A new study from the Citadel in Charleston, SC, shows that the catabolic hormone cortisol, or lack there of, may be involved in this improvement.
Researchers had active football players perform one hour of weightlifting either with a fitted Under Armour performance mouthpiece or without one. Although, in both trials, cortisol levels rose during the workout, the mouthpiece caused cortisol to drop to pre-workout levels immediately afterward. In subjects without mouthpieces, it continued to rise.
Since cortisol can impede recovery following workouts, blunting it with a mouthpiece may enhance recovery and allow for greater gains in strength and size.