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Quantification of E.M.G.

Quantification of E.M.G. RAW EMG. Continuously changing positive and negative deflections. How do you reduce this to one number for calculation?. A/D Skinfold Caliper Offset. 50 mm. Gain = Voltage difference / 50mm Skinfold thickness = (Voltage - Offset) / Gain. Voltage difference. Volts.

jesse-levine
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Quantification of E.M.G.

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  1. Quantification of E.M.G.

  2. RAW EMG Continuously changing positive and negative deflections. How do you reduce this to one number for calculation?

  3. A/D Skinfold Caliper Offset 50 mm • Gain = Voltage difference / 50mm • Skinfold thickness = (Voltage - Offset) / Gain Voltage difference Volts 0 mm Offset 0 Time

  4. RAW EMG OFFSET Signal does not oscillate around zero. Offset calculated as the average voltage

  5. Rectification After adjusting for the offset: the signal contains both positive and negative values Rectification involves the transformation of the signal into only positive deflections Average of rectified signal is used as a measure of the amount of EMG

  6. Integration Once the signal has been rectified: Integration refers to the calculation of the area under that signal waveform. This is another way of quantifying the amount of activity present during a particular period of time.

  7. Integration Value of integrated EMG is dependent upon length of time of sampling

  8. Lab Data Collection • Biceps EMG • Investigate the relationship between force and EMG • Smoothing Rectified EMG

  9. Data Collection Data Collection: 1 sec at 1000 Hz = 1000 data points Zero load - Unweighted Barbell (4 lbs) 5, 10,15, 20, 25 lbs on barbell

  10. Adjusted for offset (Subtract mean of zero load trial) • Rectified (Only positive deflections)

  11. Smoothing Rectified EMG • In the EMG custom analysis software there is a feature to smooth raw or rectified emg.

  12. Smoothing makes the pattern of change more “visible’ • Smoothing reduces amplitude • Integrated areas under the curve are similar, although slightly smaller with progressive increases in smoothing

  13. E.M.G. vs Force Relationship Calculate offset - using zero load trial Rectify five stationary trials (5 to 25lbs) Average rectified EMG Plot Ave.rect.E.M.G. and vs Force Straight line relationship?

  14. E.M.G. vs Force Relationship

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