contraction of the genioglossus stabilizes and enlarges the portion of the upper airway that is most vulnerable to collapse. relaxation of the genioglossus and geniohyoideus muscles, especially during rem sleep, is implicated in obstructive sleep apnea. given this connection, the mandible can be pulled forward to maximise the airway space, and prevent the tongue from sinking backwards under anaesthesia and obstructing the airway.