In the name of God Electromyography Electromyography (EMG) (EMG) By:sahar shahbazi

What is EMG? EMG stands for electromyography. It is the study of muscle electrical signals. EMG is sometimes referred to as myoelectric activity. Muscle tissue conducts electrical potentials similar to the way nerves do and the name given to these electrical signals is the muscle action potential. EMG stands for electromyography. It is the study of muscle electrical signals. EMG is sometimes referred to as myoelectric activity. Muscle tissue conducts electrical potentials similar to the way nerves do and the name given to these electrical signals is the muscle action potential.

What is motor unit? o oThe smallest subunit that can be controlled is called motor subunit because it is separately innervated by a motor axon. oThe number of the muscle fibers that are under control of 1 motor unit varies from 3 to 20,000 depending on the fineness of the control required.

Samples of EMG signal Samples of EMG signal o oAn EMG signal is the train of Motor Unit Action Potential (MUAP) showing the muscle response to neural stimulation.

oIn response to a stimulus from the neuron, a muscle fiber depolarizes as the signal propagates along its surface and the fiber twitches. This depolarization, accompanied by a movement of ions, generates an electric field near each muscle fiber. propagates along its surface and the fiber twitches. This depolarization, accompanied by a movement of ions, generates an electric field near each muscle fiber.

Motor unit Motor unit

EMG Applications EMG Applications oIndicator for muscle activation/deactivation oRelationship of force/EMG signal oUse of EMG signal as a fatigue index oChronic pain study

Signal processing and amplification

 1. rectification  2. Filtering and linear envelope detection  3. Integration  4. Amplification :  Amplifier impedance  common mode rejection

Outcome measures:  horizontal axis (time)  timing (percent on/off; on/off ratio) duration (sec; percent of cycle) coactivation (percent of cycle) Area under the curve (related to force)  vertical axis (voltage)  rate of rise of voltage peak amplitude

 Ellaway's cumulative sum histogram technique: Where Si is the cumulative sum up to sample i, X is the mean voltage over the trial, and xi is the voltage at sample

The measurement of EMG

 When the muscle is activated, the length of the muscle decreases and the muscle, skin and electrodes will be moving with respect to each other. The electrode signal will therefore probably show some movement artifacts.  This is not the only difficulty when measuring an EMG. When the muscle is moving, the body will show some movements as well, and the cable may move in the space between the electrode and the input of the amplifier. This space is often filled with an electro-magnetic field caused by the mains cables in the area. So we can expect more disturbances. The moving cable will show a movement artifact as well and the influence of the mains will cause a 50 or 60 Hz mains interference in the signal.  Therefore, we have at least three important noise sources when measuring the electro- physiological signal of a muscle.

50 Hz noise in the signal

Movement artifact when the electrode is moving with respect to the skin.

Artifact when the cable is moving.

 To get rid of mentioned noise, several measures can be taken.  1: Movement artifacts that are generated by the movement of the electrode with respect to the skin:  High pass filtering  TMS-I  2: Mains interference:  TMS-I

 In many EMG systems, the input amplifier is put on the electrode. This is often called an active electrode

Types of EMG oInserted Fine-wire (Intra-muscular) Needle oSurface Active passive

Fine-wire Electrodes oThe most important difference of inserted and surface electrodes is in their band width. oInserted one has higher frequency oBw:2_1000Hz(surfac e electrode’s BW:10_600Hz)

Fine-wire Electrodes oAdvantages Extremely sensitiveExtremely sensitive Record single muscle activityRecord single muscle activity Access to deep musculatureAccess to deep musculature Little cross-talk concernLittle cross-talk concern oDisadvantages Extremely sensitiveExtremely sensitive Requires medical personnelRequires medical personnel Repositioning nearly impossibleRepositioning nearly impossible Detection area may not be representative of entire muscleDetection area may not be representative of entire muscle

Surface Electrodes oActive: with amplifierwith amplifier Reduce skin impedance( no need to gel)Reduce skin impedance( no need to gel) Reduce motion artifactReduce motion artifact Increase s/nIncrease s/n oPassive: Without amplifierWithout amplifier Need to gel & skin preparingNeed to gel & skin preparing Decrease s/nDecrease s/n

Surface Electrodes oAdvantages Quick, easy to applyQuick, easy to apply No medical supervisionNo medical supervision Minimal discomfortMinimal discomfort oDisadvantages Generally used only for superficial musclesGenerally used only for superficial muscles Cross-talk concernsCross-talk concerns No standard electrode placementNo standard electrode placement May affect movement patterns of subjectMay affect movement patterns of subject

Factors affecting the surface EMG oIt’s a random signal and can’t be represented mathematically. oMany factors affect the observed surface EMG like: different days even for same persondifferent days even for same person different people; depending upon individual anatomy, thickness of fat tissue,cross talk…different people; depending upon individual anatomy, thickness of fat tissue,cross talk… Presence of gland & blood vessels.Presence of gland & blood vessels. Characteristic of recording equipmentCharacteristic of recording equipment Position of electrodes.Position of electrodes.

Observed difference from different positions

Surface electrodes

Needle electrodes

Characteristics of EMG Signal oAmplitude range: 0– 10 mV (+5 to -5) prior to amplification oUseable energy: Range of Hz oDominant energy: 50 – 150 Hz

detecting oRaw EMG signal is important Need filtering or notNeed filtering or not It’s difficult to detect signal from noiseIt’s difficult to detect signal from noise oSometimes we need LP,HP or BP filter Motion artifact, low frequencyMotion artifact, low frequency Sharp peaks, sudden movementSharp peaks, sudden movement 60 Hz, ambient noise60 Hz, ambient noise

Data : oTwo main parameters that extracted: Beginning and finishing EMG signal (on & off) (first data)Beginning and finishing EMG signal (on & off) (first data) Increase and decrease of muscle activity.Increase and decrease of muscle activity. oWhat can not we conclude? Strength of muscleStrength of muscle Compare of muscle strengthCompare of muscle strength Voluntary or involuntary motionVoluntary or involuntary motion

Abnormal results EMG is used to diagnose two general categories of disease:neuropathies and myopathies Neuropathic disease has the following defining EMG characteristics An increase in duration of the action potential A decrease in the number of motor units in the muscle (as found using motor units number estimation techniques) Myopathic disease has these defining EMG characteristics: A decrease in duration of the action potential A reduction in the area to amplitude ratio of the action potential

Maximizing Quality of EMG Signal oSignal-to-noise ratio Highest amount of information from EMG signal as possibleHighest amount of information from EMG signal as possible Minimum amount of noise contaminationMinimum amount of noise contamination oAs minimal distortion of EMG signal as possible No unnecessary filteringNo unnecessary filtering No distortion of signal peaksNo distortion of signal peaks No notch filters recommendedNo notch filters recommended

Electrode Configuration oLength of electrodes About 1 cmAbout 1 cm oDistance between electrodes Increased amplitude, will increase noise…Increased amplitude, will increase noise… 1 cm,2 cm1 cm,2 cm

Electrode Placement o Away from motor point Middle of muscle belly is generally accepted Middle of muscle belly is generally accepted o Away from tendon o Away from outer edge of muscle

EMG Electrode Placement

Surface Electrode Placement

Reference Electrode Placement (Ground) oAs far away as possible from recording electrodes oGood electrical contact Larger sizeLarger size Good adhesive propertiesGood adhesive properties

Example of the hand and wrist control using the EMG signals: the subject executed eight hand and wrist motions for about 30 s. The darkened areas indicate no motions because the square sum of EMG (n), which was defined as (1), was below the prespecified threshold. “SUS” in the discrimination results indicates the suspended discrimination where E(n) exceeds the prespecified threshold E.

The End