[en] A chiral lagrangian expansion is used in order to parametrize the unknown symmetry breaking dynamics of the standard model, in the hypothetical case of a strongly interacting symmetry breaking sector. To lowest order, O(s), the model is completely determined by the experimental fact that ρ≅1. The dependence on the underlying theory shows up to order s² where consistency requires one-loop effects to be included through two renormalized parameters. The unitarity properties and the domain of applicability of the model are studied. Some experimental prospects are also commented at the end. (orig.)