Lin and Tuckerman 7 have treated the masses as free parameters to improve the efficiency of conformational sampling in protein simulations, establishing a hierarchy of adiabatic decoupling between solvent, side-chain, and backbone motions by decreasing the solvent and side-chain masses. This approach differs from mass repartitioning because, in practice, it tends to decrease the hydrogen masses along with the total solvent mass, whereas mass repartitioning increases hydrogen masses at constant total solvent mass. Nevertheless, both approaches aim to achieve larger particle displacements per simulation step without compromising the stability and accuracy of the numerical integration. In these and similar approaches, one should keep in mind that a uniform scaling of all masses in the system does not improve the sampling efficiency, because it simply amounts to a rescaling of time.