In this paper we introduce a new tool called ``Lipschitz
triangulations'', which gives combinatorially all information
about the metric type. We show the existence of such
triangulations for semi-algebraic sets. As a consequence we
obtain a bi-Lipschitz version of Hardt's theorem. Hardt's
theorem states that, given a family definable in an o-minimal
structure, there exists (generically) a trivialization which
is definable in this o-minimal structure. We show that, for a
polynomially bounded o-minimal structure, there exists such an
isotopy which is bi-Lipschitz as well.