  The present article studies variational principles for the formulation of
static and dynamic problems involving Kirchhoff rods in a fully nonlinear
setting. These results, some of them new, others scattered in the literature,
are presented in a systematic way, helping to clarify certain aspects that have
remained obscure. In particular, the study of transversely isotropic models
reveals the delicate role that differential geometry plays in their formulation
and unveils consequently some approximations that can be made to obtain
simplified formulations.
