A deeper understanding of the evolution of the electrical properties of elastomeric composite materials undergoing mechanical deformations represents an essential prerequisite for developveloping non-destructive in-situ coupled approaches able to detect the impact of fatigues effects leading to irreversible damages. This can have numerous applications in the field of in-situ monitoring, preventive maintenance, smart rubber materials etc. In order to address this challenge, in-situ coupled electrical/mechanical investigations on EPDM based composite materials (amorphous or semi-crystalline) filled with carbon black of different structure (low structured and highly structured) and at different concentrations have been systematically carried-out. To this purpose, the electrical conductivity has been continuously measured during mechanical cycles of different amplitudes and velocity at constant strain or stress. In order to unravel the microscopic mechanisms underlying the evolution of the electrical conductivity, in-situ coupled structural investigations by X-Ray scattering have been performed. Our study brings evidence for a characteristic electrical signature of the classical mechanical Mullins effect, allowing one thereby a systematic correlation between the undergoing mechanical deformation and the resulting evolution of the electrical conductivity. This characteristic coupling signature manifested by a peak of conductivity in dependence on the deformation amplitude originates from a counterbalance between two competing mechanisms: a depercolation phenomenon taking place in the direction of mechanical stretching and a percolation mechanism taking place in the perpendicular direction. Two applications of potential impact employing the electrical/mechanical coupling will be presented and discussed in detail: (i) monitoring fatigues effects by in-situ coupled electrical measurements and (ii) quantifying the impact of extreme deformations on material properties.