  Active microrheology differs from its passive counterpart in that the probe
is actively forced through the material, rather than allowed to diffuse. Unlike
in passive microrheology, active forcing allows the material to be driven out
of equilibrium, and its nonlinear response to be probed. However, this also
renders inoperable the fluctuation-dissipation theorem used to justify passive
microrheology. Here we explore a question at the heart of active microrheology:
are its results consistent with macrorheology? We study a simple model material
-- a generalized Newtonian fluid, with a small but arbitrary
shear-rate-dependent component -- and derive a general expression for
dissipation due to probe motion, which remarkably does not require the
non-Newtonian flow to be solved. We demonstrate that the straightforward
application of active microrheology gives results that are inconsistent with
macrorheology, even when the probe is large enough for material to behave as a
continuum, unless the forcing is gentle enough to probe only the linear
response. Regardless, each technique encodes information about the material; if
suitably interpreted, the (macro-) constitutive relation can indeed be
recovered from the microrheological data. We emphasize that more, rather than
less, information would be obtained if the two methods disagree.

Soft Condensed Matter