TENS can be applied to the TMJ of an athlete for a period of time to deprogram muscles. After TENS, a desired position of the lower jaw relative to the upper jaw can be determined and recorded. The desired position can be a physiological resting position, or a performance position in which the lower jaw is positioned anteriorly relative to the physiological resting position. A mouthpiece can be prepared including bite portions configured to substantially space apart and position the jaws according to the desired position, and substantially prevent movement of the lower jaw relative to the upper jaw. A connecting portion connects the bite portions within the mouth, and may extend labially along the anterior teeth and associated gum region of the lower jaw, and may be sized and shaped to substantially lie out of the way so as to not impede speech of the athlete.