EMG

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EMG

  1. 1. Electromyography A practical guide to understanding muscle activity 1
  2. 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 2
  3. 3. Electromyography • Definition of Electromyography (EMG) – Electromyography (EMG) is the detection and recording of the electrical signal produced by muscle tissue as it contracts. 3
  4. 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 4
  5. 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 5
  6. 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. 6
  7. 7. Electromyography • EMG includes the – Detection – Amplification – Recording – Processing and analysis – Interpretation • Three ways of recording the signals • Surface electromyography (sEMG) most popular 7
  8. 8. How to measure sEMG • Positioning the patient 8 Recommendations: www.seniam.org
  9. 9. How to measure sEMG • Determine the electrode location Recommendations: www.seniam.org 9
  10. 10. How to measure sEMG • Skin preparation 10 Recommendations: www.seniam.org
  11. 11. How to measure sEMG • Place and fix the electrodes securely 11 Recommendations: www.seniam.org
  12. 12. Fine Wire EMG • Determine Position 12
  13. 13. How to measure sEMG • Test the connection and accuracy of the placement 13 Recommendations: www.seniam.org
  14. 14. Processing the signal • Raw signal 14 Not active active
  15. 15. Processing the signal • Rectified signal 15 Not active active
  16. 16. Processing the signal • Muscle timings 16 smoothed & rectified signal threshold Onset Off
  17. 17. Processing the signal • Filtered 17 Not active active
  18. 18. Processing the signal • Fatigue 18
  19. 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 19
  20. 20. Repeatability and Interpretation of EMG data 20 • 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. 21. Demonstration Demonstration of sEMG and fwEMG 21

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