  In recent years, analyses of eclipsing binary systems have unveiled
differences between the observed fundamental properties of low-mass stars and
those predicted by stellar structure models. Particularly, radius and effective
temperatures computed from models are ~ 5-10% lower and ~ 3-5% higher than
observed, respectively. These discrepancies have been attributed to different
factors, notably to the high levels of magnetic activity present on these
stars. In this paper, we test the effect of magnetic activity both on models
and on the observational analysis of eclipsing binaries using a sample of such
systems with accurate fundamental properties. Regarding stellar models, we have
found that unrealistically high spot coverages need to be assumed to reproduce
the observations. Tests considering metallicity effects and missing opacities
on models indicate that these are not able to explain the radius discrepancies
observed. With respect to the observations, we have tested the effect of
several spot distributions on the light curve analysis. Our results show that
spots cause systematic deviations on the stellar radii derived from light curve
analysis when distributed mainly over the stellar poles. Assuming the existence
of polar spots, overall agreement between models and observations is reached
when ~ 35% spot coverage is considered on stellar models. Such spot coverage
induces a systematic deviation in the radius determination from the light curve
analysis of ~ 3% and is also compatible with the modulations observed on the
light curves of these systems. Finally, we have found that the effect of
activity or rotation on convective transport in partially radiative stars may
also contribute to explain the differences seen in some of the systems with
shorter orbital periods.
