The bands are the edges of the platysma muscle, which begin to contour under the chin and eventually lengthen downwards when the neck is unbalanced and slouching occurs.
We have an anterior fascial line, which over time pulls on the soft tissues, starting from the lower third of the face. Therefore, when we slouch while sitting at a computer, the rib cage is compressed inward, pulling on the soft tissues, and the neck is pushed forward, pulling the fascial tissue along the anterior line upward and contouring the bands.
Sometimes a band forms on only one side, indicating that tension on one side is greater than on the other. For example, during work, we often tilt our head toward the shoulder or have a distorted posture.