A resistance breathing device includes a face mask having a perimeter and an aperture extending therethrough, and being adapted to overlay a user's mouth and nose such that the perimeter forms an air-tight seal with the user's face. An insert is disposed within the aperture of the face mask and has an inlet aperture extending therethrough. An adjustment slide is positioned adjacent the insert, has an inlet aperture extending therethrough, and is movable between a first position in which a first portion of the inlet aperture overlaps the inlet aperture of the insert and a second position in which a larger second portion of the inlet aperture overlaps the inlet aperture of the insert. An adjustment wheel is attached to the insert and is movable rotatably between first and second positions to cause the adjustment slide to move between its first and second positions.
