Recent results from molecular dynamics simulations have shown that significant concentrations of Frenkel pairs can be introduced by the proliferation of phonons lying at the edge of the Brillouin zone and when above the Debye temperature. Following the work of Granato (2014 Eur. Phys. J. B87 18) we extend those calculations to the influence of Frenkels on the elastic modulus. Significant softening is predicted which is confirmed by in situ measurements of the elastic modulus during flash. Frenkel pairs have been proposed to play a central role in the flash phenomena.