial electric charge E.sub.0 is set, e.g., 15 mA, 20 mA or 25 mA. This electric charge is chosen as a medium electric charge convenient for a wide class of the subjects in order to execute reliably steps (i) to (iii). Step (a) also proposes to set a muscular forces target interval I. Preferably, the interval I is an interval of the form [L,+∞[or]L,+∞[, with L a lower bound, e.g., 5 N, as detailed in the subject matter disclosure.

[0182] As illustrated in FIG. 1, the electric charge E:=E.sub.0 is used to define and perform an electrostimulation of the muscle with an isolated pulse at step (b) and to determine a (maximal) force F developed by the muscle in response to the electrostimulation of step (c). If F∈I, step (i) is executed with E=E.sub.0 as initially set. If not, through a step (d), the electric charge E is modified as E′ and steps (b) to (c) are re-executed with the new electric charge E, providing a new force F determination, and a re-evaluation of the condition F∈I via step (d). In particular E corresponds to a recursive parameter, which is recursively modified by modifications abstractly noted E′ till the condition F∈I is satisfied as it is fully explained in the subject matter disclosure.

[0183] Advantageously, as it is shown in FIG. 3, the curve 66 representing experimental measurements of any such force F determined at step (c) (read in Newton on an axis 82) at varying electric charges (read in mA on an axis 85) is substantially linear, at least for electric charges in a range of interest for the recursion of steps (b) to (d). Indeed, in most of the situations, the electric charge used at the first occurrence of step (i) will be comprised between 25 and 40 mA. As a consequence, it may be easy to determine the modified electric charge E′ at step (d), simply by applying to the current electric charge E a proportion induced by the curve gradient. As the latter may depend on the muscle, it is obtained by a ratio of a reference force (preferably L, or L+½ N, or L+1 N) to the force F lastly determined at step (c).

[0184] A time duration T for the muscle to develop the force F determined at step (c) is determined at least at the last occurrence of step (c) preceding the first occurrence of step (i), and optionally at each of the preceding occurrence of step (c) if any. This time duration if saved as T.sub.0:=T if F∈I as illustrated in FIG. 1.

[0185] FIG. 2 shown a continuous force measurement (read in Newton on axis 82)—and not only the maximal force F determined at step (c)—as a function of time (read in ms on an axis 83) during an execution of step (b). In particular, the curve 65 following from this measurement corresponds to the response of the muscle to an isolated pulse at the current electric charge E. This response is called a “twitch”. The time 0 corresponds to the moment at which the pulse is applied at level of the muscle. As it can be observed from the curve 65, the force F is reach after the time duration T generally comprised between 50 and 100 ms. The force developed by the muscle progressively decreases till the muscle returns to normal conditions, without any contraction or residual force developed due to the electrostimulation by the isolated pulse. Such normal conditions are in particular almost reached after 180 ms, and mainly reached after 300 ms.

[0186] In order to further increase the method accuracy and reliability, steps (i) to (iii) are iterated with increasing electric charge as explained hereabove and shown in FIG. 1. The electric charge E is firstly increased as E+ at a substep (iv.1). Then, steps (b) and (c) are executed with this electric charge E (still written as a current electrostimulation parameter) at a substep (iv.2), so that a force F and a time duration T are newly determined at step (c) with this updated electric charge. The time duration T is preferably compared with T.sub.0 at a substep (iv.3), and a new iteration of steps (i) to (iii) is preferably executed as a substep (iv.4) only if T−T.sub.0≈0 (e.g., |T−T.sub.0|<5 ms) for ensuring that recruited muscle fibers over repeated executions of step (i) remained homogeneous in terms of slow and fast muscle fibers.

[0187] The muscle fatigue determination at each occurrence of step (iii) can be performed for example by ratio computation of two forces F.sub.1 and F.sub.2 and/or discrete integral computation on the function associating F.sub.j to μ.sub.j for 1≤j≤n, and comparison of at least one of these computations to at least one expected value.

[0188] FIG. 4 represents graphs of the (maximal) force developed by the muscle (read in Newton on the axis 82) in response to the electrostimulations as a function of the frequency (read in Hertz on an axis 81). In other words, each point of each graph represents the force that can be determined at step (ii) in response to an electrostimulation at one of the frequencies of step (i). The curve 61 corresponds to the graph of a theoretical expected function F expressing a force developed by a non-fatigued muscle in response to such electrostimulations as a function of possible electrostimulation frequencies. The curve 62 represents a continuous and regular extension of dots cloud corresponding to the points (μ.sub.1, (μ.sub.2, F.sub.2), (μ.sub.3, F.sub.3), . . . , (μ.sub.n, F.sub.n) as measured for a fatigued muscle. It is noticed that the space between the two curves 61 and 62 is greater above low frequencies (e.g., between 10 and 40 Hz), than above high frequencies (e.g., greater than 90 Hz). This space corresponds to differences 71 and 72 between measured forces for the muscle and expected forces from function F for a non-fatigued muscle respectively at low and high frequencies. In particular, the difference 72 is so small that it can be assumed that the two curves 61 and 62 are substantially the same for high frequencies.

[0189] If it is assumed that the ratio F(20)/F(120) is either theoretically or practically known as being 65%, it is sufficient to measure the forces F.sub.1 and F.sub.2 in response to electrostimulations at μ.sub.1=20 Hz and μ.sub.2=120 Hz respectively for determining the muscle fatigue. Indeed, as F.sub.2 corresponds substantially to F(120), the measure of F.sub.2 corresponds in some sense to a reference measure while the measure of F.sub.1 allows to highlight a divergence with expected value in term of ratio to F.sub.2. In particular, when the ratio F.sub.1/F.sub.2 differs significantly from 65%, a muscle fatigue is deemed to be determined according to the method and can be quantified. This value of about 65% for the ratio is indicative and not limitative. Other values such as about 75% or 85% can also be convenient depending on the considered function F. Similarly, the values of μ.sub.1 and μ.sub.2 are completely not limitative. For instance, an identical discussion can be drawn up with μ.sub.2=100 Hz in place of 120 Hz.

[0190] A muscular force measuring device 1 for measuring the forces F.sub.1, F.sub.2, F.sub.3, . . . , F.sub.n for a lower limb muscle is illustrated in FIG. 6. This is preferably part of a whole system adapted to implement the method as described in the subject matter disclosure.

[0191] The device 1 comprises a seat 10 comprising a smooth portion 11 for receiving the human in a seated position, a rigidity frame 12 for the smooth portion 11, and positioning lower members 13 for removal positioning the seat on a horizontal support. The rigidity frame 12 contributes to the rigidity of the seat 10, in particular at level of the smooth portion 11 which can be made of a flexible and/or padded material for the human comfort. The positioning lower members 13 can be adjustable in height from 0 to 1/20 meter below the smooth portion 11 for improving the stability of the seat 10 on the horizontal support. They can be suction cups. They can have protected extremities. They are not arranged for being placed on a ground because another part of the device 1 extend much lower than them.

[0192] The device 1 comprises a leg support element 3 fixed to the seat 10 by means of a mechanical structure 2 as illustrated. The latter is in particular a mechanical frame in the device 1 illustrated on FIG. 6. The leg support element 3 includes a semi-cylindrical hollow portion for receiving and at least partially immobilizing a lower part of the lower limb leg. A measure instrument 4 is also provided for measuring any force developed by the muscle at level of the leg support element 3 when it is received and maintained by the latter, in particular in response to the electrostimulations. The mechanical structure 2 also comprises a connecting member 5 to the instrument 4 at level of the leg support element. In particular, in the illustrated configuration of FIG. 6, the instrument 4 is a strain gauge fixed along a first direction in sandwich between the leg support element 3 and the connecting member 5.

[0193] The strain gauge comprises a connecting extremity 41 for connecting the device 1 with a non represented logical unit of the disclosed system. The latter is configured for determining a muscle fatigue on basis of at least some of the forces F.sub.1, F.sub.2, F.sub.3, . . . , F.sub.n determined by the device 1 in response to the electrostimulations at each of the frequencies μ.sub.1, μ.sub.2, μ.sub.3, . . . , μ.sub.n.

[0194] The connecting member 5 comprises a position adjustment element 51 for changing the position the leg support element 3 and the instrument 4 with respect to the mechanical structure 2, along a second direction d being perpendicular to the above-mentioned first direction.

[0195] Let I.sub.0 as being the electric intensity corresponding to the electric charge E defined from steps (a) to (d), or in other words, the electric intensity to be used for the first occurrence of step (i). This electric intensity is preferably comprised between 10 and 50 mA and is typically about 25 mA. Let consider a charge step S between +0.1 mA and +5 mA, preferably of about +1 mA. Let K being an integer (so called “number of occurrences”) comprised between 5 and 30, preferably of about 10 or 15. Then, an execution of steps (i) to (iv) of the method according to representative embodiments of the disclosed subject matter comprises the following steps:

successively for each integer k between 0 and K: [0196] electrostimulating the muscle at a first frequency μ.sub.1 (preferably of (about) 20 Hz), with a repetition of N.sub.1 pulses during a period of time T.sub.1 lower than 250 ms, [0197] the pulses having a constant duration and an intensity of I.sub.0+k S; [0198] determining a (maximal) force F.sub.1 developed by the muscle in response to this electrostimulation; [0199] waiting for a first rest period R.sub.1 comprised between 300 ms and 5 s, preferably of (about) 1 second [0200] electrostimulating the muscle at a second frequency μ.sub.2 (preferably of (about) 120 Hz), with a repetition of N.sub.2 pulses during a period of time T.sub.2 lower than 250 ms, [0201] the pulses having a constant duration and an intensity of I.sub.0+k S; [0202] determining a (maximal) force F.sub.2 developed by the muscle in response to this last electrostimulation; [0203] determining at least one muscle data information, preferably a muscle fatigue of the muscle, on basis of the determined forces F.sub.1 and F.sub.2; [0204] waiting for a second rest period R.sub.2 comprised between 330 ms and 10 s, preferably of (about) 5 seconds.

[0205] Substeps (iv.2) and (iv.3) are not mentioned hereabove but they can obviously be integrated in the preceding list of steps as described previously in the subject matter disclosure and in the detailed description.

[0206] It can be noticed that the formula T.sub.1=N.sub.1/μ.sub.1 and T.sub.2=N.sub.2/μ.sub.2 makes the links between the number of pulses, the time duration of an electrostimulation and the frequency of electrostimulation. In particular, preferably, N.sub.1 is (about) 5 for μ.sub.1 being (about) 20 Hz and N.sub.2 is (about) 18 for μ.sub.2 being (about) 120 Hz. These pulses numbers allows to reach said maximal forces F.sub.1 and F.sub.2 while allowing the electrostimulation times T.sub.1 and T.sub.2 to be bounded by 250 ms to avoid voluntary perturbation of the forces measurements. For example, if it is considered N.sub.2 as being 25, T.sub.2 is still below 250 ms, but the (maximal) force F.sub.2 will remain substantially unchanged in comparison to the one for N.sub.2 being 18. These values of N.sub.1 and N.sub.2 were in particular experimentally derived by the inventors as a suitable embodiment of the present disclosure associated to the above-mentioned values of μ.sub.1 and μ.sub.2.

[0207] FIG. 5 illustrates a purely schematic curve 63 of continuous forces (typically contraction forces) developed of a human lower limb muscle (read in Newton on axis 82)—and not only the maximal forces F.sub.1 or F.sub.2 determined at step (c)—as a function of time (read on an axis 83) during part of an execution of the disclosed method according the previously introduced representative embodiments.

[0208] In particular, this figure illustrates the electrostimulation effects for an arbitrary k, comprising then a whole execution of step (i). It can easily be derived that the curve 63 repeat similarly itself after the second rest period R.sub.2 for each occurrence of step (i), i.e., for each k. If substeps (iv.2) is comprised in the considered embodiments, a curve similar to above-mentioned curve 65 of FIG. 2 is simply interposed continuously between to similarly repeating curves 63. Each curve similar to curve 65 is restricted on the interval [0, R.sub.3] of axis 83, where R.sub.3 is a third rest period comprised between 300 ms and 5 s, and preferably of (about) 1 second.

[0209] The notations T.sub.1, R.sub.1, F.sub.1, T.sub.2, R.sub.2, F.sub.2 introduced above apply similarly to FIG. 5. Similar to the curve 65, the curve 63 is based on experimental measurements. It is reproduced schematically without representing explicit experimental data. In addition, axis 82 and 83 on FIG. 5 are not necessarily endowed with a linear scale. In particular, for the sake of clarity the numbers N.sub.1 and N.sub.2 corresponding to the illustration of FIG. 5 are respectively 3 and 5, and the periods of time T.sub.1, R.sub.1, T.sub.2 and R.sub.2 are not proportionally scaled on axis 83.

[0210] It is visible on FIG. 5 that the muscle is electrostimulated at the first frequency μ.sub.1, with a repetition of 3 pulses during a period of time T.sub.1 lower than 250 ms, the pulses having a constant duration and an intensity of I.sub.0+k S. Each pulses generation corresponds to a bar 84 on the time axis 83. The effect of the pulses on the curve 63 is noted by 64 and is clearly visible as a contraction of the muscle, and then a progressive increase of the force developed by the muscle by a muscular tetanic process. In other words, as the pulses generated 84 are close enough, a kind of fusion of the muscular effect of each individual pulse is observed along the period of time T.sub.1, providing then such a staircase shaped portion of the curve 63 above the period of time T.sub.1.

[0211] The same discussion applies for the electrostimulation of the muscle at step (i) at the second frequency μ.sub.2>μ.sub.1, with a repetition of 5 pulses during a period of time T.sub.2 lower than 250 ms, the pulses having the same constant duration and intensity of I.sub.0+k S.

[0212] Each of these electrostimulations at frequencies μ.sub.1 and μ.sub.2 during the respective periods of time T.sub.1 and T.sub.2 allows to reach and determine a maximal force, respectively F.sub.1 and F.sub.2, developed by the muscle in response to the electrostimulation, as it is visible on axis 82 of FIG. 5, and consecutively to determine a muscle fatigue at step (iii). As it is visible on FIG. 5, the first and second rest periods R.sub.1 and R.sub.2 are long enough to allow the muscle to return to “normal” and/or “relaxed” conditions, without any contraction or residual force developed due to the preceding electrostimulation, and this before the beginning of the next electrostimulation. In other words, the rest periods R.sub.1 and R.sub.2 allow the curve 63 to return to a baseline. The rest period R.sub.1 occurs between the electrostimulations at the frequencies μ.sub.1 and μ.sub.2 with the same pulse intensity of the form I.sub.0+k S. The rest period R.sub.2 occurs between the electrostimulation at the frequency μ.sub.2 with a pulse intensity I.sub.0+k S and the electrostimulation at the frequency μ.sub.1 with a pulse intensity I.sub.0+(k+1) S (or the isolated pulse with a pulse intensity I.sub.0+(k+1) S if substep (iv.2) is applied).

[0213] As explained in the present disclosure, this method is convenient for avoiding disturbance effects on the determination of the forces F.sub.1 and F.sub.2. FIG. 5 illustrates also in dot lines examples of effects of such disturbances 91, 92 and 93 on the curves 63. Those are purely fictional as the method is specifically conceived for avoiding them.

[0214] Disturbance 91 shows an example of a tetanic effect on the curve 63 due to a non-respect of the above discussed lower bounds for the first rest period R.sub.1. If this period does not last enough, the muscle is still contracted and not relaxed when the next electrostimulation starts, which affects the measure of F.sub.2 as being too high due to the partial (tetanic) fusion of the effect of the electrostimulations at the frequencies μ.sub.1 and μ.sub.2. If the fusion is partial and very limited (i.e., for R.sub.1 greater than 115 ms), it is nevertheless possible to apply a direct mathematical treatment (e.g., by linear interpolation) to determine force F.sub.2 from the observed disturbed curve 91. A similar discussion can obviously apply for the second rest period R.sub.2.

[0215] Disturbance 92 shows an example of a potentiation effect on the curve 63, above the time period T.sub.1 (but the skilled person would easily understand that such effect is not limited above this time period). By not increasing the pulse intensity by a charge step S between consecutive occurrences of step (i), the muscle becomes potentiated, and then the real force F.sub.1 is disturbed, in particular higher than it should, due to a kind of training of the muscular fibers. The increasing of the intensity between consecutive occurrences of step (i) according to the present disclosure allows to avoid such potentiation effect.

[0216] Finally, disturbance 93 shows an example of a voluntary and/or reflex muscular contraction by the subject in parallel to an electrostimulation. The subject increases the force at a pulse generation and decreases it between or after the pulses. Advantageously, such disturbance cannot occur given that the time periods T.sub.1 and T.sub.2 are so short (at most 500 ms, preferably less than 250 ms) than the subject cannot react by himself during an electrostimulation.

[0217] It will be easily understood by the skilled person that the number n of electrostimulations for the class of embodiments is equal to 2, but that these embodiments can easily be generalized to any number n>1.

[0218] In other words, the above detailed disclosed subject matter relates to a muscle fatigue determination method including a step of electrostimulating a muscle at an electric charge at different frequencies. Said electric charge is determined recursively in order to generate reliable and accurate forces of the muscle in response to the electrostimulation. The method further includes the steps of determining these forces and a muscle fatigue based on them.

[0219] The disclosed subject matter has been described above in relation to the specific embodiments which have a value that is purely illustrative and should not be considered to be limiting. The skilled person will notice that the disclosed subject matter is not limited to embodiments that are illustrated and/or described here above. The disclosed subject matter comprises each of the new technical characteristics described in the present document, and their combinations. All the embodiments and advantages of the method applies mutatis mutandis to the aforementioned sport activity planning method.

[0220] The detailed description set forth above in connection with the appended drawings, where like numerals reference like elements, are intended as a description of various embodiments of the present disclosure and are not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Similarly, any steps described herein may be interchangeable with other steps, or combinations of steps, in order to achieve the same or substantially similar result.

[0221] In the foregoing description, specific details are set forth to provide a thorough understanding of exemplary embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that the embodiments disclosed herein may be practiced without embodying all of the specific details. In some instances, well-known process steps have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the present

[0222] The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure, which are intended to be protected, are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure as claimed.

[0223] While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.