WO2004049934A1

WO2004049934A1 - Method and arrangement for measuring electromuscular activity

Info

Publication number: WO2004049934A1
Application number: PCT/FI2003/000910
Authority: WO
Inventors: Teuvo Sihvonen
Original assignee: Inmeser Oy; Kuopion Yliopistollinen Sairaala
Priority date: 2002-11-29
Filing date: 2003-11-27
Publication date: 2004-06-17
Also published as: FI112845B; FI20022111A0; AU2003283463A8; AU2003283463A1

Abstract

The invention relates to a method and arrangement for measuring electromuscular activity, the arrangement comprising means (20) for detecting an EMG signal produced by a muscle from the surface of a body. The detecting means are operatively connected to data processing means (40) included in the arrangement. According to the invention, the data processing means (40) are configured to carry out a compensation for tissue influence, wherein an EMG signal value detected from the surface of the body is, by changing the EMG signal value detected from the surfaec of the body on the basis of known dependence information between the tissue information and the EMG signal available to the arrangement, corrected in order to find out a corrected EMG signal value and to eliminate individual variation due to subcuatneous tissue on the basis of tissue information about the subcutaneous tissue fed to the measurement arrangement, thus enabling measurement results of different persons to be compared.

Description

METHOD AND ARRANGEMENT FOR MEASURING ELECTROMUSCULAR ACTIVITY

FIELD

[0001] The invention relates to a method for measuring electromus- cular activity.

[0002] The invention further relates to an arrangement for measuring electromuscular activity, the arrangement comprising means for detecting an EMG signal produced by a muscle from the surface of a body, and the detecting means being operatively connected to data processing means included in the arrangement.

BACKGROUND

[0003] Prior art methods and arrangements for measuring electro- muscular activity consist either of needle EMG, fine-wire EMG or surface EMG. Measurements carried out using the needle EMG or fine-wire EMG include measuring electromuscular activity by means of a sensor wire or a sensor needle to be injected into a muscle through the skin, while an easier version, as far as the target to be measured is concerned, would be a measurement called a surface EMG, wherein electrodes are used for measuring electromuscular activity from the surface of the skin. However, a measurement result obtained by the known surface EMG measurement is imprecise since it does not take into account factors due to the human body that distort the measurement result.

BRIEF DESCRIPTION

[0004] An object of the invention is to implement a method and an arrangement implementing the method so as to achieve a method and an arrangement which, as compared with previous implementations, are less problematic and more suitable for examination and treatment practices.

[0005] This object is achieved by a method which is characterized by the method comprising detecting an EMG signal produced by a muscle from the surface of a body by using a measurement arrangement, and carrying out a compensation for tissue influence, wherein an EMG signal value detected from the surface of the body is, by changing the EMG signal value detected from the surface of the body on the basis of known dependence information between the tissue information and the EMG signal, corrected in order to find out a corrected EMG signal value and to eliminate individual variation due to subcutaneous tissue on the basis of tissue information about the subcutaneous tissue fed to the measurement arrangement.

[0006] The arrangement of the invention is characterized in that the data processing means are configured to carry out a compensation for tissue influence, wherein an EMG signal value detected from the surface of the body is, by changing the EMG signal value detected from the surface of the body on the basis of known dependence information between the tissue information and the EMG signal available to the arrangement, corrected in order to find out a corrected EMG signal value and to eliminate individual variation due to subcutaneous tissue on the basis of tissue information about the subcutaneous tissue fed to the measurement arrangement.

[0007] Preferred embodiments of the invention are disclosed in the dependent claims.

[0008] The invention is based on the idea that information about subcutaneous tissue in the human body, e.g. the tissue thickness thereof, is produced, and this measurement information is either directly or indirectly transferred to the data processing means of the measurement arrangement to be used and utilized therein, enabling, on the basis of the measurement information and, on the other hand, known dependence information between the tissue information about subcutaneous tissue and the EMG measurement, a compensation for tissue influence to be carried out to remove a factor distorting the surface EMG measurement, caused by the subcutaneous fat tissue in the human body, and thus further enabling the measurement results of different persons to be compared. The method is not a diagnostic one, but a way to obtain auxiliary information which is independent of the properties of subcutaneous tissue and comparable between different individuals, and to be utilized by professionals, such as sports coaches, physiotherapists and doctors. The tissue information about subcutaneous tissue is measured from the measurement area of a muscular signal.

[0009] Several advantages are achieved by the method and system of the invention. The most important advantage is that the comparability between individuals, accuracy and reliability of the surface EMG measurement are improved considerably while, nevertheless, using comfortable and easy-to- use equipment as far as both the subject to be measured and those using the arrangement are concerned. LIST OF DRAWINGS

[0010] The invention is now described in connection with the preferred embodiments and with reference to the accompanying drawings, in which

[0011] Figure 1 shows an arrangement implementing a method of the invention,

[0012] Figure 2 shows the thickness of a fold of skin being measured,

[0013] Figure 3 is a graph showing the dependence between tissue thickness and EMG measurement,

[0014] Figure 4 shows EMG signals, thus illustrating an intensity difference between a needle EMG measurement and a surface EMG measurement caused by the thickness of subcutaneous tissue.

DESCRIPTION OF EMBODIMENTS

[0015] Referring to the accompanying drawings, the invention relates to measuring electromuscular activity of muscles, particularly muscles associated with joints. In a preferred embodiment, the target area is the back, but other target areas are also possible. The target to be measured is indicated by reference number 1 , and the measurement arrangement is indicated by reference number 2. A muscle residing in the target area, e.g. in the back, of a person 1 being measured is indicated by reference number 1a. The measurement arrangement is divided in to two main parts: measuring means 20 and data processing means 40 processing the data of the measuring means, the data processing means 40 being a computer, such as a conventional microcomputer, in the example of Figure 1. The measuring means 20 comprise a sensor structure 21-22 measuring an EMG signal from the surface of the skin, and a signal processing block 23 connected to the sensor structure and comprising e.g. an amplifier 23a and an A/D converter 23b. The signal processing block 23, in practice the output of the signal processing block, i.e. the output of the A/D converter 23b, is connected to the data processing unit 40 e.g. via a cable 25. The sensor structure, i.e. electrodes 21-22, is connected to the signal processing block 23 via a cable 200, 200a, 200b. The measuring means 20 further comprise a measuring device 50 for measuring a fold of skin, i.e. the thickness of subcutaneous tissue. The measuring device 50 for measuring a fold of skin is also, wiredly 27 or wirelessly, connected to the data processing unit 40. An implementation is also feasible wherein a separate measuring device 60 shown in Figure 2 is used, and those who use the arrangement detect the value of tissue thickness given by the measuring device 60, the value then being fed to the data processing unit by means of a user interface 70, e.g. a keyboard. The arrangement also comprises a display 300.

[0016] In a preferred embodiment, the measuring means comprise a movement sensor 80 for measuring a movement of a target, the movement sensor also being connected to the data processing unit 40, i.e. the data processing means. The movement sensor 80 is connected to the data processing means e.g. by a cable 28. The task of the movement sensor is to measure a movement of the skeleton or joints and thus reveal mobility caused by muscular activity.

[0017] As far as the method is concerned, the invention relates to a method for measuring electromuscular activity. The idea of the method is to detect an EMG signal produced by a muscle from the surface of the body by using a measurement arrangement. A surface EMG measurement is carried out while a muscle is in action. A compensation for tissue influence is also carried out, wherein an EMG signal value detected from the surface of the body is, by changing the EMG signal value detected from the surface of the body on the basis of known dependence information between the tissue information and the EMG signal, corrected in order to find out a corrected EMG signal value and to eliminate individual variation due to subcutaneous tissue on the basis of tissue information about the subcutaneous tissue fed to the measurement arrangement.

[0018] The corrected value as accurately as possible corresponds to the value that would have been obtained by needle EMG or fine wire EMG or another (IM or IntraMuscular) method measuring from a muscle, whereby values measured from different individuals are rendered comparable.

[0019] In a preferred embodiment of the invention, the method is such that the tissue information to be fed to the measurement arrangement in the compensation for tissue influence consists of the thickness of subcutaneous tissue, e.g. in millimetres, i.e. the distance between a measuring electrode and the muscle being examined. The thickness of subcutaneous tissue is measured from the measurement area of a muscle signal.

[0020] The tissue information may consist of information indicated by units of thickness (e.g. mm), or other information describing subcutaneous tissue whose value is directly or indirectly associated with the properties of a fold of skin.

[0021] Referring to Figure 2, in a preferred embodiment of the invention, the method includes measuring tissue information by a separate meter 60, and the measurement result shown by the meter being fed to the measurement arrangement via a user interface 70. Technically, this implementation is simpler.

[0022] Referring to Figure 1 , in a preferred embodiment of the invention the method includes measuring tissue information by a measuring sensor 50 connected to the measurement arrangement in order to render the measurement result directly available to the measurement arrangement. This implementation is more automated and therefore easier to use.

[0023] Referring to Figure 3, in a preferred embodiment of the invention the method is such that the known dependence information between the tissue information and EMG measurement to be utilized in the method consists of dependence information formed from dependence measurements performed on a large number of people and stored to be available to the measurement arrangement.

[0024] The dependence information shown in Figure 3 has been achieved by performing a fine wire EMG measurement and, simultaneously, a surface EMG measurement on the back muscle of about 50 healthy people, and also by producing information about subcutaneous tissue, such as the thickness thereof. On the basis of the measurement results, the shape of a dependence curve, i.e. its mathematical function, has been found out utilizing statistical methods. One possibility to find out the dependency, i.e. a dependency indicator, is to adapt the dependency indicator to the measurement results, i.e. a curve adaptation method could be used. In Figure 3, the unit on the Y-axis is percent and it refers to the ratio of a surface EMG measurement amplitude to a needle EMG measurement amplitude, i.e. a ratio EMG-S (Sur- face)/EMG-IM (Intramuscular). The unit on the X-axis is the thickness of subcutaneous tissue (subcutis) in millimetres. It can be seen that when, for example, the tissue thickness is 20 mm, dependence indicator R gives 30% as the result, i.e. 0.30. It can be seen in Figure 3 that the dependence indicator is an exponential regression curve. According to the observations made by the applicant, the reading given by the Y-axis resides between 12% and 75%, i.e. between 0.12 and 0.75, when a fold of skin varies between 5 and 35 mm. [0025] Still referring to Figure 3, it is stated that the indicator drawn via coordination points according to the ratios EMG-S (Surface)/EMG-IM and the related thickness values of subcutaneous tissue is represented by indicator OB (Observed) while the exponential indicator adapted to the points of the observation material is designated by R.

[0026] The dependency of the type shown in Figure 3 or similar thereto is stored to be available to the measurement arrangement, most preferably in the measurement arrangement, e.g. in a memory 150 in a device according to the block diagram shown in Figure 1. In practice, the information shown in Figure 3, i.e. the information given by the Y-axis, operates as a divisor operator for the EMG measurement result in the data processing unit 40, i.e. the calculating unit 40. In other words, if the tissue thickness sc is measured to be e.g. 20 mm, the data processing unit 40, i.e. the calculating unit 40, divides the measured surface EMG amplitude value by 0.30 (i.e. 30%), which gives as a final result an EMG value which as accurately as possible corresponds to the value that would have been obtained by a needle EMG measurement or another measurement of the IM (Intramuscular) type. The data processing unit 40 is implemented by a processor, for instance.

[0027] Figure 4 shows EMG signals, thus illustrating the difference caused by tissue thickness between the amplitude value of a needle EMG measurement and a surface EMG measurement. The upper pair of patterns in Figure 4 shows EMG signals obtained by a needle EMG measurement on two persons P1 and P2, whose subcutaneous tissue thicknesses differ from each other. The lower pair of patterns in Figure 4, in turn, shows EMG signals obtained by a surface EMG measurement on two persons P1 and P2, whose subcutaneous tissue thicknesses thus differ from each other. A comparison between the upper and lower patterns reveals the damping effect of tissue thickness. Further, a comparison between the lower patterns reveals that the effect of tissue thickness on the value of the surface EMG signal is considerably more radical in connection with person P2 whose tissue thickness is larger than in connection with person P1 whose tissue thickness is smaller.

[0028] When the subject being measured is asked to activate muscles in the target area, such as to bend or straighten his or her back, according to arrow BE in Figure 2, the result is an EMG signal produced by the muscles in the back, the signal thus being measured as a surface EMG measurement and the measurement result being a signal of the type in the lower pair of pat- terns shown in Figure 4. When the compensation for tissue thickness is carried out according to the invention, a corrected EMG signal, which is of a similar type to that of the signals of the upper pair of patterns in Figure 4, can now be calculated starting from the surface EMG measurement. The result of the tissue-thickness-compensated surface EMG measurement may be shown on a display 300 of the measurement arrangement, the result, in terms of its level, i.e. amplitude, thus substantially corresponding to the result that would have been obtained by using a needle EMG measurement or another measurement of the IM (Intramuscular) type. If desired, the actual surface EMG measurements may also be shown on the display 300.

[0029] The invention may be applied e.g. in a connection similar to that disclosed in US Patent 5,755,675 of the applicant, i.e. in a preferred embodiment the user application includes measuring, simultaneously with the EMG measurement, movement measurements in the target area by means of movement sensors attached to the skin, such as 80, the results of the movement sensors being combined in order to find out the movements taking place within the area, and compared with reference values collected beforehand. In addition, the particular user interface includes estimating the extent to which the mobility and muscle function within the particular area are inhibited as a result of pain in particular. Furthermore, the particular user application includes a method step for determining the extent of fatigue of muscles on the basis of changes in the frequency contents of an electromuscular signal. Other applications are also feasible.

[0030] Although the invention has been described with reference to the example in accordance with the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in many ways within the inventive idea disclosed in the attached claims.

Claims

1. A method for measuring electromuscular activity, characterized by the method comprising: detecting an EMG signal produced by a muscle from the surface of a body by using a measurement arrangement, and carrying out a compensation for tissue influence, wherein an EMG signal value detected from the surface of the body is, by changing the EMG signal value detected from the surface of the body on the basis of known dependence information between the tissue information and the EMG signal, corrected in order to find out a corrected EMG signal value and to eliminate individual variation due to subcutaneous tissue on the basis of tissue information about the subcutaneous tissue fed to the measurement arrangement.

2. A method as claimed in claim 1, characterized in that the tissue information to be fed to the measurement arrangement in the compensation for tissue influence consists of information indicated by a unit of thickness (mm), or other information describing subcutaneous tissue.

3. A method as claimed in claim 1, characterized in that the tissue information is measured by a separate meter, and a measurement result shown by the meter is fed to the measurement arrangement via a user interface.

4. A method as claimed in claim 1, characterized in that the tissue information is measured by a measuring sensor included in the measurement arrangement in order to render the measurement result directly available to the measurement arrangement.

5. A method as claimed in claim ^characterized in that the known dependence information between the tissue information and the EMG signal to be utilized in the method consists of dependence information formed by dependence measurements performed on a sufficient number of healthy people, and it is stored to be available to the measurement arrangement.

6. An arrangement for measuring electromuscular activity, the arrangement comprising means (20) for detecting an EMG signal produced by a muscle from the surface of a body, and the detecting means being operatively connected to data processing means (40) included in the arrangement, characterized in that the data processing means (40) are configured to carry out a compensation for tissue influence, wherein an EMG signal value detected from the surface of the body is, by changing the EMG signal value detected from the surface of the body on the basis of known dependence information between the tissue information and the EMG signal available to the arrangement, corrected in order to find out a corrected EMG signal value and to eliminate individual variation due to subcutaneous tissue on the basis of tissue information about the subcutaneous tissue fed to the measurement arrangement.

7. An arrangement as claimed in claim 6, characterized in that the arrangement comprises a user interface (70) for feeding tissue information measured by a separate meter (60) to the measurement arrangement.

8. An arrangement as claimed in claim 7, characterized in that the user interface (70) is a keyboard.

9. An arrangement as claimed in claim 7, characterized in that the arrangement comprises a measuring sensor (50) measuring tissue information on subcutaneous tissue in order to render a tissue information measurement result directly available to the arrangement.

10. An arrangement as claimed in claim 6, characterized in that the arrangement comprises a memory (150) wherein the known dependence information between the tissue information about subcutaneous tissue and the EMG signal is stored.