Regular physical training leads to physical capacity and optimal sports performance, and although this relationship is usually linear, the athlete's adaptation is conditioned by multiple factors: environmental, genetic and psychological. Studies have shown that between 70 and 85% of successful and unsuccessful athletes can be identiied using psychological measures of personality and mood, a level higher than chance, but insuicient for the purpose of selecting athletes. The research indicates that the mood of the athletes exhibits a dose-response relationship with their adaptation to the training load; This inding has shown potential to reduce the incidence of overtraining syndrome in athletes who undergo rigorous physical training, through early detection using scales of perception of their mood and physiological measures such as the testosterone / cortisol index. Thus, the genetic and epigenetic modiications of the factors that regulate the hypothalamic-pituitary-adrenal axis and, therefore, the response to stress, have recently been associated with a detrimental efect on physical performance and early manifestations of the overtraining syndrome and the abandonment of training and competences.