Mathematical modeling of the propagation of fitness practice in Spain M. Alkasadi † , E. De la Poza ‡* , L. J´ odar † and A. Pricop † (†)Instituto Universitario de Matem´ atica Multidisciplinar, Universitat Polit` ecnica de Val` encia. Camino de Vera s/n. 46022, Valencia, Espa˜ na, (‡)Facultad de Administraci´ on y Direcci´ on de Empresas, Universitat Polit` ecnica de Val` encia, Universitat Polit` ecnica de Val` encia, Building 7J. Camino de Vera s/n. 46022, Valencia, Espa˜ na. 1 Introduction Our society is concerned with people’s physical appearance and an ideal body image. As a result of this trend, the physical fitness prevalence espe- cially among men has extended which leads to health benefits. However, its excess can be associated to the development of psycho-medical diseases such as bigorexia or a disorder in which the person becomes obsessed with the idea that he or she is not muscular enough. This disorder affects mainly to men, [1]. The individuals who suffer from it think their body shape and size is skinny or small,[2]. They develop obsessive and negative behaviors related with their appearance [3], affecting not only the adult men, but also young boys [4]. The aim of this study is to develop a discrete population mathematical model to forecast the future bigorexia addicts in Spain in the next five years. For this purpose, economic and psychological motivations are taken into account in order to quantify the dynamic behavior of men gym users. Personal and social consequences of this addiction are studied and public health recom- mendations are suggested. * elpopla@esp.upv.es 1