Regarding the relationship between chronic aerobic exercise interventions and the variation of BDNF blood concentration levels on human subjects, 30 human studies (Table 1) were detected, with a heterogeneous study population varying from young individuals to elderly groups; as well as from healthy study populations to groups with a wide spectrum of medical conditions (e.g., multiple sclerosis [MS], Parkinson’s and Alzheimer’s disease, major depressive disorder [MDD], obese and overweight individuals, etc.). This evidence concerns the gene BDNF and major depressive disorder.