1. Differential Amplifier

2. EMG Signal Processing

3. EMG Amplifier Specifications
Amplifiers should be described by the following:
If single, differential, double differential
Input impedance
Common Mode Rejection Ratio (CMRR)
Signal to noise ratio
Actual gain used
Frequency range of amplifier

4. Noraxon Telemyo EMG Amplifier
Input Noise < 1 μV RMS
Differential Input Impedance 16 Meg Ohms
Common Mode Rejection Ratio CMRR 85 dB
Frequency Response 16 – 500 Hz
Throughput Circuit Gain 1000

5. Electrodes Reports on surface EMG should include:
Electrode material (Ag/AgCl)
Electrode geometry (disc, bars, rectangular)
Size (diameter, radius, width x length)
Use of gel or paste, alcohol applied to cleanse skin, skin abrasion, shaving of hair
Interelectrode distance
Electrode location, orientation over muscle with respect to tendons, motor points and fiber direction
Intramuscular wire electrodes should be described by:
Wire material (stainless steel)
Single or multi strand
Insulation material
Method of insertion (hypodermic needle)
Depth of insertion
Single or bipolar wire
Location of insertion in the muscle
Interelectrode distance
Type of ground electrode used, location

6. EMG Amplitude
Root Mean Square
Average Rectified Value

7. EMG Linear Envelope
Full wave rectify the EMG
Low pass filter with a time constant?

8. EMG Filtering
Since the power density spectra of the EMG contains most of its power in the frequency range of Hz at the extremes, surface EMG should not be filtered above 10 Hz as a low cutoff and below 350 Hz as a high cutoff.
Intramuscular signals should be filtered in the Hz range.

9. EMG Frequency Spectrum
The Median Frequency is defined as the frequency that divides the power spectrum in two regions having the same power or area under the Amplitude – Frequency Curve
Explain of Power Spectrum should include:
Time epoch used for each calculation
Type of window used prior to FFT (Hamming, Hanning)
Number of zero padding points
Equation used to calculate Median or Mean Frequency
Muscle length or fixed joint angle

10. EMG - Force
Recruitment of a motor unit. A quanta of force in contributed to the muscle contraction; however, the contribution to the EMG signal amplitude depends on the proximity of the detection surfaces of the electrode to the nearest fibers of the recruited motor unit.
A newly recruited MU will increase its firing rate as the force demand increases.
The force increase rapidly as a function of the increasing firing rate, whereas the contribution to the amplitude of the EMG signal increases less rapidly

11. EMG Normalization
Subjects should be adequately trained to elicit an MVC.
Provide subjects with immediate feedback of obtained force/torque.
Give the following information relative to normalization:
How the subjects were trained to obtain MVC
Joint angle or muscle length
Rate of force development
Velocity of shortening or lengthening
Change in muscle length
Range of joint angle in non – isometric contractions
Load applied in non – isometric contractions
When normalizing the amplitude of the EMG signal, do so at values less than 80% MVC. Above this level the EMG signal and the force (torque) are exceptional unstable and do not provide a suitable reference point (De Luca, JAB 13, p. 154)

12. EMG Crosstalk
Make every effort to determine that EMG crosstalk from muscles near the muscle of interest did not contaminate the recorded signal
Select an appropriate electrode size, interelectrode distance and location when working on an area where many narrow muscles are tightly gathered
Care also should be employed when recording surface EMG from areas with subcutaneous adipose tissue as it is known that adipose tissue enhances crosstalk.