Any moving body possesses kinetic energy. If velocity is written with regard to position, we get: 

Moreover, given that the elastic force acting on the body is a conservative force, the body carries with it a certain amount of potential elastic energy, according to the expression:     

The values of kinetic and potential energy depend on the position occupied by the body. However, the total energy possessed by the body remains constant during the whole trajectory.

Click on next to verify this in the graph.