We report simulations of a two-dimensional binary Lennard-Jones system, a Cu Zr alloy and amorphous silicon subjected to shear deformation in excess of 1000%. In all cases shear bands are observed to form and to broaden as shear is applied to the system. The broadening of the shear bands can be modeled by assuming the rate of broadening is related to the strain rate in the band. However, initial investigations indicate that this simple assumption is not routinely applicable. The implications for theories of plasticity will be considered to elucidate any additional constraints these observations place on the underlying theory of the constitutive response of these systems.