Can a plastic mouth guard, designed to open up airways, improve your athletic performance? That's the claim of marketing literature from Makkar and Under Armour, who sell the gear for $595 and $495 respectively. Under Armour says its product "increases strength, increases endurance, speeds up reaction time, and reduces athletic stress". Sounds fantastic, and may be pure fantasy. The New York Times found at least one exercise physiologist with the American Council on Exercise who believes the claims could be true. Dentists, too, tell the Times that the devices do enable more oxygen to make its way to the lungs, prevent teeth clenching and align the jaw. Clenching teeth, the Times reminds us, can release of the stress hormone cortisol, which, at excessive levels, can impede athletic performance. And then, of course, there is the academic research, conducted in this case at the Citadel and Rutgers (and paid for by the manufacturers) that found that athletes wearing the mouth guards "could jump higher and perform better at their peak."
Read more about performance mouth guards in the New York Times.