  A self-consistent spectrophotometric modelling of intermediate age
post-starburst requires accurate stellar ingredients taking into account a
principal feature of the stars dominating the near-IR emission during this
phase: the variability of the AGB stars. A new library of stellar spectra based
on averages of the empirical spectra of variable AGB stars is presented. This
library is designed for convenient use in the population synthesis models. We
discuss meaningful ways to compute these averages, and the non-trivial
connection with the theoretical stellar parameters. Our library covers the near
infrared wavelength range between 0.5 micron and 2.5 micron and exhibits
fundamental differences when compared to the standard libraries using only
static giants.
