According to motivational intensity theory, energy investment in goal pursuit is determined by the motivation to avoid wasting energy. Two experiments tested this hypothesis by manipulating the difficulty of an isometric hand grip task across four levels in a between-persons (Study 1) and a within-persons (Study 2) design. Supporting motivational intensity theory’s prediction, the results showed that invested energy — indicated by exerted grip force — was a function of task difficulty: The higher the difficulty, the higher the energy investment. However, the data also indicated that participants invested considerably more energy than required, questioning the primacy of energy conservation.