We present the results of non-linear pulsation modelling of 20 bump Cepheids in the LMC .
By obtaining a optimal fit to the observed V,R MACHO lightcurves we have placed tight constraints on stellar parameters of M , L , T _ { eff } and well as quantities of distance modulus and reddening .
We describe the mass-luminosity relation for core-He burning for intermediate mass stars .
The mass-luminosity relation depends critically on the level of mixing within the stellar interior over the course of the main-sequence lifetime .
Our sample is significantly more luminous than predicted by classical stellar evolutionary models that do not incorporate extension to the convective core .
Under the paradigm of convective core overshoot our data implies \Lambda _ { c } of 0.65 \pm 0.03 l / H _ { p } .
We derive a LMC distance modulus of 18.55 \pm 0.02 .