  In a general single field inflationary model we consider the effects of long
wavelength scalar fluctuations on the effective expansion rate and equation of
state seen by a class of free falling observers, using a physical gauge
invariant formulation. In a previous work we showed that for a free massive
inflaton no backreaction is observed within some constraints. In this paper we
extend the validity of our previous results to the case of an arbitrary
self-interacting inflation potential, working to second order in cosmological
perturbation theory and to all order in slow-roll approximation. For these
general inflationary models, we also show the equivalence of the free falling
observers to the ones comoving with the inflaton field.
