Electromyography

1. Electromyography ENGR 518 – Experimental Techniques Katlin Landers

2. 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

3. 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

4. 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.

5. 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

6. 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

7. Converting mup to Electrical Signal

8. 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

9. 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

10. Post-processed Data

11. 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

12. 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

13. Questions?

14. 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