Equipment: sequential 4-channel NMES and 2-channel NMES
The sequential 4-channel NMES has four channels with adaptable amplitude, frequency, duration, and latency of current. (Supplementary Fig. Channel 1 (right) and channel 2 (left) electrodes were placed superior to the hyoid bone and posterior to the mandible, 1 cm lateral to the midline, and the targeted muscles were the bilateral digastric and mylohyoid muscles. Channel 3 electrodes were placed on the bilateral superior poles of the thyroid cartilage to target the bilateral thyrohyoid muscles, and channel 4 electrodes were placed medial to the sternocleidomastoid muscle and inferior to the thyroid cartilage, and the targeted muscles were the other infrahyoid muscles (sternohyoid, omohyoid, and sternothyroid muscles) (Supplementary Fig. In the 2-channel NMES group, electrical stimulation was applied via two sets of electrodes attached to the suprahyoid and thyrohyoid muscles, whereas no electrical stimulation was applied to the other electrodes that were placed for blinding purposes (Supplementary Fig. 