Figure 3.

Ultrasound images of the genioglossus muscle, (A) it shows the relaxed muscle (without stimulation) in a coronal view, (B) it shows the muscle during electrical stimulation and the resulting change in the diameter caused by contraction. As the muscle contracts, it shortens, pulling the pharyngeal wall towards the anterior direction. An increase in the radius by +10% results in an approximate increase in the cross-sectional area (CSA) of the muscle of +21%, assuming a round model (CSA= π × r²).