A METHOD AND AN APPARATUS IN ELECTROMYOGRAPHY

Abstract: The invention relates to a method and an apparatus for detecting muscular status. The apparatus includes electrode means (7) for acquiring analog myoelectric signals, an amplifier (1) which is followed by an A/D converter to which is connected a signal processing unit (3). A signal means (4) is connected to the signal processing unit. The analog signals acquired by the electrode means (7) are converted, after amplification, into binary signals which are frequency-analysed in the signal processing unit (3). This calculates the appearance and/or position of a frequency spectrum in relation to a predetermined initial position on commencement of the detection. Signals relating to the shift of the frequency spectrum in relation to its initial position are emitted from the signal means (4) or stored in a storage device.

Description: A method and an apparatus in electromyography The present invention relates to a method and an apparatus for collection, analysis and presentation of lηyoelectric signals (E G-s gnals) in accordance with the preamble of the independent claims. In many contexts, there is a manifest interest in establishing muscular status, by which is taken to mean both the status of muscle at rest and the status of muscle at work. It is of particular interest to be able to follow the change in the status of the muscle during work and, in such instance, preferably to obtain a continuous and/or immediate information on status with the possibility of registering this for subsequent follow-up. Such establishment of muscular status is, of course, interesting in purely scientific contexts and in the event of illnesses, but is also of considerable value in many practical appl cations, for example of people carrying out industrial assembly work or certain types of office work (e.g. terminal work at computers). By establishing muscular status, the possibility will be created, for example, for studying the effect of the design and layout of the workplace and the working position, respectively, on muscle loading, and to analyse the consequences of prolonged monotonous muscle loading. This latter working situation occurs in both the assembly industry and in office work. A correct establishment of muscular status in lengthy loading would make it possible, at best, to wholly avoid the risk of chronic muscular disorder or could be used to identify those stages of labour, which, for a given individual, cause, for instance chronic pain. The information would make it possible to modify the design of tools or the workplace in order to avoid such problems or injuries occurring. In particular, real time knowledge of the state of fatigue of the muscles could be essential in evaluating the effect of the work involved on the muscles. It is obvious that there is also a need in this art for a technique for continuous registration of muscular status. Such a technique would, thus, make it possible to establish how muscular fatigue changes during a work shift or a series of work shifts, at the same time as such registration would make it possible to objectively analyse and identify how changes in the design of the workplace, for example the design of auxiliary aids, tools etc influence the degree of muscular fatigue and its development in prolonged work. It should be observed that, at low muscular loading which is continuous for a lengthy time, the individual himself does not observe that the muscle becomes fatigued. There are firm grounds for assuming that, when such situations exist^ there is a risk of chronic muscular injury. Wishes have also been voiced for a technique which permits direct feedback to the individual of information concerning current muscular condition in order thereby to gain the possibility of warning, while work is in progress, for muscle loadings and stresses which risk resulting in injury. The present invention satisfies the above needs and wishes. This is attained by means of a method and an apparatus according to the characterizing clauses of the independent claims. According to the present invention, use is made of the circumstances, that, in increasing muscular fatigue, the frequency spectrum of the EMG signal is shifted, the amplitude of the high frequencies fading and the amplitude of the low frequencies increasing. According to the invention, these circumstances are employed to generate an output signal which reflects the above indicated change of the frequency spectrum of the EMG signal. The nature of the present invention and its aspects will be more readily understood from the following brief description of the accompanying drawings, and discussion relating thereto. In the accompanying drawings: Fig. 1 is a block diagram of an apparatus according to the present invention; Fig. 2 is a block diagram of an alternative embodiment of the apparatus according to the present invention; Fig. 3 shows an embodiment of a first amplifier stage included in the signal recording section of the apparatus; Fig. 4 shows an embodiment of a second amplifier stage included in the signal recording section of the apparatus; Fig. 5 shows one embodiment of a filter device followed by a third amplifier step; Fig. 6 shows a first embodiment of the devices of the apparatus for signal conversion, signal registration, signal analysis and presentation; Fig. 7 shows a second embodiment of the devices of the apparatus for signal conversion, signal registration, signal analysis and presentation; and Fig.8 shows an embodiment of a device for inspection of electrode contact. An apparatus according to the present invention will now be de- scribed with reference to the block diagram in Fig. 1. This diagram shows an amplifier 1 to which is connected an electrode means 7 which is adapted to acquire analog yoelectrical signals (EMG-signals). The amplifier 1 is followed by an analog to digital converter (A/D-converter) 2 for converting analog signals emitted by the am- pl fier into digital (binary represented) signals. A signal process¬ ing unit 3 connected to the device 2 for analog/digital conversion (A/D-conversion) is operative for receiving digital signals emitted therefrom. In its turn, the signal processing unit is coupled to or includes an output/storage device 4 for the output or storage of signals whose frequencies and/or amplitudes are related to the shift of the spectrum of frequencies within a given frequency interval of the analog electrical signals picked up by the electrode means 7. The stored signals are intended for subsequent output or analysis. Here¬ inafter, the term "signal means" 4 will be used to designate the output/storage device. When the signal means includes a unit for storage of information on frequency spectrum, the unit cons sts, for example, of a device for electric or magnetic storage of signals, for example a memory card, a tape memory, a diskette drive station, etc. In a preferred embodiment, a connection 6 is disposed between the signal processing unit 3 and the amplifier 1 for adjusting its am¬ plification based on signals emitted bay the unit. Requisite control and communication functions are included in the signal processing unit 3. Fig. 2 shows an alternative embodiment of the apparatus in which a separate control and communication unit 5 is provided between the A/D converter 2 and the signal means 4. The signal processing unit 3 is connected to the control and communication unit 5. In the embodiments illustrated in Figs. 1 and 2, the signal processing unit 3 and/or the control and communication unit 5 are, in certain cases, also arranged to include the signal means 4. The electrode means 7 includes three electrodes which, in one preferred embodiment, are adapted to be applied to the skin of the person whose muscular status is to be examined. These electrodes detect the slight amounts of charge which are emitted by the muscles in the region of the body where the electrodes are attached. The amplifier 1 includes the signal recording section of the appar¬ atus. In the embodiment illustrated in Figs. 3 and 4, the signal recording section includes a first amplifier stage 30 (cf. Figs. 3) which, via a high pass filter 45 (cf. Fig.4) is connected to a second amplifier stage 40. According to the embodiment illustrated in Fig. 3, the first ampli¬ fier stage 30 includes a pre-amplifier 31 with three inputs Al, A2 and A3. In one preferred embodiment, the electrode means 7 includes three electrodes El, E2 and E3 which are connected to the inputs Al, A2 and A3 of the pre-amplifier 31. In one preferred embodiment, the pre-amplifier 31 consists of an instrumentation amplifier. In the illustrated embodiment, the bipolar EMG-signal detected by the electrodes El and E2 is differentially amplified about 10 times. The third electrode E3 serves as a reference electrode. The voltage supply of the pre-amplifier is marked with the reference numerals +V and -V, respectively, while its output has the reference numeral Dl. The pre-ampl fier 31 is so arranged that it has a high ' input impedance and a low noise. The high input impedance is required in view of the extremely low signal level of those signals which are extracted by the electrodes of the electrode means 7. The potential of these signals is of the order of magnitude of 10-7 to 10-3 v. The low noise factor is necessary so as to avoid the complication that the noise which is generated within the amplifier masks the weak signals which are extracted by the electrodes. By way of one example of a suitable amplifier, mention might be made of one manufactured by Johne & Reilhofer, designated EMGV1. A shield 10 is provided to protect the signal from electrical and/or magnetic disturbances. For high quality of the analysis of the signal, such shielding is of importance at least for those stages in the apparatus, in which the signal level has not yet been raised to a level at which the effect of such disturbances on the information content of the signal, is, as a rule, no longer of any importance. Fig. 4 shows the high pass filter 45 designed as a passive RC-link, C45, R45 with a lower limit frequency of at least approx. 1 Hz, as a rule at least 5 Hz, and preferably at least approx. 10 Hz. The input D2 of the RC link 45 is connected to the output Dl of the first ampli¬ fier stage 30, while the output Fl of the RC link is connected to the input F2 of the second amplifier stage 40, which in the illustrated embodiment, consists of two cascade-connected amplifiers 41, 42. In the illustrated embodiment, the cascade-connected amplifiers are of a design in which the amplification of each respective amplifier s set by means of binary signals and in which the cascade-connected amplifiers have, to this end, three binary inputs L2, M2, N2. In one preferred embodiment, the amplification is adjustable to 1, 2, 4, 8, 16, 32, 64 and 128 times. It will be obvious to one skilled in the art that the second amplifier stage, in other embodiments of the present invention, has an architecture and amplification levels which may differ from those previously described. The voltage supply to the analog section of each respective amplifier is marked by +V1 and -VI. The voltage supply to the digital section of each respective ampli¬ fier is marked by +V2 and -V2. The output Gl from the cascade-connected amplifier stage 40 is, in one preferred embodiment, coupled to the input G2 of a first low pass link 50, ideally designed as an active low pass filter 51 (cf. Fig. 5). The requisite steepness of the filter will be achieved most si - ply by the employment of an active low pass filter. In one preferred embodiment, however a fifth order low pass filter of the Butterworth type is used. In such instance, filtering takes place in a "switched capacitor" filter. Hereby, the output signal will contain residues of a clock signal in which the residues are at a frequency which is 100 times the upper limit frequency of the filter. Consequently, the filter is followed by a second low pass link 55 in which the residues of the clock signal are removed. The figure shows an embodiment wherein a passive low pass filter is formed by a resistor R55 and a capacitor C55. In the described embodiment, the low pass link has an upper limit frequency of at most approx. 50 times, preferably at most approx. 25 times the limit frequency of the active low pass filter. The output HI from the second low pass link 55 is connected to the input H2 of a third amplifier stage 52, as a rule including an oper¬ ational amplifier 53 whose amplification is adjusted by means of a resistor R52 connected between the input H2 of the third amplifier stage and the negative input of the operational amplifier 53 and a second resistor R53 connected to the same input of the operational amplifier and to the output l of the operational amplifier. In an embodiment of the present invention, use is made as active low pass filter 51 of a filter designated "Linear LTC1062", and as operational amplifier 53, the amplifier "Analog devices" AD548 or AD648. It will be obvious to one skilled in the art that, in other embodiments, an active low pass filter is selected which includes circuits for removal of all of the residues of the clock frequency which influence the subsequent analysis of the signal. Hereby, the second low pass link 55 may be dispensed with from the apparatus. In a preferred embodiment of the invention, the total amplification of the signal from the input of the first amplifier step 30 and to the output l of the third amplifier stage 52 is adjustable within the range of between 200 and 25600 times. The amplifier 1 described with particular reference to Figs. 3-5 includes embodiments of the first amplifier stage 30, the high pass filter 45, the second amplifier stage 40, the first low pass link 50, the second low pass link 55 and the third amplifier stage 52 which correspond to a preferred design and construction of the amplifier 1. However, it will be obvious to one skilled in the art that, within the spirit and scope of the present invention, the separate sub steps which make up the amplifier may, in certain embodiments, be of devi¬ ating design and construction, that certain of the sub steps are wholly dispensed with or that certain sub steps are added without, for this reason, any major deviation taking place from the basic inventive concept as herein disclosed. Similarly, in certain embodiments, the sequence of the sub steps is modified, such that, for example the third amplifier stage 52 precedes the first low pass link 50. Fig. 6 reproduces the A/D converter 2 whose input K2 is connected to the output Kl of the third amplifier stage 52. In one preferred embodiment of the present invention, the A/D converter has at least 8, preferably at least 10 and as a rule at least 12 bits resolution. One example of a suitable A/D converter is "Crystal CS5012". The A/D converter 2 is, via a first signal connection 65, connected to a signal processing unit 60 which includes a signal processor 61 or microprocessor 61 of requisite calculation capacity. Hereinafter, the term signal processor will be used without restrictive signifi¬ cance. A memory 63 is connected to this processor by means of an address connection 77 and a data transfer connection 78. Hereinafter, the designation control connection will generally be employed for such a combination of connections, for which reason the previously disclosed combination of address connection 77 and data transfer connection 78 will hereinafter be designated first control connection 62. Between the signal processing unit 60 and the signal means 4, there is disposed a second control connection 72. The signal pro- cessing unit includes logic circuits for generating electric signals on the outputs LI, Ml, Nl when the unit, for example the signal pro¬ cessor of the signal processing unit, identifies that the incoming signal to the unit represents signal values beyond predetermined limit values, for example excessively high or low effective values for frequencies included in the frequency spectrum. The outputs LI, Ml, Nl of the signal processing unit are connected to the inputs L2, M2, N2 of the second amplifier stage 40 in order to form the feedback coupling 6 (cf. Figs. 1 and 2) between the amplifier device 1 and the signal processing unit 3. Fig. 7 illustrates an alternative embodiment of the present invention in which the A D converter is connected to the control and communi¬ cation unit 5, which, in its turn, s connected to the signal pro¬ cessing unit 60 and the memory 63. In the embodiment shown on the drawing, this consists of a dual-port memory 63a. Between the signal processing unit 60 and the dual-port memory, there is disposed a third control connection 66. The first signal connection 65 from the A/D converter, is, in this instance, connected to a control unit 64. A first databus 70 and a second databus 71 are connected thereto, with which both the dual-port memory 63a and the storage unit 76 are in communication. A fourth control connection 69 is disposed between the signal processing unit 60 and the control unit 64, a fifth con¬ trol connection 74 is disposed between the control unit 64 and the dual-port memory 63a, and a sixth control connection 75 is disposed between the control unit 64 and a storage unit 76. A second signal connection or alternatively a seventh control connection 73, is disposed between the control unit 64 and the signal means 4. The control and communication unit 5, is in one preferred embodiment, also provided with outputs LI, Ml and Nl which are connected to inputs L2, M2 and N2 of the second amplifier stage 40 in order to form the feedback connection 6 between the signal processing unit 3 and the amplifier 1. The control unit 64 is shownas provided with the outputs. In certain embodiments, the storage unit 76 is included in the above-described signal means 4. Fig. 8 shows an embodiment of the present invention in which is included a unit for checking the quality of electrode contact between the electrode means 7 and the surface of the skin. A voltage source V3 is connected, via a resistor R54, to the one input Bl of means 80 with high input impedance, while the other input B2 of the means is earthed. The electrodes of the electrode means 7, with these applied on the surface of the skin, are connected pairwise to the two inputs of the unit and the impedance between the electrodes and the skin is determined by that voltage which said means 80 registers. An indica¬ tor 81, for example a signal lamp is used to indicate that too high voltage, and as a conseqence too high impedance is present between electrodes and skin. The voltage source V3 is, in such instance, disposed via a resistor to be actuable and deactuable to one of the inputs of an amplifier e.g. the pre-amplifier 31 shown in fig 3. The voltage of the output of the amplifier is here employed as a measure of the impedance between the electrodes and controls the indicator. The measurement of the impedance provides the user with requisite information for improving electrode-skin contact on those occasions when the impedance is so high that measurement accuracy would have been jeopardized. When the apparatus according to the present invention is reduced into practice, the electrodes are applied against the skin in a region adjacent that muscle whose status is to be established. Alterna¬ tively, at least one of the electrodes is inserted in the muscle. Every measurement occasion is unique and depends upon the specific conditions prevailing and upon such factors as skin thickness, attained skin-electrode contact, tissue attenuation etc. Conse¬ quently, it is necessary to begin each measurement with an adjustment of the amplification of the equipment and determination of the frequency spectrum of the specific muscle which is under examination. This adjustment process is a form of calibration of the equipment. In such instance, the patient assumes a position in which the muscle is subjected to a certain loading, whereafter the amplifi¬ cation of the amplifier 1 is adjusted such that the signal to the A/D converter assumes a value within a predetermined size range. Hereby, the size of the amplified signals will be adapted with reference to the size of the electric signals which are emitted from the muscle and the damping which occurs between the muscle and the electrodes. The extracted signals are amplified and filtered in the amplifier 1, converted to binary signals in the A/D converter and passed to the signal processing unit 60. Herein, the frequency spectrum of the signals is analyzed and thereafter information on the configuration and/or location, e.g. median or mean value frequency of spectra are stored in the memory 63, 63a of the signal processing unit. The result of the analysis is continually stored and, in prolonged load¬ ing, a shift is, after a time, registered of the frequency spectrum towards lower frequencies in relation to the values registered during the "calibration". Within the spirit and scope of the present invention, the signal processing unit 3 is, as a rule, programmed, so as on "calibration", itself to ascertain that a steady signal which represents the frequency spectrum and which has a signal level within a predeter- mined interval arrives at the signal processing unit. During the calibration and on a steady incoming signal, the signal processing unit is programmed to adjust, via the feedback connection 6, the amplification of the amplifier so that signals transmitted to the signal processing unit are kept within the predetermined interval. On the "calibration" the configuration and location of the frequency spectrum are thereafter registered. The signal processing unit also attends to the modification of the amplification during the subse¬ quent measurement process when the signal level is changed such that the levels of incoming signals to the signal processing unit are no longer located within the predetermined interval. The system is programmed, in the analysis of incoming frequency spectra, to compensate for adopted modifications of the amplification. In a preferred embodiment such compensation is made by the signal processing unit. When the size of the shift exceeds a predetermined level, this is detected by the system e.g. by the signal processing unit 3 or by the control or communication unit 5 and a signal is emitted via the second control connection 72 or 73 to the signal means 4. It is evident to a person skilled in the art that the analysis of the frequency spectrum is could be made by using any known method for analysing and representing the frequency spectrum of a signal. As a rule, the signal means 4 is designed to receive binary signals which the signal means translates into, for example, acoustic signals whose amplitude and/or frequency for example increase according as the frequency spectrum is shifted. In certain embodiments, the signal processing unit 3 emits a signal to the signal means 4 when the size of the shift of the frequency spectrum in relation to its original position exceeds a predetermined level during a predetermined minimum time interval, the signals emitted to the signal device being trans¬ lated, for example, to acoustic signals whose intensity and/or frequency are modified when the shift of the spectrum of the EMG signal exceeds the predetemined level for a lengthy period of time. In certain embodiments the acoustic signals are replaced by optical signals, by tactile signals or by combinations of acoustic, optical and/or tactile signals. As a rule, all signal processing steps in the apparatus are provided with a shield 10 which protects against electric and/or magnetic disturbances. At least shielding of those steps in the apparatus in which the signals are analog is of importance to protect these from superimposed disturbance or, in the worst case, wholly masking elec¬ tric and/or magnetic disturbances. Such shielding is necessary in the establishment of muscular status for people carrying out working duties in environments where the external level of disturbance is high, for example certain working duties within the engineering industry, the automotive industry, etc. The signal processing unit 3 is didposed, as a rule by means of software, to establish the location and configuration of a frequency spectrum. The unit receives binary signals which it evaluates and classifies to generate at least one binary s gnal (parameter) which characterizes the frequency spectrum of the EMG signal. At each calculation said parameter or parameters are designated a value representing at least the location of the EMG signal in the frequency plane. In a preferred embodiment the parameter or parameters are representing the shift of the EMG signal in relation to its original location. The expression "original location" means the location of the EMG spectrum on commencement of the detection. The shift of the spectrum of frequencies are reflected by the signals emitted by the signal means 4. The signal processing of the EMG signal is executed in data sequences comprising a certain number of samples and a correspondingly adapted sample frequency. In one preferred embodiment, the combination of a sampling frequency of 1024 Hz and data sequences of 256 samples has been employed. This,choice also determines the upper limit frequency of the active low pass filter 51 to a practical level of approx. 400 Hz (the sampling theorem gives the theoretical value of 512 Hz). It is obvious that, on certain measurement conditions, the limit fre¬ quency may need to be selected to be lower. A halfing of the limit frequency is, as a rule, more than sufficient. Alternatively, the option may be chosen, in such situations, to increase the sampling frequencies. The location and configuration of the frequency spectrum are determined by means of a Fourier algorithm which divides up the original signal into different frequency bands. The resolution in the frequency plane is determined by the quotient between the sampling frequency and the data sequence length. By using computerized signal processing, the system ' s sensitivity to disturbances is reduced, frequency analysis is facilitated and possibilities are opened for combining continuously provided information on muscular status with registration of muscular status (spectrum of frequencies) during a lengthy period of time, for example for subsequent analysis. In greater detail, it applies on using the design and construction of the amplifier 1 as illustrated in Figs. 3-5 that the signals from the electrodes El, E2 of the electrode means 7 are fed to the inputs Al, A2 of the pre-amplifier 31 of the first amplifier stage 30. The differential input of the pre-ampl fier reduces disturbances deriving from the mains frequency and disturbances of types such as motion artefacts. The output signal from the amplifier step passes via its output Dl to the input D2 of the high pass filter 45, in which the D.C. voltage component of the signal is filtered off and present low frequency disturbances such as motion artefacts are further damped. The thus processed signal continues via the output Fl of the high pass filter to the input F2 of the second amplifier stage 40 and, after ampl fication therein, via its output Gl to the input G2 of the first low pass link 50 in which substantially all frequency compo- nents above a predetermined upper limit frequency and included in the signal emitted by the second amplifier stage 40 are filtered off. The signal is thereafter fed to the second low pass link 55 in which any possible residual undesired frequency components are removed. For example when use is made of an active low pass filter in the first low pass link 50, traces of a clock signal employed in the low pass filter are, where applicable, removed. The thus processed signal is fed, via the output HI of the second low pass link to the input H2 of the third amplifier stage 52. From the output Kl of the third ampli¬ fier stage, the signal is thereafter fed to the input K2 of the A/D converter 2. The signal is now limited to the frequency range within which EMG signals of interest occur and amplified to a level which makes it suitable for transfer to the A/D converter. According to the embodiment illustrated in Fig. 6, the signal emitted in binary form from the A/D converter is transmitted via the first signal connection 65 direct to the signal processing unit 60. There¬ in, the above described analysis of the signal takes place, in which event the signal processing unit, via the first control connection 62 stores information in the memory 63, the memory constituting, on the one hand, an intermediate store medium during analysis by the signal processing unit of the incoming signal, and, on the other hand, generally constitutes a temporary memory for storage of the result of the analysis by the signal processing unit. In certain embodiments, the memory 63 is upgraded so as also to constitute a storage unit 76 for permanent storage of information represented in binary form. In certain embodiments, the storage unit corresponds, in this instance, to the signal means 4. Once the signal processing unit has completed the analysis of the incoming signal, the result of such analysis is passed via the signal connection 72 to the signal means 4 and/or to the permanent storage unit 76. The signal processing unit 60 or in some embodiments the control unit 64 constitutes that device which, via the first signal connection 65, controls the A/D converter for the sampling of the data sequences as described above. During ongoing analysis of a data sequence, the signal processor 61 allows incoming signals from the A/D converter to pass to the memory 63 to be stored therein and fed back to the signal processor in conjunction with its analysis of the data sequence which follows upon the data sequence which the signal processor is currently engaged in analysing. Signals on the outputs LI, Ml, Nl are fed back to the inputs L2, M2, N2 of the second ampli¬ fier stage 40 for adjustment of the amplification. In the embodiment illustrated in Fig. 7 the A/D converter 61 emits its binary signals via the first signal connection 65 to the control unit 64. In such instance, the control unit 64 controls the A/D converter for sampling of the data signals. The signal is further transmitted from the control unit via the first databus 70 to the dual-port memory 63a. The control unit simultaneously controls addressing of the information storage via the fifth control con¬ nection 74. When the control unit registers that a complete data sequence has been stored in the memory 63a, the control unit con- trols, via the fourth control connection 69 the signal processor 61 so that this retrieves information via the third control connection 66 concerning the recently stored data sequence in the memory 63a for analysis of its frequency contents. When the analysis has been com¬ pleted, the result thereof is transferred to the dual-port memory, at the same time as the control unit 64, via the fifth control connec¬ tion 74, ensures that information corresponding to the analysis result stored in the memory 63a is retrieved from the memory via the second databus 71. Here, the control unit guides the information to the storage unit 76, to the signal means 4 or to both the storage unit and the signal means. In certain embodiments, the signal means 4 constitutes a part of the signal processing unit 3. As a rule, the storage unit 76 is jacked in so as to make possible easy replacement of storage units and to make possible the retrieval of information from every separate storage unit on a later occasion, for example to a computer hardware and thereafter processed therein. The disclosures of this paragraph apply to both the embodiment according to Fig. 6 and the embodiment accord¬ ing to Fig. 7. It is obvious that the technique described above provides the possi¬ bility for extremely compact design and construction and immediate information on the results of the analysis of the extracted EMG sig¬ nals. In certain embodiments of the present invention, the equipment is designed to be portable, whereby it may be used direct at the workplace during daily work without constituting any appreciable hindrance to the user. The above immediate indication of muscular status for example makes it possible to rapidly implement measures to avoid injury arising out of an unsuitably designed schedule or pro¬ gram of movement. It also provides the possibility of practising suitable techniques for movement in preventive or rehabilitation purposes and also the possibility for evaluating those ergonomic measures which should be implemented to improve the working environ¬ ment. It is also obvious that the possibility encompassed by the present invention for continuous registration during a lengthy period of time for muscular status for an individual muscle group opens up opportunities for results follow-up of the muscular status of indi- vidual people, for example for research purposes. The present invention is also of value given the fact that load strain illnesses, have, in recent years, shown a marked tendency to increase probably because more and more static and repetitive loading moments have become included in working life. Studies in working life in respect of measurement, analys s and remedial proposals have earlier been difficult to carry out since there has been no simple and dependable measurement equipment for routine load studies. However, the present invention makes such studies possible. In this context, it should be observed that it is difficult to carry out muscular load studies since there are no adequate mechanical mod¬ els for loading conditions in muscles. The present invention makes it possible, in connection with muscular activity, to sample and analyse the signals transmitted by the muscles either directly within the muscle itself or, for superficial muscles, by electrodes applied to the surface of the skin. According to the present invention muscle status is indicated by the shift of the frequency spectrum. As a consequence an essential advantage is obtained as variations in the level of the acquired myoelectric signal could be compensated by an adjustment of the amplification of the signal, which in turn means that the signal level always has a value ensuring an analysis without any substantial impact from disturbances and noise. By checking the configuration (shape) of the frequency spectrum, amplification could be excluded when the signal only consists of noise. The invention also makes it possible to eliminate frequencies round the power frequency, which means that the detection of the muscle status could be made without any impact of not relevant information emanating from disturbances caused by the power supply. The above detailed description has referred to but a limited number of embodiments of the present invention, but one skilled in the art will readily perceive that the present invention encompasses a large number of embodiments without departing from the spirit and scope of the appended claims.

Claims: CLAIMS 1. A method for detecting substantially continually, over a period of time, muscular status by an apparatus including an electrode means (7) for acquiring analog myoelectric signals, and an amplifier (1) for said signals, the analog signals acquired by the electrode means (7), after amplification in the amplifier (1), being converted into binary signals, in successive calculation occasions samples of the binary signals being frequency analysed in a signal processing unit (3), and at least one signal being formed by the signal processing unit to characterize the frequency spectrum of the acquired signals, c h a r a c t e i z e d in that at each calculation occasion the signal processing unit (3) assigns to said signal or signals values representing the position of the frequency spectrum in the frequency plane in relation to an initial position for the fre¬ quency spectrum being determined on commencement of the detec¬ tion, and that said signal or signals representing the position of the frequency spectrum is transferred to a storing means (76) or transferred to a signal means (4) for transforming the signals being received to information which could be percieved by a human being e.g. by being transformed to optic, acoustic or tactile signals. 2. The method of detecting muscular status as claimed in claim 1, c h a r a c t e r i z e d in that in the signal processing unit (3) a signal processor (61) or a microprocessor (61) and a memory (63,76) cooperate for temporary and/or permanent storage in the memory of binary information relating to the frequency spectrum for myoelectric signals acquired by the electrode means (7). 3. The method of detecting muscular status as claimed in claim 1 or 2, c h a r a c t e r i z e d in that signals are emitted from the signal means (4) when the shift of the frequency spectrum in relation to its position on commencement of detection exceed predetermined values. 4. The method of detecting muscular status as claimed in claim 3, c h a r a c t e r i z e d in that signals from the signal means (4) are emitted at a frequency, an amplitude and/or at an inten¬ sity related to the size of the shift of the frequency spectrum in relation to its position on commencement of detection. 5. An apparatus for detecting muscular status, the apparatus including an electrode means (7) for aquiring analog myoelectric signals, an amplifier (1) for said signals, a device (2), for converting electric analog signals into digital signals, being connected to the amplifier (1) for receiving analogue signals emitted thereby, a signal processing unit (3) being connected to the device (2) for analogue-to-digital conversion, for receiving signals thereby, and the signal processing unit (3) being arranged to form at least one signal which contains informatation related to the frequency spectrum of the myoelectric signals, c h a r a c t e r i z e d in that the signal processing unit (3) is disposed to calculate, at a number of subsequent calculation occasions, the shift in the frequency plane of the frequency spectrum in relation to an initial positon being determined on commencement of the detection, that the signal processing unit (3) is disposed with means for emitting at least one signal representing at each calculating occasion said shift of the frequency spectrum, and that the signal processing unit is connected with a storing means (76) for storage of the signals representing the shift of the frequency spectrum and/or is connected with a signal means (4) for transforming said signals to information percievable by a human being, e.g. transforming the signals to optical, acoustic and/or tactile signals. 6. The apparatus as claimed in claim 5, c h a r a c t e r i z e d in that the signal means (4) is disposed for emitting signals at a frequency and/or an amplitude related to the shift of the frequency spectrum within a predetermined frequency range for the signals acquired by the electrode means. (7) 7. The apparatus as claimed in claim 5 or 6, c h a r a c t e r ¬ i z e d in that the signal means (4) includes an element for converting electric signals to acoustic signals. 8. The apparatus as claimed in any one of claims 5-7, c h a r a c t e r i z e d in that a control and communication unit (5) is interconnected between the signal processing unit (3) and the signal means (4) or that the control and communication unit (5) includes the signal means (4). 9. The apparatus as claimed in any one of claims 5-8, c h a r a c ¬ t e r i z e d in that the signal means (4) is disposed to emit signals whose ampl tude and/or frequency are changed when the frequency spectrum of the signals acquired by the electrode device (7) is shifted towards lower frequencies. 10. The apparatus as claimed in claims 9 or 10, c h a r a c t e r ¬ i z e d in that the control and communication unit (5) is disposed to emit analog and/or binary signals. 11. The apparatus as claimed in any of claims 5-10, c h a r a c ¬ e i z e d in that the signal processing unit (3) or the control or communication unit (5) are disposed to emit control signals to the signal means (4) for adjusting the frequency and/or amplitude of the signals emitted by said means. 12. The apparatus as claimed in any of claims 5-11, c h a r a c - t e r i z e d in that the signal processing unit (3) is disposed to store, in a storage unit (76), binary information relating to the frequency spectrum for myoelectric signals acquiered by the electrode means (7), and that the storage unit is disposed to be easily separated from the apparatus.

Inventors: KADEFORS ROLAND, OEBERG TOMMY, SANDSJOE LEIF, KADEFORS, ROLAND, OEBERG, TOMMY, SANDSJOE, LEIF
Applicants: BIOLIN AB
Application year: 1990
Main classification: A61B5
IPC codes: A61B5, G06F17