electromyography (emg) instrumentation
DESCRIPTION
Electromyography (EMG) Instrumentation. David Groh University of Nevada – Las Vegas. Research Applications of Surface EMG. Indicator for muscle activation/deactivation Relationship of force/EMG signal Use of EMG signal as a fatigue index. Types of EMG. Electrode Categories Inserted - PowerPoint PPT PresentationTRANSCRIPT
ElectromyographyElectromyography (EMG) (EMG)
InstrumentationInstrumentationDavid GrohDavid Groh
University of Nevada – Las VegasUniversity of Nevada – Las Vegas
Research Applications of Research Applications of Surface EMGSurface EMG
Indicator for muscle activation/deactivationIndicator for muscle activation/deactivation
Relationship of force/EMG signalRelationship of force/EMG signal
Use of EMG signal as a fatigue indexUse of EMG signal as a fatigue index
Types of EMGTypes of EMG
Electrode CategoriesElectrode Categories InsertedInserted
Fine-wire (Intra-muscular)Fine-wire (Intra-muscular)
NeedleNeedle SurfaceSurface
Fine-wire ElectrodesFine-wire Electrodes
AdvantagesAdvantages Extremely sensitiveExtremely sensitive Record single muscle activityRecord single muscle activity Access to deep musculatureAccess to deep musculature Little cross-talk concernLittle cross-talk concern
DisadvantagesDisadvantages Extremely sensitiveExtremely sensitive Requires medical personnel, certificationRequires medical personnel, certification Repositioning nearly impossibleRepositioning nearly impossible Detection area may not be representative of entire Detection area may not be representative of entire
musclemuscle
Surface ElectrodesSurface Electrodes
AdvantagesAdvantages Quick, easy to applyQuick, easy to apply No medical supervision, required certification No medical supervision, required certification Minimal discomfortMinimal discomfort
DisadvantagesDisadvantages 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 Limitations with recording dynamic muscle activityLimitations with recording dynamic muscle activity
Electrode Comparison StudiesElectrode Comparison Studies
Giroux & Lamontagne - Giroux & Lamontagne - Electromyogr. Clin. Electromyogr. Clin. Neurophysiol., 1990Neurophysiol., 1990 Purpose: to compare EMG surface electrodes Purpose: to compare EMG surface electrodes
and intramuscular wire electrodes for and intramuscular wire electrodes for isometric and dynamic contractionsisometric and dynamic contractions
Results Results No significant difference in either isometric or No significant difference in either isometric or dynamic conditionsdynamic conditions
However: However: dynamic activity was not very dynamic activity was not very “dynamic”“dynamic”
EMG ManufacturersEMG Manufacturers
NoraxonNoraxon
Motion Lab SystemsMotion Lab Systems
DelsysDelsys
General ConcernsGeneral Concerns
Signal-to-noise ratioSignal-to-noise ratio Ratio of energy of EMG signal divided by Ratio of energy of EMG signal divided by
energy of noise signalenergy of noise signal
Distortion of the signalDistortion of the signal EMG signal should be altered as minimally as EMG signal should be altered as minimally as
possible for accurate representationpossible for accurate representation
Characteristics of EMG SignalCharacteristics of EMG Signal
Amplitude range: 0–Amplitude range: 0–10 mV (+5 to -5) prior 10 mV (+5 to -5) prior to amplificationto amplification
Useable energy: Useable energy: Range of 0 - 500 Hz Range of 0 - 500 Hz
Dominant energy: 50 Dominant energy: 50 – 150 Hz– 150 Hz
Characteristics of Electrical Characteristics of Electrical NoiseNoise
Inherent noise in electronics equipmentInherent noise in electronics equipment
Ambient noiseAmbient noise
Motion artifactMotion artifact
Inherent instability of signalInherent instability of signal
Inherent Noise in Electronics Inherent Noise in Electronics EquipmentEquipment
Generated by all electronics equipmentGenerated by all electronics equipment
Frequency range: 0 – several thousand HzFrequency range: 0 – several thousand Hz
Cannot be eliminatedCannot be eliminated
Reduced by using high quality Reduced by using high quality componentscomponents
Ambient NoiseAmbient Noise
Electromagnetic radiation sourcesElectromagnetic radiation sources Radio transmissionRadio transmission Electrical wiresElectrical wires Fluorescent lightsFluorescent lights
Essentially impossible to avoidEssentially impossible to avoid
Dominant frequency: 60 HzDominant frequency: 60 Hz
Amplitude: 1 – 3x EMG signalAmplitude: 1 – 3x EMG signal
Motion ArtifactMotion Artifact
Two main sourcesTwo main sources Electrode/skin interfaceElectrode/skin interface Electrode cableElectrode cable
Reducible by proper circuitry and set-upReducible by proper circuitry and set-up
Frequency range: 0 – 20 HzFrequency range: 0 – 20 Hz
Inherent Instability of SignalInherent Instability of Signal
Amplitude is somewhat random in natureAmplitude is somewhat random in nature
Frequency range of 0 – 20 Hz is especially Frequency range of 0 – 20 Hz is especially unstableunstable
Therefore, removal of this range is Therefore, removal of this range is recommendedrecommended
Factors Affecting the EMG Factors Affecting the EMG SignalSignal
Carlo De LucaCarlo De Luca Causative Factors – direct affect on signalCausative Factors – direct affect on signal
Extrinsic – electrode structure and placementExtrinsic – electrode structure and placement
Intrinsic – physiological, anatomical, biochemicalIntrinsic – physiological, anatomical, biochemical Intermediate Factors – physical & Intermediate Factors – physical &
physiological phenomena influenced by one physiological phenomena influenced by one or more causative factorsor more causative factors
Deterministic Factors – influenced by Deterministic Factors – influenced by intermediate factorsintermediate factors
Factors Affecting the EMG Factors Affecting the EMG SignalSignal
Maximizing Quality of EMG Maximizing Quality of EMG SignalSignal
Signal-to-noise ratioSignal-to-noise ratio Highest amount of information from EMG signal as Highest amount of information from EMG signal as
possiblepossible Minimum amount of noise contaminationMinimum amount of noise contamination
As minimal distortion of EMG signal as possibleAs 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
Ex: 60 HzEx: 60 Hz
Solutions for Signal Interruption Solutions for Signal Interruption Related to Electrode and Amplifier Related to Electrode and Amplifier
DesignDesign
Differential amplificationDifferential amplification Reduces electromagnetic radiation noiseReduces electromagnetic radiation noise Dual electrodesDual electrodes
Electrode stabilityElectrode stability Time for chemical reaction to stabilizeTime for chemical reaction to stabilize Important factors: electrode movement, perspiration, Important factors: electrode movement, perspiration,
humidity changeshumidity changes
Improved quality of electrodesImproved quality of electrodes Less need for skin abrasion, hair removalLess need for skin abrasion, hair removal
Differential AmplificationDifferential Amplification
Ambient Ambient (electromagnetic) (electromagnetic) noise is constantnoise is constant
System subtracts two System subtracts two signalssignals
Resultant difference Resultant difference is amplifiedis amplified
Double differential Double differential techniquetechnique
Electrode ConfigurationElectrode Configuration
Length of electrodesLength of electrodes # of included fibers vs. increased noise***# of included fibers vs. increased noise*** Delsys – 1 cmDelsys – 1 cm Noraxon - ?Noraxon - ?
Distance between electrodesDistance between electrodes Increased amplitude vs. misaligning electrodes, Increased amplitude vs. misaligning electrodes,
Multiple motor unit action potentials (MUAP) Multiple motor unit action potentials (MUAP) Muscle fibers of motor units are distributed evenly, Muscle fibers of motor units are distributed evenly,
thus large muscle coverage is not necessary thus large muscle coverage is not necessary (De Luca).(De Luca).
Delsys – 1 cmDelsys – 1 cm Noraxon – 2 cm?Noraxon – 2 cm?
Electrode PlacementElectrode Placement
Away from motor pointAway from motor point MUAP traveling in opposite directionsMUAP traveling in opposite directions Simultaneous (+) & (-) AP’s Simultaneous (+) & (-) AP’s
Resultant increased frequency componentsResultant increased frequency components
More jagged signalMore jagged signal Middle of muscle belly is generally acceptedMiddle of muscle belly is generally accepted
Electrode PlacementElectrode Placement
Away from tendonAway from tendon Fewer, thinner muscle fibersFewer, thinner muscle fibers Closer to other muscle origins, insertionsCloser to other muscle origins, insertions
More susceptible to cross-talkMore susceptible to cross-talk
Away from outer edge of muscleAway from outer edge of muscle Closer to other musculatureCloser to other musculature
Orientation parallel to muscle fibersOrientation parallel to muscle fibers More accurate conduction velocityMore accurate conduction velocity Increased probability of detecting same signalIncreased probability of detecting same signal
EMG Electrode PlacementEMG Electrode Placement
Surface Electrode PlacementSurface Electrode Placement
Reference Electrode PlacementReference Electrode Placement(Ground)(Ground)
As far away as possible from recording As far away as possible from recording electrodeselectrodes
Electrically neutral tissueElectrically neutral tissue Bony prominenceBony prominence
Good electrical contactGood electrical contact Larger sizeLarger size Good adhesive propertiesGood adhesive properties
Off to the Lab!Off to the Lab!
ReferencesReferences
Basmajian JV, De Luca CJ. Muscles Alive: their Basmajian JV, De Luca CJ. Muscles Alive: their functions revealed by electromyography (functions revealed by electromyography (fifth edfifth ed.). .). Williams & Wilkins, Baltimore, Maryland, 1985Williams & Wilkins, Baltimore, Maryland, 1985Cram JR, Kasman GS. Introduction to surface Cram JR, Kasman GS. Introduction to surface electromyography. Aspen Publishers, Inc. Gaithersburg, electromyography. Aspen Publishers, Inc. Gaithersburg, Maryland, 1998Maryland, 1998De Luca CJ: Surface electromyography: detection and De Luca CJ: Surface electromyography: detection and recording. DelSys, Inc., 2002recording. DelSys, Inc., 2002De Luca CJ: The use of surface electromyography in De Luca CJ: The use of surface electromyography in biomechanics. J App Biomech 13: 135-163, 1997 biomechanics. J App Biomech 13: 135-163, 1997 MyoResearch: software for the EMG professional. MyoResearch: software for the EMG professional. Scottsdale, Arizona, Noraxon USA, 1996-1999 Scottsdale, Arizona, Noraxon USA, 1996-1999