  We have investigated the influence of a driving force on the elastic coupling
(Labusch parameter) of the field-cooled state of the flux line lattice (FLL) in
400 nm thick YBa$_2$Cu$_3$O$_7$ superconducting films. We found that the FLL of
a field-cooled state without driving forces is not in an equilibrium state.
Results obtained for magnetic fields applied at $0^\circ$ and 30$^\circ$
relative to CuO$_2$ planes, show an enhancement of the elastic coupling of the
films at driving current densities several orders of magnitude smaller than the
critical one. Our results indicate that the FLL appears to be in a relatively
ordered, metastable state after field cooling without driving forces.
