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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

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electromyography emg instrumentation

Electromyography (EMG) Instrumentation

David Groh

University of Nevada – Las Vegas

research applications of surface emg
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
Types of EMG
  • Electrode Categories
    • Inserted
      • Fine-wire (Intra-muscular)
      • Needle
    • Surface
fine wire electrodes
Fine-wire Electrodes
  • Advantages
    • Extremely sensitive
    • Record single muscle activity
    • Access to deep musculature
    • Little cross-talk concern
  • Disadvantages
    • Extremely sensitive
    • Requires medical personnel, certification
    • Repositioning nearly impossible
    • Detection area may not be representative of entire muscle
surface electrodes
Surface Electrodes
  • Advantages
    • Quick, easy to apply
    • No medical supervision, required certification
    • Minimal discomfort
  • Disadvantages
    • Generally used only for superficial muscles
    • Cross-talk concerns
    • No standard electrode placement
    • May affect movement patterns of subject
    • Limitations with recording dynamic muscle activity
electrode comparison studies
Electrode Comparison Studies
  • Giroux & Lamontagne - Electromyogr. Clin. Neurophysiol., 1990
    • Purpose: to compare EMG surface electrodes and intramuscular wire electrodes for isometric and dynamic contractions
    • Results
      • No significant difference in either isometric or dynamic conditions
      • However: dynamic activity was not very “dynamic”
emg manufacturers
EMG Manufacturers
  • Noraxon
  • Motion Lab Systems
  • Delsys
general concerns
General Concerns
  • Signal-to-noise ratio
    • Ratio of energy of EMG signal divided by energy of noise signal
  • Distortion of the signal
    • EMG signal should be altered as minimally as possible for accurate representation
characteristics of emg signal
Characteristics of EMG Signal
  • Amplitude range: 0–10 mV (+5 to -5) prior to amplification
  • Useable energy: Range of 0 - 500 Hz
  • Dominant energy: 50 – 150 Hz
characteristics of electrical noise
Characteristics of Electrical Noise
  • Inherent noise in electronics equipment
  • Ambient noise
  • Motion artifact
  • Inherent instability of signal
inherent noise in electronics equipment
Inherent Noise in Electronics Equipment
  • Generated by all electronics equipment
  • Frequency range: 0 – several thousand Hz
  • Cannot be eliminated
  • Reduced by using high quality components
ambient noise
Ambient Noise
  • Electromagnetic radiation sources
    • Radio transmission
    • Electrical wires
    • Fluorescent lights
  • Essentially impossible to avoid
  • Dominant frequency: 60 Hz
  • Amplitude: 1 – 3x EMG signal
motion artifact
Motion Artifact
  • Two main sources
    • Electrode/skin interface
    • Electrode cable
  • Reducible by proper circuitry and set-up
  • Frequency range: 0 – 20 Hz
inherent instability of signal
Inherent Instability of Signal
  • Amplitude is somewhat random in nature
  • Frequency range of 0 – 20 Hz is especially unstable
  • Therefore, removal of this range is recommended
factors affecting the emg signal
Factors Affecting the EMG Signal
  • Carlo De Luca
    • Causative Factors – direct affect on signal
      • Extrinsic – electrode structure and placement
      • Intrinsic – physiological, anatomical, biochemical
    • Intermediate Factors – physical & physiological phenomena influenced by one or more causative factors
    • Deterministic Factors – influenced by intermediate factors
maximizing quality of emg signal
Maximizing Quality of EMG Signal
  • Signal-to-noise ratio
    • Highest amount of information from EMG signal as possible
    • Minimum amount of noise contamination
  • As minimal distortion of EMG signal as possible
    • No unnecessary filtering
    • No distortion of signal peaks
    • No notch filters recommended
      • Ex: 60 Hz
solutions for signal interruption related to electrode and amplifier design
Solutions for Signal Interruption Related to Electrode and Amplifier Design
  • Differential amplification
    • Reduces electromagnetic radiation noise
    • Dual electrodes
  • Electrode stability
    • Time for chemical reaction to stabilize
    • Important factors: electrode movement, perspiration, humidity changes
  • Improved quality of electrodes
    • Less need for skin abrasion, hair removal
differential amplification
Differential Amplification
  • Ambient (electromagnetic) noise is constant
  • System subtracts two signals
  • Resultant difference is amplified
  • Double differential technique
electrode configuration
Electrode Configuration
  • Length of electrodes
    • # of included fibers vs. increased noise***
    • Delsys – 1 cm
    • Noraxon - ?
  • Distance between electrodes
    • Increased amplitude vs. misaligning electrodes, Multiple motor unit action potentials (MUAP)
    • Muscle fibers of motor units are distributed evenly, thus large muscle coverage is not necessary

(De Luca).

    • Delsys – 1 cm
    • Noraxon – 2 cm?
electrode placement
Electrode Placement
  • Away from motor point
    • MUAP traveling in opposite directions
    • Simultaneous (+) & (-) AP’s
      • Resultant increased frequency components
      • More jagged signal
    • Middle of muscle belly is generally accepted
electrode placement22
Electrode Placement
  • Away from tendon
    • Fewer, thinner muscle fibers
    • Closer to other muscle origins, insertions
      • More susceptible to cross-talk
  • Away from outer edge of muscle
    • Closer to other musculature
  • Orientation parallel to muscle fibers
    • More accurate conduction velocity
    • Increased probability of detecting same signal
reference electrode placement ground
Reference Electrode Placement(Ground)
  • As far away as possible from recording electrodes
  • Electrically neutral tissue
    • Bony prominence
  • Good electrical contact
    • Larger size
    • Good adhesive properties
references
References
  • Basmajian JV, De Luca CJ. Muscles Alive: their functions revealed by electromyography (fifth ed.). Williams & Wilkins, Baltimore, Maryland, 1985
  • Cram JR, Kasman GS. Introduction to surface electromyography. Aspen Publishers, Inc. Gaithersburg, Maryland, 1998
  • De Luca CJ: Surface electromyography: detection and recording. DelSys, Inc., 2002
  • De Luca CJ: The use of surface electromyography in biomechanics. J App Biomech 13: 135-163, 1997
  • MyoResearch: software for the EMG professional. Scottsdale, Arizona, Noraxon USA, 1996-1999