Final answer:
The infrahyoid muscles are the antagonistic muscle group when the hyoid bone is elevated, opposing the suprahyoid muscles that perform the elevation.
Step-by-step explanation:
The muscle group that acts as antagonists when the hyoid bone is elevated are the infrahyoid muscles. These muscles primarily function to depress the hyoid bone and control the position of the larynx. In contrast, the suprahyoid muscles, including the digastric, stylohyoid, mylohyoid, and geniohyoid muscles, act to elevate the hyoid bone during swallowing (deglutition) and stabilizing it during other actions. Therefore, when the hyoid is lifted by the suprahyoid muscles, the infrahyoid muscles must relax; when they contract, they will lower the hyoid bone.
Lastly, the sternocleidomastoid muscles play a role in rotating and flexing the head but are not directly involved with the movement of the hyoid bone. The digastric muscles are part of the suprahyoid group and thus are not antagonists to elevation of the hyoid bone; they are actually the primary elevators of it.