The energy and the force methods are the most fundamental approach for receiving the deformation and fracture laws for materials and structures. It is well known that the fracture mechanics as a science was originated by a Griffith’s energy concept which allows to formulate the strength criterion. According to this criterion the defects like cracks in a solid body were introduced. In our work a criterion of fatigue strength is formulated. The results of modern experimental investigations on latent energy stored in metallic materials during the active plastic deformation are used.