Presentation Agenda. Presentation Agenda. Presentation Agenda. Electromyography. A scientific view of

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1 1 Presentation Agenda Presented by: Ali Maleki A scientific view of Electromyography Usable and Available References EMG recording Skin preparation Electrodes Electrode placement Amplifiers Sampling Noise consideration SENIAM recommendations for surface electromyography Presentation Agenda Presentation Agenda EMG Processing Time-domain Frequency-domain Time-frequency domain (wavelet) Advanced methods (fractal dimention, IAE Entropy) Pre-processings (time & amplitude normalization) Applications Fatigue analysis Electromechanical delay (EMD) Force-EMG relatioship Sensing valence & confusion &... Off-the-shelf instruments AD-Instruments Noraxon Biometrics BIOPAC Laboratory EMG recording EMG processing (as an excercise) References

2 2 Usable & available Refrences Usable & available Refrences Perotto, Delaqi, azzetti and Morrison, Anatomical guide for the electromyographers: the limbs and trunk, Charles Thomas Publisher Ltd., (Iran Medical Science, 1975) Preston and Shapiro, Electromyography and neuromuscular disorders: Clinical Electromyographic correlation, Butterworth- Heinemann, Weiss, Silver and Weiss, Easy EMG (1 st ed.), Butterworth- Heinemann, Greenberg, EMG pearls, Hanley & Belfus, (Tarbiat Modares) Merletti and Parker, Electromyography: physiology, engineering and noninvasive applications, IEEE, John Wiley and Sons, (khaje nasir) Tan, EMG secrets, Hanley & Belfus, Williams and Wilkins, Clinical electromyography: nerve conduction studies, Publisher, (amirkabir Univ.) Leis and Trapani, Easy Electromyography, Oxford University Press, Elsevier, Electromyography, (amirkabir) Basmajian, Muscles alive: their functions revealed by electromyography, William & Wilkins, (Sharif: 1 st ed., 1974) Lenman, Clinical electromyography, Publisher, (Iran Medical scince) electromyogram Greek derivative: electron + mys + gramma English: (amber) (muscle) (something written) Acronym : EMG History of Electromyograms or Why frogs hate scientists? Electromyogram: electrical activity associated with the contraction of a muscle Electromyography: preparation, study of, and interpretation of electromyogram.

3 3 Jan Swammerdam ( ) Discovered that stroking the innervating nerve of the frog s m. gastrocnemius generated a contraction Alessandro Volta ( ) Developed a device which produced electricity, which could be used to stimulate muscles. Invented the first electric battery. The modern term volt comes from his name. Luigi Galvani father of neurophysiology 1791 : Showed that electrical stimulation of muscular tissue produces contraction and force. Because of limited instrumentation, his work was not fully accepted until almost 40 years later. Emil Du Bois-Reymond ( ) 1848 : First to detect electrical activity in voluntary muscle contractions of man Had subjects place fingers in saline solution Removed skin to reduce transfer resistance Detected signal through electrodes connected to galvanometer when subjects contracted muscles

4 4 Herbert Jasper ( ) : Constructed the first electromyograph at McGill University (Montreal Neurological Institute). We have come a long way!!! We have come a long way!!! Electromyograph circa 1946 with 35 mm Recording camera and loudspeaker from Huddleston & Golseth Arch Phys Med 29:92-98, 1948 Carlo J. De Luca Probably the most influential person in recent EMG history. Wrote the oft-cited paper The Use of Surface Electromyography in Biomechanics

5 5 Electromyography is a seductive muse because it provides an easy access to physiological processes that cause the muscle to generate force, produce movement and accomplish the countless functions which allow us to interact with the world around us. The current state of Surface Electromyography is enigmatic. It provides many important and useful applications, but it has many limitations which must be understood, considered and eventually removed so that the discipline is more scientifically based and less reliant on the art of use. To its detriment, electromyography is too easy to use and consequently too easy to abuse. C. J. De Luca, 1993 John Basmajian (1921- ) wrote the bible of electromyography entitled: Muscles Alive. Today : 4 Dec. 2007, a lot of books! Today : 4 Dec. 2007, a lot of instruments

6 6 Today : 4 Dec. 2007, a lot of software applications Today : 4 Dec. 2007, a lot of applications Prosthesis control Rehabilitation Muscle fatigue analysis Clinical Diagnosis Gait analysis Analysis of muscle activation patterns in sport movements Evaluation of (strength) training excercises A side note The muscles around the eyes are only active during a genuine smile. An insincere smile involves only the muscles of the mouth. So, everyone can tell when you re faking it. Electromyogram: electrical activity associated with the contraction of muscle Neuromuscular System

7 7 Muscle Fascicle Muscle fiber Myfibril Sarcomere actin + myosin Motoneuron and innervated fibers Motor unit : Recruitment : Activation of motor unit Motoneuron and innervated fibers: Variation in size of motor units: Eye Gastrocnemius Fiber types: type I slow-twitch oxidative (SO) smallest type IIA fast-twitch oxidative(glicolytic) (FO)(FOG) type IIB fast-twitch glicolytic (FG) largest Fiber composition - same type in one motor unit - all types in any one muscle ratio varies

8 8 slow-twitch versus fast-twitch fibers: slow-twitch versus fast-twitch fibers: Skeletal muscle fibers characteristics: Size Principle: recruitment proceeds from smallest fibers to largest fibers SO FOG FG Influence of excercise and training on motor unit activation.

9 9 Size Principle: recruitment proceeds from smallest fibers to largest fibers SO FOG FG Firing of motor units: Rate coding Size Principle Muscle activity for the three muscle types is shown for three support phases in walking (Henneman s size principle) Action Potential travels down the motor neuron Activates all muscle fibers of the motor unit Post-synaptic membrane is depolarized Signal propagates in BOTH directions along the muscle fiber Thus, this generates ion movement across cell membrane and produces an ELECTROMAGNETIC field End-plate potential (EPP) End-plate region = neuromuscular junction Rest potential : -90 mv With sufficient EPP stimulation, rises to mv

10 10 This field is detected by an electrode placed near the activated muscle fibers Resulting waveform is termed the Motor Unit Action Potential MUAP : signal from depolarization of a motor unit action potential from multiple fiber in a motor unit are simultaneously recorded. Signal associated with single electrode and ground Signal associated with voltage difference when two electrodes are used at one site Motor units fire randomly, with different rates Each has its own amplitude, duration & waveform If we place an electrode over a muscle, the EMG signal recorded is the algebraic summation of all MUAP detected.

11 11 EMG Recording EMG Recording : Skin Preparation To get a good electrode-skin contact to obtain: better SMEG recording (in term of amplitude characteristics) fewer and smaller artifacts (electrical interference) less risk of imbalance between electrodes (smaller common disturbance signal) less noise (better S/N ratio) EMG Recording : Skin Preparation EMG Recording : Skin Preparation 1. Removing the hair weak ahesion specially in humid conditions, sweaty skin discomfort when removing the tape 2. Cleaning the skin dead skin cells produce high impedance skin oil increase the impedance, producing artifact 1. Removing the hair Is recommended to improve the adhesion of the electrodes under humid conditions for sweaty skin types dynamic movement conditions It may be beneficial to help decrease discomfort when the tape is being removed.

12 12 EMG Recording : Skin Preparation EMG Recording : Skin Preparation 2. Cleaning the skin: method I: using abrasive paste 2. Cleaning the skin: method II: using a very fine sandpaper Special abrasive and conducting paste are available which remove dead skin cells and clean the skin from dirt and sweat. A soft and controlled pressure in 3 or 4 sweeps usually is enough to get a good result. Attention: avoid any harm to the skin from rubbing too hard! Use of sandpaper should be combined skin with an alcohol pad. ADInstrument : abrasive pad EMG Recording : Skin Preparation EMG Recording : Skin Preparation 2. Cleaning the skin: method III: pure using the alcohol Alcohol used with a textile towel (that allows soft rubbing) This method may be sufficient for static muscle function test in easy condition Qualitative criteria: to the extent that the skin surface should be slightly red from rubbing the skin. Quantittive criteria: Impedance test to verify proper skin preparation:

13 13 EMG Recording : Electrodes EMG Recording : Electrodes Electrode types: Surface Electrodes Indwelling Surface electrodes: Non-invasive Not selective :Detect average activity of superficial muscles Give more reproducable results Gelled Dry Fine-wire Needle Pre-gelled Not pre-gelled EMG Recording : Electrodes EMG Recording : Electrodes Disadvantages of Surface electrodes: Limited to study of surface muscles Not-selective for small muscles in proximity to large muscles Crosstalk Movement artifacts Contact pressure fluctuations Needle electrodes: Invasive (inserted through skin into muscle) Small detection area suted to study individual motor units Can be repositioned during use to record from different MU

14 14 EMG Recording : Electrodes EMG Recording : Electrodes Disadvantages of needle electrodes: Pain, specially during forceful contractions Requires medical personnel, certification Repositioning nearly impossible Fine-wire electrodes: Invasive (inserted through skin into muscle) Large detection area vs needle Not painful Access to deep musculature EMG Recording : Electrodes EMG Recording : Electrodes Disadvantages of fine-wire electrodes: Requires medical personnel, certification Repositioning nearly impossible Migration Detection area may not be representative of entire muscle Gelled electrodes versus dry electrodes Electrode gel is used to reduce the electrode-skin impedance.

15 15 EMG Recording : Electrodes EMG Recording : Electrodes Pre-gelled electrodes versus not pre-gelled electrodes The use of electrodes which have to be gelled before being applied on a muscle is very cumbersom and time consuming. If not done properly, there is a high risk of bad SEMG recording. Active sensors: They are sensitive devices and may be damaged by ESD. Prior placement, each electrode should be cleaned with alcohol and allowed to dry. The use of electrod gel is not recommended because any excess gel moves between contacts may short it out. EMG Recording : Electrodes EMG Recording : Electrodes Active sensors: They should secuerd by long strips of hypoallergenic tape or elastic belt around the limb to ensure thet all contacts maintain a constant connection with the skin surface. If the pre-amplifier has been applied propperly, then you should see three circles impressed into the skin when it is removed. These marks will be fade within minutes. Steps in making a bipolar fine-wire electrode

16 16 EMG Recording : Electrodes EMG Recording : Electrodes Steps in insertion of a bipolar fine-wire electrode You can stimulate the muscle to chech the electrode insertion. Which electrode? Surface electrode: i.e. Superficial muscles Thin wire electrodes: i.e. Deep mescles (covered by surface muscles or bones) Needle electrode: MUAP characteristics, control proerties of MU such as firing rate Limitations and capabilities of available setup EMG Recording : Electrode Placement EMG Recording : Electrode Placement factors which influence obtaining a good and stable EMG: presence of motor points presence of tendons presence of other active muscles near the sensor Motor-point of muscle (innervation zone) OK. Edge of muscle Myotendonus junction Midline of belly between innervation zone and myotendonous junction.

17 17 EMG Recording : Electrode Placement EMG Recording : Electrode Placement Bipolar v.s. Monopolar sensors: Sensor: electrodes, cables and (if applicable) pre-amplifier Monopolar sensor: record difference in voltage relative to ground. Bipolar sensor: two contacts to measure electrical potential, each relative to a common ground. Multipolar sensor: one or two dimentional array of electrodes. EMG Recording : Electrode Placement EMG Recording : Electrode Placement Why bipolar sensor is most common sensor? bipolar sensor + differential amplifier Inter-electrode distance for Bipolar sensors: Direction of Bipolar sensors: parallel to muscle fiber

18 18 EMG Recording : Electrode Placement EMG Recording : Electrode Placement M M EMG Recording : Electrode Placement EMG Recording : Amplifying Reference electrode placement: As far away as possible from recording electrodes Electrically neutral tissue (bony prominence) Good electrical contact (larger size, good adhesive properties) EMG amplifier: Factors to be considered in amplifying EMG signal: Gain Bandwidth Imput impedance CMRR

19 19 EMG Recording : Amplifying EMG Recording : Amplifying Gain and bandwidth: Linear amplification over entire bandwidth Full-range frequency response should be fast enough to handle highest EMG frequencies. Do not overdrive the amplifier system (large signals clipped off) Input impedance: High so that not to attenuate the EMG signal. EMG Recording : Amplifying EMG Recording : Sampling CMRR (Common Mode Rejection Ratio) Human body is a good conductor and acts as an antenna to electromagnetic radiation Differential amplifier: A{(V hum +emg 1 )-(V hum +emg 2 )}=A{emg 1 -emg 2 } single-ended amplifier differential amplifier

20 20 EMG Recording : Sampling EMG Recording : Sampling EMG Recording : Sampling EMG Recording : Sampling Aliasing Sampling theorem of nyquist: sampling rate must be at least twice as high as the maximum expected frequency of the signal Anti-aliasing filter

21 21 EMG Recording : Noise consideration EMG Recording : Noise consideration EMG disturbances: 1. Inherent noise in electronic equipments 1. Inherent noise in electronic equipments 2. Ambient noise 3. Biological noise 4. Motion artifact Frequency range from 0 to several thousand Hz Can not be eliminated Reduced by using high quality components EMG Recording : Noise consideration EMG Recording : Noise consideration 2. Ambient noise Electromagnetic radiation sources Radio transmission Electrical wires Fluorescent lights Essentially impossible to avoid Dominant frequency 50 Hz Amplitude 1-3x EMG signal 3. Biological noise ECG Upper trunk and shoulder muscles Can be reduced by very good skin preparation Can be reduced by modified position of ground electrode Having a center frequency of 80 Hz Other muscles

22 22 EMG Recording : Noise consideration EMG Recording : Congratulation! 4. Motion artifact Sources: touching electrodes, moving cables Reduced by proper circuitry and setup Frequency range 0-20 Hz At the end, as soon as you are sure that the data is usable: -- Start to remove the tape and electrodes from the subject -- It may helpful to hold the skin tight as you pull off the tape -- You may also use alcohol over the tape to assist at removing the tape CONGRATULATION! You finished EMG recording. EMG Recording : SENIAM recommendations EMG Recording : SENIAM recommendations SENIAM Surface Electromyography for the Non-Invasive Assesment of Muscles: Electrode shape defined as the shape of the conductive area of the SEMG electrodes. rectangular (square) circular (oval) as long as the total surface area is the same, the skin impedance will almost be equal. SENIAM has found no clear and objectice criteria for recommendation for electrode shape.

23 23 EMG Recording : SENIAM recommendations EMG Recording : SENIAM recommendations Electrode size defined as the size of the conductive area of a SEMG electrode. Increase of the electrode size perpendicular to the muscle fibers, increase the view of the electrodes. Increase of the electrode size in the direction of the muscle fibers, increase the detected amplitude and decreasing the high frequency contents (integrative effect). Electrode size For bipolar sensors, in general, the size of electrodes should be large enough to be able to record a reasonable pool of motor units, but small enough to avoid crosstalk from other muscles. SENIAM recommends that the size of the electrodes in the direction of the muscle fibers is maximum 10mm. EMG Recording : SENIAM recommendations EMG Recording : SENIAM recommendations Inter-electrode distance Defined as the center to center distance between the conductive areas of two bipolar electrodes. Electrode material Ag AgCl Ag/AgCl Au SENIAM recommendation for inter-electrode distance: 20mm. SENIAM recommendation: pre-gelled Ag/AgCl electrodes.

24 24 EMG Recording : SENIAM recommendations EMG Recording : SENIAM recommendations Sensor costruction Determination of sensor location: General recommendation: defined as the mechanical construction which is used to integrate the electrodes, the cables and (if applicable) the pre-amplifier. Inter-electrode distance variation during muscle contraction: affect the amplitude and frequency characteristics of signal. Movement of electrodes and cables: movement artifact SENIAM recommendations: A construction with fixed inter-electrode distance, built from light weight material. Cables need to be fixed using tape or elastic band. With respect to the longitudinal location of the sensor on the muscle, place the sensor halfway the most distal motor end-plate zone and the distal tendon. With respect to transversal location of the sensor on the muscle, place the sensor at the surface away from the edge with other subdivisions or muscles so that the geometrical distance of the muscle to these subdivisions and other muscles is maximized. EMG Recording : SENIAM recommendations EMG Recording : SENIAM recommendations Sensor location for biceps brachii: Starting posture: Electrode location: Electrode Orientation: Reference Electrode Clinical test: Sensor location for deltoideus medius: Starting posture: Electrode location: Electrode Orientation: Clinical test:

25 25 EMG Recording : SENIAM recommendations EMG Recording : SENIAM recommendations Sensor location for triceps brachii (lateral head) : Starting posture: Electrode location: Electrode Orientation: Clinical test: Sensor location for triceps brachii (long head) : Starting posture: Electrode location: Electrode Orientation: Clinical test: EMG Recording : SENIAM recommendations EMG Processing SENIAM recommendation for preparation the skin: 1. Shave the patient if the skin surface is covered by hair 2. Clean the skin with alcohol and allow the alcohol to vaporise so that the skin will be dry before the electrode will be placed t (s)

26 26 EMG Processing : Time domain EMG Processing : Time domain Raw EMG: Raw EMG: On-off and more-less characteristics By scientific recommendation (ISEK, SENIM), the EMG recording should not use any hardware filters (e.g. notch filter), except the amplifier band-pass ( Hz) filter that are needed to avoid anti-aliasing effects. On-off and more-less characteristics By scientific recommendation (ISEK, SENIM), the EMG recording should not use any hardware filters (e.g. notch filter), except the amplifier band-pass ( Hz) filter that are needed to avoid anti-aliasing effects. EMG Processing : Time domain EMG Processing : Time domain Half-wave rectification Full-wave rectification

27 27 EMG Processing : Time domain EMG Processing : Time domain Smoothing: moving average SENIAM: Average Rectified Value (ARV) Integral of Absolute Value (IAV) Smoothing: root mean square (RMS) Reflects the mean power of the signal Preferred recommendation for smoothing EMG Processing : Time domain EMG Processing : Time domain Smoothing: moving average and RMS Very similar in shape, the RMS algorithm (lower trace) shows higher EMG amplitude data than the moving average (upper trace) Smoothing: moving average and RMS Time window: ms 20ms: fast movements like jump, reflex studies 500ms: slow or static activities 50 and 100ms works well in most conditions The higher the time window is selected, the higher the risk of a phase shift

28 28 EMG Processing : Time domain EMG Processing : Frequency domain Smoothing: low-pass filtering e.g. a butterworth, 2 nd order or higher LPF at 6 Hz Question? Hz BPF 6 Hz LPF Frequency contents Tool : Fast Fourier Transform EMG Processing : Frequency domain EMG Processing : Frequency domain Frequency contents Tool : Fast Fourier Transform Peak power Total power Mean frequency Median frequency

29 29 EMG Processing : Normalization EMG Applications : Fatigue analysis EMG amplitude data are strongly vary between electrode sites, subjects and even day to day measure of the same muscle site. One solution to overcome this uncertain character is: the normalization to reference value e.g. Maximum Voluntary Contraction (MVC) value of a reference contraction. Static sub-maximal contraction Classical test requires a constant load level at a well defined angle position/ muscle length. Over contraction time: The amplitude shows an increase Mean or median frequency show a decrease Applications: Identify weak muscles (analysis of low back pain patients) Prove the efficiency of strength training excercises EMG Applications : Fatigue analysis Off-the-shelf instruments : ADInstruments Static sub-maximal contraction Dual BioAmp + PowerLab Over contraction time: The amplitude shows an increase Mean or median frequency show a decrease

30 30 Off-the-shelf instruments : ADInstruments Off-the-shelf instruments : DelSys Dual BioAmp + PowerLab Active sensor: No Wireless: No Gain: Amplification range 5uv to 100mv Bandwidth: Software selectable (LPF: Hz, HPF: Hz) CMRR: >85dB ADC: 16 bit (313 uv resolution on 10 v range) Max. sampling rate: 200kHz for 2 inputs & 20kHz for 16 inputs Number of channels: 4, 8, 16 Input impedance : 200 Mohm DelSys Bagnoli + Active sensors Off-the-shelf instruments : DelSys Off-the-shelf instruments : Noraxon DelSys Bagnoli + Active sensors Active sensor: Yes Wireless: No Gain: 100, 1000 & * (10 :preamplifier) Bandwidth: Hz, pre-amplifier open CMRR: 92dB ADC: Max. sampling rate: Number of channels: 2, 4, 8, 16 Input impedance : > ohm Myosystem 1400A

31 31 Off-the-shelf instruments : Noraxon Off-the-shelf instruments : Noraxon Myosystem 1400A Active sensor: Yes Wireless: No (USB) Gain: 500, 1000, 2000, 2500, 4000, 5000 Bandwidth: Hz (SEMG) & Hz (finewire) CMRR: >100dB ADC: 12 bit resolution Max. sampling rate: 1000, 2000, 3000 & 6000sample/sec/channel Number of channels: 16 Input impedance : >100 Mohm TeleMyo 2400T + TeleMyo 2400M Off-the-shelf instruments : Noraxon Off-the-shelf instruments : Biometrics Telemyo 2400T + telemyo 2400M Active sensor: Yes Wireless: Yes (WIFI: 100m & Flash Memory Card: 4 Mb) Gain: 500 Bandwidth: Hz, Hz & Hz CMRR: >100dB ADC: 16 bit resolution Max. sampling rate: 1500 or 3000 sample/sec/channel Number of channels: 16 Input impedance : >100 Mohm Biometrics W4X4 + Active sensors

32 32 Off-the-shelf instruments : Biometrics Off-the-shelf instruments : Biometrics Biometrics W4X4 + Active sensors Active sensor: Yes Wireless: Yes (Bluetooth & MMC Flash: 2 Mb) Gain: 1000 (active sensor) Bandwidth: Hz CMRR: >96dB ADC: 13 bit resolution Max. sampling rate: 1~20KHz (MMC mode) 1~8kHz (Bluetooth) Number of channels: 8 Input impedance : >10 7 Mohm Biometrics K800 + Active sensors Off-the-shelf instruments : Biometrics Biometrics K800 + Active sensors Active sensor: Yes Wireless: No (RS422) Gain: 1000 (active sensor) Bandwidth: Hz CMRR: >96dB ADC: Max. sampling rate: Number of channels: 8 Input impedance : >10 7 Mohm Off to the Lab!