  We provide new insights into backbending phenomenon within the
symmetry-adapted framework which naturally describes the intrinsic deformation
of atomic nuclei. For $^{20}\text{Ne}$, the canonical example of backbending in
light nuclei, the ab initio symmetry-adapted no-core shell model shows that
while the energy spectrum replicates the backbending from experimental energies
under the rigid rotor assumption, there is no change in the intrinsic
deformation or intrinsic spin of the yrast band around the backbend. For the
traditional example of $^{48}\text{Cr}$, computed in the valence shell with
empirical interactions, we confirm a high-spin nucleus that is effectively
spherical, in agreement with previous models. However, we find that this
spherical distribution results, on average, from an almost equal mixing of
deformed prolate shapes with deformed oblate and triaxial shapes. Microscopic
calculations confirm the importance of spin alignment and configuration mixing,
but surprisingly unveil no anomalous increase in moment of inertia. This
finding opens the path toward further understanding the rotational behavior and
moment of inertia of medium-mass nuclei.
