An oral appliance includes a frame for mounting to a user's teeth and a tongue contacting retaining member extending from the frame and configured in use to limit movement of the tongue toward the user's throat when the user is exercising or sleeping to maintain an open air passageway. The retaining member is positioned relative to the frame such that in use the retaining member contacts the tongue in a zone behind the second molars and in front of the pharyngeal reflex region of the tongue. The retaining member is further configured to lightly contact the tongue, and to apply a restraining force to the tongue as the tongue begins to move toward the user's throat during exercise or as the user falls asleep.