Electrode array for carrying out surface electromyography on a muscle
The electrode grid with oblong electrodes oriented at specific angles addresses the limitations of existing grids by improving spatial resolution and sensitivity for unipennate and bipennate muscles, particularly the rectus femoris, by aligning with muscle fibers and curvature, enhancing detection accuracy.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- UNIV DE TECH DE COMPIEGNE UTC
- Filing Date
- 2024-12-27
- Publication Date
- 2026-07-02
Smart Images
Figure FR2024051778_02072026_PF_FP_ABST
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: ELECTRODE GRID FOR PERFORMING A SURFACE ELECTROMYOGRAM OF A MUSCLE
[0003] Technical field of the invention
[0004] The invention relates to an electrode grid for performing a surface electromyogram of a muscle.
[0005] The invention is particularly interested in the use of such a grid for a unipennate muscle or a bipennate muscle, for example in the latter case, the rectus femoris muscle ("Rectus Femoris")
[0006] Technical background
[0007] Electrode grids for surface electromyography are widely used. They generally come in the form of a flexible sheet incorporating a set of point electrodes which are arranged either in a linear form (1D) or in a matrix form (2D).
[0008] Reference can be made to the article by R. Merletti et al., Tutorial. Surface EMG detection in space and time: Best practices, J. of Electromyography and Kinesiology, 49 (2019) 102363, which gives an overview of the designs (linear or matrix) and problems encountered in the analysis of signals.
[0009] The article by Loubna Imrani et al., High-density Surface Electromyography as Biomaker of Muscle Aging, J. Gerontol. A Biol Sci Med Sci, 2022, vol. XX, n°XX, 1-9, proposes a complete study on the characterization of muscle aging with a grid in the form of a matrix (32 electrodes, 4 columns by 8 rows) to analyze sarcopenia (age-related muscle disease).
[0010] The article by Kohei Watanabe et al., Regional neuromuscular regulation within human rectus femoris muscle during gait in young and elderly men, J. Biomechanics 49 (2016), pp.
[0011] 19-25 proposes to study the behavior of the rectus femoris muscle with a linear grid of bar electrodes extending along the length of the muscle.
[0012] One objective of the invention is to provide an improved electrode array for performing a surface electromyogram of a muscle, particularly a unipennate or bipennate muscle such as the rectus femoris. Summary of the invention
[0013] To solve the aforementioned objective, the invention proposes an electrode grid for performing a surface electromyogram of a muscle, said grid having for this purpose an oblong shape with longitudinal axis, said grid further comprising: - a first column of oblong electrodes parallel to each other, said electrodes thus defining a first longitudinal direction, further oriented with reference to the longitudinal axis of the grid, according to an angle A, taken in a given clockwise direction, such that 20° < A < 60 or 100° < A < 150;
[0014] - a second column of parallel oblong electrodes, said electrodes thus defining a longitudinal direction, which is also oriented with reference to the longitudinal axis of the grid, according to an angle A, taken in an opposite clockwise direction, such that 20° < A < 60°.
[0015] The process according to the invention may include at least one of the following additional steps, taken alone or in combination:
[0016] each electrode has a length of at least 10mm;
[0017] Each electrode has a length between 15 and 20mm; each electrode has a width between 2 and 5mm;
[0018] two successive electrodes of the same column of electrodes are separated by an inter-electrode distance of between 5 and 15mm;
[0019] Each column of electrodes contains between 12 and 20 electrodes;
[0020] the two columns of electrodes are separated by a distance of between 5 and 15mm;
[0021] said grid having a length between 140 and 180mm and a width between 40 and 60mm;
[0022] the electrodes are all identical;
[0023] The electrodes of at least one of the two electrode columns are curved. The invention also provides for various uses of the electrode grid.
[0024] Thus, the invention provides for the use on a unipennate muscle of an electrode grid according to the invention in which the electrodes of the second column of electrodes are oriented in the same direction as the electrodes of the first column of electrodes.
[0025] The unipennate muscle can notably be a "Vastus Lateralis" muscle (vastus lateral muscle).
[0026] The use of an electrode grid according to the invention is also envisaged on a bipennate muscle, wherein the electrodes of the first column of electrodes are oriented with reference to the longitudinal axis of the grid, at an angle A, taken in a given clockwise direction, such that 40° < A < 50° and the electrodes of the second column of electrodes are oriented with reference to the longitudinal axis of the grid, at an angle A, taken in said other opposite clockwise direction, such that 40° < A < 50°.
[0027] For this use on a bipennate muscle, it can be predicted more precisely that the electrodes of the second column of electrodes are arranged symmetrically, according to a symmetry of longitudinal axis of the grid, with respect to the electrodes of the first column of electrodes.
[0028] The bipennate muscle can notably be a "Rectus Femoris" muscle (rectus femoris muscle).
[0029] Finally, it is possible to foresee use on a bipennate muscle with curved muscle fibers of the grid according to the invention in which the electrodes of the first column of electrodes are oriented with reference to the longitudinal axis of the grid, at an angle A, taken in a given clockwise direction, such that 100° < A < 150 and the electrodes of the second column of electrodes are oriented with reference to the longitudinal axis of the grid, at an angle A', taken in said other opposite clockwise direction, such that 20° < A' < 60°.
[0030] The bipennate muscle with curved muscle fibers can notably be an "Extensor Digitorum" muscle (extensor muscle of the toes).
[0031] Brief description of the figures
[0032] Other objects and features of the invention will become clearer in the following description, made with reference to the accompanying figures, in which:
[0033] Figure 1 is a diagram of an electrode grid according to the invention adapted for a unipennate muscle, in this case without pennation curvature;
[0034] Figure 2 is a diagram of an electrode grid according to the invention adapted for a bipennate muscle;
[0035] Figure 3 is a diagram of an electrode grid according to the invention adapted for a bipennate muscle with a pennation curvature;
[0036] Figure 4 represents signals recorded by an electrode array according to Figure 2 on a bipennate muscle, in this case a rectus femoris muscle;
[0037] Figure 5 represents comparative test results of the grid according to the invention of Figure 2 and prior art grids on a bipennate muscle, in this case a rectus femoris muscle, obtained from signals of the type illustrated in Figure 4, for a person;
[0038] Figure 6 shows results of tests similar to those in Figure 5, for another person.
[0039] Detailed description of the invention
[0040] The invention relates to a grid G of electrodes for performing a surface electromyogram of a muscle, said grid having for this purpose an oblong shape with longitudinal axis XX'.
[0041] Grid G comprises a first column PCE of parallel oblong electrodes, said electrodes ELC1 thus defining a first longitudinal direction DL1, oriented with respect to the longitudinal axis XX' of the grid, at an angle A, taken in a given clockwise direction. Furthermore, grid G comprises a second column of parallel oblong electrodes DCE, said electrodes ELC2 thus defining a second longitudinal direction DL2, oriented with respect to the longitudinal axis XX' of grid G, at an angle A' defined in the opposite clockwise direction to that of angle A.
[0042] The characteristics described above are common to all embodiments.
[0043] In contrast, according to a first embodiment (Figure 1), grid G includes a second DCE column of ELC2 electrodes defining a second longitudinal direction DL2, which is identical to the first longitudinal direction DL1. This allows for improved spatial analysis based on pennation. The DL1, DL2 direction is then defined with an angle A such that 100° < A < 150°, preferably such that 120° < A < 145°, and even more preferably such that 130° < A < 140°. The orientation angle is adapted to the muscle's pennation.
[0044] According to a second embodiment (Figure 2), grid G comprises a second DCE column of ELC2 electrodes defining a second longitudinal direction DL2 which is oriented with reference to the longitudinal axis XX' of the grid, at an angle A', taken in a clockwise direction opposite to that used to define angle A, such that 20° < A < 60°, preferably such that 25° < A < 55°, and even more preferably such that 40° < A' < 50°. The orientation angle will be adapted to the pennation of the muscle being analyzed. For example, and without limitation, particularly in the case of the "Rectus femoris", angle A is such that 40° < A < 50° and angle A' is also such that 40° < A' < 50°. In particular, still according to this second embodiment, the ELC2 electrodes of the second column of DCE electrodes can be arranged symmetrically, according to a symmetry of longitudinal axis XX' of the grid, with respect to the ELC1 electrodes of the first column of PCE electrodes.This means that the absolute values of angles A and A' are equal. This arrangement then allows for the consideration of two muscle regions with pennation symmetry.
[0045] Finally, Figure 3 depicts a third embodiment, designed to better adapt to the anatomy of a muscle, specifically a curved unipennate muscle. In this case, the electrodes of at least one of the two columns of PCE and DCE electrodes are curved along an arc compatible with the curvature observed in the muscle anatomies studied, for example, the extensor digitorum muscle. In the illustration in Figure 3, the ELC1 electrodes of the first column of PCE electrodes are slightly curved, and the ELCS electrodes of the second column are more curved. Thus, the electrodes precisely follow the curvatures of the muscle and accurately represent its health status.The DL1 direction is then defined with an angle A (measured between the ends of the electrode, with the electrode curved; always defined in a given clockwise direction) such that 100° < A < 150°, preferably such that 100° < A < 130°, and even more preferably, such that 100° < A < 120°. The orientation angle is adapted to the pennation of the muscle. The DL2 direction is then defined with an angle A' (measured between the ends of the electrode, with the electrode curved; always defined in the opposite clockwise direction) such that 20° < A < 60°, preferably such that 25° < A < 55°, and even more preferably, such that 40° < A < 50°. Within the framework of the invention, a grid is therefore proposed for analyzing by surface electromyography (sEMG), the muscle which is not presented in the form of a matrix (2D) of point electrodes nor, moreover, in the form of a line (1D) of point electrodes or in bars perpendicular to the line of pennation of the muscle.
[0046] Indeed, the electrode array according to the invention is particularly well-suited to unipennate or bipennate muscle (where the muscle fibers are oriented at an angle to the muscle alignment) to optimize surface electromyography analysis in several ways. Firstly, it provides two separate columns of PCE and DCE electrodes, which, for unipennate muscle, allow for improved spatial resolution with two columns of electrodes aligned with the muscle fibers (Figure 1, for example), or which, for bipennate muscle, are each adapted to a specific part of the bipennate muscle to analyze each muscle compartment according to the alignment of the muscle fibers (Figure 2, for example, and also Figure 3).Secondly, each ECL1, ECL2 electrode is oblong (and therefore not a point) and forms a non-zero angle with the longitudinal direction XX' of the grid G. This allows the electrode to extend according to the pennation angle of the muscle fibers and over a certain length of muscle fiber. This is the case whether the grid is intended for use with a unipennate muscle or a bipennate muscle.
[0047] More specifically, each ELC1, ELC2 (oblong) electrode can have a length L of at least 10 mm, and in particular between 15 and 20 mm. Furthermore, each ELC1, ELC2 electrode can have a width I between 2 and 5 mm (within the range of currently marketed grids). Thus, an electrode can have an aspect ratio, defined as the ratio of length to width, between 3 and 10.
[0048] Furthermore, two successive electrodes ELC1, ELC2 of the same PCE, DCE column of electrodes can be separated by an inter-electrode distance DIE of between 5 and 15 mm. This allows for maintaining good spatial resolution for analysis.
[0049] Advantageously, the ELC1 and ELC2 electrodes are all identical.
[0050] The two columns of PCE and DCE electrodes can be separated by a distance D between 5 and 15 mm. This allows for good spatial resolution of analysis.
[0051] Grid G may be rectangular or nearly rectangular. The length LG can then be between 120 and 200 mm, preferably between 130 and 190 mm, and even more preferably between 140 and 180 mm. As a non-limiting example, the grid length LG for the Rectus Femoris muscle will be between 140 and 180 mm. The width IG will be between 40 and 80 mm. As a non-limiting example, the grid width IG for the Rectus Femoris muscle will then be between 40 and 60 mm. These dimensions are compatible with the anatomy of the Rectus Femoris muscle for the bipennate configuration, but also with the anatomy of the Vastus Lateralis muscle for the unipennate configuration.
[0052] Such dimensions of the grid G typically allow, given the previously provided geometric characteristics of each electrode, for each column of electrodes PCE, DCE to contain between 12 and 20 electrodes. It is also possible to reduce the length of each electrode and the inter-electrode distance DIE to introduce a third column of electrodes for the unipennate configuration (not shown) or a fourth column of electrodes for the bipennate configuration (not shown) in order to maintain symmetry in the analysis.
[0053] In these particular embodiments, the length of each electrode can be adapted to add the aforementioned third and fourth columns of oblong electrodes, parallel to each other, thereby improving the spatial resolution of the grid. In this case, the characteristics of the third and fourth columns can be the same as those of the first and second columns and oriented in the same way as ECL1 or ECL2.
[0054] Each electrode ECL1, ECL2 is connected to the same analog-to-digital converter board (shown only in Figure 2) for the signals acquired during a surface electromyogram (sEMG). This board and the connection to the electrodes are standard and are therefore not described in further detail.
[0055] The details provided above are applicable to all embodiments. However, a particular embodiment of an electrode array according to the second embodiment of the invention (application to a bipennate muscle) may be such as (Figure 2):
[0056] - On the grid: LG = 159mm, IG = 52mm
[0057] - Per electrode column: 16 electrodes,
[0058] - Between the two electrode columns: D = 10mm,
[0059] - For one electrode (all identical): L = 18mm, I = 4mm, A = A' = 45° (without taking into account the sign) and DIE = 10mm.
[0060] Furthermore, another particular embodiment of an electrode grid according to the third embodiment of the invention (application to a bipennate muscle with curved muscle fiber lines) could be such as (figure 3):
[0061] - On the grid: LG = approximately 160mm, IG = approximately 50mm
[0062] - Per electrode column: 16 electrodes,
[0063] - Between the two electrode columns: D = 10mm,
[0064] - For an electrode in the first PCE column: L = 17mm, I = 4mm and angle A = approximately 100 (defined from the ends of an electrode, since it is curved - without taking into account the sign),
[0065] - For an electrode in the second DCE column: L = 17mm, I = 4mm and angle A = 45° (defined from the ends of an electrode, since it is curved - without taking into account the sign).
[0066] Grid G of the exemplary embodiment according to the second embodiment of the invention (32 electrodes) was tested in comparison to two reference grids (known in the prior art: GRefi, GRera), specifically on a bipennate muscle such as the "Rectus Femoris" muscle. The first reference grid, Gpefi, is in the form of an 8x4 matrix of point electrodes. The second reference grid, GRefi, is also shown. e f2 is presented in the form of an 8x8 matrix of point electrodes, of which only the signals from an 8x4 sub-matrix are exploited.
[0067] For all grids, we therefore use the information provided by the 32 electrodes. We asked two healthy people to remain at rest for 30 seconds, then to perform three trials of "sit-stand" tasks with 5 seconds of rest between each task.
[0068] The signals from the different grids are shown in Figure 4. The first column relates to the grid according to the invention, the second column to the GRefi grid (prior art), and the third column to the GR grid. e f2 (previous art). Furthermore, the first line provides the raw signals, the second line the muscle contractions, and the third line the filtered version of the contractions in the 10 to 450Hz band. It is these latter signals that are then used to perform the muscle analysis of the person.
[0069] From these signals, for each contraction, for each person and for each grid, we calculate the root mean square value of the signal measured for each electrode (RMS for "Root Mean Square" according to Anglo-Saxon terminology) on the 32 electrodes.
[0070] Next, for each person and each grid, an average matrix of RMS values (a type of color map, more commonly known as a "heatmap" in English) is calculated across the three "sit-stand" task trials. These maps allow visualization of the spatial activation of the muscle being studied.
[0071] It is observed that the signal obtained by the grid according to the invention has similarities with the signal obtained with the GRefi grids, while exhibiting specificities related to the importance of the alignment of the electrode with the muscle fibers.
[0072] The results obtained for the first person are shown in Figure 5, with the grid according to the invention on the left, the GRefi grid in the middle, and the GR grid on the right. e f2.
[0073] For all three grids, it is noted that the highest values on the root mean square value are detected in approximately the same areas, see boxes E1, E2 and E3 (medial proximal zone).
[0074] However, the intensity of these values is greater and more homogeneous across several lines of the map for the grid according to the invention than for the GRefi and GR grids. e f2, the latter being less sensitive than the other two.
[0075] Furthermore, due to its geometry, only the grid according to the invention is capable of detecting activity further from the medial zone, specifically at the lateral level of the Rectus Femoris muscle (see box E4). The results obtained for the second person are shown in Figure 6, with the grid according to the invention on the left, the GRefi grid in the middle, and the GR grid on the right. e f2.
[0076] For this individual, the grid conforming to the invention is found to be significantly more sensitive than the other two, particularly in the proximal medial areas (the same boxes as those in Figure 4 can be used). A much less pronounced lateralization is also observed for the anterior art grids. It is reasonable to assume that the placement of oblong electrodes conforming to the pennation angle of the muscle fibers has a positive effect on the grid's sensitivity, allowing it to detect greater electrical activity.
[0077] Furthermore, the grid according to the invention allows for the detection of significant muscle activity in the medial distal zone, less pronounced than in the proximal zone (see box E5). The proximal zone corresponds to the lower part of the figures, and the distal zone to the upper part. Grids of the anterior art cannot, of course, achieve this level of detection due to their limited length (half the size).
[0078] For the two individuals tested, it was also noted that the grid according to the invention allows for the definition of two homogeneous data columns (similar colors) in the maps, each corresponding to a specific part of the muscle. The results obtained highlight a certain independence between these two parts, related to a muscle activation strategy specific to the chair lift, which is difficult or even impossible to identify with reference grids (prior art) that provide greater heterogeneity in the maps (color variations).
Claims
DEMANDS 1. Electrode grid (G) for performing a surface electromyogram of a muscle, said grid having for this purpose an oblong shape with longitudinal axis (XX'), said grid (G) further comprising: a first column (PCE) of parallel oblong electrodes, said electrodes (ELC1) thus defining a first longitudinal direction (DL1), which is also oriented with reference to the longitudinal axis (XX') of the grid, at an angle A, taken in a given clockwise direction, such that 20° < A < 60 or 100° < A < 150; a second column (DCE) of parallel oblong electrodes, said electrodes (ELC2) thus defining a longitudinal direction (DL2), which is also oriented with reference to the longitudinal axis (XX') of the grid, at an angle A', taken in the opposite clockwise direction, such that 20° < A' < 60°.
2. Grid (G) of electrodes for performing a surface electromyogram of a muscle according to claim 1, wherein each electrode (ELC1, ELC2) has a length (L) of at least 10mm.
3. Grid (G) of electrodes for performing a surface electromyogram of a muscle according to any one of the preceding claims, wherein each electrode (ELC1, ELC2) has a length (L) between 15 and 20mm.
4. Grid (G) of electrodes for performing a surface electromyogram of a muscle according to any one of the preceding claims, wherein each electrode (ELC1, ELC2) has a width (I) between 2 and 5mm.
5. Grid (G) of electrodes for performing a surface electromyogram of a muscle according to any one of the preceding claims, wherein two successive electrodes of the same column of electrodes (PCE, DCE) are separated by an inter-electrode distance (DIE) of between 5 and 15mm.
6. Electrode grid (G) for performing a surface electromyogram of a muscle according to any one of the preceding claims, wherein each column of electrodes (PCE, DCE) comprises between 12 and 20 electrodes.
7. Electrode grid (G) for performing a surface electromyogram of a muscle according to any one of the preceding claims, wherein the two columns of electrodes (PCE, DCE) are separated by a distance D of between 5 and 15 mm.
8. Grid (G) of electrodes for performing a surface electromyogram of a muscle according to any one of the preceding claims, said grid (G) having a length (LG) between 140 and 180mm and a width (IG) between 40 and 60mm.
9. Grid (G) of electrodes for performing a surface electromyogram of a muscle according to any one of the preceding claims, wherein the electrodes (ELC1, ELC2) are all identical.
10. Grid (G) of electrodes for performing a surface electromyogram of a muscle according to any one of claims 1 to 8, wherein the electrodes (ELC1, ELC2) of at least one of the two electrode columns (PCE, DCE) are curved.
11. Use on a unipennate muscle of an electrode grid (G) according to any one of the preceding claims wherein the electrodes (ELC2) of the second electrode column (DCE) are oriented in the same direction (DL1, DL2) as the electrodes (ELC1) of the first electrode column (PCE).
12. Use on a bipennate muscle of an electrode grid (G) according to any one of claims 1 to 10, wherein: - the electrodes (ELC1) of the first column of electrodes (PCE) are oriented with reference to the longitudinal axis (XX') of the grid, according to an angle A, taken in a given clockwise direction, such that 40° < A < 50; - the electrodes (ELC2) of the second column of electrodes (DCE) are oriented with reference to the longitudinal axis (XX') of the grid, at an angle A', taken in said opposite clockwise direction, such that 40° < A < 50°.
13. Use according to the preceding claim, wherein the electrodes (ELC2) of the second electrode column (DCE) are arranged symmetrically, according to a longitudinal axis symmetry (XX') of the grid, with respect to the electrodes (ELC1) of the first electrode column (PCE).
14. Use according to any one of claims 12 or 13, wherein the bipennate muscle is a "Rectus Femoris" muscle.
15. Use on a bipennate muscle with curved muscle fibers of an electrode grid (G) according to any one of claims 1 to 10, wherein: - the electrodes (ELC1) of the first column of electrodes (PCE) are oriented with reference to the longitudinal axis (XX') of the grid, according to an angle A, taken in a given clockwise direction, such that 100° < A < 150; - the electrodes (ELC2) of the second column of electrodes (DCE) are oriented with reference to the longitudinal axis (XX') of the grid, according to an angle A, taken in said other opposite clockwise direction, such that 20° < A < 60°.