Hypoglossal nerve is the motor nerve that stimulates seven of the eight tongue muscles (Fig. 62.1). Hypoglossal nerve is not homogeneous with regard to the location of its axons and the stimulation of the nerve means that nerve fibers of different characteristics are stimulated at the simultaneously. The anterior and the posterior parts of the tongue are anatomically very different. The muscle fibers on the anterior part of the tongue have a diverse pattern while the fibers on its posterior part lie parallel to each other forming a single pattern. Physiological features of muscle fibers are associated with myosin heavy chain (MHC) subtypes. MHC type 1 fibers contract slowly but exert their effect for a long while, they use oxygen and energy substrates. MHC type 2 fibers contract more rapidly but exert their effects for a shorter period of time and can contract without needing oxygen. The posterior part of the tongue is rich from MHC type 1, and the anterior part predominantly has MHC type 2 fibers. This explains the dominance of type 2 fibers in the contraction of anterior tongue muscles responsible for functions like chewing and talking while there is dominance of type 1 fibers in the muscles realizing posterior tongue functions like oropharyngeal airway stability and prevention of the entering of the tongue to the posterior airways. In a rabbit experiment, when the tongue was stimulated with electricity, type 1 fibers increased in the genioglossus muscles while type 2 muscles had a relative decrease [3]. One of the objectives of HGNS is to achieve an increase in type 1 fiber function.