  We review the recent work on the mechanics of fast moving strings in anti-de
Sitter space times a sphere and discuss the role of conserved charges. An
interesting relation between the local conserved charges of rigid solutions was
found in the earlier work. We propose a generalization of this relation for
arbitrary solutions, not necessarily rigid. We conjecture that an infinite
combination of local conserved charges is an action variable generating
periodic trajectories in the classical string phase space. It corresponds to
the length of the operator on the field theory side.
