  The coefficients appearing at leading and subleading order in the $1/m$
expansion of bilinear heavy quark currents are related to each other by
imposing reparametrization invariance on both the effective current operators
and the short-distance coefficient functions in the heavy quark effective
theory. When combined with present knowledge about the leading order
coefficients, the results allow to calculate all coefficients appearing at
order $1/m$ to next-to-leading order in renormalization-group improved
perturbation theory. They also provide a meaningful definition of the velocity
transfer variable $v\cdot v'$ to order $1/m$.
