This study compares flat lattice girders mounted on two supports, based on various design parameters, to determine which have better structural performance and what geometries are more efficient. The fundamental goal is to determine the relationship of performance and structural behavior of each type of framework structure, with respect to the principle of optimization and improvement in the efficiency of the trusses if their geometry adapts to the directions of the principal stresses and, of course, to the trajectory of the isostatic lines of the equivalent continuous structural resistant element under the loading actions. In this study, 256 models of lattice girders, with different triangulations, are analyzed to determine their performance and structural behavior. The results conclude that the trusses gain up to 25-35% efficiency when they identify the trajectory of the isostatic lines generates by the acting loads.