MUSCLE FATIGUE DETERMINATION METHOD

Abstract

A method for determining a muscle fatigue of a muscle includes the step of electrostimulating the muscle at a given electric charge at different frequencies. The method further includes the steps of determining forces developed by the muscle in response to the electrostimulations and determining a muscle fatigue on basis of the forces The steps are repeated a number of times with increasing electric charge, wherein the electric charge is increased by a charge step between two occurrences of the electrostimuation step.

Claims

1. A method for determining a muscle fatigue of a muscle, the method comprising the following steps: (i) electrostimulating the muscle at a given electric charge at different frequencies; (ii) determining forces developed by the muscle in response to the electrostimulations of step (i); (iii) determining a muscle fatigue on basis of the forces determined at step (ii); and (iv) repeating steps (i), (ii) and (iii), a number of times with increasing electric charge, the electric charge at step (i) being increased by a charge step between two occurrences of step (i).

2. The method according to claim 1, wherein the electrostimulation comprises, at each frequency, a repetition of pulses, and wherein the electric charge is defined by one of electric intensity of the pulses and duration of pulses.

3. The method according to claim 2, wherein the electric intensity for a constant pulse duration is increased between 10 and 100 mA, the number of times being between 5 to 30, and the charge step being an intensity increasing between +0.1 and +10 mA.

4. The method according to claim 3, wherein the electric intensity is increased from 25 to 40 mA with 15 charge steps of +1 mA.

5. The method according to claim 1, wherein a first rest period comprised between 100 ms and 10 s occurs between two electrostimulations at different frequencies at step (i).

6. The method according to claim 5, wherein a duration of the first rest period is between 115 ms and 5 s.

7. The method according to claim 5, wherein a second rest period occurs between two occurrences of step (i), the duration of the first rest period being less than a duration than the second rest period.

8. The method according to claim 7, wherein the duration of the second rest period is between 100 ms and 5 minutes.

9. The method according to claim 8, wherein the duration of the second rest period is between 145 ms and 10 s.

10. The method according to claim 1, wherein the electrostimulation comprises, at each frequency, repetition of pulses during a period of time lower than 5 s.

11. The method according to claim 10, wherein the period of time is lower than 500 ms.

12. The method according to claim 1, wherein the electrostimulation comprises, at each frequency, pulses repeated between 2 and 50 times.

13. The method according to claim 1, comprising, before step (i), a preliminary electrostimulating step of the muscle with an isolated pulse, wherein a third rest period having a duration between 100 ms and 10 s occurs between this preliminary electrostimulating step and step (i).

14. The method according to claim 1, wherein: the frequencies of step (i) are between 0 and 500 Hz and comprise: a first frequency, and a second frequency greater than the first frequency, wherein the first frequency differs by at least 10% from the second frequency, and the forces 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.

15. The method according to claim 14, wherein the first frequency is between 0 and 50 Hz.

16. The method according to claim 15, wherein step (i) comprises: electrostimulating the muscle with a repetition of 3, 4, 5, or 6 pulses at the first frequency of about 10, 15, 20 or 25 Hz; and electrostimulating the muscle with a repetition of 16, 17, 18 or 19 pulses at the second frequency of about 100, 110, 120 or 130 Hz; during the period of time between 100 and 250 ms.

17. The method according to claim 1, wherein step (iii) comprises a comparison of the forces determined at step (ii), and a determination of the muscle fatigue based on the comparison of the forces.

18. The method according to claim 14, wherein step (iii) comprises a computation of a ratio of the first force to the second force, a comparison of the computed ratio to a threshold, and a determination of the muscle fatigue based on this comparison of the computed ratio to the threshold.

19. The method according to claim 1, wherein the forces are determined in steps (ii) by direct force measurements by at least one of a strain gauge and a dynamometer.

20. The method according to claim 1, comprising, before step (i): (a) providing a device comprising: a seat configured to receive the human in a seated position and adapted to be positioned on a horizontal support; a leg support element mechanically coupled to the seat and adapted to receive at least part of a leg of a lower limb; and an instrument configured to measure the forces at level of the leg support element; (b) positioning the seat on the horizontal support; (c) positioning the human on the seat, in a seated position; and (d) positioning at least part of the leg on the leg support element, wherein the forces are determined at step (ii) by the instrument, and wherein the device remains substantially stationary with respect to the horizontal support during an execution of steps (i) and (ii) in response to a weight of the human exerted at level of the seat.

21. 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 determination method according to claim 1 for determining a muscle fatigue of the muscle identified at step (0); and (v) planning the sports activity on basis of the muscle fatigue determined at step (1).

Description

Description of the Drawings

[0154] 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:

[0155] FIG. 1 illustrates a flow chart of the determination method according to a representative embodiment of the present disclosure;

[0156] FIG. 2 illustrates curves of the (global and/or maximal) force developed by a muscle in response to an electrostimulation at a given frequency as a function of this frequency;

[0157] FIG. 3 illustrates a device of a system for implementing a representative embodiment of the disclosed muscle fatigue determination method;

[0158] FIG. 4 illustrates schematic experimental curves of forces measured in function of time during an execution of the method according to a representative embodiment of the present disclosure.

[0159] 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.

[0160] 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

[0161] 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.

[0162] As shown in FIG. 1, the illustrated muscle fatigue determination method proposes to electro-stimulate a muscle at different frequencies μ.sub.1, μ.sub.2, μ.sub.3, . . . μ.sub.n, for a number of electrostimulations n, for example 2≤n≤50, preferably 2≤n≤5, to determine, 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, and 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. Such a determination can be performed for example by ratio computation of two forces and/or discrete integral computation, and comparison of at least one of these computations to at least one expected value, as fully explained above.

[0163] FIG. 2 illustrates graphs of the (maximal) force developed by the muscle in response to the electrostimulations as a function of the frequency.

[0164] The force is read on the vertical axis 82 (in Newton), and the frequency is read on the horizontal axis 81 (in Hertz). 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 the electrostimulation frequencies. The curve 62 represents a continuous and regular extension of dots cloud corresponding to the points (μ.sub.1, F.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 for low frequencies (e.g. between 10 and 40 Hz), than for 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.

[0165] If it is assumed that the ratio F(20)/F(120) is known to be about 65%, it is then sufficient to measure the forces F.sub.1 and F.sub.2 developed by the muscle in response to electrostimulations at μ.sub.1=20 Hz and μ.sub.2=120 Hz respectively for determining the muscle fatigue, advantageously without the need for knowing a specific human dependent curve for the same muscle but non-fatigued.

[0166] 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.

[0167] 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 60%, or about 70% or about 80% can be convenient depending on the considered function F. Similarly, these 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.

[0168] An advantageous 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. 3. The device is advantageous to implement the muscle fatigue determination method. 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 removable positioning the seat on a horizontal support. The rigidity frame 12 contributes to the rigidity of the seat, 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.

[0169] The device 1 comprises a leg support element 3 fixed to the seat 10 by means of a mechanical frame 2 as illustrated. 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. It integrates an instrument 4 for measuring a force developed by the muscle at level of the leg support element 3, in particular in response to the electrostimulations. The mechanical frame 2 comprises a connecting member 5 to the instrument 4 at level of the leg support element. In particular, in the illustrated configuration of FIG. 3, 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. The strain gauge comprises a connecting extremity 41 for connecting the device 1 with a non represented logical unit of the disclosed determination 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.

[0170] The connecting member 5 also comprises a position adjustment element 51 for changing the position the leg support element 3 and the instrument 4 with respect to the mechanical frame 2, along a second direction d which is perpendicular to the above-mentioned first direction.

[0171] The execution of the method according to representative embodiments of the disclosed subject matter comprising the following steps: [0172] for a given initial electric intensity I.sub.0 comprised between 10 and 50 mA, preferably of (about) 25 mA, [0173] for a given charge step S comprised between 0.1 and 10 mA, preferably of (about) 1 mA, [0174] and successively for each integer k between 0 and K (the so called “number of time”), K being comprised between 5 and 30, preferably of (about) 15: [0175] electrostimulating the muscle at a first frequency μ.sub.1 (preferentially of (about) 20 Hz), with a repetition of N.sub.1 pulses during a period of time T.sub.1 lower than 250 ms, [0176] the pulses having a constant duration and an intensity of I.sub.0+k S; [0177] determining a (maximal) force F.sub.1 developed by the muscle in response to this electrostimulation; [0178] awaiting for a first rest period R.sub.1 comprised between 300 ms and 5 s, preferably of (about) 1 second [0179] electrostimulating the muscle at a second frequency μ.sub.2 (preferentially of (about) 120 Hz), with a repetition of N.sub.2 pulses during a period of time T.sub.2 lower than 250 ms, [0180] the pulses having a constant duration and an intensity of I.sub.0+k S; [0181] determining a (maximal) force F.sub.2 developed by the muscle in response to this last electrostimulation; [0182] 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; [0183] awaiting for a second rest period R.sub.2 comprised between 330 ms and 10 s, preferably of (about) 5 seconds.

[0184] 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 number of pulses allows to reach 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.

[0185] FIG. 4 illustrates a purely schematic curve 63 of (contraction) forces developed of a human lower limb muscle in function of time during part of an execution of the method according a representative embodiment of the present disclosure. In particular, this figure illustrated the electrostimulation effects for an arbitrary k, comprising then a whole execution of step (i). It can easily be derived that the curve repeat similarly itself after the second rest period R.sub.2 for each occurrence of step (i), i.e. for each k. 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. 4.

[0186] The graph of FIG. 4 is distinct from the one of FIG. 2 expressing only the maximal force determined at step (ii) for each frequency. The curve 63 is based on experimental measurements and reproduced in a schematic way. The measured forces (e.g. by a strain gauge) is still read on the vertical axis 82 (in Newton), but the horizontal axis 83 indicates now the time. FIG. 4 is schematic and do not represent explicit experimental data. The axis are not necessarily endowed with a linear scale. In particular, for the present sake of clarity the numbers N.sub.1 and N.sub.2 corresponding to the illustration of FIG. 4 are respectively 3 and 5, and the periods of time T.sub.1, R.sub.1, T.sub.2 and R.sub.2 noted on axis 83 are not proportionally scaled.

[0187] It is visible on FIG. 4 that the muscle is electro-stimulated 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.

[0188] 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.

[0189] 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. 4, and consecutively to determine a muscle fatigue at step (iii). As it is visible on FIG. 4, 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.

[0190] As widely 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. 4 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.

[0191] 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.

[0192] 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.

[0193] 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 250 ms) than the subject cannot react by himself during an electrostimulation.

[0194] 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.

[0195] In other words, the present disclosure relates to a determination method of a muscle fatigue based on information arising from forces developed by the muscle in response to electrostimulations of the latter at different frequencies, the steps of the method being repeated and accompanied with an increase of the electric charge of the electrostimulation.

[0196] The disclosed subject matter has been described 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 the examples 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. The embodiments and advantage of the determination method applies mutatis mutandis to the aforementioned sport activity planning method.