Energy expenditure in strength training has been the subject of several studies over the last decades. However, the evaluated protocols present important and significant differences, making it impossible to compare them and reach definitive conclusions. The use of work units (sets x repetitions x load), adding the exercise execution and recovery phase, seems to allow for a better for the understanding of energy expenditure in strength training, being that energy expenditure increases with increasing work level. This, together with the use of observed absolute values (kcal or liters of O2) instead of relative values (kcal/min), may allow for a better understanding of the influence on different variables.