Magnetic frustration due to competing exchange interactions in spin systems that cannot be satisfied simultaneously is the source of exotic ground states, like spiral-spin liquids, spin-ice, or spin-orbital liquids evidenced recently in magnetic spinels. External magnetic fields of the order of the magnetic exchange can overcome frustration and frustrated antiferromagnets often undergo a sequence of phase transitions accompanied by anomalies in their magnetic and structural properties.  Here we review recent results of ultrasound and magnetization experiments performed in ultra-high magnetic fields up to 120 T on a series of frustrated chromium oxide and chalcogenide spinels.  In CoCr2O4 distinct anomalies with significant change in the sound velocity and attenuation are found at the onset of long-range incommensurate spiral-spin order at Ts = 27 K and at the transition from the incommensurate to commensurate state at Tl =14 K, evidencing strong spin-lattice coupling. The sound velocity manifests a step-like increase in a field of 55 T revealing a transition into a new magneto-structural state with enhanced stiffness and high irreversibility. The transition field shows non-monotonous temperature dependence while the magnetization evolves gradually with field without anomalies at the high-field transition suggesting its purely structural origin.  In ZnCr2S4 at temperatures below the antiferromagnetic transition at TN1 ≈ 14 K the sound velocity as function of magnetic field reveals a sequence of steps followed by plateaus indicating a succession of crystallographic structures with constant stiffness. At the same time, the magnetization evolves continuously with field up to full polarization without any plateaus in contrast to geometrically frustrated chromium oxide spinels.  In MnCr2S4 magnetization and ultrasound experiments up to 120 T reveal an extremely robust magnetization plateau with an unusual spin structure and two intermediate phases, indicating possible realizations of supersolid phases. The magnetization plateau characterizes fully polarized chromium moments, without any contributions from manganese spins. At the middle of the plateau, a regime evolves, where sound waves propagate almost without dissipation. The external magnetic field compensates the Cr–Mn exchange field and decouples Mn and Cr sublattices. In analogy to predictions of quantum lattice-gas models, the changes of the spin order of the Mn ions at the boundaries of the magnetization plateau are interpreted as transitions to supersolid phases.  The observed high-field magneto-structural states are discussed within H-T phase diagrams taking into account the field and temperature evolution of spin structures and subsequent lattice transformations induced by magnetic field. The structural transformations are ascribed to a symmetry recovery by high magnetic field due to the interplay of the structural and spin degrees of freedom competing with magnetic frustration.