This study proposes a flexible method to track and quantify the ac-coupled gain variations in electrode to tissue interface (ETI) of adhesive/reusable electrodes. Particularly, this study focuses on the effects of multiplicative motion artifacts (MMA) on ETIs and proposes a continuously monitoring technique to assess ETI multiplicative variations. The proposed method only requires one additional channel of self electrocardiogram (self-ECG). Both gel-covered and foam-based adhesive electrodes were tested. Empirical results show that the ETI multiplicative variations can be characterized by the proposed convenient method. Meanwhile, we successfully demonstrate different characteristics for two types of electrodes under five motion postures including suppress motion, fist/stretch palm, twist, bent inward and arm lift, Furthermore, The long-Term degradation experiment illustrates that the average characteristics variation of ETI is less than 6% within 3-day of use.