Owing to its wide applicability, the usage of the US is accompanied by a lot of methodological development. To provide some examples of the current methodological developments on US simulations for calculating the binding free energy, Woo and Roux 17 demonstrated that applying position restraints on the system during the US restricts the sampled configurational space, which needs to be corrected to obtain the binding free energy. The approach was further developed by Doudou et al. using linear restraints and Chipot et al. using a set of geometrical restraints, the best combination of which was further scrutinized. It has been shown that without using such restraints the resulting PMFs do not correspond well to the experimental values. As the reference configurations for US along a one-dimensional reaction coordinate are often obtained from one-dimensional pulling simulations, in which usually one part of the complex is pulled into the solvent, as generally advised, the US procedure has been criticized for its unidirectional nature. To overcome this issue, other methods such as metadynamics, adaptive-biasing force, and adaptive weight histogram have been developed. The advantage of these methods is that they iteratively alter the underlying potential energy surface and enhance the sampling along the selected reaction coordinate in all directions, meaning multiple binding/unbinding events occur during a single simulation.