1. Electromyography
A practical guide to understanding
muscle activity
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2. Muscle function
• Muscles are the physiological motors of the
human body
• Kinematics and kinetics give us a good
indication of the muscle groups
• For increased specificity we measure a muscles
activity during gait
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3. Electromyography
• Definition of Electromyography (EMG)
– Electromyography (EMG) is the detection and
recording of the electrical signal produced by
muscle tissue as it contracts.
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4. Muscle activation (sEMG)
• Measurement of electrical signals within the
muscle with two electrodes
• A summation of the action potentials generated
during contractions due to a change in the cell’s
membrane potential
• The size of the signal is dependent on the
number and frequency of firing of motor units
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5. Why measure sEMG?
• Measuring the muscle activity during gait allows:
– an indication to whether the muscle is active
– to see relative changes in timing of the muscles
– to assess motor control and coordination
– to determine any evidence of spasticity
– to evaluate muscle function post-surgical transfer
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6. EMG does not tell us:
• The strength of the muscle
• What type of movement the signal represents
• Whether the activity is compensatory or the
primary abnormality.
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7. Electromyography
• EMG includes the
– Detection
– Amplification
– Recording
– Processing and analysis
– Interpretation
• Three ways of recording the signals
• Surface electromyography (sEMG) most popular
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8. How to measure sEMG
• Positioning the patient
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Recommendations: www.seniam.org

9. How to measure sEMG
• Determine the electrode location
Recommendations: www.seniam.org
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10. How to measure sEMG
• Skin preparation
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Recommendations: www.seniam.org

11. How to measure sEMG
• Place and fix the electrodes securely
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Recommendations: www.seniam.org

12. Fine Wire EMG
• Determine Position
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13. How to measure sEMG
• Test the connection and accuracy of the
placement
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Recommendations: www.seniam.org

14. Processing the signal
• Raw signal
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Not
active
active

15. Processing the signal
• Rectified signal
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Not
active
active

16. Processing the signal
• Muscle timings
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smoothed
& rectified
signal
threshold
Onset Off

17. Processing the signal
• Filtered
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Not
active
active

18. Processing the signal
• Fatigue
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19. Factors that affect sEMG signal
• Impedance of the tissue
• Cross-talk between muscles
• Changes in geometry between muscle and
electrodes
• External noise
• All of these can be reduced using the 3P’s
– Position, Preparation and Placement of the electrodes
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20. Repeatability and Interpretation
of EMG data
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• Very few studies in the general literature
• Displayed the same way as general gait data
• Normalisation methods need to be appropriate
• sEMG alongside kinematics and kinetics can
offer further details about muscle function
• However, many labs choose specific individuals

21. Demonstration
Demonstration of
sEMG and fwEMG
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