  The general structure of the $1/m$ corrections at zero recoil is studied. The
relevant matrix elements are forward matrix elements of local higher
dimensional operators and their time ordered products with higher order terms
from the Lagrangian. These matrix elements may be classified in a simple way
and the analysis at the non recoil point for the form factor of heavy quark
currents simplifies drastically. The second order recoil corrections to the
form factor $h_{A1}$ of the axial vector current, relevant for the $|V_{cb}|$
determination from $B \to D^*$ decays, are estimated to be $-5\% < h_{A1} - 1 <
0$.
