  We present predicted relations connecting pulsational and evolutionary
parameters, as based on a wide set of convective pulsating models of RR Lyrae
stars with Z=0.001, Y=0.24 and mass and luminosity suitable for the ``old''
(age $>$ 8 Gyr) variables observed in globular clusters. The relations are
collated with sound constraints on the mass of pulsators, as inferred from
up-to-date evolutionary models of horizontal branch stars, in order to provide
a self-consistent theoretical framework for the analysis of observed variables.
The theoretical predictions are tested through a detailed comparison with
measurements of RR Lyrae stars in the globular cluster M3. We show that the
predicted relations satisfy a variety of observed data, thus providing a
"pulsational" route to the determination of accurate distances to RR Lyrae-rich
globular clusters with intermediate metal content. We discuss the effect of
different physical inputs in evolutionary computations, as well as of different
bolometric corrections adopted to convert bolometric luminosity into absolute
magnitude. We show that the constraints inferred by pulsation theory support
the large value of the mixing-length parameter adopted to fit observed RGB,
but, at the same time, they would yield that the luminosity of updated HB
models is too bright. Such discrepancy is significantly reduced if element
diffusion is properly taken into account.
