presentation agenda - semnan...

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A scientific view of

Electromyography

Presented by:Ali Maleki

Presentation Agenda

Usable and Available ReferencesHistory of ElectromyographyOrigin of EMG EMG recording

Skin preparationElectrodesElectrode placementAmplifiersSamplingNoise considerationSENIAM recommendations for surface electromyography

Presentation Agenda

EMG ProcessingTime-domainFrequency-domainTime-frequency domain (wavelet)Advanced methods (fractal dimention, IAE Entropy)Pre-processings (time & amplitude normalization)

ApplicationsFatigue analysisElectromechanical delay (EMD)Force-EMG relatioshipSensing valence & confusion & ...

Presentation Agenda

Off-the-shelf instrumentsAD-InstrumentsNoraxonBiometricsBIOPAC

LaboratoryEMG recordingEMG processing (as an excercise)

References

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Usable & available Refrences

Perotto, Delaqi, azzetti and Morrison, Anatomical guide for the electromyographers: the limbs and trunk, Charles Thomas Publisher Ltd., 2005. (Iran Medical Science, 1975)Preston and Shapiro, Electromyography and neuromuscular disorders: Clinical Electromyographic correlation, Butterworth-Heinemann, 2005. Weiss, Silver and Weiss, Easy EMG (1st ed.), Butterworth-Heinemann, 2004.Greenberg, EMG pearls, Hanley & Belfus, 2004. (Tarbiat Modares)Merletti and Parker, Electromyography: physiology, engineering and noninvasive applications, IEEE, John Wiley and Sons, 2004. (khaje nasir)

Usable & available Refrences

Tan, EMG secrets, Hanley & Belfus, 2003.Williams and Wilkins, Clinical electromyography: nerve conduction studies, Publisher, 2003. (amirkabir Univ.)Leis and Trapani, Easy Electromyography, Oxford University Press, 2000.Elsevier, Electromyography, 1995. (amirkabir)Basmajian, Muscles alive: their functions revealed by electromyography, William & Wilkins, 1985. (Sharif: 1st ed., 1974)Lenman, Clinical electromyography, Publisher, 1983. (Iran Medical scince)

History of Electromyography

electromyogram

Greek derivative: electron + mys + gramma English: (amber) (muscle) (something written)Acronym : EMG

Electromyogram: electrical activity associated with the contraction of a muscle

Electromyography:preparation, study of, and interpretation of electromyogram.


History of Electromyograms or Why frogs hate scientists?

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Jan Swammerdam (1637-1680)Discovered that stroking the innervatingnerve of the frog’s m. gastrocnemius generated a contraction


Alessandro Volta (1745-1827)

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 neurophysiology1791 : 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 (1818-1896)1848 :First to detect electrical activity in voluntary muscle contractions of manHad subjects place fingers in saline solutionRemoved skin to reduce transfer resistanceDetected signal through electrodes connected to galvanometer when subjects contracted muscles

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Herbert Jasper (1906-1999)1942-1944 :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 mmRecording camera and loudspeaker fromHuddleston & GolsethArch 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

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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

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Today : 4 Dec. 2007, a lot of software applications


Today : 4 Dec. 2007, a lot of applications

Prosthesis controlRehabilitationMuscle fatigue analysisClinical DiagnosisGait analysisAnalysis of muscle activation patterns in sport movementsEvaluation 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.

Origin of EMG

Electromyogram:electrical activity associated with the contraction of muscle

Neuromuscular System

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Origin of EMG

MuscleFascicleMuscle fiberMyfibrilSarcomereactin + myosin

Origin of EMG

Motoneuron andinnervated fibers

Motor unit :

Recruitment :Activation of motor unit

Origin of EMG

Motoneuron and innervated fibers:

Variation in size of motor units:

EyeGastrocnemius

Origin of EMG

Fiber types:type I slow-twitch oxidative (SO)

smallesttype 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

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Origin of EMG

slow-twitch versus fast-twitch fibers:

Origin of EMG

slow-twitch versus fast-twitch fibers:

Origin of EMG

Skeletal muscle fibers characteristics:

Origin of EMG

Size Principle:recruitment proceeds from smallest fibers to largest fibersSO FOG FG

Influence of excercise and training on motor unit activation.

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Origin of EMG

Size Principle:recruitment proceeds from smallest fibers to largest fibersSO FOG FG

Muscle activity for the three muscle types is shown for three support phases in walking

Origin of EMG

Firing of motor units:Rate codingSize Principle

(Henneman‘s size principle)

Origin of EMG

Action Potential travels down the motor neuronActivates all muscle fibers of the motor unitPost-synaptic membrane is depolarized

End-plate potential (EPP)

End-plate region =neuromuscular junction

Origin of EMG

Signal propagates in BOTH directions along the muscle fiberThus, this generates ion movement across cell membrane and

produces an ELECTROMAGNETIC field

Rest potential : -90 mvWith sufficient EPP stimulation,

rises to 30-40 mv

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Origin of EMG

This field is “detected” by an electrode placed near the activated muscle fibersResulting waveform is termed the “Motor Unit Action Potential”MUAP : signal from depolarization of a motor unitaction potential from multiple fiber in a motor unit are

simultaneously recorded.

Origin of EMG

Signal associated with single electrode and ground

Origin of EMG

Signal associated with voltage difference when two electrodes are used at one site

Origin of EMG

Motor units fire randomly, with different ratesEach has its own amplitude, duration & waveformIf we place an electrode over a muscle, the EMG signal recorded

is “the algebraic summation” of all MUAP detected.

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EMG Recording EMG Recording : Skin Preparation

To get a good electrode-skin contactto 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

1. Removing the hairweak ahesion specially in humid conditions, sweaty skin …discomfort when removing the tape

2. Cleaning the skindead skin cells produce high impedanceskin oil increase the impedance, producing artifact


1. Removing the hairIs recommended to improve the adhesion of the electrodes under

humid conditionsfor sweaty skin typesdynamic movement conditions

It may be beneficial to help decrease discomfortwhen the tape is being removed.

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2. Cleaning the skin:method I: using abrasive paste

Special abrasive and conducting paste are available which remove dead skin cells and clean the skin from dirt and sweat.


2. Cleaning the skin:method II: using a very fine sandpaper

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


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 shouldbe slightly red from rubbing the skin.

Quantittive criteria: Impedance test to verify proper skin preparation:

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EMG Recording : Electrodes

Electrode types:Electrodes

Surface Indwelling

Gelled Dry Fine-wire Needle

Pre-gelled

Not pre-gelled


Surface electrodes:Non-invasiveNot selective :Detect average activity of superficial muscles Give more reproducable results


Disadvantages of Surface electrodes:Limited to study of surface musclesNot-selective for small muscles in proximity to large musclesCrosstalkMovement artifactsContact pressure fluctuations


Needle electrodes: Invasive (inserted through skin into muscle)Small detection area suted to study individual motor unitsCan be repositioned during use to record from different MU

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Disadvantages of needle electrodes: Pain, specially during forceful contractionsRequires medical personnel, certificationRepositioning nearly impossible


Fine-wire electrodes: Invasive (inserted through skin into muscle)Large detection area vs needle Not painfulAccess to deep musculature


Disadvantages of fine-wire electrodes: Requires medical personnel, certificationRepositioning nearly impossibleMigrationDetection area may not be representative of entire muscle


Gelled electrodes versus dry electrodes

Electrode gel is used to reduce the electrode-skin impedance.

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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.


Active sensors:They should secuerd by long strips of hypoallergenic tape or elastic

beltaround 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 10-20minutes.


Steps in making a bipolar fine-wire electrode

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Steps in insertion of a bipolar fine-wire electrodeYou 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

factors which influence obtaining a good and stable EMG:presence of motor pointspresence of tendonspresence 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.

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EMG Recording : Electrode Placement EMG Recording : Electrode Placement

Bipolar v.s. Monopolar sensors:Sensor: electrodes, cables and (if applicable) pre-amplifierMonopolar 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.


Why bipolar sensor is most common sensor?bipolar sensor + differential amplifier

Direction of Bipolar sensors: parallel to muscle fiber


Inter-electrode distance for Bipolar sensors:

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M


M


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 Recording : Amplifying

EMG amplifier:

Factors to be considered in amplifying EMG signal:GainBandwidthImput impedanceCMRR

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Gain and bandwidth:Linear amplification over entire bandwidthFull-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.


CMRR (Common Mode Rejection Ratio)Human body is a good conductor and acts as an antenna to

electromagnetic radiationDifferential amplifier: A{(Vhum+emg1)-(Vhum+emg2)}=A{emg1-emg2}

single-ended amplifier differential amplifier

EMG Recording : Sampling

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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

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EMG Recording : Noise consideration

EMG disturbances:

1. Inherent noise in electronic equipments2. Ambient noise 3. Biological noise4. Motion artifact


1. Inherent noise in electronic equipments

• Frequency range from 0 to several thousand Hz• Can not be eliminated• Reduced by using high quality components


2. Ambient noise

• Electromagnetic radiation sourcesRadio transmissionElectrical wiresFluorescent lights

• Essentially impossible to avoid• Dominant frequency 50 Hz• Amplitude 1-3x EMG signal


3. Biological noise• ECG

Upper trunk and shoulder musclesCan be reduced by very good skin preparationCan be reduced by modified position of ground electrodeHaving a center frequency of 80 Hz

• Other muscles

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4. Motion artifact

• Sources: touching electrodes, moving cables• Reduced by proper circuitry and setup• Frequency range 0-20 Hz

EMG Recording : Congratulation!

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

SENIAMSurface Electromyography for the Non-Invasive Assesment of Muscles:


Electrode shapedefined 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 recommendationfor electrode shape.

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Electrode sizedefined 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 sizeFor bipolar sensors, in general, the size of electrodes should be largeenough to be able to record a reasonable pool of motor units, butsmall enough to avoid crosstalk from other muscles.

SENIAM recommends that the size of the electrodes in the directionof the muscle fibers is maximum 10mm.


Inter-electrode distanceDefined as the center to center distance between the conductive areas of two bipolar electrodes.

SENIAM recommendation for inter-electrode distance: 20mm.


Electrode material

Ag AgCl Ag/AgCl Au

SENIAM recommendation: pre-gelled Ag/AgCl electrodes.

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Sensor costruction

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.


Determination of sensor location: General recommendation:

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 themuscle to these subdivisions and other muscles is maximized.


Sensor location for biceps brachii:Starting posture:Electrode location:Electrode Orientation:Reference ElectrodeClinical test:


Sensor location for deltoideus medius:Starting posture:Electrode location:Electrode Orientation:Clinical test:

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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:


SENIAM recommendation for preparation the skin:1. Shave the patient if the skin surface is covered by hair2. Clean the skin with alcohol and allow the alcohol to vaporise so that

the skin will be dry before the electrode will be placed

EMG Processing

t (s)

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EMG Processing : Time domain

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 (10-500 Hz) filter that are needed to avoid anti-aliasing effects.


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 (10-500 Hz) filter that are needed to avoid anti-aliasing effects.


Half-wave rectification


Full-wave rectification

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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


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: 20-500ms• 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

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Smoothing: low-pass filtering• e.g. a butterworth, 2nd order or higher LPF at 6 Hz• Question?• 10-500 Hz BPF• 6 Hz LPF

EMG Processing : Frequency domain

Frequency contents• Tool : Fast Fourier Transform


Frequency contents• Tool : Fast Fourier Transform


• Peak power• Total power• Mean frequency• Median frequency

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EMG Processing : Normalization

• 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.

EMG Applications : Fatigue analysis

• 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

Static sub-maximal contraction

Over contraction time:• The amplitude shows an

increase• Mean or median frequency

show a decrease

Off-the-shelf instruments : ADInstruments

Dual BioAmp + PowerLab

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Off-the-shelf instruments : ADInstruments

Dual BioAmp + PowerLabActive sensor: NoWireless: NoGain: Amplification range 5uv to 100mvBandwidth: Software selectable (LPF:50-5000Hz, HPF:0.02-10Hz)CMRR: >85dBADC: 16 bit (313 uv resolution on 10 v range)Max. sampling rate: 200kHz for 2 inputs & 20kHz for 16 inputsNumber of channels: 4, 8, 16Input impedance : 200 Mohm

Off-the-shelf instruments : DelSys

DelSys Bagnoli + Active sensors

Off-the-shelf instruments : DelSys

DelSys Bagnoli + Active sensorsActive sensor: YesWireless: NoGain: 100, 1000 & 10000 * (10 :preamplifier)Bandwidth: 20-450 Hz, pre-amplifier openCMRR: 92dBADC:Max. sampling rate:Number of channels: 2, 4, 8, 16Input impedance : > 1015 ohm

Off-the-shelf instruments : Noraxon

Myosystem 1400A

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Myosystem 1400AActive sensor: YesWireless: No (USB)Gain: 500, 1000, 2000, 2500, 4000, 5000Bandwidth: 10-500 Hz (SEMG) & 10-1000Hz (finewire)CMRR: >100dBADC: 12 bit resolutionMax. sampling rate: 1000, 2000, 3000 & 6000sample/sec/channelNumber of channels: 16Input impedance : >100 Mohm


TeleMyo 2400T + TeleMyo 2400M


Telemyo 2400T + teleMyo 2400MActive sensor: YesWireless: Yes (WIFI: 100m & Flash Memory Card: 4 Mb)Gain: 500Bandwidth: 10-500 Hz, 10-1000 Hz & 10-1500 HzCMRR: >100dBADC: 16 bit resolutionMax. sampling rate: 1500 or 3000 sample/sec/channelNumber of channels: 16Input impedance : >100 Mohm

Off-the-shelf instruments : Biometrics

Biometrics W4X4 + Active sensors

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Biometrics W4X4 + Active sensorsActive sensor: YesWireless: Yes (Bluetooth & MMC Flash: 2 Mb)Gain: 1000 (active sensor)Bandwidth: 20-460 HzCMRR: >96dBADC: 13 bit resolutionMax. sampling rate: 1~20KHz (MMC mode) 1~8kHz (Bluetooth)Number of channels: 8Input impedance : >107 Mohm


Biometrics K800 + Active sensors


Biometrics K800 + Active sensorsActive sensor: YesWireless: No (RS422)Gain: 1000 (active sensor)Bandwidth: 20-460 HzCMRR: >96dBADC:Max. sampling rate:Number of channels: 8Input impedance : >107 Mohm

Origin of EMG

Off to the Lab!

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