A mouth piece assembly (20) for relaxing muscles associated with a jaw of a person having teeth (22). The assembly includes a mouth piece body (24) having a cross-section presenting a pocket (38). The mouth piece body (24) is engaged to the teeth (22) of the person and the persons vertical dimension of occlusion is measured and compared to a predetermined range of 19±2 mm. At least one calibrating member (44) is inserted into the pocket (38) of the mouth piece body (24) to increase the height of the mouth piece body (24) so that the persons vertical dimension of occlusion is increased into the range of 19±2 mm. While wearing the resulting mouth piece assembly (20), the person experiences increased strength, stamina, and balance.
