In the late 19th century Europe, the image of a thermal machine, ruled by thermodynamic laws, became one of the primary metaphors to explain societal operating mechanism. At the end of 19th century, experts in fatigue, nutrition and human motor physiology strove to get a supposedly neutral and objective solution to political and economic conflicts corresponding to industrialized cities, in the quest to maximize productivity while preserving energy within the worker bodies. This paper will explore some of the reforms and social projects in Restoration Spain that were informed by the energetic productivism doctrine. The way this doctrine was based on a new perception of both human body and social body as closely related to a thermodynamic system is highlighted. In turn this point draws attention on the importance of considering other knowledge different to the medical and biological ones to rationalize and manage body and population.