Another set of optional restraints for APR calculations are conformational restraints that can be applied to either or both host and guest to facilitate sampling during simulations of the pull phase. These types of restraints are also referred to as "jack" restraints. Jack restraints were turned on in the attach phase (over 15 windows) by scaling the force constants using l scaling coefficients from 0 to 1, as described earlier for guest restraints. The free energy contributions of applying jack restraints on a host molecule was calculated. In the release phase, jack restraints were turned off over 15 windows by scaling the force constants from 1 to 0. The free energy cost of releasing the jack restraints in the unbound state was calculated explicitly.