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? 16

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

4. RAW EMG Signal does not oscillate around zero.
OFFSET
Signal does not oscillate around zero.
Offset calculated as the average voltage 16

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 15

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. 15

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 17

10. 16

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

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

15. 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

16. 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? 18

17. E.M.G. vs Force Relationship