Pressure allows fine-tuning of interatomic interactions by the gradual change of interatomic distances. This feature will allow us to delve deeper into the mechanism of the pressure-induced pre-MMB to MMB transformation in group-15 and -16 elements. For this purpose, we make use of several theoretical bond descriptors, such as ES and ET, ρ and ∇ 2 ρ, ELF, DOS, COOP, pCOHP, IpCOHP, and ICOBI that have been previously used to describe MMBs . In particular, we analyze here the pressure dependence of the primary and secondary bond distances, d1 and d2, and their corresponding values of charge densities, ρd1 and ρd2, and ELF, ELFd1 and ELFd2, at the BCPs for the A7 (A8) phase of group-15 ( ) elements. We also analyze the evolution of the pCOHP and COBI parameters and their integrated values along the two distances d1 and d2. These values will help us to understand the bonding, non-bonding, or antibonding character of the different orbitals involved in the different bonds . Similar calculations will be also performed for the Ah and Ai phases of Po. Finally, we analyze the ELF isosurfaces to see the evolution of the LEPs of the A7 (A8) phase of group-15 (-16) elements at HP, when they undergo the PT to the Ah (Ai) phase, and to understand the mechanism of the pre-MMB to MMB transformation.