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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.