1. Electromyography (EMG) Instrumentation
David Groh
University of Nevada – Las Vegas

2. Research Applications of Surface EMG
Indicator for muscle activation/deactivation
Relationship of force/EMG signal
Use of EMG signal as a fatigue index

3. Types of EMG Electrode Categories Inserted Surface
Fine-wire (Intra-muscular)
Needle
Surface

4. Fine-wire Electrodes Advantages Disadvantages Extremely sensitive
Record single muscle activity
Access to deep musculature
Little cross-talk concern
Disadvantages
Requires medical personnel, certification
Repositioning nearly impossible
Detection area may not be representative of entire muscle

5. Surface Electrodes Advantages Disadvantages 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

6. 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”

7. EMG Manufacturers
Noraxon
Motion Lab Systems
Delsys

8. General Concerns Signal-to-noise ratio Distortion of the signal
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

9. Characteristics of EMG Signal
Amplitude range: 0–10 mV (+5 to -5) prior to amplification
Useable energy: Range of Hz
Dominant energy: 50 – 150 Hz

10. Characteristics of Electrical Noise
Inherent noise in electronics equipment
Ambient noise
Motion artifact
Inherent instability of signal

11. 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

12. Ambient Noise Electromagnetic radiation sources
Radio transmission
Electrical wires
Fluorescent lights
Essentially impossible to avoid
Dominant frequency: 60 Hz
Amplitude: 1 – 3x EMG signal

13. Motion Artifact Two main sources
Electrode/skin interface
Electrode cable
Reducible by proper circuitry and set-up
Frequency range: 0 – 20 Hz

14. 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

15. 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

16. Factors Affecting the EMG Signal

17. 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

18. 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

19. Differential Amplification
Ambient (electromagnetic) noise is constant
System subtracts two signals
Resultant difference is amplified
Double differential technique

20. 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).
Noraxon – 2 cm?

21. 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

22. Electrode Placement Away from tendon Away from outer edge of muscle
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

23. EMG Electrode Placement

24. Surface Electrode Placement

25. 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

26. Off to the Lab!

27. 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: , 1997
MyoResearch: software for the EMG professional. Scottsdale, Arizona, Noraxon USA,