Strain-induced crystallization is classically assumed to be responsible for the hysteresis loop observed in the mechanical response of cis-1,4-polyisoprene. The aim of the present study is to investigate where does this energy go. Energy balances carried out using infrared thermography have shown that the hysteresis loop is due neither to intrinsic nor thermal dissipation, but is entirely used by the material to change its microstructure. Thus, significant changes in the internal energy accompany SIC. Experiments performed show that the mechanical energy brought to deform the material is stored elastically in the amorphous phase (chain alignment and accumulation of topological constraints in the crystallite vicinity) and is released with a different kinetics during crystallite melting. The demonstration that NR is able to store mechanical energy without converting it into heat is a realistic way to explain its extraordinary resistance to crack growth. (C) 2017 Elsevier Ltd. All rights reserved.