The hysteresis observed in the mechanical response of rubbers (especially filled rubbers) is classically assumed to be fully due to viscosity. Complete energy balances carried out during cyclic deformation show that viscosity is not systematically the preponderant contribution to the hysteresis loop: the mechanical energy brought to the material is not entirely dissipated into heat but can be predominantly used by the material to change its microstructure. Predicting changes in temperature, and consequently the self-heating, is therefore not possible from the mechanical response only. This has been evidenced by defining a ratio in terms of energy. A new way of interpretation of the rubber resistance can therefore by found through its ability to store mechanical energy.