  A new set of functions, which form a basis of the massive nonpower expansion
for physical observables, is presented in the framework of the analytic
approach to QCD at the four-loop level. The effects due to the $\pi$ meson mass
are taken into account by employing the dispersion relation for the Adler
function. The nonvanishing pion mass substantially modifies the functional
expansion at low energies. Specifically, the spacelike functions are affected
by the mass of the $\pi$ meson in the infrared domain below few GeV, whereas
the timelike functions acquire characteristic plateaulike behavior below the
two-pion threshold. At the same time, all the appealing features of the
massless nonpower expansion persist in the considered case of the nonvanishing
pion mass.
