The aim of this paper is to define the role and duties of a design engineer involved in a collaborative ergonomic design session supported by a 3D collaborative virtual environment. For example, such a session can be used to adapt the manual task an operator must achieve in the context of an industrial assembly line. We first present the interest of such collaborative sessions. Then we present a related work explaining the need of proper 3DCVE and metaphors to obtain efficient collaborative ergonomic design sessions. Then, after a short definition of the role of the engineer in such sessions, we propose a use case highlighting the type of metaphor such engineers need to have to be efficient in such a framework. Discussion and future works ends the paper.