It is the rotator cuff (is the group of muscles and their tendons that act to stabilize the shoulder). Its common for watresses, and even waiters, to have shoulder pain. It is usually caused from carrying heavy food trays and even a cocktail trays that may have a bunch of heavy beer mugs on it. It happens in busy places where they have to manuever around patrons and are carrying it with one hand. Especially if they are not use to it and are a little out of shape physically. Tendenitis is also a problem which many bartenders often get.
Carrying heavy trays stresses the muscles in the back, shoulder and neck.
To avoid it : your muscles need to be strengthening them first ( biceps, triceps, rotator cuff )
Sometimes, all it takes is stretching the neck and shoulder after carrying heavy trays, to prevent muscle pain.
To cure it : If the injurie is not to deep ( rotator cuff tears) The tuina treatment is the best way to heal it
For more information don t hesitate to contact me