Equivalent Electrical Representation of the Sweat Layer and Gain Compensation of the EMG Amplifier

The sweat layer, formed on the surface of the skin, causes a partial short-circuit of the surface electrodes in an electromyographic (EMG) channel. As a result, the effective input impedance of the channel varies at random and, along with the impedance, the output voltage varies. In this note, the sweat layer has been represented as a variable resistance connected across the input stage of the EMG channel and the effect is analyzed. It has also been shown that the sweat layer´s equivalent resistance can also be used for the continuous and automatic gain compensation of the EMG amplifier.