Various classes of life distributions and their duals have been introduced to describe several types of distribution (improvement) than accompany aging. A new class of life distributions, namely, new better (worse) than used in average at specific interval presented (NBUASI). Closure of NBUASI class under formation of parallel systems is given. Shock models, where shocks are arriving according to homogeneous and nonhomogeneous Poisson process, are established. A cumulative damage model is also investigated.