The objective of this article is to show that the notion of physical strength as a natural characteristic of men, counterpart to women’s fragility, is the result of the social construction of masculinity and feminity. We have focused on the building trade. In this sector, the notion of physical strength succeeded in both forbidding and hiding women’s presence. The building trade cannot be considered as a typical non-mixed trade, since women have always played an important role therein. However, it is constructed around characteristics of masculinity. Physical strength therefore appears to be a structural notion of the professions of this trade. Being a woman in the building trade is neither meaningless nor natural. For that reason, women who are nevertheless active in that field are either negated or confined to certain professions, tasks and functions.