This paper presents a platform dedicated to a full body interaction between a virtual agent and human or between two virtual agents. It is based on the notion of coupling and the metaphor of the alive communication that come from studies in psychology. The platform, based on a modular architecture , is composed of modules that communicate through messages. Four modules have been implemented for human tracking, motion analysis, decision computation and rendering. The paper describes all of them. Part of the decision module is generic, that is it could be used for different interactions based on sensorimotor, while part of it is strictly dependent on the type of scenario one wants to obtain. An application example for a fitness exergame scenario is also presented in this work.