Carbon particle-filled polymers are frequently used as stretchable conductors and strain sensors. Many of the proposed resistance-based stretchable strain sensors show non-monotonic strain response, especially under dynamic conditions. This is commonly attributed to the competing destruction and reformation of the conductive network, but the underlying mechanism is still unknown. Therefore, systematic cyclic tensile tests are performed with carbon black-filled silicone yarns, which show that the non-monotonic behavior found depends on strain rate, strain history, and maximum applied strain. Based on the experimental results, a novel model is developed that incorporates the visco-elastic nature of the polymer and representations of the percolative networks in strain direction as well as the transversal direction. It is shown that the non-monotonic behavior is a result of the combination of visco-elasticity and transversal contraction of the percolative network. The model is an equivalent circuit model and its simulation results are in good agreement with the experimental results. The model can be used to further understand the strain sensing behavior of conductive polymers and optimize sensor systems.