Physiological and psychological stress causes changes in homeostasis characterized by an imbalance of activity between the autonomic nervous systems. Overactivity of the sympathetic nervous system leads to physical, psychological, and behavioral disorders.
 Diaphragmatic breathing exercises routinely have been shown to suppress sympathetic nerve activity through activation of the parasympathetic nervous system and an increase in tidal volume that creates a change in the cell membrane potential to hyperpolarization, with the result being an improvement in physiological and psychological stress conditions, which appear in various parameters. This paper reviews the anatomy, physiology, and biomechanics of the diaphragm muscle, as well as the mechanism of diaphragmatic breathing exercises in improving physiological and psychological stress conditions from a Physical Medicine and Rehabilitation point of view.
 Keywords: breathing, diaphragm, exercise, physiological stress, psychological stress