BDNF and major depressive disorder: Additionally, they present a wide range of potential biomarkers, including brain-derived biomarkers (GFAP, α-synuclein, glutamine synthetase), exerkines (myostatin, myonectin), neurotrophic factors (BDNF, nerve growth factor (NGF)), miRNAs, and stress and inflammation signaling mediators (interleukins/cytokines, C reactive protein (CRP)), that hold promise in the field of exercise and depression research (Soares et al., 2021).