Abstract: An athletic mouth guard and breathing trainer having arcuate buccal wall, an arcuate lingual wall spaced apart from the arcuate buccal wall, a tooth bed disposed between the arcuate lingual wall and arcuate buccal wall, a valve box including an air passage with an opening in the front portion of the arcuate buccal wall, and a one-way valve disposed in the valve box opening. The valve has an open position and a closed position and can be opened with an exhalation through the valve insert opening, though not with an inhalation, such that after exhalation the valve returns to a closed position, thus encouraging the user to inhale through the nose and to engage in circular breathing.