Electromyography
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Electromyography. ENGR 518 – Experimental Techniques Katlin Landers. outline. Overview of Electromyography Significance Theory How Electromyography Systems work Converting MUP to Electrical Signal Acquiring Signal Post-processing Methods Common Factors Affecting EMG Summary

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Electromyography

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Electromyography

Electromyography

ENGR 518 – Experimental Techniques

Katlin Landers


Outline

outline

  • Overview of Electromyography

  • Significance

  • Theory

  • How Electromyography Systems work

    • Converting MUP to Electrical Signal

    • Acquiring Signal

    • Post-processing Methods

  • Common Factors Affecting EMG

  • Summary

  • References


Overview of electromyography

Overview of Electromyography

  • Electromyography

    • Used to evaluate and record skeletal muscle activation

    • Electrical potential is detected

  • Used in Biomechanics

    • Research

    • Medical Evaluation

    • Therapy

http://www.amputation.research.va.gov/images/emg_testing.png


Significance

Significance

  • Research

    • Analyze muscle patterns

      • During static and dynamic movements

    • Optimize athlete performance

  • Medical Evaluation

    • Detect neuromuscular abnormalities

      • Involuntary muscle twitching

      • Muscular dystrophy

  • Therapy

    • Evaluate muscle recovery post-injury or surgery

    • Help control movement of devices

H. Hendricks, M. IJzerman, J de, Kroon, and G. Zilvold, “Functional electrical stimulation by means of the ‘Ness HandmasterOrthosis’ in chronic stroke patients: an exploratory study,” Clinical Rehabilitation, vol.15, pp.217-220, 2001.


Theory

Theory

  • Resting Membrane Potential

    • -70 to -90 mV

  • Nerve Action Potential (NAP)

    • Releases chemical transmitter

    • Depolarizes muscle fibers

  • Muscle Action Potential (MAP)

    • Electrical potential of muscle

      fiber

  • Motor Unit Potential (MUP)

    • Superimposed MAP from

      multiple fibers


Converting mup to electrical signal

Converting mup to Electrical Signal

http://sine.ni.com/images/products/us/040716_usb6008_m.jpg;http://smpp.northwestern.edu/bmec66/weightlifting/images/emg_electrode.jpg;http://noraxon.com/products/instruments.php3; http://www.officeclipart.com/office_clipart_images/laptop_computer_0515-0909-2120-0444_SMU.jpg


Converting mup to electrical signal1

Converting mup to Electrical Signal


Acquiring signal

Acquiring signal

  • Surface Electrodes

    • Commonly used

  • Intramuscular Electrodes

    • Used for access to deep muscles

    • Needle and fine- wire electrodes

http://www.noraxon.com/img/electrodes/dual-electrodes.jpg

http://www.rehab.research.va.gov/jour/02/39/6/Knutsonf01.jpg


Post processing methods

Post-processing methods

  • Evaluate offset

  • Rectify Data

    • Take the absolute value of the acquired data

  • Low Pass Filter Data

  • Normalize Data

    • With maximum EMG contraction

  • Result is a percent of Maximum contraction


Post processed data

Post-processed Data


Common factors affecting emg

Common factors affecting emg

  • Electrical Noise

    • Decreased Impedance

      • Use of gel, shave hair, abrade skin

    • Grounding

    • Motion Artifact

  • Electrode Placement

    • Incorrect muscle

    • Incorrect placement on desired muscle

      • Correct: Belly of muscle

      • Incorrect: muscle-tendon connection


Summary

Summary

  • Electromyography has a variety of uses

  • EMG is a process which converts action potentials into electrical signals

  • Systems used to record signals

    • Surface vs intramuscular

    • Wireless vs wired

  • Negative aspects

    • Mechanical adjustments

    • Post-processing


Questions

Questions?


References

References

  • Human Factors BME 533

  • “Occupational Biomechanics (4thEd.)” Don B. Chaffin, Gunnar B. J. Andersson, Bernard J. Martin Wiley Interscience, 2006

  • http://www.noraxon.com/

  • http://psychology.uchicago.edu/people/faculty/cacioppo/jtcreprints/fc86.pdf


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