Research analysis of electrode-skin impedance of a TENS medical device was assessed over a three-month period. Electrode- skin impedance was measured and calculated using Ag/AgCl electrodes, arranged in a bipolar configuration along the anterior longitudinal axis on the brachioradialis and the pronator teres muscles to the trochlear notch. A sinewave of known input frequencies and constant input voltage was applied using a signal generator through the electrodes. Output voltage signals were recorded using DS1000Z Series oscilloscope for half-hour intervals with necessary breaks in between varying frequencies. Larger phase shifts of the impedance signal were observed at lower frequencies. At high frequencies impedance phase shifts decreased as the impedance only relied on the resistive aspect of the skin and electrode. Furthermore, representing the electrode-skin interface using a parallel resistor and capacitor component circuit shows the relationship of impedance being frequency dependent and a purely resistive property.