The aims of the present work were: to calculate lifting energy consumption (LEC) in work activities designed to have a growing lifting index (LI) by means of revised NIOSH lifting equation; to evaluate the relationship between LEC and forces at the L₅-S₁ joint. The kinematic and kinetic data of 20 workers were recorded during the execution of lifting tasks in three conditions. We computed kinetic, potential and mechanical energy and the corresponding LEC by considering three different centers of mass of: 1) the load (CoM_L); 2) the multi-segment upper body model and load together (CoM_Upp+L); 3) the whole body and load together (CoM_Tot). We also estimated compression and shear forces. Results shows that LEC calculated for CoM_Upp+L and CoM_Tot grew significantly with the LI and that all the lifting condition pairs are discriminated. The correlation analysis highlighted a relationship between LEC and forces that determine injuries at the L₅-S₁ joint.