Physical interfaces have an important role in achieving efficient, safe and comfortable transmission of forces between the exoskeleton and the human body. They are normally composed of different compliant elements disposed in series between the skin of the user and the exoskeleton frame. Modelling how the compliant properties of physical interface will affect the transmission of forces may be useful to improve the design process towards more effective, safe and user-specific exoskeletal devices. As a first step in this direction, we propose a simplified 2-dimensional model representing the interaction of a single-actuated-joint exoskeleton with the human limb through a compliant element. We studied the effects of stiffness value associated to the tissues in the behavior of the whole system with simulated results of the model.