Taking breaths using your diaphragm muscles instead of your perpetually tight chest muscles rests the chest, he says. It also draws air deeper in to your lungs and activates the vagus nerve, the control nerve for the part of your nervous system that calms you. "'Breath breaks' shift you away from the fight-or-flight, adrenaline-driven half of the nervous system, which, for many people, is the habitual mode," Dr. Merrell says. "And deeper breathing causes better oxygenation. All of this means using less energy and being able to make more energy at the same time. A win-win [situation] if there ever were one."