Analog Conditioning1 Quantification of E.M.G.

Analog Conditioning2 RAW EMG Continuously changing positive and negative deflections. How do you reduce this to one number for calculation?

Analog Conditioning3 A/D Skinfold Caliper Offset l Gain = Voltage difference / 50mm l Skinfold thickness = (Voltage - Offset) / Gain 0 Volts Time 0 mm 50 mm Offset Voltage difference

Analog Conditioning4 OFFSET Signal does not oscillate around zero. Offset calculated as the average voltage RAW EMG

Analog Conditioning5 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

Analog Conditioning6 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.

Analog Conditioning7 Integration Value of integrated EMG is dependent upon length of time of sampling

Analog Conditioning8 Lab Data Collection l Biceps EMG l Investigate the relationship between force and EMG l Smoothing Rectified EMG

Analog Conditioning9 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

Analog Conditioning10

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

Analog Conditioning12 Smoothing Rectified EMG l In the EMG custom analysis software there is a feature to smooth raw or rectified emg.

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

Analog Conditioning16 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?

Analog Conditioning17 E.M.G. vs Force Relationship