The trapezius (traps) is a muscle that supports the shoulders and arms, running vertically from the back of the beck down the spine, and extending horizontally to the shoulders.
If theses muscles are overdevelpoed, they may cause your neck to look shorter and your shoulder line rather masculine. It may also be the cause of neck/ shoulder pain.
Shoulder/ Trapezius Btoxin injections can relax and lower the trapezius muscle to create a feminine shoulder line and the appearance of a longer neck. This can also help with chronic neck/shoulder pain as well, pain that is caused by overdeveloped muscles.