Sport is considered beneficial to health (WHO, 1995). However, Noger (2009) mentions an inverted U-shaped relationship between these two concepts, meaning that beyond a certain threshold, practice can lead to psychological risks. From this perspective, my research has two main lines of enquiry. Firstly, my research concerns the study of the process of athlete burnout in adolescents involved in training centers. Indeed, more and more studies in psychology are interested in the psychological risks linked to intensive practice, and consequently in athlete burnout, which is a syndrome of reduced accomplishment, physical and emotional exhaustion, and devaluation of sport (Raedeke, 1997). My studies focus on the developmental, motivational, and emotional determinants of this syndrome. In a second axis, my research focuses on the practice of physical activities for health purposes, particularly within companies. In this perspective, I study more particularly the determinants and barriers to the practice of physical activities, as well as the consequences of these activities on the psychosociological and physical health of employees.